JP6665769B2 - Cart - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a bogie capable of changing a traveling direction back and forth.

  For example, Patent Literature 1 discloses a structure in which a bogie capable of changing its traveling direction back and forth can ensure stable straight-line traveling in both forward and backward traveling directions.

JP 2015-107665 A

  However, in the bogie having the structure disclosed in Patent Literature 1, since the lowermost part of the free wheels and the lowermost part of the fixed wheels are different from each other, the cargo bed is always inclined with respect to the running surface. For this reason, the workability of cargo handling may be affected. Further, it is not suitable for transporting parts or the like that require horizontal accuracy.

  The present invention has been made in view of the above-described problems, and provides a bogie that does not incline with respect to a running surface and that can stably run while ensuring straightness in both forward and backward traveling directions. The purpose is to do.

In order to solve the above-described problems, one embodiment of the present invention provides a pair of a loading platform and a first supporting portion that is provided as a pair on a front lower surface of the loading platform and rotatably supports the first wheel and the first wheel. A first pedestal portion fixed to the loading platform and rotatably supporting the first support portion; and a disk-shaped member provided on the first support portion and rotating integrally with the rotation shaft of the first support portion. A first universal wheel having a first cam plate and capable of changing the direction of the wheels; and a second universal wheel provided on a rear lower surface of the loading platform for rotatably supporting the second wheel and the second wheel. And a second pedestal portion fixed to the carrier and rotatably supporting the second support portion, and provided on the second support portion and rotating integrally with the turning shaft of the second support portion. comprising a disk-shaped second cam plate, and a second universal wheel freely change the orientation of the wheel, the first universal wheel and the second universal It provided in one pair in the vicinity of the first universal wheels between the wheels, a third wheel, a third supporting portion for rotatably supporting the third wheel, fixed to the loading platform and the loading platform surface A third pedestal portion supporting the third support portion via a spring material so as to be displaceable in a vertical direction perpendicular to the first support portion, and a first cam plate provided on the third support portion and via a plate; a third cam wheel rolling contact, the third fixed wheel which bed longitudinally oriented fixed, the second universal between the first universal wheel and the second universal wheel provided in one pair in the vicinity of the wheel, the fourth wheel, the fourth supporting portion which rotatably supports the fourth wheel, displaced in the vertical direction perpendicular to the fixed and the bed surface in the bed A fourth pedestal portion for supporting the fourth support portion via a spring material as possible, and a fourth pedestal portion provided on the fourth support portion. A fourth cam wheels that roll in contact with the second cam plate via the over preparative comprises a fourth fixed wheel which bed longitudinally oriented fixed, a first universal wheel Is moved forward in the traveling direction, the first cam plate operates so as to release the third cam wheel from pushing down the third wheel, and the third fixed wheel urges the running surface. And the second cam plate operates to push down the fourth wheel with the fourth cam wheel, the fourth fixed wheel urges the running surface, and the second universal wheel moves in the traveling direction. When forward, the first cam plate operates to push down the third wheel with the third cam wheel, the third fixed wheel urges the running surface, and the second cam plate The plate is operative to release the fourth wheel from being depressed by the fourth cam wheel; Is a bogie that does not bias the running surface.

