High-lift work vehicle

Abstract

To provide a high-lift work vehicle capable of easily arranging a coil spring in an optimal position.SOLUTION: A high-lift work vehicle has a parallel link mechanism composed of a boom side vertical member, an upper horizontal link member, a lower horizontal link member, and a work platform fixing member. The high-lift work vehicle is equipped with a coil spring attached between the boom side vertical member and the work platform fixing member and expanding and contracting according to the load on the work platform, a spring lower end receiving part 417 attached to the boom side vertical member and supporting the lower end of the coil spring, and a load detection device that detects the load on the work platform based on the vertical displacement of the work platform due to the expansion and contraction of the coil spring. The spring lower end receiving part 417 is provided with a groove part 417a that determines the position on a plane perpendicular to the central axis of the coil spring, and a screw hole 417b and a low head bolt 418 that determine the position in the rotational direction around the central axis of the coil spring.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an aerial work platform in which a workbench is attached to the tip of a boom provided on a vehicle body so as to be able to undulate via a parallel link mechanism.

Background Art

[0002] Conventionally, there is an aerial work platform in which a workbench is supported via a parallel link mechanism at the tip of a boom so as to be swingable in the vertical direction. Among such aerial work platforms, a coil spring is disposed between a support arm extending integrally from the workbench and a support member that supports the parallel link mechanism on the tip side of the boom, and there is one provided with a limit switch that is turned on in response to compression of this coil spring (see, for example, Patent Document 1). And it is set so that the loading load of the workbench when the workbench moves downward due to compression of the coil spring and the support arm turns on the limit switch becomes the maximum allowable load. Specifically, it is possible to detect that the loading load of the workbench has exceeded the allowable load (overloading) by the on-operation of the limit switch.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the aerial work platform described in Patent Document 1, when a heavy object is placed at a position deviated from the center in the left-right direction of the work platform, there is a risk that a torsional load is applied to the work platform, resulting in variations in the value of the load detected according to the position where the heavy object is placed. Further, such variations in the value of the load vary according to the position where the coil spring is attached and the position in the rotational direction about the central axis of the support spring. For this reason, when arranging the coil spring between the support arm and the support member, it is desirable to arrange the coil spring at an optimal position where the variations in the value of the detected load are small, but it has not been easy to arrange the coil spring at such an optimal position.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide an aerial work platform capable of easily arranging a coil spring at an optimal position.

Means for Solving the Problems

[0006] In order to solve the above problems, the aerial work vehicle according to the present invention is an aerial work vehicle configured by attaching a work platform to the tip of a boom that is provided on the vehicle body so as to be able to rise and fall via a parallel link mechanism. The parallel link mechanism includes a boom-side vertical member that is pivotally connected to the tip of the boom and extends in the vertical direction, an upper horizontal link member whose base end side is pivotally connected to the boom-side vertical member and extends in the horizontal direction, a work platform-side vertical member that is pivotally connected to the tip end side of the upper horizontal link member and extends in the vertical direction and to which the work platform is fixed, and a lower horizontal link member that is located below the upper horizontal link member, extends in the horizontal direction, has its base end side pivotally connected to the boom-side vertical member, and has its tip end side pivotally connected to the work platform-side vertical member. The work platform is displaceable in the vertical direction with respect to the boom-side vertical member, and includes a coil spring that is attached between the boom-side vertical member and the work platform-side vertical member and expands and contracts according to the load of the work platform, a spring lower end receiving portion that is attached to the boom-side vertical member and supports the lower end of the coil spring, and a load detection device (for example, the transmission mechanism 61R and the potentiometer 62R in the embodiment) that detects the load of the work platform based on the vertical displacement of the work platform accompanying the expansion and contraction of the coil spring. A plane positioning portion (for example, the groove portion 417a in the embodiment) and a rotational positioning portion (for example, the screw hole 417b and the countersunk head bolt 418 in the embodiment) that defines the position in the rotational direction around the central axis of the coil spring are provided.

