Transport trolley

Abstract

To provide a carrying truck capable of mitigating the impact applied on a load when the load is placed on a loading space.SOLUTION: In a carrying truck 10, a driving device expanding / contracting an expansion mechanism 70 in a vertical direction by rotation of an electric motor to lift / lower a loading space 50, has back drive performance in which the electric motor is rotated by the expansion / contraction of the expansion mechanism 70 accompanying the lifting / lowering of the loading space 50 due to external force. When the lowering of the loading space 50 held at a prescribed lifting / lowering position and the increase in a load acting on the loading space 50 are detected based on output signals of a rotation sensor for detecting the rotation of the electric motor and a current sensor for detecting a driving current of the electric motor, a control device controls the electric motor so as to lift and hold the lowered loading space 50 at the prescribed lifting / lowering position or hold the loading space at a lifting / lowering position lower than the prescribed lifting / lowering position.SELECTED DRAWING: Figure 17

Description

Technical Field

[0001] The present invention relates to a transport cart capable of raising and lowering a loading platform.

Background Art

[0002] As an example of this type of transport cart, Patent Document 1 describes a transport cart in which a lift arm (X-shaped arm) is telescopically driven by an electric cylinder (electric actuator) to raise and lower a loading platform.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a transport cart capable of raising and lowering a loading platform, the loading platform is usually fixedly held at a predetermined lifting position such as the uppermost position or an intermediate position between the uppermost position and the lowermost position. For this reason, there has been a problem that when a load is placed on the loading platform, the load is likely to receive an impact from the loading platform.

[0005] Therefore, an object of the present invention is to provide a transport cart capable of reducing the impact received by a load when placed on the loading platform.

Means for Solving the Problems

[0006] According to one aspect of the present invention, a transport cart is provided. The transport cart includes a base with wheels attached to the lower part, a loading platform disposed above the base, a telescopic mechanism provided between the base and the loading platform and capable of telescoping in the vertical direction, a driving device that expands and contracts the telescopic mechanism in the vertical direction by the rotation of an electric motor to raise and lower the loading platform, a rotation sensor that detects the rotation of the electric motor and outputs a signal, a current sensor that detects the drive current of the electric motor and outputs a signal, and a control device that controls the electric motor to raise and lower the loading platform to a predetermined raising and lowering position based on an operation command and hold the loading platform at the predetermined raising and lowering position. The driving device has a back-driving property in which the electric motor rotates due to the expansion and contraction of the telescopic mechanism accompanying the raising and lowering of the loading platform by an external force, and the control device, when detecting a decrease in the loading platform held at the predetermined raising and lowering position and an increase in the load acting on the loading platform based on the output signals of the rotation sensor and the current sensor, controls the electric motor to raise the lowered loading platform and hold it at the predetermined raising and lowering position or hold it at a raising and lowering position below the predetermined raising and lowering position. The telescopic mechanism includes a pair of first left X-shaped arms and first right X-shaped arms that can be telescoped in the vertical direction. Each of the first left X-shaped arm and the first right X-shaped arm has two arms that cross in an X shape in a side view and are combined so as to be relatively rotatable with each other. One end of one of the two arms of the first left X-shaped arm is rotatably attached near the left end of a connecting shaft extending in the left-right direction, and one end of the arm corresponding to the one arm of the first left X-shaped arm among the two arms of the first right X-shaped arm is rotatably attached near the right end of the connecting shaft. The driving device includes the electric motor, a ball screw shaft that extends in the front-rear direction and is rotationally driven by the electric motor via a speed reduction mechanism, a ball screw nut that moves in the axial direction of the ball screw shaft as the ball screw shaft rotates, a movable body provided integrally with the ball screw nut, a first link member having one end rotatably connected to the movable body, a second link member having one end rotatably connected to the connecting shaft and the other end rotatably connected to the other end of the first link member via a shaft member, and a guide member in which a guide hole or a guide groove for guiding the movement of the shaft member accompanying the movement of the movable body is formed. It is configured such that the first left X-shaped arm and the first right X-shaped arm are telescoped in the vertical direction via the first link member and the second link member by the movement of the movable body. The guide hole or the guide groove is formed to be curved in a substantially U shape so that the shaft member is moved obliquely downward and then obliquely upward as the movable body moves in the direction of raising the loading platform.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a transport cart capable of alleviating the impact received by a load when placed on the loading platform.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

[0010] [First Embodiment] Figs. 1 to 4 show the configuration of a carrier truck 10 with a push handle according to the first embodiment of the present invention. Fig. 1 is a view of the carrier truck 10 seen from the front, Fig. 2 is a view of the carrier truck 10 seen from the rear, Fig. 3 is a view of the carrier truck 10 seen from the right side, and Fig. 4 is a view of the carrier truck 10 seen from the left side.

[0011] As shown in Figs. 1 to 4, the carrier truck 10 according to the embodiment includes a base 30, a push handle (hereinafter referred to as "handle") 40, a loading platform 50 disposed above the base 30, a telescopic mechanism 70 provided between the base 30 and the loading platform 50, a driving device 90 for driving (telescoping) the telescopic mechanism 70, and a control device 100 for controlling the driving device 90.

[0012] Fig. 5 is a perspective view mainly showing the base 30 and the handle 40 of the carrier truck 10.

[0013] As shown in Fig. 5, the base 30 is formed as a rectangular frame-shaped frame. The base 30 has a front frame member 31A and a rear frame member 31B extending in the left-right direction, and a pair of left and right frame members (left frame member 32L and right frame member 32R) extending in the front-rear direction. Further, free caster wheels (front wheels) 33, 33 are attached to the lower parts of the front two corners among the four corners of the base 30, and electric drive wheels (rear wheels) 34, 34 in which, for example, in-wheel motors are incorporated are attached to the lower parts of the rear two corners.

[0014] In the base 30, a left rail portion 35L extending in the front-rear direction is provided on the inner surface of the front side of the left frame member 32L, and a right rail portion 35R paired with the left rail portion 35L is provided on the inner surface of the front side of the right frame member 32R. Further, on the rear side of the base 30, a pair of mounting portions (left mounting portion 36L and right mounting portion 36R) spaced apart in the left-right direction are provided. Furthermore, an installation portion 37 where the drive device 90 and the control device 100 are installed is provided inside the base 30 and at a position lower than the base 30.

[0015] The handle 40 is attached to the rear frame member 31B in an upright state. The handle 40 is made of, for example, a pipe material and is formed in a substantially portal shape (substantially inverted U shape). Specifically, the handle 40 has a pair of left and right support portions 41, 41 that extend substantially vertically upward from the rear frame member 31B and then extend obliquely rearward, and a gripping portion 43 that extends substantially horizontally between the tip ends of the pair of left and right support portions 41, 41. The gripping portion 43 is a portion mainly gripped by an operator or the like (hereinafter simply referred to as "operator") who uses the transport cart 10.

[0016] Returning to FIGS. 1 to 4, the loading platform 50 has a rectangular top plate portion 51 on which a load (not shown) is placed on the upper surface, and a peripheral wall portion 53 that hangs down from the peripheral edge portion of the top plate portion 51. On the front side of the lower surface of the top plate portion 51, a pair of left and right rail members (left rail member 55L and right rail member 55R) each having a rail groove are provided, and on the rear side of the lower surface of the top plate portion 51, a pair of mounting portions (left mounting portion 56L and right mounting portion 56R) spaced apart in the left-right direction project.

