TRANSPORT CART

A cart equipped with a smaller electric actuator as a drive source to raise and lower a loading platform and having a movable part 93 driven and moved by an electric actuator 91, a first link member 951R (951L) coupled to the movable part 93, a second link member 953R (953L) coupled to the first link member 951R (951L) and right and left X-shaped arms 71L and 71R (75L and 75R) via a shaft member 952R (952L), and a guide 97R (97L) having a hole 971R (971L) for guiding the shaft member 952R (952L) that moves with the movable part 93. The loading platform 50 is raised and lowered by vertically extending and retracting the pair of X-shaped arms via the first and second link members 951R and 951L (953R and 953L) along with movement of the movable part 93.

TECHNICAL FIELD

The present invention relates to a cart that can raise and lower its loading platform.

BACKGROUND ART

As an example of this kind of carts, Patent Document 1 discloses a cart that raises and lowers its loading platform by extending and retracting its lifting arms (X-shaped arms) with its electric cylinder (electric actuator).

REFERENCE DOCUMENT LIST

Patent Document

Patent Document 1: JP 2010-274704 A

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

When a loading platform is raised and lowered by extending and retracting X-shaped arms, normally, more power is needed to raise the loading platform located at its lowest position than to raise the loading platform located at any other positions. Thus, if an electric actuator is used as a drive source to raise and lower the loading platform, it is necessary to adopt an electric actuator that can produce an output sufficient for raising the loading platform which is located at its lowest position and on which a load is placed. That is, it has been difficult to reduce the size of the electric actuator.

Thus, an object of the present invention is to provide a cart that can be equipped with a smaller electric actuator as a drive source to raise and lower a loading platform.

Means for Solving the Problem

In one aspect of the present invention, a novel cart is provided. The cart includes a base having a lower part to which a wheel is attached, a loading platform that is disposed above the base, a pair of right and left X-shaped arms that is disposed between the base and the loading platform and that is capable of vertically extending and retracting, and a drive device that raises and lowers the loading platform by extending and retracting the pair of right and left X-shaped arms. The drive device of the cart includes an electric actuator, a movable part that is driven and moved by the electric actuator, a first link member having one end that is rotatably coupled to the movable part, a second link member having one end that is rotatably coupled to the pair of right and left X-shaped arms and having another end that is rotatably coupled to another end of the first link member via a shaft member, and a guide member having a guide part for guiding the shaft member that moves with movement of the movable part. The drive device is constructed to vertically extend and retract the pair of right and left X-shaped arms via the first link member and the second link member along with movement of the movable part.

Effects of the Invention

According to the present invention, there is provided a cart that can be equipped with a smaller electric actuator as a drive source to raise and lower a loading platform.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIGS.1to4illustrate the construction of a push handle cart10according to an example of the present invention.FIG.1is a front view of the cart10,FIG.2is a rear view of the cart10,FIG.3is a view of the cart10from the right, andFIG.4is a view of the cart10from the left.

As illustrated inFIGS.1to4, the cart10according to this example includes a base30, a push handle40(hereinafter referred to as “handle”), a loading platform50disposed above the base30, an extendable mechanism70disposed between the base30and the loading platform50, a drive device90that drives (extends and retracts) the extendable mechanism70, and a control device100that controls the drive device90.

FIG.5is a perspective view, mainly illustrating the base30and the handle40of the cart10.

As illustrated inFIG.5, the base30is formed as a rectangular frame. The base30includes a front frame member31A and a rear frame member31B extending laterally, and a pair of right and left frame members (a left frame member32L and a right frame member32R) extending longitudinally. Swivel caster wheels (front wheels)33,33are attached to lower parts at the two front corners of the four corners of the base30. In addition, electrically driven wheels (rear wheels)34,34, into which, for example, in-wheel motors are incorporated, are attached to lower parts at the two rear corners.