According to another aspect of the present invention, there is provided a loading platform, a pair of first free wheels provided on a front lower surface of the loading platform, the directions of the wheels being freely changeable, and a pair of wheels provided on a rear lower surface of the loading platform. of the second universal wheel freely change the orientation, provided in one pair in the vicinity of the first universal wheel between the first universal wheel and the second universal wheel, third wheel, the third A third supporting portion rotatably supporting the wheel, fixed to the carrier, displaceable in a vertical direction perpendicular to the surface of the carrier via a spring material, and the surface of the carrier via the third plate member; A third pedestal portion for supporting the third support portion, a third pin provided on the third support portion, and a third plate member so as to be steerable in the left-right direction that is horizontal with respect to. a third hole consisting of a substantially elliptical shape and a substantially fan-shaped third pin is inserted, a third switching wheels, a first universal wheel first Provided in one pair in the vicinity of the second universal wheels between the universal wheel, the fourth wheel, the fourth supporting portion which rotatably supports the fourth wheel is fixed to the bed, the spring member Supports the fourth support portion so that it can be displaced in the vertical direction perpendicular to the surface of the cargo bed via the first plate member and can be steered in the horizontal direction horizontal to the surface of the cargo bed via the fourth plate member. A fourth pedestal portion, a fourth pin provided on the fourth support portion, and a fourth hole formed on the fourth plate member and formed in a substantially elliptical shape and a substantially fan shape into which the fourth pin is inserted. A fourth switching wheel, wherein the third pin inserted into the third hole is brought into contact with the rear of the third hole when the first universal wheel moves forward in the traveling direction. contact, by a state in which the third pin can move substantially fan-shaped range of the arc of the third hole, the third wheel orientation is not fixed, and the A fourth pin inserted in the hole comes into contact with the rear of the fourth hole, that the fourth pin is in a state unmovable fixed by the fourth hole, the fourth wheel loading platform in the longitudinal direction When the second universal wheel is forward in the traveling direction, the third pin inserted into the third hole abuts behind the third hole, and the third pin The third wheel is fixed by the third hole and cannot move, so that the direction of the third wheel is fixed in the longitudinal direction of the carrier, and the fourth pin inserted into the fourth hole is connected to the fourth hole. The fourth wheel is a bogie in which the direction is not fixed by abutting rearward and allowing the fourth pin to move within a substantially fan-shaped arc of the fourth hole .

  With this structure, the free wheels can be arranged in the forward direction of the bogie, and the fixed wheels can be arranged in the rear direction of the bogie. With this arrangement, since the lateral flow of the bogie in the traveling direction can be suppressed and the straightness of the bogie can be ensured, the bogie can run stably.

  Further, since the fixed wheel can be displaced in the direction of the running surface by the spring material, the lowermost portion of the wheel to be brought into contact with the running surface can be the same as the free wheels before and after the loading platform. Thus, the carrier of the bogie does not tilt with respect to the running surface.

  According to the bogie of the present invention, the luggage carrier does not incline with respect to the traveling surface, and the vehicle can travel stably in both forward and backward traveling directions while ensuring straight traveling.

The figure which shows the structural example of the trolley | bogie which concerns on one Embodiment of this invention. The figure explaining the movement of the cart according to the present embodiment The figure which shows the structural example of the trolley | bogie which concerns on the modification 1 of one Embodiment of this invention. The figure which shows the structural example of the trolley | bogie concerning the modification 2 in one Embodiment of this invention. The figure explaining the movement of the cart according to the present embodiment

[Overview]
In the truck of the present invention, fixed wheels are arranged between the free wheels before and after the loading platform. The fixed wheel has a structure in which the wheel is urged to the running surface by a spring material on the free wheel side which is rearward with respect to the traveling direction of the bogie. According to this structure, the fixed wheels can be arranged behind the traveling direction of the bogie, so that the lateral flow of the bogie in the traveling direction can be suppressed, and the straightness of the bogie can be ensured.

[Dolly structure]
FIG. 1 is a front view (a) and a bottom view (b) showing a structural example of a cart 10 according to an embodiment of the present invention. As shown in FIG. 1, a bogie 10 according to the present embodiment includes a carrier 11, first universal wheels 12, second universal wheels 13, and fixed wheels 14.

  The loading platform 11 includes a substantially rectangular flat plate 11b on which luggage and the like can be placed, and a handle 11h that can be gripped by an operator. The handle 11h is provided on the upper surface at one end (hereinafter, referred to as “the front part of the carrier 11”) in the longitudinal direction of the flat plate 11b. In addition, a slide lock portion 11k described later is provided on the other end (hereinafter, referred to as "the rear portion of the loading platform 11") in the longitudinal direction of the flat plate 11b.