[0017] The telescopic mechanism 70 is configured such that a pair of left and right X-shaped arms (also called pantograph arms) expand and contract in the vertical direction to raise and lower the loading platform 50 relative to the base 30 in a parallel state. Here, the telescopic mechanism 70 is usually extended and retracted when the transport cart 10 is on a horizontal plane, that is, when the base 30 is in a horizontal state. For this reason, it can also be said that the telescopic mechanism 70 is configured to raise and lower the loading platform 50 in a horizontal state by the expansion and contraction of a pair of left and right X-shaped arms in the vertical direction. In the present embodiment, the telescopic mechanism 70 is formed as an X-shaped link mechanism having a two-stage structure in which a pair of left and right X-shaped arms are stacked vertically.

[0018] Figures 6 to 8 show the configuration of the telescopic mechanism 70. Figure 6 is a view of the telescopic mechanism 70 seen from the right side, Figure 7 is a view of the telescopic mechanism 70 seen from the left side, and Figure 8 is a perspective view of the telescopic mechanism 70.

[0019] As shown in Figures 6 to 8, in the present embodiment, the telescopic mechanism 70 includes a pair of left and right X-shaped arms on the lower stage side (left lower stage X-shaped arm 71L and right lower stage X-shaped arm 71R), and a pair of left and right X-shaped arms on the upper stage side (left upper stage X-shaped arm 75L and right upper stage X-shaped arm 75R).

[0020] Each of the left lower stage X-shaped arm 71L and the right lower stage X-shaped arm 71R, which are a pair of left and right X-shaped arms on the lower stage side, is formed by combining an inner lower arm and an outer lower arm that cross each other in an X shape in a side view and are relatively rotatable with respect to each other. Specifically, in the present embodiment, the left lower stage X-shaped arm 71L is configured such that the central portion of the inner lower arm 72L and the central portion of the outer lower arm 74L are rotatably attached near the left end portion of the lower connecting shaft 81 extending in the left-right direction (see Figures 7 and 8). Similarly, the right lower stage X-shaped arm 71R is configured such that the central portion of the inner lower arm 72R and the central portion of the outer lower arm 74R are rotatably attached near the right end portion of the lower connecting shaft 81 (see Figures 6 and 8).

[0021] Each of the left upper X-shaped arm 75L and the right upper X-shaped arm 75R, which are a pair of left and right X-shaped arms on the upper stage, is also formed by combining an upper inner arm and an upper outer arm that cross each other in an X shape in a side view and are relatively rotatable with respect to each other. Specifically, in the present embodiment, the left upper X-shaped arm 75L is configured such that the central portion of the upper inner arm 76L and the central portion of the upper outer arm 78L are each rotatably attached in the vicinity of the left end portion of the upper connecting shaft 82 that extends in the left-right direction above the lower connecting shaft 81 (see FIGS. 7 and 8). Similarly, the right upper X-shaped arm 75R is configured such that the central portion of the upper inner arm 76R and the central portion of the upper outer arm 78R are each rotatably attached in the vicinity of the right end portion of the upper connecting shaft 82 (see FIGS. 6 and 8).

[0022] The pair of left and right X-shaped arms on the lower stage (left lower X-shaped arm 71L and right lower X-shaped arm 71R) and the pair of left and right X-shaped arms on the upper stage (left upper X-shaped arm 75L and right upper X-shaped arm 75R) are connected via a rear connecting shaft 83 and a front connecting shaft 84 that extend in the left-right direction.

[0023] Specifically, in the present embodiment, the rear end portion of the lower inner arm 72L that constitutes the left lower X-shaped arm 71L and the rear end portion of the upper outer arm 78L that constitutes the left upper X-shaped arm 75L are each rotatably attached in the vicinity of the left end portion of the rear connecting shaft 83 (see FIGS. 7 and 8), and the rear end portion of the lower inner arm 72R that constitutes the right lower X-shaped arm 71R and the rear end portion of the upper outer arm 78R that constitutes the right upper X-shaped arm 75R are each rotatably attached in the vicinity of the right end portion of the rear connecting shaft 83 (see FIGS. 6 and 8).

[0024] Further, the front end portions of the lower outer arm 74L that constitutes the lower left X-shaped arm 71L and the upper inner arm 76L that constitutes the upper left X-shaped arm 75L are each rotatably attached in the vicinity of the left end portion of the front connecting shaft 84 (see FIGS. 7 and 8). The front end portions of the lower outer arm 74R that constitutes the lower right X-shaped arm 71R and the upper inner arm 76R that constitutes the upper right X-shaped arm 75R are each rotatably attached in the vicinity of the right end portion of the front connecting shaft 84 (see FIGS. 6 and 8).

[0025] The front end portion of the lower inner arm 72L that constitutes the lower left X-shaped arm 71L is rotatably attached inside the left end portion of the lower moving shaft 85 that extends in the left-right direction below the front connecting shaft 84 and is movable in the front-rear direction (see FIGS. 7 and 8). The front end portion of the lower inner arm 72R that constitutes the lower right X-shaped arm 71R is rotatably attached inside the right end portion of the lower moving shaft 85 (see FIGS. 6 and 8).

[0026] The left end portion of the lower moving shaft 85 is inserted into the left rail portion 35L provided on the left frame member 32L of the base 30, and the right end portion of the lower moving shaft 85 is inserted into the right rail portion 35R provided on the right frame member 32R of the base 30 (see FIGS. 3 to 8). That is, in the present embodiment, both ends of the lower moving shaft 85 are supported by the left rail portion 35L and the right rail portion 35R provided on the base 30, and it is configured to be movable in the front-rear direction along the left rail portion 35L and the right rail portion 35R.

[0027] [[ID= (12)]]Further, the rear end portion of the lower outer arm 74L that constitutes the lower left X-shaped arm 71L is rotatably fixed via the pin member P1 to the left attachment portion 36L provided on the rear side of the base 30. The rear end portion of the lower outer arm 74R that constitutes the lower right X-shaped arm 71R is rotatably fixed via the pin member P1 to the right attachment portion 36R provided on the rear side of the base 30 (see FIGS. 3 to 8).

[0028] The front end of the upper outer arm 78L that constitutes the upper left X-shaped arm 75L extends horizontally above the front connecting shaft 84 and is rotatably attached inside the left end of the upper moving shaft 86 that can move in the front-rear direction (see FIGS. 7 and 8). The front end of the upper outer arm 78R that constitutes the upper right X-shaped arm 75R is rotatably attached inside the right end of the upper moving shaft 86 (see FIGS. 6 and 8).

[0029] The left end of the upper moving shaft 86 is inserted into the rail groove of the left rail member 55L provided on the lower surface of the loading platform 50 (the top plate portion 51 thereof). The right end of the upper moving shaft 86 is inserted into the rail groove of the right rail member 55R provided on the lower surface of the loading platform 50 (the top plate portion 51 thereof), which is paired with the left rail member 55L (see FIGS. 1 to 4, FIGS. 6 to 8). That is, in the present embodiment, the upper moving shaft 86 is supported at both ends by the left rail member 55L and the right rail member 55R provided on the lower surface of the loading platform 50, and is configured to be movable in the front-rear direction along the rail groove of the left rail member 55L and the rail groove of the right rail member 55R.