[0007] Further, in the aerial work vehicle having the above configuration, it is preferable that the rotational positioning portion is provided at a position in the rotational direction where the variation in the value of the load in the left-right direction of the work platform detected by the load detection device is minimized.

[0008] Further, in the aerial work vehicle having the above configuration, it is preferable that the plane positioning portion is provided such that the position of the central axis of the coil spring is located on the center line in the left-right direction of the work platform.

[0009] In addition, in the aerial work platform having any of the above configurations, it is preferable that the planar positioning portion is a groove that houses the lower portion of the coil spring.

[0010] Furthermore, in the aerial work platform having the above configuration, the rotational positioning portion is a screw hole provided in the bottom surface of the groove and a screw (for example, the lowering bolt 418 in the embodiment) that is screwed into the screw hole, and it is preferable that the rotational position of the coil spring is determined by the screw head of the screw abutting against the lower cut end of the coil spring.

Advantages of the Invention

[0011] According to the aerial work platform of the present invention, a spring lower end receiving portion attached to the boom side vertical member is provided with a planar positioning portion that defines a position on a plane orthogonal to the central axis of the coil spring and a rotational positioning portion that defines a rotational position around the central axis of the coil spring. Therefore, by providing the planar positioning portion and the rotational positioning portion at the optimal arrangement positions of the coil spring, the coil spring can be easily arranged at the optimal position.

[0012] In addition, in the aerial work platform having the above configuration, preferably, the rotational positioning portion is provided at a rotational position where the variation in the load value in the left-right direction of the work platform detected by the load detection device is minimized. Also, the planar positioning portion is provided such that the position of the central axis of the coil spring coincides with the central position in the left-right direction of the work platform. Thereby, the coil spring can be easily arranged at a position where the variation in the load value in the left-right direction of the work platform is minimized.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. As an example of an aerial work vehicle equipped with a workbench load detection device which is an embodiment according to the present invention, a side view of a self-propelled aerial work vehicle 1 is shown in FIG. 1. The aerial work vehicle 1 includes a traveling body 10 configured to be capable of traveling, a revolving body 20 provided on the upper part of the traveling body 10 and capable of turning in the horizontal direction, a boom 30 provided on the upper part of the revolving body 20 and capable of rising and falling, and a parallel link mechanism 40 and a workbench 50 provided at the tip of the boom 30. In addition, in FIG. 1, a part of the length of the boom 30 is omitted in the illustration.

[0015] The traveling body 10 has a pair of left and right steering wheels 12 rotatably provided on a traveling body frame 11 and a pair of left and right drive wheels 13. A slewing mechanism 15 is provided at the upper center of the traveling body frame 11, and the slewing mechanism 15 is configured to enable the slewing body 20 to swing horizontally. The slewing mechanism 15 has an outer ring fixed to the traveling body frame 11, an inner ring engaged with the outer ring and fixed to the slewing body 20, and a rotary center joint (not shown) for supplying hydraulic oil to various actuators provided on the traveling body 10. A boom 30 is provided on the upper part of the slewing body 20, and the boom 30 can swing (pitch) vertically about a pivot pin 34. The boom 30 has a base boom 31 pivotally connected to the slewing body 20, an intermediate boom 32 and a tip boom 33 that are nested and combined with the base boom 31, and these booms are configured to be telescopically movable.

[0016] Next, with reference to FIG. 2, the configuration for supporting the workbench 50 at the tip of the boom 30 will be described. Here, FIG. 2 is a side view showing the side of the tip of the boom 30 including the workbench 50. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0017] In FIG. 2, a boom head 36 is provided at the tip of the tip boom 33, and the boom head 36 is pivotally connected to a workbench support member 38 by a pivot pin 36a. Further, the workbench support member 38 is pivotally connected to a piston rod 37 of a boom-side leveling cylinder (not shown) provided inside the tip boom 33 by a pivot pin 37a. By expanding and contracting the boom-side leveling cylinder 37 according to the pitching motion of the boom 30 to perform leveling control of the workbench 50, the workbench 50 can be swung vertically with respect to the tip of the boom 30 while keeping the floor surface of the workbench 50 horizontal.