  The first universal wheel 12 is a so-called universal wheel whose direction can be freely changed. The first universal wheels 12 are provided as a pair on the left and right sides on the lower surface on the front side of the loading platform 11. The first universal wheel 12 includes a wheel 12w, a support portion 12s that rotatably supports the wheel 12w, and a pedestal portion 12b that is fixed to the carrier 11 and rotatably supports the support portion 12s. ing. In the first universal wheel 12, since the turning axis of the supporting portion 12s and the rotating axis of the wheel 12w are in the twisted position, the rolling direction of the wheel 12w can be freely changed in accordance with the traveling direction of the carrier 11 (cart 10). Can be.

  The second universal wheel 13 is a so-called universal wheel whose direction can be freely changed. The second universal wheels 13 are provided in a pair on the left and right sides on the lower surface on the rear side of the loading platform 11. The second universal wheel 13 is also the same as the first universal wheel 12, and includes a wheel 13w, a support portion 13s that rotatably supports the wheel 13w, and a support portion 13s that is fixed to the carrier 11 and pivots freely on the support portion 13s. And a supporting base 13b. Also in the second universal wheel 13, since the turning axis of the support portion 13s and the rotating axis of the wheel 13w are in the twisted position, the rolling direction of the wheel 13w can be freely changed in accordance with the traveling direction of the carrier 11 (cart 10). Can be.

  As described above, in the cart 10 according to the present embodiment, the two first universal wheels 12 and the two second universal wheels 13 are arranged near the four corners on the lower surface of the loading platform 11, and are pulled, for example. Thus, it has a structure capable of traveling both forward and backward with respect to the longitudinal direction of the bed 11.

  On the lower surface of the loading platform 11, a pair of left and right slide rails 11r parallel to the longitudinal direction of the loading platform 11 are provided between the first universal wheel 12 and the second universal wheel 13. The slide rail 11r is configured so that the fixed wheel 14 can be freely moved from the front rail end of the loading platform 11 to the rear rail end of the loading platform 11.

  The above-described slide lock portion 11k is provided to restrict the movement of the fixed wheel 14 by the slide rail 11r when the operator uses the cart 10 as a hand cart with the handle 11h. By fixing the fixed wheel 14 by the slide lock portion 11k, the rear side of the bed 11 which is the traveling direction is a fixed wheel (fixed wheel 14), and the front side of the bed 11 is a free wheel (first free wheel 12). ). Therefore, it is possible to provide a wheel arrangement suitable for, for example, transporting heavy objects using the cart 10 as a hand cart.

  The fixed wheel 14 is a third wheel in which the direction of the wheel is fixed. The fixed wheels 14 are provided as a pair on the left and right sides between the first universal wheel 12 and the second universal wheel 13 on the lower surface of the carrier 11. More specifically, the fixed wheels 14 are movably attached to slide rails 11r provided on a pair of left and right sides on the lower surface of the loading platform 11, respectively.

  The fixed wheel 14 includes a wheel 14w, a supporting portion 14s that rotatably supports the wheel 12w, and a supporting portion 14s via a spring material 14a that can be displaced in a vertical direction perpendicular to the surface of the loading platform 11. The pedestal portion 14b includes a supporting portion 14b to be supported, and a fitting portion 14r that slidably fits the pedestal portion 14b to the slide rail 11r of the loading platform 11. The spring member 14a is a member that can be elastically deformed. As the mechanism of the fitting portion 14r that slides the pedestal portion 14b on the slide rail 11r, for example, a mechanism including wheels that roll on the slide rail 11r can be used.

  The pedestal portion 14b is configured such that, when no load is applied to the spring member 14a, the lowermost portion of the wheel 14w, that is, the point of contact with the running surface, is connected to the lowermost portion of the wheel 12w of the first universal wheel 12 and the The support portion 14s is supported so as to protrude from the lowermost portion of the wheel 13w of the second universal wheel 13 toward the traveling surface side. Therefore, in the posture in which the bogie 10 shown in FIG. 1 is used, the fixed wheel 14 is urged against the running surface by the elastic force of the spring member 14a (arrow in FIG. 1). With this biasing, the starting resistance of the wheel 14w with respect to the running surface is higher than the starting resistance of the fitting portion 14r with respect to the slide rail 11r.