[0030] The rear end of the upper inner arm 76L that constitutes the upper left X-shaped arm 75L is rotatably fixed via a pin member P2 to the left attachment portion 56L protruding from the lower surface of the loading platform 50 (the top plate portion 51 thereof) (see FIGS. 2, 4, and 6 to 8). Further, the rear end of the upper inner arm 76R that constitutes the upper right X-shaped arm 75R is rotatably fixed via a pin member P2 to the right attachment portion 56R protruding from the lower surface of the loading platform 50 (the top plate portion 51 thereof), which is paired with the left attachment portion 56L (see FIGS. 2, 3, and 6 to 8).

[0031] The drive device 90 is installed on an installation portion 37 provided inside the base 30 and one step lower than the base 30. The drive device 90 expands and contracts a pair of left and right X-shaped arms on the lower stage (left lower stage X-shaped arm 71L and right lower stage X-shaped arm 71R) and a pair of left and right X-shaped arms on the upper stage (left upper stage X-shaped arm 75L and right upper stage X-shaped arm 75R) that constitute the expansion and contraction mechanism 70 by the rotation of an electric motor as a drive source, and thereby is configured to raise and lower the loading platform 50.

[0032] Also, in the present embodiment, the drive device 90 is configured to have so-called back drivability. Specifically, the drive device 90 is configured such that an electric motor as a drive source rotates by the vertical expansion and contraction of the expansion and contraction mechanism 70 (a pair of left and right X-shaped arms on the lower stage and a pair of left and right X-shaped arms on the upper stage) accompanying the raising and lowering of the loading platform 50 due to an external force (and change in external force).

[0033] Figs. 9 to 11 show the configuration of the drive device 90. Fig. 9 is a view of the drive device 90 seen from the right side, Fig. 10 is a view of the drive device 90 seen from the left side, and Fig. 11 is a view A of Fig. 9.

[0034] As shown in Figs. 9 to 11, in the present embodiment, the drive device 90 includes an electric actuator 91, a movable body 93 that is driven by the electric actuator 91 to move, a pair of left and right link mechanisms (left link mechanism 95L, right link mechanism 95R) as a connection mechanism that connects the movable body 93 and the expansion and contraction mechanism 70, and a pair of left and right guide members (left guide member 97L, right guide member 97R).

[0035] The electric actuator 91 is a linear actuator that converts the rotational motion of an electric motor as a drive source into linear motion by a ball screw mechanism and outputs it. In the present embodiment, the electric actuator 91 includes an electric motor (servo motor) 911, a pulley-belt mechanism 913A and a planetary gear mechanism 913B as a speed reduction mechanism, and a ball screw mechanism (ball screw shaft 915A and ball screw nut 915B).

[0036] The operation of the electric motor 911 is controlled by the control device 100. An unexcited operation type brake 912 is attached to the output shaft of the electric motor 911 via, for example, a coupling, and an encoder (rotation sensor) 914 that detects the rotation of the electric motor 911 and outputs a signal is attached to the electric motor 911.

[0037] The pulley-belt mechanism 913A and the planetary gear mechanism 913B as the speed reduction mechanisms reduce the rotation of the output shaft of the electric motor 911 and transmit it to the ball screw shaft 915A. The pulley-belt mechanism 913A constitutes the first-stage speed reduction mechanism, and the planetary gear mechanism 913B constitutes the second-stage speed reduction mechanism. That is, in the present embodiment, the rotation of the electric motor 911 is reduced in two stages and transmitted to the ball screw mechanism (ball screw shaft 915A). However, it is not limited to this. The speed reduction mechanism only needs not to impair the above-described backdriveability, and may be a single-stage speed reduction mechanism or a multi-stage speed reduction mechanism.

[0038] The ball screw shaft 915A extends in the front-rear direction and is rotatably supported by support members 916A and 916B to which bearings (not shown) are attached. The ball screw shaft 915A is rotationally driven by the electric motor 911 via the pulley-belt mechanism 913A and the planetary gear mechanism 913B. The ball screw nut 915B is screwed onto the ball screw shaft 915A and moves axially on the ball screw shaft 915A (that is, linearly moves in the front-rear direction) as the ball screw shaft 915A rotates.

[0039] The movable body 93 is fixed to the ball screw nut 915B and moves integrally with the ball screw nut 915B. In the present embodiment, a linear slider 94 is installed below the ball screw shaft 915A. The linear slider 94 has a slide rail 94A extending in the front-rear direction and a slide block 94B that moves on the slide rail 94A. The lower part of the movable body 93 fixed to the ball screw nut 915B is fixed to the slide block 94B.

[0040] As the left link mechanism 95L and the right link mechanism 95R as the connection mechanisms, by pushing and pulling the rear connection shaft 83 of the expansion and contraction mechanism 70 as the movable body 93 moves, a pair of left and right X-shaped arms on the lower stage (left lower stage X-shaped arm 71L and right lower stage X-shaped arm 71R) and a pair of left and right X-shaped arms on the upper stage (left upper stage X-shaped arm 75L and right upper stage X-shaped arm 75R) are configured to expand and contract in the vertical direction.

[0041] Specifically, in this embodiment, the left link mechanism 95L includes a first link member 951L whose front end is rotatably connected to the left side surface of the movable body 93, and a rear end is rotatably connected to the rear connection shaft 83 of the expansion and contraction mechanism 70 (that is, a pair of left and right X-shaped arms 71L, 71R on the lower stage and a pair of left and right X-shaped arms 75L, 75R on the upper stage), and a second link member 953L whose front end is rotatably connected to the rear end of the first link member 951L via a shaft member 952L. Similarly, the right link mechanism 95R includes a first link member 951R whose front end is rotatably connected to the right side surface of the movable body 93, and a rear end is rotatably connected to the rear connection shaft 83 of the expansion and contraction mechanism 70, and a second link member 953R whose front end is rotatably connected to the rear end of the first link member 951R via a shaft member 952R. Further, the first link member 951L of the left link mechanism 95L and the first link member 951R of the right link mechanism 95R are connected by a connection plate 954.

[0042] The left guide member 97L and the right guide member 97R are respectively arranged on both the left and right sides of the electric actuator 91 with the electric actuator 91 sandwiched therebetween on the rear side of the installation portion 37 provided one step lower than the base 30 inside the base 30. A guide hole 971L for guiding the movement of the shaft member 952L of the left link mechanism 95L as the movable body 93 moves is formed in the left guide member 97L, and a guide hole 971R for guiding the movement of the shaft member 952R of the right link mechanism 95R as the movable body 93 moves is formed in the right guide member 97R. The guide hole 971L of the left guide member 97L and the guide hole 971R of the right guide member 97R are formed in the same shape.

[0043] The shapes of the guide holes 971L of the left guide member 97L and the guide holes 971R of the right guide member 97R are determined as follows, for example. Here, the shape of the guide hole 971R of the right guide member 97R will be described with reference to FIG. 9, but the same applies to the shape of the guide hole 971L of the left guide member 97L.

[0044] First, when the loading platform 50 moves up and down between the lowest position and the uppermost position, it is assumed that the first connection part J1 between the movable body 93 and the front end part of the first link member 951R moves on the X axis, and the second connection part J2 between the second link member 953R and the rear connection shaft 83 moves on the Y axis (see FIG. 9).

[0045] Next, the relationship between the position (x, 0) of the first connection part J1 and the position (0, y) of the second connection part J2, that is, the relationship between x and y, is determined by physical laws (here, the principle of virtual work). The relationship between y and x (for example, dy / dx) may be a constant, linear, or non-linear. In the present embodiment, the relationship (dy / dx) between y and x is set as a constant, so that, as will be described later, the output of the electric actuator 91 (electric motor 911) is substantially constant while the loading platform 50 is raised from the lowest position to the uppermost position.

