Workbench load detector

Abstract

To provide a workbench load detector capable of detecting load on a workbench according to changes in the load.SOLUTION: A parallel linkage mechanism comprises a boom side vertical member 41, an upper horizontal linkage member 42, a lower horizontal linkage member 43, and a workbench fixing member 52. The parallel linkage mechanism comprises a spring 60 which is installed between the boom side vertical member 41 and the workbench fixing member 52 and expands and contracts according to load on the workbench, a transfer mechanism 61R to transfer the vertical displacement of the workbench due to the expansion and contraction of the spring 60, and a potentiometer 62R to output a signal according to the workbench displacement transferred by the transfer mechanism. The load on the workbench is detected by the output signal from the potentiometer 62R.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a work platform load detection device that detects the load of a work platform in an aerial work vehicle configured by attaching a work platform to the tip of a boom provided on a vehicle body via a parallel link mechanism so as to be able to move up and down freely.

Background Art

[0002] Generally, an aerial work vehicle includes a traveling body having wheels or a crawler device and capable of traveling, a turntable provided on the traveling body so as to be horizontally rotatable, a boom provided on the turntable so as to be able to move up and down and extend and contract, and a work platform supported at the tip of the boom so as to be able to swing. Further, an operating device is provided on the work platform, and by an operator boarding the work platform and operating this operating device, control of the turning operation of the turntable, the up-and-down operation of the boom, the swinging operation of the work platform, etc. is made possible.

[0003] When performing work on a work object located at a high place using an aerial work vehicle as described above, an operator boards the work platform together with tools, materials, etc., and by the operator operating an operating device provided on the work platform, the work platform can be moved to the work object at a high place. At this time, a moment (hereinafter referred to as "overturning moment") that tries to tilt the vehicle body in the direction of the work platform always acts on the aerial work vehicle. Since the overturning moment increases due to an increase in the loading load on the work platform, an extension operation of the boom, etc., some aerial work vehicles detect the loading load on the work platform and regulate the operating range of the boom according to the detected loading load, so that the stability of the vehicle body is not impaired by the overturning moment that changes according to the operation of the boom.

[0004] As a device for detecting the load on the work platform as described above, there is a conventional high-altitude work vehicle in which the work platform is supported at the tip of the boom so as to be able to swing up and down via a parallel link mechanism, and a support spring is provided between a support arm that extends integrally from the work platform and a support member that supports the parallel link mechanism at the tip of the boom, and a limit switch that turns on in accordance with the compression of this support spring is provided (see, for example, Patent Document 1). In this work platform load detection device, the load on the work platform is set to the allowable load when the work platform moves downward due to the compression of the support spring and the support arm turns on the limit switch, and it is possible to detect when the load on the work platform exceeds the allowable load (overload) by turning on the limit switch. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-128497 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The workbench load detection device described in Patent Document 1 detects overloading of the workbench by the activation of a limit switch. Therefore, for example, during pre-work inspections, it was difficult to confirm whether the limit switch was functioning correctly using only the weight of one worker. Furthermore, the maximum load capacity of the workbench within a predetermined work area (the movable area of ​​the workbench) must be set to an allowable load capacity when the workbench is in a position where the tipping moment is maximized while maintaining the stability of the vehicle. However, if the limit switch is activated and the movement of the workbench is restricted when the maximum load capacity is exceeded, for example, within a predetermined work area, it is difficult to determine whether the tipping moment is relatively small (the maximum load capacity determined by the method described above). Even when moving the workbench to a position where the vehicle's stability is not compromised even if the load capacity is exceeded, exceeding the maximum load capacity restricts the movement of the workbench. This means that while safety can be maintained, the working area is limited.

[0007] Therefore, in order to enable more effective movement of the workbench, it is conceivable to install multiple limit switches with different load capacities for each workbench, and expand or contract the work area based on the activation of each limit switch (i.e., according to the load capacities of the workbench). However, due to constraints such as installation space, the number of limit switches that can be installed is limited, making it difficult to finely set the limitations on the work range according to the load capacities of the workbench using this method.

[0008] This invention has been made in view of the above problems, and aims to provide a workbench load detection device that can detect loads in accordance with changes in the load on the workbench. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a work platform load detection device for a high-altitude work vehicle configured in which a work platform is attached to the tip of a boom that is provided on the vehicle body so as to be able to move up and down, via a parallel link mechanism, and the parallel link mechanism comprises a boom-side vertical member (for example, boom-side vertical member 41) pivotally connected to the tip of the boom and extending vertically, an upper horizontal link member (for example, upper horizontal link member 42 in the embodiment) pivotally connected to the base end of the boom-side vertical member and extending horizontally, a work platform-side vertical member (for example, work platform fixing member 52 in the embodiment) pivotally connected to the tip side of the upper horizontal link member and extending vertically, to which the work platform is fixed, and a member located below the upper horizontal link member and extending horizontally, with its base end on the boom side The system comprises a lower horizontal link member (for example, a lower horizontal link member 43 in the embodiment) pivotally connected to a vertical member and having its tip pivotally connected to the workbench-side vertical member, the workbench being displaceable vertically relative to the boom-side vertical member, a spring member (for example, a spring 60 in the embodiment) mounted between the boom-side vertical member and the workbench-side vertical member and contracting in accordance with the load on the workbench, a transmission mechanism (for example, a transmission mechanism 61R in the embodiment) that transmits the vertical displacement of the workbench due to the expansion and contraction of the spring member, and a displacement signal outputter (for example, a potentiometer 62R in the embodiment) that outputs a signal corresponding to the displacement of the workbench transmitted by the transmission mechanism, and the load on the workbench is detected based on the signal output from the displacement signal outputter.