  Further, in a state where the fixed wheel 14 protrudes to the running surface side from the wheel 12w of the first universal wheel 12 and the wheel 13w of the second universal wheel 13, the fixed wheel 14 is urged to the running surface by the spring material 14a. For this reason, as illustrated in FIG. 5, it is possible to secure the grounding (ground contact load) of the running surface by the fixed wheels 14 even on the running surface having some unevenness.

[Dolly movement]
The movement of the cart 10 according to one embodiment of the present invention will be described with reference to FIG. In FIG. 2, the handle 11 h and the slide lock portion 11 k provided on the carrier 11, which are not directly related to the movement of the carriage 10, are drawn.

  As illustrated in FIG. 2A, when the bogie 10 is traveling in one direction (rightward in the drawing), the second universal wheel 13 is a front wheel in the traveling direction, and the first universal wheel 12 is It is the rear wheel in the direction of travel. The fixed wheel 14 advances in a state where the fixed wheel 14 is in contact with the rail end of the slide rail 11r on the first free wheel 12 side. That is, at this time, the second universal wheel 13 can be arranged in front of the traveling direction, and the fixed wheel 14 can be arranged behind the traveling direction.

  When the traveling direction of the carriage 10 is switched from one direction to the opposite direction (left direction in the drawing), that is, when the carriage 10 is switched back, the carriage 10 temporarily stops as illustrated in FIG. 2B.

  Then, as illustrated in FIG. 2C, the first universal wheel 12 and the second universal wheel 13 turn and change directions, and the first universal wheel 12 becomes a front wheel in the traveling direction, and Becomes the rear wheel in the traveling direction, and the bogie 10 starts to travel in the opposite direction.

  Here, the fixed wheel 14 is urged to the running surface by the spring material 14a such that the starting resistance of the wheel 14w with respect to the running surface is higher than the starting resistance of the fitting portion 14r with the slide rail 11r of the carrier 11. ing. For this reason, as long as the fitting portion 14r of the fixed wheel 14 can slide (slide) on the slide rail 11r of the loading platform 11, as illustrated in FIG. 2C and FIG. The slide rail 11r slides while staying at the same place on the running surface.

  Eventually, as illustrated in FIG. 2 (e), the fitting portion 14 r of the fixed wheel 14 comes into contact with the rail end of the slide rail 11 r of the loading platform 11 on the side of the second free wheel 13. Thereafter, the fixed wheel 14 starts traveling in the opposite direction together with the first universal wheel 12 and the second universal wheel 13. Thereby, the first universal wheel 12 can be arranged in the front in the traveling direction, and the fixed wheel 14 can be arranged in the rear in the traveling direction.

[Operations and effects according to the present embodiment]
As described above, the bogie 10 according to one embodiment of the present invention is configured such that the slide rail 11r moves in the front-rear direction between the first free wheel 12 and the second free wheel 13 provided in front of and behind the carrier 11. A movable fixed wheel 14 is arranged. The fixed wheel 14 attaches the wheel 14w to the running surface with a spring material 14a on either the first universal wheel 12 or the second universal wheel 13 which is rearward with respect to the traveling direction of the bogie 10. Force structure.

  With this structure, one of the first universal wheel 12 and the second universal wheel 13 can be arranged in front of the bogie 10 in the traveling direction, and the fixed wheel 14 can be arranged behind the bogie 10 in the traveling direction. With this arrangement, since the lateral flow of the bogie 10 in the traveling direction can be suppressed and the straightness of the bogie 10 can be ensured, the bogie 10 can run stably (for example, follow the towing vehicle).