[0046] Next, based on the relationship between the position (x, 0) of the first connection part J1, the length L1 of the first link member 951R, the position (0, y) of the second connection part J2, and the length L2 of the second link member 953R, specifically by inverse kinematics or the geometric relationship of the mechanism, the displacement angle θ1 (angle with respect to the X axis) of the first link member 951R is obtained.

[0047] Then, based on the position (x, 0) of the first connecting portion J1, the length L1 of the first link member 951R, and the displacement angle θ1 of the first link member 951R, the position (x0, y0) of the center J3 of the shaft member 952R is obtained, and the shape of the guide hole 971R is determined by connecting the obtained positions (x0, y0) of the center J3 of the shaft member 952R. Here, there are two solutions for the displacement angle θ1 of the first link member 951R (the displacement angle θ1 can take two values). In the present embodiment, mainly to reduce the sizes of the guide holes 971L and 971R, the smaller of the two solutions (two values) is adopted as the displacement angle θ1 of the first link member 951R. As a result, the guide holes 971L and 971R have the shapes shown in FIG. 9, FIG. 10, etc.

[0048] Note that the guide hole 971R is formed to have a curved shape so that the shaft member 952R can move smoothly. In the present embodiment, the guide hole 971R is curved in a substantially U shape (or substantially V shape) so that the shaft member 952R moves obliquely downward backward and then obliquely upward as the movable body 93 moves in the direction of raising the loading platform 50.

[0049] The control device 100 is installed adjacent to the electric motor 911 in an installation portion 37 provided inside the base 30 and one step lower than the base 30. FIG. 12 is a diagram showing a schematic configuration of the control device 100. As shown in FIG. 12, the control device 100 includes a power source 101, a control circuit 102, a motor drive circuit 103, and a current sensor 104 that detects the current (motor drive current) flowing through the electric motor 911 and outputs a signal. Further, output signals of the encoder 914 and the current sensor 104 are input to the control circuit 102, and an operation command of the loading platform 50 is input via an input portion (not shown).

[0050] The control device 100 (control circuit 102) controls the electric motor 911 based on the operation command of the loading platform 50 input via the input unit. In the present embodiment, the operation command includes a raising command for raising the loading platform 50, a lowering command for lowering the loading platform 50, and a stop command for stopping the raising and lowering of the loading platform 50. Further, the input of the stop command includes the stop of the input of the raising command and / or the stop of the input of the lowering command. Then, when the raising command is input, the control device 100 rotationally drives the electric motor 911 in the first direction (hereinafter referred to as "forward rotation drive"), and when the lowering command is input, the control device 100 rotationally drives the electric motor 911 in the second direction opposite to the first direction (hereinafter referred to as "reverse rotation drive"). Also, when the stop command is input, the control device 100 controls the electric motor 911 to hold the loading platform 50 at the raising and lowering position at that time.

[0051] Also, in the present embodiment, when the control device 100 holds the loading platform 50 at a predetermined raising and lowering position, if it detects the lowering of the loading platform 50 based on the output signal of the encoder 914, and detects an increase in the motor drive current based on the output signal of the current sensor 104, in other words, an increase in the load acting on the loading platform 50, it controls the electric motor 911 to raise the lowered loading platform 50 to the predetermined raising and lowering position and hold the loading platform 50 at the predetermined raising and lowering position.

[0052] Furthermore, in the present embodiment, when the control device 100 holds the loading platform 50 at a predetermined raising and lowering position, if it detects the raising of the loading platform 50 based on the output signal of the encoder 914, and detects a decrease in the motor drive current based on the output signal of the current sensor 104, in other words, a decrease in the load acting on the loading platform 50, it controls the electric motor 911 to lower the raised loading platform 50 to the predetermined raising and lowering position and hold the loading platform 50 at the predetermined raising and lowering position.

[0053] Next, an operation example of the transport cart 10 will be described.

[0054] (Raising and lowering operation of the loading platform 50) FIG. 13 shows the states of the telescopic mechanism 70 and the drive device 90 when the loading platform 50 is in the lowest position, FIG. 14 shows the states of the telescopic mechanism 70 and the drive device 90 when the loading platform 50 is in the intermediate position, and FIG. 15 shows the states of the telescopic mechanism 70 and the drive device 90 when the loading platform 50 is in the uppermost position.

[0055] For example, when an operator inputs the raising command via the input unit while the loading platform 50 is in the lowest position, the control device 100 drives the electric motor 911 to rotate forward. Then, the movable body 93 moves rearward, and the rear connecting shaft 83 of the telescopic mechanism 70 is pushed upward via the left link mechanism 95L (the first link member 951L, the shaft member 952L, and the second link member 953L) and the right link mechanism 95R (the first link member 951R, the shaft member 952R, and the second link member 953R). As a result, the telescopic mechanism 70, more specifically, the pair of left and right X-shaped arms on the lower stage side (the left lower stage X-shaped arm 71L and the right lower stage X-shaped arm 71R) and the pair of left and right X-shaped arms on the upper stage side (the left upper stage X-shaped arm 75L and the right upper stage X-shaped arm 75R) extend upward, and the loading platform 50 rises. Then, when the loading platform 50 rises to the uppermost position, the control device 100 stops the forward rotation drive of the electric motor 911 and controls the electric motor 911 to hold the loading platform 50 in the uppermost position (FIG. 13 → FIG. 14 → FIG. 15).

[0056] Also, for example, when an operator inputs the lowering command via the input unit while the loading platform 50 is in the uppermost position, the control device 100 drives the electric motor 911 to rotate reversely. Then, the movable body 93 moves forward, and the rear connecting shaft 83 of the telescopic mechanism 70 is pulled downward via the left link mechanism 95L and the right link mechanism 95R. As a result, the telescopic mechanism 70, more specifically, the pair of left and right X-shaped arms on the lower stage side (the left lower stage X-shaped arm 71L and the right lower stage X-shaped arm 71R) and the pair of left and right X-shaped arms on the upper stage side (the left upper stage X-shaped arm 75L and the right upper stage X-shaped arm 75R) contract downward, and the loading platform 50 descends. Then, when the loading platform 50 descends to the lowest position, the control device 100 stops the reverse rotation drive of the electric motor 911 (FIG. 15 → FIG. 14 → FIG. 13).

[0057] When the operator inputs the stop command via the input unit when the loading platform 50 has risen or fallen to the intermediate position, the control device 100 stops the forward or reverse drive of the electric motor 911 and controls the electric motor 911 to hold the loading platform 50 at the lifting position (intermediate position) at that time (Fig. 14).

[0058] Here, in the present embodiment, a non-excitation operation type brake 912 is attached to the output shaft of the electric motor 911. For this reason, even when the supply of power to the electric motor 911 is stopped, the loading platform 50 is held at its position at that time.

[0059] Fig. 16 is a diagram showing an example of a comparison result between the transport cart 10 according to the embodiment and a conventional transport cart of the same type, and shows the output of the electric actuator when the loading platform with a load placed thereon is raised from the lowest position to the highest position.