[0018] At the tip of the workbench support member 38, a swing motor SWM for swinging the workbench 50 (swinging in the horizontal direction) is provided. Inside the swing motor SWM, a vertical post 39 (see Fig. 4) is provided, and the vertical post 39 supports the workbench 50 via a parallel link mechanism 40 so that it can swing horizontally. Then, by swinging the parallel link mechanism 40 horizontally around the vertical post 39 by the swing motor SWM, the swing movement of the workbench 50 is enabled. Also, the workbench 50 can swing vertically with respect to the tip of the workbench support member 38 while keeping the floor surface horizontal by the parallel link mechanism 40.

[0019] The parallel link mechanism 40 mainly includes a boom-side vertical member 41 fixed to the vertical post 39, a workbench fixing member 52 to which the workbench 50 is fixed, an upper horizontal link member 42, and a lower horizontal link member 43. The upper horizontal link member 42 and the lower horizontal link member 43 connect the boom-side vertical member 41 and the workbench fixing member 52 to each other. An operating device 51 is provided on the workbench 50. By an operator boarding the workbench 50 operating the operating device 51, controls such as the traveling of the traveling body 10 shown in Fig. 1, the swinging movement of the slewing body 20, the raising and lowering movement of the boom 30, and the swinging movement of the workbench 50 become possible.

[0020] Next, with reference to Figs. 3 and 4, the parallel link mechanism 40 and its surrounding configuration will be described. Here, Fig. 3 is a perspective view of the tip of the boom 30 seen from obliquely behind, and Fig. 4 is a side view showing the configuration of the parallel link mechanism 40. In Fig. 3, the illustration of the workbench 50 is omitted. Also, in Figs. 3 and 4, the same components as those in Fig. 1 are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0021] As shown in FIGS. 3 and 4, the parallel link mechanism 40 includes a boom-side vertical member 41 for fixing the parallel link mechanism 40 to a vertical post 39 provided on the workbench support member 38, an upper horizontal link member 42, a lower horizontal link member 43, and a workbench fixing member 52 to which the workbench 50 is fixed. The boom-side vertical member 41 is composed of a left side plate 411L, a right side plate 411R, an upper flat plate 415, and a lower flat plate 416. The left side plate 411L and the right side plate 411R have the same shape and are arranged to face each other with a predetermined interval. Also, the upper flat plate 415 and the lower flat plate 416 are horizontally attached between the left side plate 411L and the right side plate 411R. As shown in FIG. 4, the upper end of the vertical post 39 is fixed to the upper flat plate 415, and the lower end of the vertical post 39 is fixed to the lower flat plate 416.

[0022] As shown in FIG. 4, an upper pivot hole 412 for passing a boom-side upper pivot pin 421 (see FIG. 3) is provided at the upper part of the right side plate 411R, and a lower pivot hole 413 for passing a boom-side lower pivot pin 431 is provided at the lower part of the right side plate 411R. Also, a fan-shaped opening 414 is provided between the upper pivot hole 412 and the upper flat plate 415. Although not shown, the upper pivot hole 412, the lower pivot hole 413, and the opening 414 are also provided at positions on the left side plate 411L that face the upper pivot hole 412, the lower pivot hole 413, and the opening 414 provided on the right side plate 411R. Further, a spring lower end receiving portion 417 to which the lower end of the spring 60 shown in FIG. 4 is attached is attached to the upper surface of the upper flat plate 415.