  In addition, since the fixed wheel 14 can be displaced in the direction of the running surface (vertical direction) by the spring material 14a, the lowermost portion of the wheel 14w to be brought into contact with the running surface is provided at the first and second positions provided before and after the loading platform 11. Can be the same as the universal wheel 12 and the second universal wheel 13. Thus, the carrier 11 of the carriage 10 does not tilt with respect to the running surface.

[Modification 1]
FIGS. 3A and 3B are a front view (a) and a partial perspective view (b) showing a structural example of the bogie 20 according to a first modification of the embodiment of the present invention. The trolley 20 according to the first modification differs from the trolley 10 according to the embodiment in the structure of the first universal wheel 22, the second universal wheel 23, and the fixed wheel 24.

  The fixed wheel 24 is a third wheel having the same structure in which the direction of the wheel is fixed. The fixed wheels 24 are provided in a pair on the left and right sides in the vicinity of the first universal wheel 22 and the vicinity of the second universal wheel 23 on the lower surface of the loading platform 11.

  The fixed wheel 24 includes a wheel 24 w, a support portion 24 s that rotatably supports the wheel 24 w, and a spring member that is fixed to the loading platform 11 and is displaceable in a vertical direction perpendicular to the surface of the loading platform 11. And a pedestal portion 24b that supports the support portion 24s via 24a and 24d. The spring member 24a is a member that can be elastically deformed, and functions to vertically displace the support portion 24s based on the ground contact with the running surface of the wheel 24w. The support portion 24s includes a cam wheel 24c that rolls by contacting a cam plate 23c (described later) of the second universal wheel 23 via a plate 24p. The spring member 24d is a member that can be elastically deformed, and functions to displace the support portion 24s in the vertical direction based on the contact of the cam wheel 24c with the cam plate 23c.

  The first universal wheel 22 and the second universal wheel 23 are wheels having the same structure that can change the direction of the wheel. The first universal wheels 22 are provided on the lower surface on the front side of the loading platform 11 as a pair of left and right wheels. The second universal wheels 23 are provided on the lower surface on the rear side of the loading platform 11 as a pair of left and right wheels. Hereinafter, the structure of the second universal wheel 23 will be described as a representative.

  The second universal wheel 23 includes a wheel 23w, a support portion 23s that rotatably supports the wheel 23w, and a pedestal portion 23b that is fixed to the carrier 11 and rotatably supports the support portion 23s. ing. In the second universal wheel 23, since the turning axis of the support portion 23s and the rotating axis of the wheel 23w are in the twisted position, the rolling direction of the wheel 23w can be freely changed in accordance with the traveling direction of the carrier 11 (cart 20). Can be. Further, the support portion 23s of the second universal wheel 23 is provided with a disk-shaped cam plate 23c that rotates integrally with the turning shaft of the support portion 23s.

  The cam plate 23c comes into contact with the cam wheel 24c of the fixed wheel 24, and changes the contact state of the fixed wheel 24 with the running surface of the wheel 24w. Specifically, when the second universal wheel 23 is located rearward in the traveling direction, the cam plate 23c operates to push down the cam wheel 24c to urge the wheel 24w of the fixed wheel 24 to the running surface. (FIG. 3B). On the other hand, when the second universal wheel 23 is located forward in the traveling direction, the cam plate 23c operates to release the depression of the cam wheel 24c, and lifts the wheel 24w of the fixed wheel 24 from the running surface to touch the ground. (See the fixed wheel 24 on the first free wheel 22 side shown in FIG. 3A).

  With this structure, as described above, since the lateral flow of the carriage 20 in the traveling direction can be suppressed and the straightness of the carriage 20 can be ensured, the carriage 20 can run stably. Further, the carrier 11 of the carriage 20 does not incline with respect to the running surface.

[Modification 2]
FIG. 4 is a front view (a), a partial perspective view (b1), and (b2) showing a structural example of a truck 30 according to Modification 2 of one embodiment of the present invention. The truck 30 according to the second modification differs from the truck 10 according to the above embodiment in the structure of the switching wheels 34.