[0060] As shown by the broken line in Fig. 16, in a conventional transport cart of the same type, the output of the electric actuator is maximum when raising the loading platform at the lowest position, and then the output of the electric actuator decreases as the loading platform rises. In contrast, in the transport cart 10 according to the embodiment, as shown by the solid line in Fig. 16, the output of the electric actuator when raising the loading platform 50 at the lowest position is smaller than that of the conventional transport cart of the same type, and during the raising of the loading platform 50 from the lowest position to the highest position, the output F of the electric actuator 91 is substantially constant. Accordingly, during the raising of the loading platform 50 from the lowest position to the highest position, the raising speed of the loading platform 50 also becomes constant.

[0061] (Operation when a load is placed on the loading platform 50) Fig. 17 is a diagram for explaining an example of the operation of the transport cart 10 when a load is placed on the loading platform 50.

[0062] First, the operator inputs the lifting command via the input unit to raise the platform 50 at the lowest position to a predetermined lifting position (hereinafter referred to as the "first lifting position") (FIG. 17(A)). Thereby, the control device 100 controls the electric motor 911 to hold the platform 50 at the first lifting position.

[0063] Next, the operator places the load W on the platform 50 held at the first lifting position. Here, as described above, in the present embodiment, the driving device 90 has back-drivability, and is configured such that the electric motor 911 rotates due to the vertical expansion and contraction of the expansion and contraction mechanism 70 accompanying the lifting and lowering of the platform 50 by an external force (or change in external force). Therefore, when the load W is placed on the platform 50, the load of the placed load W (that is, the increase in the load applied to the platform 50) causes the platform 50 to descend from the first lifting position and the expansion and contraction mechanism 70 to contract downward (FIG. 17(B)), and as a result, the electric motor 911 rotates in the second direction. The rotation of the electric motor 911 in the second direction at this time is detected by the encoder 914, and the encoder 914 outputs a signal corresponding to the rotation of the electric motor 911 in the second direction to the control circuit 102 of the control device 100. Further, the output signal of the current sensor 104 is input to the control circuit 102 of the control device 100.

[0064] The control circuit 102 of the control device 100 detects the rotation of the electric motor 911 in the second direction (that is, the lowering of the platform 50) based on the output signal of the encoder 914 and detects the increase in the motor drive current based on the output signal of the current sensor 104. Then, the control device 100 determines that the load applied to the platform 50 has increased due to the load W being placed on the platform 50, and as a result, the platform 50 has descended from the first lifting position where it was held. In this case, the control device 100 controls the electric motor 911 to raise the lowered platform 50 and hold the platform 50 at the first lifting position.

[0065] For example, the control device 100 obtains the increase amount of the motor drive current based on the output signal of the current sensor 104, and estimates the increase amount of the load acting on the loading platform 50 based on the obtained increase amount of the motor drive current. Further, the control device 100 obtains the rotation amount of the electric motor 911 in the second direction based on the output signal of the encoder 914, and estimates the descent amount of the loading platform 50 from the first lifting position based on the obtained rotation amount. Note that the control device 100 may obtain the rotation speed of the electric motor 911 in the second direction based on the output signal of the encoder 914, and estimate the increase amount of the load acting on the loading platform 50 based on the obtained rotation speed and the increase amount of the motor drive current. Then, the control device 100 increases the output (torque) of the electric motor 911 according to the estimated increase amount of the load acting on the loading platform 50, and drives the electric motor 911 to rotate forward according to the estimated descent amount to raise the loading platform 50, and holds the loading platform 50 at the raised position. Thereby, the loading platform 50 is held at the first lifting position even after the load W is placed thereon (FIG. 17(C)).

[0066] (Operation when the load is removed from the loading platform 50) FIG. 18 is a diagram for explaining an example of the operation of the carrier 10 when the load is removed from the loading platform 50.

[0067] FIG. 18(A) shows the carrier 10 in a state where the load W is placed on the loading platform 50 and the loading platform 50 is held at a predetermined lifting position (hereinafter referred to as the "second lifting position"). In this case, the control device 100 controls the electric motor 911 to hold the loading platform 50 at the second lifting position.

[0068] When an operator takes out a load W from the loading platform 50 held at the second lifting position, the load acting on the loading platform 50 decreases by the amount of the taken-out load W. For this reason, the electric motor 911 rotates in the first direction and the loading platform 50 rises from the second lifting position (FIG. 18(B)). The rotation of the electric motor 911 in the first direction at this time is detected by the encoder 914, and the encoder 914 outputs a signal corresponding to the rotation of the electric motor 911 in the first direction to the control device 100 (control circuit 102 thereof). Further, the output signal of the current sensor 104 is input to the control circuit 102 of the control device 100.

[0069] The control device 100 (control circuit 102 thereof) detects the rotation of the electric motor 911 in the first direction (i.e., the rise of the loading platform 50) based on the output signal of the encoder 914 and detects the decrease in the motor drive current based on the output signal of the current sensor 104. Then, the control device 100 determines that the load acting on the loading platform 50 has decreased because the load W has been taken out from the loading platform 50, and as a result, the loading platform 50 has risen from the second lifting position, which is the held position. In this case, the control device 100 controls the electric motor 911 to lower the raised loading platform 50 and hold the loading platform 50 at the second lifting position.

[0070] For example, the control device 100 obtains the decrease amount of the motor drive current based on the output signal of the current sensor 104, and estimates the decrease amount of the load acting on the loading platform 50 based on the obtained decrease amount of the motor drive current. Further, the control device 100 obtains the rotation amount of the electric motor 911 in the first direction based on the output signal of the encoder 914, and estimates the ascending amount of the loading platform 50 from the second lifting position based on the obtained rotation amount. Note that the control device 100 may obtain the rotation speed of the electric motor 911 in the first direction based on the output signal of the encoder 914, and estimate the decrease amount of the load acting on the loading platform 50 based on the obtained rotation speed and the decrease amount of the motor drive current. Then, the control device 100 reversely drives the electric motor 911 according to the estimated ascending amount to lower the loading platform 50, decreases the output (torque) of the electric motor 911 according to the estimated decrease amount of the load acting on the loading platform 50, and holds the loading platform 50 at the lowered position. Thereby, the loading platform 50 is held at the second lifting position even after the load W is taken out (FIG. 18(C)).

[0071] As described above, in the carrier cart 10 according to the first embodiment, the drive device 90 has an electric motor 911 as a drive source, and is configured to expand and contract the expansion and contraction mechanism 70 in the vertical direction by the rotation of the electric motor 911 to raise and lower the loading platform 50. Further, the control device 100 is configured to control the electric motor 911 to raise and lower the loading platform 50 to a predetermined lifting position and hold it at the predetermined lifting position based on an operation command of the loading platform 50. Here, the drive device 90 has back drivability, and is configured such that the electric motor 911 rotates due to the vertical expansion and contraction of the expansion and contraction mechanism 70 accompanying the lifting and lowering of the loading platform 50 by an external force (change in external force). And in the carrier cart 10, when a load is placed on the loading platform 50 and the load on the loading platform 50 increases, the loading platform 50 descends from the lifting position (the first lifting position) at which it is held at that time. Therefore, the impact received by the load from the loading platform 50 when placed on the loading platform 50 can be alleviated. In particular, when the load is thrown onto the loading platform 50, an impact load acts on the loading platform 50 and the loading platform 50 descends more quickly, so that damage to the load can be suppressed from occurring.