[0023] On the left and right side surfaces of the workbench fixing member 52 as viewed from the direction shown in FIG. 3, as shown in FIG. 4, an upper pivot hole 521 and a lower pivot hole 522 are provided. These upper pivot hole 521 and lower pivot hole 522 are provided at positions facing each other on the left and right side surfaces of the workbench fixing member 52. Also, the vertical interval between the upper pivot hole 521 and the lower pivot hole 522 is the same dimension as the vertical interval between the upper pivot hole 412 and the lower pivot hole 413 provided on the left side plate 411L and the right side plate 411R of the boom side vertical member 41. Below the upper pivot hole 521, a horizontal plate 523 extending from the left side surface to the right side surface of the workbench fixing member 52 is provided, and on the lower surface of the horizontal plate 523, a spring upper end receiving portion 524 to which the upper end portion of the spring 60 is attached is formed.

[0024] As shown in FIGS. 3 and 4, the upper horizontal link member 42 is composed of a left upper side plate 420L and a right upper side plate 420R, a boom side pivot pin 421, and a workbench side pivot pin 422. The left upper side plate 420L and the right upper side plate 420R have the same shape as each other, and each is provided with a boom side pivot pin hole into which the boom side pivot pin 421 shown in FIG. 4 is inserted, and a workbench side pivot pin hole into which the workbench side pivot pin 422 is inserted. Thus, by aligning the positions of the boom side pivot pin holes provided on the left upper side plate 420L and the right upper side plate 420R with the positions of the upper pivot holes 412 provided on the left side plate 411L and the right side plate 411R of the boom side vertical member 41 and passing the boom side pivot pin 421 therethrough, the upper horizontal link member 42 is pivotally connected to the boom side vertical member 41. Also, split pins SP are attached to both end portions of the boom side pivot pin 421. Regarding the workbench 50 side as well, by aligning the positions of the workbench side pivot pin holes provided on the left upper side plate 420L and the right upper side plate 420R with the positions of the upper pivot holes 521 provided on the workbench fixing member 52 and passing the workbench side pivot pin 422 therethrough and fixing it, the upper horizontal link member 42 is pivotally connected to the workbench fixing member 52.

[0025] The lower horizontal link member 43 is also composed of a lower left side plate (not shown) and a lower right side plate 430R, a boom-side pivot pin 431, and a workbench-side pivot pin 432, similar to the upper horizontal link member 42. The lower left side plate and the lower right side plate 430R have the same shape as each other, and each is provided with a boom-side pivot pin hole into which the boom-side pivot pin 431 shown in FIG. 4 is inserted, and a workbench-side pivot pin hole into which the workbench-side pivot pin 432 is inserted. Thus, by aligning the positions of the boom-side pivot pin holes provided in the lower left side plate and the lower right side plate 430R with the positions of the lower pivot holes 413 provided in the left side plate 411L and the right side plate 411R of the boom-side vertical member 41, and passing the boom-side pivot pin 431 through, the lower horizontal link member 43 is pivotally connected to the boom-side vertical member 41. Also, split pins SP are attached to both ends of the boom-side pivot pin 431. Regarding the workbench 50 side, by aligning the positions of the workbench-side pivot pin holes provided in the lower left side plate and the lower right side plate 430R with the positions of the lower pivot holes 522 provided in the workbench fixing member 52, and passing the workbench-side pivot pin 432 through, the lower horizontal link member 43 is pivotally connected to the workbench fixing member 52.

[0026] In the above-described parallel link mechanism 40, as a configuration for detecting the load of the workbench 50, a spring 60, a transmission mechanism 61R, and a potentiometer 62R are provided. The spring 60 is a compression coil spring, and is attached between a spring lower end receiving portion 417 provided in the boom-side vertical member 41 and a spring upper end receiving portion 524 provided in the workbench fixing member 52 when the upper horizontal link member 42 and the lower horizontal link member 43 are pivotally connected to the boom-side vertical member 41 and the workbench fixing member 52. The potentiometer 62R is a rotary potentiometer having a rotary shaft RS with a male screw formed at its tip, and is attached to the right side plate 411R of the boom-side vertical member 41. Also, the potentiometer 62R is configured such that its resistance value changes according to the rotation angle of the rotary shaft RS, and by configuring a voltage dividing circuit using the potentiometer 62R, a voltage signal corresponding to the rotation angle of the rotary shaft RS can be obtained.