In addition, a left rail part35L extending longitudinally is formed on the front inner surface of the left frame member32L of the base30. Similarly, a right rail part35R, which pairs with the left rail part35L, is formed on the front inner surface of the right frame member32R. In addition, a pair of attachment parts (a left attachment part36L and a right attachment part36R), which are separated from each other laterally, are formed on the rear side of the base30. Furthermore, an installation part37, on which the drive device90and the control device100are disposed, is formed inside the base30at a position lower than the base30.

The handle40is attached to the rear frame member31B such that the handle40stands on the rear frame member31B. The handle40is, for example, a pipe member, and is formed to have an approximately gate shape (an approximately inverted U-shape). Specifically, the handle40has a pair of right and left supporting parts41,41, which first approximately vertically extend upward from the rear frame member31B and next extend diagonally backward. The handle40also has a grip part43, which approximately horizontally extends between end parts of the right and left supporting parts41. The grip part43is held by an operator or the like (hereinafter simply referred to as “operator”) that mainly uses the cart10.

Referring back toFIGS.1to4, the loading platform50has a rectangular top board part51, and a load (not illustrated) is placed on the top surface of the top board part51. The loading platform50also has a peripheral wall part53extending downward from the peripheral part of the top board part51. A pair of rail members (a left rail member55L and a right rail member55R), each of which has a rail groove, are formed on the front side of the lower surface of the top board part51. A pair of attachment parts (a left attachment part56L and a right attachment part56R), which are separated from each other laterally, are formed to vertically extend on the rear side of the lower surface of the top board part51.

The extendable mechanism70is constructed to vertically extend and retract a pair of right and left X-shaped arms (also referred to as “pantograph arms”) and to raise and lower the loading platform50in parallel to the base30. Normally, when the cart10is on a horizontal surface, that is, when the base30is disposed horizontally, the extendable mechanism70extends and retracts. That is, by extending and retracting the pair of right and left X-shaped arms vertically, the extendable mechanism70can horizontally raise and lower the loading platform50. According to the present example, the extendable mechanism70is formed as an X-shaped link mechanism in which two right X-shaped arms are vertically stacked on each other and two left X-shaped arms are vertically stacked on each other.

FIGS.6to8illustrate the construction of the extendable mechanism70.FIG.6is a view of the extendable mechanism70from the right,FIG.7is a view of the extendable mechanism70from the left, andFIG.8is a perspective view of the extendable mechanism70.

As illustrated inFIGS.6to8, according to the present example, the extendable mechanism70includes a pair of lower right and left X-shaped arms (a lower left X-shaped arm71L and a lower right X-shaped arm71R) and a pair of upper right and left X-shaped arms (an upper left X-shaped arm75L and an upper right X-shaped arm75R).

Each of the lower left X-shaped arm71L and the lower right X-shaped arm71R, which form the pair of lower right and left X-shaped arms, is formed by a lower inner arm and a lower outer arm that cross each other in the shape of the letter “X” in side view. The lower inner arm and the lower outer arm are coupled to each other in such a manner that these arms can mutually rotate. Specifically, according to the present example, the lower left X-shaped arm71L is formed by a lower inner arm72L and a lower outer arm74L, and the center portions thereof are rotatably attached to each other near the left end of a lower coupling shaft81extending laterally (seeFIGS.7and8). Similarly, the lower right X-shaped arm71R is formed by a lower inner arm72R and a lower outer arm74R, and the center portions thereof are rotatably attached to each other near the right end of the lower coupling shaft81(seeFIGS.6and8).

Each of the upper left X-shaped arm75L and the upper right X-shaped arm75R, which form the pair of upper right and left X-shaped arms, is formed by an upper inner arm and an upper outer arm that cross each other in the shape of the letter “X” in side view. The upper inner arm and the upper outer arm are coupled to each other in such a manner that these arms can mutually rotate. Specifically, according to the present example, the upper left X-shaped arm75L is formed by an upper inner arm76L and an upper outer arm78L, and the center portions thereof are rotatably attached to each other near the left end of an upper coupling shaft82extending laterally above the lower coupling shaft81(seeFIGS.7and8). Similarly, the upper right X-shaped arm75R is formed by an upper inner arm76R and an upper outer arm78R, and the center portions thereof are rotatably attached to each other near the right end of the upper coupling shaft82(seeFIGS.6and8).