[0072] Further, when the control device 100 detects the descent of the loading platform 50 from the first lifting position and the increase in the load acting on the loading platform 50 based on the output signals of the encoder 914 and the current sensor 104, the control device 100 controls the electric motor 911 to raise the lowered loading platform 50 to the first lifting position and hold the loading platform 50 at the first lifting position. Therefore, the loading platform 50 can be held at the same position before and after the load is placed on the loading platform 50. However, it is not limited to this. The control device 100 may control the electric motor 911 to quickly stop the loading platform 50 when detecting the descent of the loading platform 50 from the first lifting position. In this case, the loading platform 50 will be held at a lifting position lower than the first lifting position.

[0073] When a load is removed from the loading platform 50 and the load acting on the loading platform 50 decreases, the loading platform 50 rises from the lifting position (the second lifting position) held at that time. Then, when the control device 100 detects the rise of the loading platform 50 from the second lifting position and the decrease in the load acting on the loading platform 50 based on the output signals of the encoder 914 and the current sensor 104, the control device 100 lowers the raised loading platform 50 to the second lifting position and controls the electric motor 911 to hold the loading platform 50 at the second lifting position. Therefore, the loading platform 50 can be held at the same position before and after the load is removed from the loading platform 50. However, it is not limited to this. When the control device 100 detects the rise of the loading platform 50 from the second lifting position, the control device 100 may control the electric motor 911 to quickly stop the loading platform 50. In this case, the loading platform 50 will be held at a lifting position above the second lifting position.

[0074] [Second Embodiment] FIG. 19 is a view of the carrier truck 20 with a hand-held handle according to the second embodiment as seen from the right side. The main difference between the carrier truck 10 according to the first embodiment and the carrier truck 20 according to the second embodiment is that the carrier truck 20 according to the second embodiment further includes a position detection unit 110 capable of detecting the vertical position of the upper surface of the loading platform 50 and the vertical position of the upper surface of the load placed on the loading platform 50. For the components that are the same as those of the carrier truck 10 according to the first embodiment, the same reference numerals are used and their descriptions are omitted. Hereinafter, the differences from the carrier truck 10 according to the first embodiment will be mainly described.

[0075] In the carrier truck 20 according to the second embodiment, the position detection unit 110 includes, for example, a TOF distance measurement image sensor having a predetermined range on the upper surface of the loading platform 50 as a measurement area, and is arranged toward the loading platform 50 at a predetermined position above the handle 4 by using a holder 120 attached to the handle 40. The holder 120, like the handle 40, can be formed, for example, in a substantially portal shape (substantially inverted U shape) and can be configured to hold the position detection unit 110 via a bracket (not shown).

[0076] When no load is placed on the loading platform 50, the position detection unit 110 can detect the vertical position of the upper surface of the loading platform 50, and when a load is placed on the loading platform 50, it can detect the vertical position of the upper surface of the load placed on the loading platform 50. The position detected by the position detection unit 110 is output to the control device 100.

[0077] In the carrier truck 20 according to the second embodiment, when the stop command is input (or when the loading platform 50 is held at the predetermined lifting position), the control device 100 stores the position detected by the position detection unit 110 at that time as a reference position, and until the lifting position at which the loading platform 50 is held is changed, the control device 100 is configured to control the electric motor 911 so that the position detected by the position detection unit 110 matches the reference position.

[0078] Next, an operation example of the carrier truck 20 according to the second embodiment will be described. Since the "lifting operation of the loading platform 50" is the same as that of the carrier truck 10 according to the first embodiment, the description thereof will be omitted, and here, the "operation when a load is placed on the loading platform 50" and the "operation when a load is removed from the loading platform 50" will be described.

[0079] (Operation when a load is placed on the loading platform 50) FIG. 20 is a diagram for explaining an example of the operation of the carrier truck 20 when a load is placed on the loading platform 50.

[0080] First, the operator inputs the raising command via the input unit to raise the loading platform 50 at the lowest position to a predetermined lifting position (hereinafter referred to as the "third lifting position") (FIG. 20(A)). Thereby, the control device 100 controls the electric motor 911 to hold the loading platform 50 at the first lifting position. Further, the control device 100 stores the position detected by the position detection unit 110 (here, the vertical position of the upper surface of the loading platform 50) as a reference position (hereinafter referred to as the "first reference position").

[0081] Next, the operator places the load W1 on the platform 50 held at the third lifting position. When the load W1 is placed on the platform 50, the platform 50 descends from the third lifting position due to the load of the placed load W1 (i.e., the increase in the load acting on the platform 50), and the telescopic mechanism 70 contracts downward (FIG. 19(B)). As a result, the electric motor 911 rotates in the second direction. The rotation of the electric motor 911 in the second direction at this time is detected by the encoder 914, and the encoder 914 outputs a signal corresponding to the rotation of the electric motor 911 in the second direction to the control device 100 (control circuit 102). Also, the output signal of the current sensor 104 is input to the control circuit 102 of the control device 100.

[0082] The control device 100 (control circuit 102) detects the rotation of the electric motor 911 in the second direction (i.e., the descent of the platform 50) based on the output signal of the encoder 914 and detects the increase in the motor drive current based on the output signal of the current sensor 104. Then, the control device 100 determines that the load acting on the platform 50 has increased due to the placement of the load on the platform 50, and as a result, the platform 50 has descended from the first lifting position. In this case, the control device 100 controls the electric motor 911 to hold the platform 50 at the fourth lifting position below the third lifting position.

[0083] For example, when the control device 100 detects the rotation of the electric motor 911 in the second direction based on the output signal of the encoder 914, it obtains the increase amount of the motor drive current based on the output signal of the current sensor 104, and estimates the increase amount of the load acting on the loading platform 50 based on the obtained increase amount of the motor drive current. Note that the control device 100 may obtain the rotation speed of the electric motor 911 in the second direction based on the output signal of the encoder 914, and estimate the increase amount of the load acting on the loading platform 50 based on the obtained rotation speed and the increase amount of the motor drive current. Then, the control device 100 increases the output (torque) of the electric motor 911 according to the estimated increase amount of the load acting on the loading platform 50, and controls the electric motor 911 so that the position detected by the position detection unit 110 (here, the vertical position of the upper surface of the load W1 placed on the loading platform 50) coincides with the first reference position. The control of the electric motor 911 may be to drive the electric motor 911 forward, or to drive the electric motor 911 in reverse, or to drive the electric motor 911 forward and in reverse. As a result, the upper surface of the load W1 placed on the loading platform 50 coincides with the first reference position (that is, the position of the upper surface of the loading platform 50 before the load W is placed), and the loading platform 50 is held at the fourth lifting position below the third lifting position (FIG. 20(C)).

[0084] Although not shown in the figure, when another load W2 is placed on the loading platform 50, specifically, when another load W2 is further stacked on the load W1, the control device 100 controls the electric motor 911 so that the position detected by the position detection unit 110 (the vertical position of the upper surface of the additional load W2) coincides with the first reference position. As a result, the loading platform 50 is held at a lifting position below the fourth lifting position.

[0085] (Operation when the load is removed from the loading platform 50) FIG. 21 is a diagram for explaining an example of the operation of the transport cart 20 when the load is removed from the loading platform 50.

[0086] Figure 21(A) shows the carrier vehicle 10 in a state where the goods W1 and W2 are placed on the loading platform 50 and the loading platform 50 is held at a predetermined lifting position (hereinafter referred to as the "fifth lifting position"). In this case, the control device 100 controls the electric motor 911 to hold the loading platform 50 at the fifth lifting position. Further, the control device 100 stores, as a reference position (hereinafter referred to as the "second reference position"), the position detected by the position detection unit 110 (here, the vertical position of the upper surface of the goods W2 placed on the loading platform 50).