[0027] The transmission mechanism 61R transmits the vertical movement of the workbench fixing member 52 to the rotation axis RS of the potentiometer 62R, and is composed of a crank member 610, an upper spacer 611, a connecting shaft 612, and a lower spacer 613 as shown in FIG. 5. A mounting hole CH is formed at one end of the crank member 610. The rotation axis RS of the potentiometer 62R is passed through this mounting hole CH, and the rotation axis RS is fixed to the crank member 610 by a nut NT1 shown in FIG. 4. An upper spacer 611 is fixed to the other end of the crank member 610, and the upper spacer 611 is rotatably fixed to the upper connecting portion 612a of the connecting shaft 612. A lower spacer 613 is rotatably fixed to the lower connecting portion 612b of the connecting shaft 612. A male screw MC is formed at the tip of the lower spacer 613, and is fixed to a mounting hole BH formed in the workbench fixing member 52 by a nut NT2 shown in FIG. 4.

[0028] Although FIG. 3 shows a potentiometer 62L attached to the left side plate 411L of the boom side vertical member 41, a transmission mechanism (not shown) similar to the above-described transmission mechanism 61R is also attached to the potentiometer 62L.

[0029] According to the above configuration, when a load is applied to the workbench 50, the workbench fixing member 52 moves downward, and this movement amount is converted into an angle with respect to the rotation axis RS of the potentiometer 62R by the transmission mechanism 61R. Thereby, a voltage signal having a voltage value corresponding to the angle with respect to the rotation axis RS is generated by the potentiometer 62R, and based on this voltage signal, for example, a controller (not shown) detects the load applied to the workbench 50. As a method for detecting this load, for example, the characteristic of the magnitude of the voltage value of the voltage signal generated by the potentiometer 62R with respect to the magnitude of the load applied to the workbench 50 is measured in advance, and the load is detected based on the measured characteristic. It is conceivable to measure in advance the characteristic of the magnitude of the voltage value of the voltage signal generated by the potentiometer 62R with respect to the magnitude of the load applied to the workbench 50, and to detect the load based on the measured characteristic.

[0030] Next, referring to FIGS. 6 and 7, the structure of the coil spring 60 and the spring lower end receiving portion 417 will be described. FIG. 6 is a perspective view of the coil spring 60 and the spring lower end receiving portion 417 as viewed obliquely from above. Hereinafter, the left-right direction, the front-back direction, and the up-down direction in the case of description with reference to FIG. 6 follow the arrows shown in FIG. 6. Here, in FIG. 6, the back direction is the side of the workbench 50, and the front direction is the side of the boom 30. FIG. 7 is a view showing the structure around the lower part of the coil spring 60. FIG. 7(a) is a side view of the structure around the lower part of the coil spring 60, showing a state in which a part of the spring lower end receiving portion 417 is broken. FIG. 7(b) is a plan view of the coil spring 60 as viewed from the direction of arrow a in FIG. 7(a). In these figures, the same components as those in FIG. 4 are denoted by the same reference numerals, and their detailed description is omitted.