In addition, the pair of lower right and left X-shaped arms (the lower left X-shaped arm71L and the lower right X-shaped arm71R) and the pair of upper right and left X-shaped arms (the upper left X-shaped arm75L and the upper right X-shaped arm75R) are coupled to each other via a rear coupling shaft83and a front coupling shaft84extending laterally.

Specifically, according to the present example, the rear end of the lower inner arm72L of the lower left X-shaped arm71L and the rear end of the upper outer arm78L of the upper left X-shaped arm75L are rotatably attached to each other near the left end of the rear coupling shaft83(seeFIGS.7and8). The rear end of the lower inner arm72R of the lower right X-shaped arm71R and the rear end of the upper outer arm78R of the upper right X-shaped arm75R are rotatably attached to each other near the right end of the rear coupling shaft83(seeFIGS.6and8).

In addition, the front end of the lower outer arm74L of the lower left X-shaped arm71L and the front end of the upper inner arm76L of the upper left X-shaped arm75L are rotatably attached to each other near the left end of the front coupling shaft84(seeFIGS.7and8). The front end of the lower outer arm74R of the lower right X-shaped arm71R and the front end of the upper inner arm76R of the upper right X-shaped arm75R are rotatably attached to each other near the right end of the front coupling shaft84(seeFIGS.6and8).

The front end of the lower inner arm72L of the lower left X-shaped arm71L is rotatably attached inside the left end of a lower movable shaft85, which extends laterally below the front coupling shaft84and is movable longitudinally (seeFIGS.7and8). The front end of the lower inner arm72R of the lower right X-shaped arm71R is rotatably attached inside the right end of the lower movable shaft85(seeFIGS.6and8).

The left end of the lower movable shaft85is inserted into the left rail part35L formed on the left frame member32L of the base30, and the right end of the lower movable shaft85is inserted into the right rail part35R formed on the right frame member32R of the base30(seeFIGS.3to8). That is, according to the present example, both ends of the lower movable shaft85are supported by the left rail part35L and the right rail part35R formed on the base30, and are movable longitudinally along the left rail part35L and the right rail part35R.

In addition, the rear end of the lower outer arm74L of the lower left X-shaped arm71L is rotatably fixed to the left attachment part36L formed on the rear end of the base30via a pin member P1. The rear end of the lower outer arm74R of the lower right X-shaped arm71R is rotatably fixed to the right attachment part36R formed on the rear end of the base30via a pin member P1(seeFIGS.3to8).

The front end of the upper outer arm78L of the upper left X-shaped arm75L is rotatably attached inside the left end of an upper movable shaft86, which extends laterally above the front coupling shaft84and is movable longitudinally (seeFIGS.7and8). The front end of the upper outer arm78R of the upper right X-shaped arm75R is rotatably attached inside the right end of the upper movable shaft86(seeFIGS.6and8).

The left end of the upper movable shaft86is inserted into the rail groove of the left rail member55L, which is formed on the bottom surface of the loading platform50(the top board part51), and the right end of the upper movable shaft86is inserted into the rail groove of the right rail member55R, which pairs with the left rail member55L and is formed on the bottom surface of the loading platform50(the top board part51) (seeFIGS.1to4andFIGS.6to8). That is, according to the present example, both ends of the upper movable shaft86are supported by the left rail member55L and the right rail member55R formed on the bottom surface of the loading platform50, and are movable longitudinally along the rail groove of the left rail member55L and the rail groove of the right rail member55R.

In addition, the rear end of the upper inner arm76L of the upper left X-shaped arm75L is rotatably fixed to the left attachment part56L formed to vertically extend on the bottom surface of the loading platform50(the top board part51) via a pin member P2(seeFIG.2,FIG.4, andFIGS.6to8). In addition, the rear end of the upper inner arm76R of the upper right X-shaped arm75R is rotatably fixed to the right attachment part56R, which pairs with the left attachment part56L and is formed to vertically extend on the bottom surface of the loading platform50(the top board part51), via a pin member P2(seeFIG.2,FIG.3,FIGS.6to8).