[0087] When the operator takes out the goods W2 from the loading platform 50 held at the fifth lifting position, the load acting on the loading platform 50 decreases by the amount of the taken-out goods W2. For this reason, the electric motor 911 rotates in the first direction and the loading platform 50 rises from the fifth lifting position (Figure 21(B)). The rotation of the electric motor 911 in the first direction at this time is detected by the encoder 914, and the encoder 914 outputs a signal corresponding to the rotation of the electric motor 911 in the first direction to the control device 100 (control circuit 102). Further, the output signal of the current sensor 104 is input to the control circuit 102 of the control device 100.

[0088] The control device 100 (control circuit 102) detects the rotation of the electric motor 911 in the first direction (i.e., the rise of the loading platform 50) based on the output signal of the encoder 914 and detects the decrease in the motor drive current based on the output signal of the current sensor 104. Then, the control device 100 determines that the load on the loading platform 50 has decreased because the goods have been taken out from the loading platform 50, and as a result, the loading platform 50 has risen from the fifth lifting position. In this case, the control device 100 controls the electric motor 911 to hold the loading platform 50 at the sixth lifting position above the fifth lifting position.

[0089] For example, when the control device 100 detects the rotation of the electric motor 911 in the first direction based on the output signal of the encoder 914, it obtains the decrease amount of the motor drive current based on the output signal of the current sensor 104, and estimates the decrease of the load acting on the loading platform 50 based on the obtained decrease amount of the motor drive current. Note that the control device 100 may obtain the rotation speed of the electric motor 911 in the first direction based on the output signal of the encoder 914, and estimate the decrease amount of the load acting on the loading platform 50 based on the obtained rotation speed and the decrease amount of the motor drive current. Then, the control device 100 decreases the output (torque) of the electric motor 911 according to the estimated decrease amount of the load, and controls the electric motor 911 so that the position detected by the position detection unit 110 (here, the vertical position of the upper surface of the load W1 remaining on the loading platform 50) coincides with the second reference position. The control of the electric motor 911 may be to drive the electric motor 9 / 11 forward, or to drive the electric motor 911 in reverse, or to drive the electric motor 911 forward and in reverse. As a result, the upper surface of the load W1 remaining on the loading platform 50 coincides with the second reference position (that is, the vertical position of the upper surface of the load W2), and the loading platform 50 is held at the sixth lifting position above the fifth lifting position (FIG. 21(C)).

[0090] Although not shown in the figure, when the load W1 is further taken out from the loading platform 50, there is no load on the loading platform 50. Therefore, the control device 100 controls the electric motor 911 so that the position of the upper surface of the loading platform 50 detected by the position detection unit 110 coincides with the second reference position. As a result, the loading platform 50 is held at a lifting position above the sixth lifting position.

[0091] Thus, also in the carrier cart 20 according to the second embodiment, the drive device 90 has back drivability, and when a load is placed on the loading platform 50 and the load on the loading platform 50 increases, the loading platform 50 descends from the lifting position at which it is held at that time. Therefore, similar to the carrier cart 10 according to the first embodiment, also in the carrier cart 20 according to the second embodiment, the impact received by the load from the loading platform 50 when the load is placed on the loading platform 50 is alleviated.

[0092] Further, the control device 100 detects the lowering of the loading platform 50 from the third lifting position and the increase in the load acting on the loading platform 50 based on the output signals of the encoder 914 and the current sensor 104. When the control device 100 detects the lowering of the loading platform 50 from the third lifting position and the increase in the load acting on the loading platform 50, it controls the electric motor 911 to hold the loading platform 50 at a fourth lifting position below the third lifting position. Specifically, the control device 100 controls the electric motor 911 so that the position detected by the position detection unit 110 (the position in the vertical direction of the upper surface of the load placed on the loading platform 50) coincides with the first reference position (the position in the vertical direction of the upper surface of the loading platform 50 before the load is placed). For this reason, especially when an operator places a plurality of loads on the loading platform 50, the vertical positions at which each load is placed can be maintained substantially constant, and the burden on the operator when placing a load on the loading platform 50 can be reduced.

[0093] On the other hand, when the load W2 is taken out from the loading platform 50 and the load acting on the loading platform 50 decreases, the loading platform 50 rises from the lifting position (the fifth lifting position) at which it is held at that time. The control device 100 detects the rising of the loading platform 50 from the fifth lifting position and the decrease in the load acting on the loading platform 50 based on the output signals of the encoder 914 and the current sensor 104. When the control device 100 detects the rising of the loading platform 50 from the fifth lifting position and the decrease in the load acting on the loading platform 50, it controls the electric motor 911 to hold the loading platform 50 at a sixth lifting position above the fifth lifting position. Specifically, the control device 100 controls the electric motor 911 so that the position detected by the position detection unit 110 (the position in the vertical direction of the upper surface of the remaining load W1 on the loading platform 50) coincides with the second reference position (the position in the vertical direction of the upper surface of the load W2 before it is taken out from the loading platform 50). For this reason, when an operator takes out a plurality of loads placed on the loading platform 50, the vertical positions at which each load is taken out can be maintained substantially constant, and the burden on the operator when taking out a load from the loading platform 50 can be reduced.

[0094] In addition, in each of the above-described embodiments, the telescopic mechanism 70 is formed as an X-shaped link mechanism having a two-stage structure in which a pair of left and right X-shaped arms are stacked vertically. However, the present invention is not limited to this. The telescopic mechanism 70 may be formed as an X-shaped link mechanism having a single-stage structure composed of a pair of left and right X-shaped arms, or may be formed as an X-shaped link mechanism having a three-stage or more structure in which three or more pairs of left and right X-shaped arms are stacked vertically.

[0095] Further, in the drive device 90 of each of the above-described embodiments, a guide hole 971L for guiding the movement of the shaft member 952L of the left link mechanism 95L accompanying the movement of the movable body 93 is formed in the left guide member 97L, and a guide hole 971R for guiding the movement of the shaft member 952R of the right link mechanism 95R accompanying the movement of the movable body 93 is formed in the right guide member 97R. However, the present invention is not limited to this. A guide groove may be formed in the left guide member 97L instead of the guide hole 971L, and / or a guide groove may be formed in the right guide member 97R instead of the guide hole 971R.

[0096] Further, in each of the above-described embodiments, the guide holes 971L of the left guide member 97L and the guide holes 971R of the right guide member 97R are formed to be curved in a substantially U shape (or a substantially V shape) so that the shaft members 952L and 952R are moved obliquely downward rearward and then obliquely upward as the movable body 93 moves in the direction of raising the loading platform 50. However, the present invention is not limited to this. The shapes of the guide holes 971L and 971R vary depending on the lengths L1 of the first link members 951L and 951R and the lengths L2 of the second link members 953L and 953R. For example, as shown in FIG. 22 corresponding to FIG. 9, they may be formed so that the shaft members 952L and 952R are moved horizontally rearward and then obliquely upward as the movable body 93 moves in the direction of raising the loading platform 50.

[0097] However, when the front - rear space for installing the electric actuator 91 is the same, compared with the modification shown in Fig. 21, in each of the above - described embodiments, the first link members 951L and 951R and / or the second link members 953L and 953R can be made longer, and accordingly, the loading platform 50 can be raised higher. Conversely, when the height by which the loading platform 50 is raised is the same, the above - described embodiments require a smaller front - rear space for installing the electric actuator 91 compared with the modification shown in Fig. 22. Therefore, in a case where the front - rear space for installing the electric actuator 91 is limited, such as in a transport cart, it can be said that the above - described embodiments are more advantageous than the modification shown in Fig. 21.