[0031] The coil spring 60 is a coil spring with a rectangular cross-section (so-called square spring). On the upper and lower parts of the coil spring 60, flat machining (the dotted pattern parts in FIGS. 6 and 7) is performed so that the coil spring 60 can maintain an upright posture when arranged in a plane. Specifically, cutting is performed so that the part from the end of the coil spring 60 to a predetermined position becomes a plane orthogonal to the central axis C of the coil spring 60 (which becomes the center point when the coil spring 60 is viewed in plan). Here, the end of the coil spring 60 is referred to as the "cut end". The upper cut end of the coil spring 60 is called the upper cut end 601U (see FIG. 6), and the lower cut end is called the lower cut end 601L (see FIG. 7). Also, the portion where the above flat machining is performed on the coil spring 60 is referred to as the "flat machining portion". The upper flat machining portion of the coil spring 60 is called the upper flat machining portion 602U (see FIG. 6), and the lower flat machining portion is called the lower flat machining portion 602L (see FIG. 7(b)). One end of the flat machining portion becomes the "cut end", while the other end is called the "machining end". Here, the upper machining end of the coil spring 60 is called the upper machining end 603U (see FIG. 6), and the lower machining end is called the lower machining end 603L (see FIG. 7(b)).

[0032] In the coil spring 60, the angle from the cut end with an arc-shaped flat processing part to the processing end is more than 180°. When a torsional load is applied to such a coil spring, the strongest force is applied to the peripheral area around the processing end and the area facing the peripheral area across the center point in the flat processing part. For example, in the lower part of the coil spring 60 shown in FIG. 7(b), the strongest force is applied to the area surrounded by the broken line, and the same area also receives the strongest force in the upper part of the coil spring 60.

[0033] As shown in FIG. 6, inside the coil spring 60, a collar 63, which is a cylindrical member for restricting the contraction amount of the coil spring 60, is inserted. This prevents damage to the potentiometers 62L and 62R and other members due to excessive contraction of the coil spring 60. The spring lower end receiving part 417 is formed with a groove part 417a for defining the arrangement position of the coil spring 60 on a plane in the left-right direction and the front-back direction (in other words, a plane orthogonal to the central axis C of the coil spring 60). The bottom surface of the groove part 417a is circular, and its diameter is sized to accommodate the lower part of the coil spring 60 (a size slightly larger than the diameter of the coil spring 60). The groove part 417a is formed such that when the coil spring 60 is arranged in the groove part 417a, the central axis C of the coil spring 60 is located on the center line in the left-right direction of the workbench 50. Further, on the bottom surface of the groove part 417a, a screw hole 417b and a countersunk head bolt 418 for screwing and defining the position in the rotational direction around the central axis C of the coil spring 60 (hereinafter also referred to as the "rotational position") are formed.

[0034] With the above configuration, when arranging the coil spring 60 in the spring lower end receiving part 417, first, fit the lower part of the coil spring 60 into the groove part 417a and then turn it clockwise around the central axis C. Then, as shown in FIG. 7(a), the position where the lower cut end 601L of the coil spring 60 abuts against the head of the countersunk head bolt 418 becomes the specified rotational position.

[0035] Next, with reference to FIGS. 8 and 9, the position of the screw hole 417b provided in the bottom surface of the groove portion 417a will be described. FIG. 8 is a graph showing the magnitude of the variation in the load detected according to the location where a heavy object is placed on the workbench 50 and the variation in the variation according to the rotational position of the coil spring 60. FIG. 9 is an explanatory diagram for explaining the measurement conditions of the load variation shown in the graph of FIG. 8. FIG. 10 is an explanatory diagram for explaining the desirable rotational position of the coil spring 60.

[0036] In the graph of FIG. 8, the vertical axis represents the load (unit: Newton (symbol: N)) detected by the strain gauge attached to the coil spring 60, and the horizontal axis represents the rotational position of the coil spring 60. Here, with reference to FIG. 9(a), the rotational position of 0° on the horizontal axis of the graph of FIG. 8 will be described. FIG. 9(a) is a diagram schematically showing the state of the coil spring 60 viewed from above. The same parts as those in FIG. 6 in this figure are denoted by the same reference numerals, and their detailed description is omitted. In FIG. 9(a), the center line CL passing through the center point C of the coil spring 60 and the center line CL in the left-right direction of the workbench 50 shown in FIG. 9(b) described later are the same. Therefore, the torsional center when a torsional load is applied to the workbench 50 is the center line CL.