The drive device90is installed on the installation part37located inside and below the base30. The drive device90vertically extends and retracts the pair of lower right and left X-shaped arms (the lower left X-shaped arm71L and the lower right X-shaped arm71R) and the pair of upper right and left X-shaped arms (the upper left X-shaped arm75L and the upper right X-shaped arm75R) of the extendable mechanism70. In this way, the drive device90raises and lowers the loading platform50.

FIGS.9to11illustrate the construction of the drive device90.FIG.9is a view of the drive device90from the right,FIG.10is a view of the drive device90from the left, andFIG.11is a top view seen from an arrow A inFIG.9.

As illustrated inFIGS.9to11, according to the present example, the drive device90includes an electric actuator91, a movable part93that is driven and moved by the electric actuator91, and a pair of right and left link mechanisms (a left link mechanism95L and a right link mechanism95R) and a pair of right and left guide members (a left guide member97L and a right guide member97R) used as a coupling mechanism for coupling the movable part93and the extendable mechanism70.

The electric actuator91is a linear actuator that converts the rotational motion of the electric motor into linear motion by using a linear motion mechanism (for example, a ball screw mechanism) and outputs the linear motion. According to the present example, the electric actuator91includes an electric motor (a servo motor)911, a speed reduction mechanism913, and a linear motion mechanism (a linear motion shaft (a screw shaft)915A and a linear motion nut915B).

The operation of the electric motor911is controlled by the control device100. A non-excited brake912is attached to the output shaft of the electric motor911, for example, via a coupling, and an encoder (a rotation sensor)914that detects the rotation of the electric motor911and outputs a signal is attached to the electric motor911.

The speed reduction mechanism913reduces the speed of the rotation of the output shaft of the electric motor911and transfers the resultant rotation to the linear motion shaft915A of the linear motion mechanism. The construction, etc., of the speed reduction mechanism913is not limited to any particular construction, etc. For example, the number of stages of the speed reduction mechanism913is not limited to any particular number.

The linear motion shaft915A extends longitudinally and is rotatably supported by supporting members916A and916B to which a bearing (not illustrated) is attached. The linear motion shaft915A is rotated by the electric motor911via the speed reduction mechanism913. The linear motion nut915B is threadably mounted on the linear motion shaft915A and moves in the axial direction on the linear motion shaft915A along with the rotation of the linear motion shaft915A (that is, the linear motion nut915B moves linearly and longitudinally).

The movable part93is fixed to the linear motion nut915B and moves with the linear motion nut915B. According to the present example, a linear slider94is installed below the linear motion shaft915A. The linear slider94includes a slide rail94A extending longitudinally and a slide block94B moving on the slide rail94A. The lower part of the movable part93fixed to the linear motion nut915B is fixed to the slide block94B.

The left link mechanism95L and the right link mechanism95R as the coupling mechanism are constructed to push and pull the rear coupling shaft83of the extendable mechanism70along with the movement of the movable part93. Consequently, the left link mechanism95L and the right link mechanism95R vertically extend and retract the pair of lower right and left X-shaped arms (the lower left X-shaped arm71L and the lower right X-shaped arm71R) and the pair of upper right and left X-shaped arms (the upper left X-shaped arm75L and the upper right X-shaped arm75R).

Specifically, according to the present example, the left link mechanism95L includes a first link member951L of which the front end is rotatably coupled to the left side of the movable part93and a second link member953L of which the rear end is rotatably coupled to the rear coupling shaft83of the extendable mechanism70(that is, the pair of lower right and left X-shaped arms71L and71R and the pair of upper right and left X-shaped arms75L and75R) and of which the front end is rotatably coupled to the rear end of the first link member951L via a shaft member952L. Similarly, the right link mechanism95R includes a first link member951R of which the front end is rotatably coupled to the right side of the movable part93and a second link member953R of which the rear end is rotatably coupled to the rear coupling shaft83of the extendable mechanism70and of which the front end is rotatably coupled to the rear end of the first link member951R via a shaft member952R. In addition, the first link member951L of the left link mechanism95L and the first link member951R of the right link mechanism95R are coupled to each other via a coupling plate954.