  The switching wheel 34 is a third wheel that can switch the direction of the wheel between fixed and movable. The switching wheels 34 are provided in a pair on the left and right sides in the vicinity of the first universal wheel 12 and the vicinity of the second universal wheel 13 on the lower surface of the loading platform 11.

  The switching wheel 34 is displaced in a vertical direction which is fixed to the loading platform 11 and is perpendicular to the surface of the loading platform 11 via a spring material 34a, a wheel 34w, a supporting portion 34s rotatably supporting the wheel 34w. And a pedestal portion 34b that supports the support portion 34s so as to be capable of being steered in the left-right direction that is horizontal to the surface of the loading platform 11 via the plate member 34f. Two pins 34p are erected on the support portion 34s. The plate 34f is formed with two substantially elliptical and substantially fan-shaped holes 34h, into which the two pins 34p of the support portion 34s are inserted.

  The switching wheel 34 provided near the first universal wheel 12 and the switching wheel 34 provided near the second universal wheel 13 are arranged as targets. Specifically, the switching wheel 34 is provided with the substantially elliptical hole 34h of the pedestal portion 34b facing outward of the carrier 11 and the substantially fan-shaped hole 34h of the pedestal portion 34b facing inward of the carrier 11.

  Due to the above arrangement, the switching wheels 34 in front of the traveling direction of the bogie 10 have the pins 34p of the support portions 34s abut against the rear of the holes 34h of the pedestal portions 34b, respectively, as illustrated in FIG. The pin 34p inserted into the fan-shaped hole 34h can move in the range of the arc. On the other hand, as a result of the above arrangement, the switching wheels 34 that are rearward in the traveling direction of the bogie 10 have the pins 34p of the support portions 34s abut on the rear sides of the holes 34h of the pedestal portions 34b, as illustrated in FIG. 4B2. The pin 34p inserted into the substantially fan-shaped hole 34h is fixed and cannot move. Therefore, the switching wheel 34 whose movement is fixed, that is, the fixed wheel, is disposed behind the bogie 10 in the traveling direction. The wheel 34w of the switching wheel 34 whose direction is fixed is biased to the running surface by the spring material 34a and is grounded.

  With this structure, as described above, since the lateral flow of the carriage 30 in the traveling direction can be suppressed, and the straightness of the carriage 30 can be ensured, the carriage 30 can run stably. Further, the carrier 11 of the carriage 30 does not tilt with respect to the running surface.

  INDUSTRIAL APPLICABILITY The present invention can be used for a bogie that can change the direction of travel in the forward and backward directions. It is useful when you want to.

10, 20, 30 Cart 11 Carrier 11b Flat plate 11h Handle 11k Slide lock 11r Slide rail 12, 13, 22, 23 Free wheel 12b, 13b, 14b, 23b, 24b, 34b Base 12s, 13s, 14s, 23s, 24s , 34s Supporting portions 12w, 13w, 14w, 23w, 24w, 34w Wheels 14, 24 Fixed wheels 14a, 24a, 24d, 34a Spring material 14r Fitting portion 23c Cam plate 24c Cam wheel 34 Switching wheel 34h Hole 34p Pin

Claims (2)