[0037] The rotational position of 0° on the horizontal axis of the graph in Fig. 8 is, as shown in Fig. 9(a), a position where the position of the upper cutting edge 601U is rotated counterclockwise by 24.5° from the position of the center line CL. Taking this position as 0°, the angle by which the coil spring 60 is rotated clockwise about the central axis C of the coil spring 60 becomes the value on the horizontal axis of the graph in Fig. 8. In the graph of Fig. 8, the dots of "△", "×" and "〇" respectively indicate the loads detected by the strain gauges attached to the coil spring 60 when a weight with a size of 450 mm square and a weight of 4650 [N] is placed at a predetermined position on the workbench 50 shown in Fig. 9(b). Fig. 9(b) schematically shows a plan view of the workbench 50 as seen from above. In this figure, the width of the workbench 50 is the value W and the depth is the value D. Also, "right" is a position where the upper side of the weight is in contact with the center line in the depth direction of the workbench 50 and the left side of the weight is separated from the right end of the workbench 50 by 1 / 4W. "Front back" is a position where the upper side of the weight is in contact with the center line in the depth direction of the workbench 50 and the center of the weight coincides with the center line CL. "Left" is a position where the upper side of the weight is in contact with the center line in the depth direction of the workbench 50 and the right side of the weight is separated from the left end of the workbench 50 by 1 / 4W.

[0038] In the graph of FIG. 8, the "Δ" dots indicate the load values detected when the above-described weight was placed at the "front rear" position of the workbench 50 shown in FIG. 9(b). The "×" dots indicate the load values detected when the above weight was placed at the "left" position of the workbench 50 shown in FIG. 9(b). The "〇" dots indicate the load values detected when the above-described weight was placed at the "right" position of the workbench 50 shown in FIG. 9. Further, the "●" dots indicate the average value (sensitivity) of the loads detected when the above-described weight was placed at the "front rear", "left", and "right" positions of the workbench 50 shown in FIG. 9(b). The "◇" dots indicate the variation (desired SN ratio) of the loads detected when the above-described weight was placed at the "front rear", "left", and "right" positions of the workbench 50 shown in FIG. 9(b). The numerical values in parentheses attached to the "◇" dots indicate the values of the desired SN ratio (dB), and the larger this value is, the less the variation means.

[0039] In the present embodiment, in order to set the region where the strongest force is applied when a torsional load is applied to the coil spring 60 as the position of the torsion center, the line connecting the upper processing end 603U or the lower processing end 603L and the center point C of the coil spring 60 is made to coincide with the position of the torsion center, and the rotational position of the coil spring 60 is determined. Here, in the graph of FIG. 8, the value of the rotational position D° is within the range of B, the rotational positions where the line connecting the upper processing end 603U and the center point C is on the center line CL and the upper processing end 603U is located on the workbench 50 side are included. When the value of the rotational position D° is within the range of C, the rotational positions where the line connecting the lower processing end 603L and the center point C is on the center line CL and the lower processing end 603L is located on the boom 30 side are included. When the value of the rotational position D° is within the range of D, the rotational positions where the line connecting the upper processing end 603U and the center point C is on the center line CL and the upper processing end 603U is located on the boom 30 side are included. When the value of the rotational position D° is within the range of A, the rotational positions where the line connecting the lower processing end 603L and the center point C is on the center line CL and the lower processing end 603L is located on the workbench 50 side are included.

[0040] When comparing the respective desired SN ratios (variations) in the ranges A to D described above, it can be said that the ranges of A and C are comparable, and the variation is smaller than that of the ranges of B and D. Also, when comparing the respective sensitivities (average values of the detected loads) in the ranges of A and C, it can be said that the range of A has a higher sensitivity (close to the weight of the weight 4650 [N]). From this, it can be seen that the rotational position of the coil spring 60 is optimal in the range of A, and at the rotational position where the line connecting the lower processing end 603L and the center point C is on the center line CL and the lower processing end 603L is located on the workbench 50 side, it is advisable to provide the screw hole 417b at the position where the lower cutting end 601L of the coil spring 60 abuts against the screw head of the countersunk head bolt 418.