The left guide member97L and the right guide member97R are disposed behind the installation part37located inside and below the base30, and are disposed on the left side and the right side of the electric actuator91. The left guide member97L has a guide hole971L for guiding the shaft member952L of the left link mechanism95L that moves with the movement of the movable part93. In addition, the right guide member97R has a guide hole971R for guiding the shaft member952R of the right link mechanism95R that moves with the movement of the movable part93. The guide hole971L in the left guide member97L and the guide hole971R in the right guide member97R are formed to have the same shape.

For example, the shape of the guide hole971L in the left guide member97L and the guide hole971R in the right guide member97R are determined as follows. Hereinafter, although the shape of the guide hole971R in the right guide member97R will be described with reference toFIG.9, the following description also applies to the shape of the guide hole971L in the left guide member97L.

First, when the loading platform50is raised or lowered between its lowest position and its highest position, a first coupling part J1where the movable part93and the front end of the first link member951R are coupled to each other moves on the X axis, and a second coupling part J2where the second link member953R and the rear coupling shaft83coupled to each other moves on the Y axis (seeFIG.9).

Next, a relationship between the position (x,0) of the first coupling part J1and the position (0,y) of the second coupling part J2, that is, a relationship between x and y, is determined by a physical law (herein, principle of virtual work). The relationship between y and x (for example, dy/dx) may be expressed by a constant or may be a linear or non-linear relationship. The present example assumes that the relationship (dy/dx) between y and x is expressed by a constant. Therefore, as will be described below, when the loading platform50is raised from its lowest position to its highest position, the electric actuator91maintains its output at approximately the same level.

Next, a displacement angle θ1(an angle from the X axis) of the first link member951R is determined based on the inverse kinematics or the geometrical relationship of the mechanism, specifically, based on the relationship among the position (x,0) of the first coupling part J1, a length L1of the first link member951R, the position (0,y) of the second coupling part J2, and a length L2of the second link member953R.

Next, the position (x0,y0) of a center J3of the shaft member952R is determined based on the position (x,0) of the first coupling part J1, the length L1of the first link member951R, and the displacement angle θ1of the first link member951R. By connecting the determined position (x0,y0) of the center J3of the shaft member952R, the shape of the guide hole971R is determined. There are two solutions for the displacement angle θ1of the first link member951R (there are two possible values for the displacement angle θ1). The present example adopts the smaller one of the two solutions (the two values) for the displacement angle θ1of the first link member951R, mainly to minimize the size of the guide holes971L and971R. As a result, the guide holes971L and971R have the shapes as illustrated inFIGS.9,10, etc.

The guide hole971R is formed to have a curved shape such that the shaft member952R can be smoothly moved therein. In the present example, the guide hole971R is formed to have a curved shape approximately like the letter “U” (or “V”). In this way, when the movable part93is moved in the direction that raises the loading platform50, the shaft member952R is first moved diagonally downward in the rear direction, and is next moved diagonally upward in the rear direction.

The control device100includes a power supply and a control circuit, and is installed adjacent to the electric motor911on the installation part37located inside and below the base30. The control device100receives the output signal of the encoder (rotation sensor)914.

The control device100controls the electric motor911of the electric actuator91based on the operation commands that are input via an input unit (not illustrated). In the present example, examples of the operation commands include an up command for raising the loading platform50, a down command for lowering the loading platform50, and a stop command for stopping the raising or lowering of the loading platform50. The stop command signifies stopping of the input of the up command and/or stopping of the input of the stop command Upon receiving the up command, the control device100rotates the electric motor911in a first direction (this rotation will be hereinafter referred to as “normal rotation”). Upon receiving the down command, the control device100rotates the electric motor911in a second direction opposite to the first direction (this rotation will be hereinafter referred to as “reverse rotation”). In addition, upon receiving the stop command, the control device100controls the electric motor911such that the loading platform50is held at its current vertical position.