With a carrier,
A first wheel, a first support portion rotatably supporting the first wheel, a first wheel, a first support portion rotatably supporting the first wheel, and a first support portion rotatably fixed to the load platform. A first pedestal portion pivotally supported on the first support portion, and a disc-shaped first cam plate provided on the first support portion and rotating integrally with a turning shaft of the first support portion. A first freely changeable wheel;
A second wheel, a second support portion rotatably supporting the second wheel, a second wheel, a second support portion rotatably supporting the second wheel, and the second support portion being rotatably fixed to the load platform. Changing the direction of the wheel, comprising: a second pedestal portion pivotally supported; and a disk-shaped second cam plate provided on the second support portion and rotating integrally with the turning shaft of the second support portion. A second free wheel,
Wherein provided in the first universal wheels and a pair in the vicinity of the first universal wheel in between the second universal wheel, the first for rotatably supporting a third wheel, said third wheel 3, a third pedestal portion fixed to the loading platform and supporting the third supporting portion via a spring material so as to be vertically displaceable and perpendicular to a surface of the loading platform; and provided on the supporting portion of the 3 and through the plate comprises a third cam wheel rolling in contact with the first cam plate, and a third fixed wheel longitudinally in the direction of the loading platform is fixed ,
Wherein provided in the first universal wheels and a pair in the vicinity of the second free wheel between the said second free wheel, the rotatably supports the fourth wheel, the fourth wheel A fourth supporting portion, a fourth pedestal portion fixed to the loading platform and supporting the fourth supporting portion via a spring material so as to be vertically displaceable and perpendicular to a surface of the loading platform; and provided on the supporting portion 4 and through the plate comprises a fourth cam wheels that roll in contact with the second cam plate, and a fourth fixed wheel longitudinally in the direction of the loading platform is fixed ,
When the first universal wheel moves forward in the traveling direction, the first cam plate operates to release the third cam wheel from pushing down the third wheel, and the third cam wheel releases the third wheel . Does not bias the running surface, and the second cam plate operates to push down the fourth wheel with the fourth cam wheel, so that the fourth fixed wheel moves on the running surface. Biased,
When the second universal wheel moves forward in the traveling direction, the first cam plate operates to push down the third wheel with the third cam wheel, and the third fixed wheel Urges the running surface, and the second cam plate operates to release the depression of the fourth wheel by the fourth cam wheel, and the fourth fixed wheel is moved to the running surface. Not energized,
Trolley. With a carrier,
A first universal wheel, which is provided as a pair on the front lower surface of the loading platform and is capable of changing the direction of the wheel,
A second universal wheel, which is provided as a pair on the rear lower surface of the loading platform and is capable of changing the direction of the wheels,
Wherein provided in the first universal wheels and a pair in the vicinity of the first universal wheel in between the second universal wheel, the first for rotatably supporting a third wheel, said third wheel The third support portion is fixed to the carrier, is displaceable in a vertical direction perpendicular to the surface of the carrier via a spring material, and is horizontal to the surface of the carrier via a third plate member. A third pedestal portion supporting the third support portion, a third pin provided on the third support portion, and the third plate member provided on the third plate so as to be steerable in the left-right direction. A third switching wheel including a third hole having a substantially elliptical shape and a substantially fan shape into which the pin is inserted ,
Wherein provided in the first universal wheels and a pair in the vicinity of the second free wheel between the said second free wheel, the rotatably supports the fourth wheel, the fourth wheel The support portion of 4 is fixed to the carrier, is displaceable in a vertical direction perpendicular to the surface of the carrier via a spring material, and is horizontal to the surface of the carrier via a fourth plate member. A fourth pedestal portion supporting the fourth support portion, a fourth pin provided on the fourth support portion, and the fourth plate member provided on the fourth plate member so as to be steerable in the left-right direction. A fourth switching wheel including a fourth hole having a substantially elliptical shape and a substantially fan shape into which the pin is inserted ,
When the first universal wheel moves forward in the traveling direction, the third pin inserted in the third hole abuts behind the third hole, and the third pin is By being able to move within the range of the substantially arc of the third hole, the direction of the third wheel is not fixed, and the fourth pin inserted into the fourth hole is The fourth wheel is fixed to the rear of the fourth hole so that the fourth pin is fixed by the fourth hole and cannot move, so that the fourth wheel is fixed in the longitudinal direction of the loading platform,
When the second universal wheel is forward in the traveling direction, the third pin inserted into the third hole comes into contact with the rear of the third hole, and the third pin is The third wheel is fixed by the third hole so that it cannot be moved, so that the third wheel is fixed in the longitudinal direction of the carrier, and the fourth pin inserted into the fourth hole is The fourth wheel is not fixed in direction by abutting behind the fourth hole and being in a state where the fourth pin can move within a substantially fan-shaped arc of the fourth hole .
Trolley.

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