[0041] In this way, by determining the position of the screw hole 417b provided on the bottom surface of the groove portion 417a shown in FIG. 6, when arranging the coil spring 60 in the groove portion 417a, by bringing the lower cutting end 601L of the coil spring 60 into contact with the screw head of the countersunk head bolt 418, the coil spring 60 can be easily adjusted to the optimal rotational position.

[0042] In this embodiment, in the spring lower end receiving portion 417, in order to define the arrangement position of the coil spring 60 on a plane orthogonal to the central axis C of the coil spring 60, a circular groove portion 417a is provided. However, the shape of the groove portion is not limited to a circle, and may be a polygon such as a triangle or a quadrilateral. Also, instead of providing the groove portion 417a, as shown in FIG. 10(a), a circular convex portion 419 having a diameter slightly smaller than the inner diameter of the collar 63 (or the inner diameter of the coil spring 60 when the collar 63 is not provided) may be formed. In this case, by fitting the collar 63 onto the circular protrusion, the coil spring 60 can be arranged at the optimal position on a plane orthogonal to the central axis C of the coil spring 60. Further, instead of the countersunk head bolt 418 that defines the rotational position of the coil spring 60, for example, as shown in FIG. 10(b), a contact portion 420 may be formed inside the groove portion 417a.

Explanation of Signs

[0043] 40 Parallel link mechanism 41 Boom side vertical member 42 Upper horizontal link member 43 Lower horizontal link member 50 Workbench 52 Workbench fixing member 60 Coil spring 61R Transmission mechanism 62R Potentiometer 417 Spring lower end receiving part 417a Groove part 417b Threaded hole 418 Nodding bolt

Claims

1. An aerial work platform configured by attaching a workbench to the tip of a boom that is provided on the vehicle body so as to be able to undulate, via a parallel link mechanism, wherein the parallel link mechanism includes a boom-side vertical member pivotally connected to the tip of the boom and extending vertically, an upper horizontal link member having its proximal end pivotally connected to the boom-side vertical member and extending horizontally, a workbench-side vertical member pivotally connected to the distal end side of the upper horizontal link member and extending vertically, to which the workbench is fixed, and a lower horizontal link member positioned below the upper horizontal link member and extending horizontally, having its proximal end pivotally connected to the boom-side vertical member and its distal end pivotally connected to the workbench-side vertical member, and the workbench is displaceable in the vertical direction with respect to the boom-side vertical member, a coil spring attached between the boom-side vertical member and the workbench-side vertical member and expanding and contracting according to the load of the workbench, a spring lower end receiving portion attached to the boom-side vertical member for supporting the lower end of the coil spring, and a load detection device for detecting the load of the workbench based on the vertical displacement of the workbench accompanying the expansion and contraction of the coil spring, wherein a planar positioning portion for defining a position on a plane orthogonal to the central axis of the coil spring and a rotational positioning portion for defining a position in the rotational direction centered on the central axis of the coil spring are provided on the spring lower end receiving portion. An aerial work platform characterized by this.

2. The aerial work platform according to claim 1, wherein the rotational positioning portion is provided at a position in the rotational direction where the variation in the value of the load in the left-right direction of the workbench detected by the load detection device is minimized.

3. The aerial work platform according to claim 1, wherein the planar positioning portion is provided such that the position of the central axis of the coil spring is located on the center line in the left-right direction of the workbench.

4. The aerial work platform according to any one of claims 1 to 3, wherein the planar positioning portion is a groove for accommodating the lower part of the coil spring.

5. The aerial work platform according to claim 4, wherein the rotational positioning portion is a screw hole provided inside the groove and a screw that is screwed into the screw hole, and the rotational position of the coil spring is determined by the screw head of the screw abutting against the cut end below the coil spring.

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