[0098] Also, in the above - described embodiments, the relationship (dy / dx) between y and x when determining the shape of the guide holes 971L and 971R is set as a constant. However, it is not limited to this. As described above, it is also possible to make the relationship (dy / dx) between y and x linear or non - linear. And when the relationship between y and x is changed, the shape of the guide holes 971L and 971R changes. When the shape of the guide holes 971L and 971R changes, the output of the electric actuator 91 required in the process of raising the loading platform 50 and the raising speed of the loading platform 50 change. In other words, it is possible to change the lifting characteristics of the loading platform 50 according to the shape of the guide holes 971L and 971R. Therefore, according to the transport carts 10 and 20 according to the embodiments, there is also an advantage that it is possible to respond relatively flexibly to the requirements regarding the lifting characteristics of the loading platform 50.

[0099] As described above, the embodiments and modifications of the present invention have been explained. However, the present invention is not limited to the above - described embodiments and modifications, and it goes without saying that further modifications and changes are possible based on the technical idea of the present invention.

Explanation of Reference Numerals

[0100] 10, 20... transport cart, 30... base, 40... handle, 50... loading platform, 70... telescopic mechanism, 71L... lower left X-shaped arm, 71R... lower right X-shaped arm, 72L, 72R... lower inner arms, 74L, 74R... lower outer arms, 75L... upper left X-shaped arm, 75R... upper right X-shaped arm, 76L, 76R... upper inner arms, 78L, 78R... upper outer arms, 81... lower connecting shaft, 82... upper connecting shaft, 83... rear connecting shaft, 84... front connecting shaft, 85... lower moving shaft, 86... upper moving shaft, 90... drive device, 91... electric actuator, 93... movable body, 94... linear slider, 95L... left link mechanism, 95R... right link mechanism, 97L... left guide member, 97R... right guide member, 100... control device, 104... current sensor, 110... position detection unit (position detection part), 911... electric motor, 913A... pulley-belt mechanism, 913B... planetary gear mechanism, 914... encoder (rotation sensor), 915A... ball screw shaft, 915B... ball screw nut, 951L, 951R... first link members, 952L, 952R... shaft members, 953L, 953R... second link members, 971L, 971R... guide holes (guide parts)

Claims

1. a base with wheels attached to the lower part thereof, a loading platform disposed above the base, a telescopic mechanism provided between the base and the loading platform and capable of telescoping in the vertical direction, a driving device that expands and contracts the telescopic mechanism in the vertical direction by the rotation of an electric motor to raise and lower the loading platform, a rotation sensor that detects the rotation of the electric motor and outputs a signal, a current sensor that detects the drive current of the electric motor and outputs a signal, and a control device that controls the electric motor so as to raise and lower the loading platform to a predetermined raising and lowering position based on an operation command and hold the loading platform at the predetermined raising and lowering position, the driving device has a backdrive property in which the electric motor rotates due to the expansion and contraction of the telescopic mechanism accompanying the raising and lowering of the loading platform by an external force, when the control device detects a decrease in the loading platform being held at the predetermined raising and lowering position and an increase in the load acting on the loading platform based on the output signals of the rotation sensor and the current sensor, the control device controls the electric motor to raise the lowered loading platform and hold it at the predetermined raising and lowering position or hold it at a raising and lowering position below the predetermined raising and lowering position, the telescopic mechanism includes a pair of first left and right X-shaped arms that can expand and contract in the vertical direction, each of the first left and right X-shaped arms has two arms that intersect in an X shape in a side view and are combined so as to be relatively rotatable with respect to each other, one end of one of the two arms of the first left X-shaped arm is rotatably attached in the vicinity of the left end of a connecting shaft extending in the left-right direction, and one end of the arm corresponding to the one arm of the first left X-shaped arm among the two arms of the first right X-shaped arm is rotatably attached in the vicinity of the right end of the connecting shaft, The drive device includes: the electric motor; a ball screw shaft that extends in the front-rear direction and is rotationally driven by the electric motor via a speed reduction mechanism; a ball screw nut that moves in the axial direction of the ball screw shaft as the ball screw shaft rotates; a movable body provided integrally with the ball screw nut; a first link member having one end rotatably connected to the movable body; a second link member having one end rotatably connected to the connecting shaft and the other end rotatably connected to the other end of the first link member via a shaft member; and a guide member in which a guide hole or a guide groove for guiding the movement of the shaft member accompanying the movement of the movable body is formed. The movable body is configured to expand and contract the first left X-shaped arm and the first right X-shaped arm in the vertical direction via the first link member and the second link member. The guide hole or the guide groove is formed to be curved in a substantially U shape so that the shaft member moves obliquely downward and then obliquely upward as the movable body moves in the direction of raising the loading platform. Transport cart.

2. When no load is placed on the loading platform, it detects the vertical position of the upper surface of the loading platform, and when a load is placed on the loading platform, it has a position detection unit capable of detecting the vertical position of the upper surface of the load placed on the loading platform. When holding the loading platform at the predetermined lifting position, the control device sets the position detected by the position detection unit as a first reference position. When detecting a descent of the loading platform being held at the predetermined lifting position, the control device controls the electric motor so that the position detected by the position detection unit matches the first reference position. The transport cart according to claim 1.

3. When the control device detects an increase in the loading platform being held at the predetermined lifting position and a decrease in the load acting on the loading platform based on the output signals of the rotation sensor and the current sensor, the control device controls the electric motor to lower the raised loading platform and hold it at the predetermined lifting position or hold the loading platform at a lifting position above the predetermined lifting position. The transport cart according to claim 1 or 2.

4. When no load is placed on the loading platform, it detects the vertical position of the upper surface of the loading platform, and when a load is placed on the loading platform, it has a position detection unit capable of detecting the vertical position of the upper surface of the load placed on the loading platform. When the control device holds the loading platform at the predetermined lifting position, the control device sets the position detected by the position detection unit as the second reference position. When detecting an upward movement of the loading platform while it is being held at the predetermined lifting position, the control device controls the electric motor so that the position detected by the position detection unit matches the second reference position. The carrier truck according to claim 3.

5. The carrier truck further includes a pair of second left X-shaped arms and a pair of second right X-shaped arms provided between the pair of first left X-shaped arms and first right X-shaped arms and the loading platform, and capable of expanding and contracting in the vertical direction. Each of the first left X-shaped arm and the first right X-shaped arm has a first inner arm and a first outer arm as the two arms. Each of the second left X-shaped arm and the second right X-shaped arm has a second inner arm and a second outer arm that intersect in an X shape when viewed from the side and are combined so as to be relatively rotatable with respect to each other. One end of the first inner arm of the first left X-shaped arm and one end of the second outer arm of the second left X-shaped arm are rotatably attached in the vicinity of the left end of the connecting shaft, and one end of the first inner arm of the first right X-shaped arm and one end of the second outer arm of the second right X-shaped arm are rotatably attached in the vicinity of the right end of the connecting shaft. The drive device is configured to expand and contract the first left X-shaped arm, the first right X-shaped arm, the second left X-shaped arm, and the second right X-shaped arm in the vertical direction through the first link member and the second link member by the movement of the movable body. The carrier truck according to any one of claims 1 to 4.

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