Next, examples of the raising and lowering operations of the loading platform50of the cart10will be described with reference toFIGS.12to14. Although the following description will be made for a case in which no load is placed on the loading platform50, the following description also applies to a case in which a load is placed on the loading platform50.

FIG.12illustrates the state of the extendable mechanism70and the drive device90when the loading platform50is located at its lowest position.FIG.13illustrates the state of the extendable mechanism70and the drive device90when the loading platform50is located at an intermediate position.FIG.14illustrates the state of the extendable mechanism70and the drive device90when the loading platform50is located at its highest position.

For example, when the loading platform50is located at its lowest position, if an operator enters the up command to the input unit, the control device100causes the electric motor911of the electric actuator91to perform the normal rotation. Accordingly, the movable part93is moved backward, and the rear coupling shaft83of the extendable mechanism70is raised by the left link mechanism95L (the first link member951L, the shaft member952L, and the second link member953L) and the right link mechanism95R (the first link member951R, the shaft member952R, and the second link member953R). As a result, the pair of lower right and left X-shaped arms (the lower left X-shaped arm71L and the lower right X-shaped arm71R) and the pair of upper right and left X-shaped arms (the upper left X-shaped arm75L and the upper right X-shaped arm75R) extend upward, and the loading platform50is consequently raised. When the loading platform50reaches its highest position, the control device100stops the normal rotation of the electric motor911of the electric actuator91and controls the electric motor911of the electric actuator91such that the loading platform50is held at its highest position (FIG.12→FIG.13→FIG.14).

In addition, for example, when the loading platform50is located at its highest position, if the operator enters the down command to the input unit, the control device100causes the electric motor911of the electric actuator91to perform the reverse rotation. Accordingly, the movable part93is moved forward, and the rear coupling shaft83of the extendable mechanism70is lowered by the left link mechanism95L and the right link mechanism95R. As a result, the pair of lower right and left X-shaped arms (the lower left X-shaped arm71L and the lower right X-shaped arm71R) and the pair of upper right and left X-shaped arms (the upper left X-shaped arm75L and the upper right X-shaped arm75R) retract downward, and the loading platform50is consequently lowered. When the loading platform50reaches its lowest position, the control device100stops the reverse rotation of the electric motor911of the electric actuator91(FIG.14→FIG.13→FIG.12).

When the loading platform50has been raised or lowered to an intermediate position, if the operator enters the stop command to the input unit, the control device100stops the normal rotation or the reverse rotation of the electric motor911of the electric actuator91and controls the electric motor911of the electric actuator91such that the loading platform50is held at its current vertical position (the intermediate position) (FIG.13).

In the present example, the non-excited brake912is attached to the output shaft of the electric motor911of the electric actuator91. Thus, even when the power supply to the electric actuator91(the electric motor911) is stopped, the loading platform50is held at its current position.

FIG.15illustrates an example of a result of a comparison between the cart10according to the present example and a conventional cart of the same kind. Specifically,FIG.15illustrates the outputs of the electric actuators of these carts when their respective loading platforms on which a load is placed are raised from their lowest position to their highest position.

As indicated by a dashed line inFIG.15, in the case of the conventional cart of the same kind, the output of the electric actuator for raising the loading platform located at its lowest position is at its maximum level, and next, the output of the electric actuator decreases as the loading platform is raised. In contrast, in the case of the cart10according to the present example, as indicated by a solid line inFIG.15, the output of the electric actuator for raising the loading platform50located at its the lowest position is less than that of the conventional cart of the same kind. In addition, the output F of the electric actuator91is held at approximately the same level during the raising of the loading platform50from its lowest position to its highest position. Accordingly, the loading platform50is raised from its lowest position to its highest position at a constant speed.

As described above, the drive device90of the cart10according to the present example raises and lowers the loading platform50by vertically extending and retracting the pair of lower right and left X-shaped arms and the pair of upper right and left X-shaped arms. The drive device90includes the electric actuator91, the movable part93driven and moved by the electric actuator91, the pair of right and left link mechanisms (the left link mechanism95L and the right link mechanism95R), and the pair of right and left guide members (the left guide member97L and the right guide member97R).

The left link mechanism95L (the right link mechanism95R) includes a first link member951L (951R) of which the front end is rotatably coupled to the movable part93and a second link member953L (953R) of which the rear end is rotatably coupled to the rear coupling shaft83of the extendable mechanism70(that is, the pair of lower right and left X-shaped arms and the pair of upper right and left X-shaped arms) and of which the front end is rotatably coupled to the rear end of the first link member951L (951R) via a shaft member952L (952R). In addition, the left guide member97L (the right guide member97R) has the guide hole971L (the guide hole971R) for guiding the shaft member952L (the shaft member952R) that moves with the movement of the movable part93. The guide hole971L (971R) has a curved shape such that the shaft member952L (952R) can be smoothly moved therein.

The drive device90controls the electric actuator91such that the movable part93is moved longitudinally. With this movement of the movable part93, the rear coupling shaft83of the extendable mechanism70is pushed or pulled by the first link member951L (951R) and the second link member953L (953R). In this way, because the pair of upper right and left X-shaped arms and the pair of lower right and left X-shaped arms are extended or retracted vertically, the loading platform50is consequently raised or lowered.

The electric actuator91of the cart according to the present example needs a lower output for raising the loading platform50located at its lowest position than the output needed by the electric actuator of the conventional cart of the same kind. In addition, the fluctuation of the output of the electric actuator91needed to raise the loading platform50is reduced (seeFIG.15). Therefore, because the electric actuator91(the electric motor911) can have a smaller size than conventional electric actuators, the cost of the cart10can be reduced. In addition, the fluctuation in the rate of raising and lowering the loading platform50can be reduced.

In the example described above, the extendable mechanism70is formed as an X-shaped link mechanism in which a pair of right and left X-shaped arms are vertically stacked in two stages. However, the present invention is not limited to this example. The extendable mechanism70may be formed as an X-shaped link mechanism having a pair of right and left X-shaped arms in one stage or in three or more stages.

In addition, in the example described above, the left guide member97L has the guide hole971L for guiding the shaft member952L of the left link mechanism95L that moves with the movement of the movable part93, and the right guide member97R has the guide hole971R for guiding the shaft member952R of the right link mechanism95R that moves with the movement of the movable part93. However, the present invention is not limited to this example. The left guide member97L may have a guide groove instead of the guide hole971L, and/or the right guide member97R may have a guide groove instead of the guide hole971R.

In addition, in the example described above, the guide hole971L of the left guide member97L and the guide hole971R of the right guide member97R are formed to have a curved shape approximately like the letter “U” (or “V”). In this way, when the movable part93is moved in the direction that raises the loading platform50, the shaft members952L and952R are first moved diagonally downward in the rear direction and is next moved diagonally upward in the rear direction. However, the present invention is not limited to this example. The shape of the guide holes971L and971R varies depending on the length L1of the first link members951L and951R and the length L2of the second link members953L and953R. For example, as illustrated inFIG.16corresponding toFIG.9, the guide hole971L and the guide hole971R may be formed such that the shaft members952L and952R will first be moved horizontally in the rear direction and will next be moved diagonally upward as the movable part93is moved in the direction that raises the loading platform50.

If the longitudinal space for installing the electric actuator91is the same, the example described above can adopt longer first link members951L and952R and/or longer second link members953L and953R than the modification illustrated inFIG.16. As a result, the loading platform50can be raised to a higher position. In other words, if the loading platform50is raised to the same height, the example described above needs a smaller longitudinal space for installing the electric actuator91than the modification illustrated inFIG.16. Therefore, when the longitudinal space for installing the electric actuator91is limited, which is usually the case with carts, the example described above is more advantageous than the modification illustrated inFIG.16.

In addition, in the example described above, the electric actuator91is formed as a linear actuator that converts the rotational motion of the electric motor into linear motion by using a linear motion mechanism (for example, a ball screw mechanism) and outputs the linear motion. However, the present invention is not limited to this example. The electric actuator91may be any electric actuator that moves the movable part93linearly and longitudinally.

In addition, in the example described above, the relationship (dy/dx) between y and x for determining the shape of the guide holes971L and971R is expressed by a constant. However, the present invention is not limited to this example. As described above, the relationship (dy/dx) between y and x may be a linear or a non-linear relationship. If the relationship between y and x varies, the shape of the guide holes971L and971R varies. If the shape of the guide holes971L and971R varies, the output of the electric actuator91that is needed to raise the loading platform50and the raising speed of the loading platform50vary. In other words, the raising characteristics of the loading platform50can be changed based on the shape of the guide holes971L and971R. Therefore, the cart10according to the example is advantageous in that demands about the raising characteristics of the loading platform50can be accommodated relatively flexibly.

In addition, as illustrated inFIG.17, the cart10may further include a position detection unit110that can detect the vertical position of the top surface of the loading platform50and the vertical position of the top surface of a load placed on the loading platform50. Although the construction of the position detection unit110is not particularly limited, the position detection unit110includes a TOF range image sensor that sets a predetermined range on the top surface of the loading platform50as its range area, for example. The position detection unit110is disposed at a predetermined position on a support120attached to the handle40, the predetermined position being located above the handle40, and is disposed to face the loading platform50. As with the handle40, the support120has an approximately gate shape (an approximately inverted U-shape), for example, and holds the position detection unit110via a bracket (not illustrated).

When no load is placed on the loading platform50, the position detection unit110can detect the vertical position of the top surface of the loading platform50. When a load is placed on the loading platform50, the position detection unit110can detect the vertical position of the top surface of the load placed on the loading platform50. The position detected by the position detection unit110is output to the control device100.

The cart10illustrated inFIG.17can perform the following operations, in addition to raising and lowering the loading platform50and holding the loading platform50at predetermined vertical positions.

For example, to place a load on the loading platform50, an operator enters the up command to the input unit, and the loading platform50on which no load has been placed is raised to a predetermined vertical position from its lowest position. Next, the operator enters the stop command to the input unit. As a result, the loading platform50is held at the predetermined vertical position, and the operator starts to place a load on the loading platform50held at the predetermined vertical position.

When the control device100receives the stop command (or when the loading platform50is held at the predetermined vertical position), the control device100stores the position detected by the position detection unit110then as a reference position. The control device100controls the electric motor911of the electric actuator91such that the position detected by the position detection unit110maintains the reference position until the vertical position at which the loading platform50is held is changed.

In this case, when a load is placed on the loading platform50, the position detection unit110detects a position higher than the reference position. Thus, the control device100causes the electric motor911to perform the reverse rotation and lowers the loading platform50such that the position detected by the position detection unit110matches the reference position. Next, when the cart is moved to the transportation destination of the load and the load is removed from the loading platform50, the position detection unit110detects a position lower than the reference position. Thus, the control device100causes the electric motor911to perform the normal rotation and raises the loading platform50such that the position detected by the position detection unit110matches the reference position.

In this way, the vertical position of the top surface of the loading platform50on which no load is placed and the vertical position of the top surface of a load placed on the loading platform50, that is, the position on which the operator places a load and the position from which the operator removes a load are held at approximately the same level. That is, when the operator places loads on the loading platform50in a plurality of stages, the operator can place each load on the loading platform50located at the same height. In addition, when the operator removes loads placed in a plurality of stages on the loading platform50, the operator can remove each load from the loading platform50located at the same height. Thus, the burden on the operator can be greatly reduced.

Although examples and modifications of the present invention have thus been described, the present invention is not limited thereto. Further variations and modifications are of course possible based on the basic technical concepts of the present invention.

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