[0010] Furthermore, in the workbench load detection device with the above configuration, if the amount of contraction of the spring member decreases and the workbench is displaced upward due to a load applied to the workbench from below upward, it is preferable to detect the load applied to the workbench from below upward based on the signal output from the displacement signal output device.

[0011] Furthermore, in the workbench load detection device with the above configuration, the displacement signal output device is preferably a rotary type potentiometer (for example, potentiometer 62R in the embodiment) equipped with a rotating shaft and outputting an electrical signal corresponding to the rotation angle of the rotating shaft, and the transmission mechanism preferably comprises a crank member (for example, crank member 610 and upper spacer 611 in the embodiment) with one end fixed to the rotating shaft of the potentiometer, and a connecting member (for example, connecting shaft 612 in the embodiment) with one end rotatably attached to the other end of the crank member and the other end rotatably attached to the vertical member on the workbench side.

[0012] Furthermore, in the workbench load detection device with the above configuration, the displacement signal output device is a linear type potentiometer equipped with a linearly movable slider that outputs an electrical signal corresponding to the amount of movement of the slider. The chometer is preferably a sliding member fixed to the vertical member on the workbench side, which slides the slider in accordance with the vertical displacement of the workbench (for example, a link member that converts the vertical movement of the workbench fixing member 52 in the embodiment into horizontal movement). [Effects of the Invention]

[0013] According to the work platform load detection device of the present invention, in an aerial work platform in which a work platform is attached to the tip of a boom that is pivotably mounted on the vehicle body via a parallel link mechanism, the device comprises a spring member installed between the boom-side vertical member and the work platform-side vertical member constituting the parallel link mechanism, which contracts in accordance with the load on the work platform; a transmission mechanism that transmits the vertical displacement of the work platform due to the expansion and contraction of the spring member; and a displacement signal outputter that outputs a signal corresponding to the displacement of the work platform transmitted by the transmission mechanism, and the load on the work platform is detected based on the signal output from the displacement signal outputter. In this way, since the load on the work platform is detected based on a signal corresponding to the displacement of the work platform output from the displacement signal outputter, load detection in accordance with changes in the load on the work platform becomes possible.

[0014] Furthermore, in the workbench load detection device with the above configuration, preferably, when a load is applied to the workbench from below upward, causing the amount of contraction of the spring member to decrease and the workbench to be displaced upward, the load applied to the workbench from below upward is detected based on the signal output from the displacement signal outputter. This makes it possible to detect the load reduction caused by a force that pushes the workbench upward, for example, when the boom is lowered or retracted, causing the bottom surface of the workbench to be pressed against the ground or a building. [Brief explanation of the drawing]

[0015] [Figure 1] This is a side view showing the external appearance of an aerial work platform equipped with a work platform load detection device according to the present invention. [Figure 2] This is a side view showing the configuration of the boom tip, parallel link mechanism, and work platform of the above-mentioned aerial work platform. [Figure 3] A perspective view showing the configuration of the boom tip and parallel link mechanism of the above-mentioned aerial work platform. [Figure 4] This is a side view showing the configuration and mounting position of the parallel link mechanism of the above-mentioned aerial work platform and the work platform load detection device according to the present invention. [Figure 5] This is a perspective view showing the external appearance of the transmission mechanism that constitutes the workbench load detection device described above. [Figure 6] This is an explanatory diagram illustrating the displacement of each part of the workbench load detection device in response to changes in the load on the workbench. [Modes for carrying out the invention]

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. As an example of an aerial work platform equipped with a workbench load detection device according to an embodiment of the present invention, a self-propelled aerial work platform 1 is shown in FIG. 1. The aerial work platform 1 includes a traveling body 10 configured to be capable of traveling, a swivel body 20 provided above the traveling body 10 and capable of swiveling in the horizontal direction, a boom 30 provided above the swivel 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, the length of the boom 30 is partially omitted for illustration.

[0017] 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 swivel mechanism 15 is provided at the upper center of the traveling body frame 11, and the swivel body 20 is configured to be swiveling in the horizontal direction by the swivel mechanism 15. The swivel 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 swivel 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 above the swivel body 20, and the boom 30 swings in the vertical direction about a pivot pin 34 freely (capable of rising and falling). The boom 30 has a base boom 31 pivotally connected to the swivel 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 extendable.

[0018] Next, referring 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 addition, in FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0019] 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 the 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. Then, by expanding and contracting the boom side leveling cylinder 37 according to the raising and lowering operation of the boom 30 to perform leveling control of the workbench 50, the workbench 50 can be swung in the vertical direction with respect to the tip of the boom 30 while keeping the floor surface of the workbench 50 horizontal.

[0020] A swing motor SWM for swinging the workbench 50 (swinging in the horizontal direction) is provided at the tip of the workbench support member 38. A vertical post 39 (see FIG. 4) is provided inside the swing motor SWM, and the vertical post 39 supports the workbench 50 so as to be swingable in the horizontal direction via a parallel link mechanism 40. Then, by swinging the parallel link mechanism 40 in the horizontal direction about the vertical post 39 by the swing motor SWM, the swing operation of the workbench 50 is enabled. Further, the workbench 50 can swing in the vertical direction with respect to the tip of the workbench support member 38 while keeping the floor surface horizontal by the parallel link mechanism 40.

[0021] 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, and is configured by connecting the boom side vertical member 41 and the workbench fixing member 52 to each other by the upper horizontal link member 42 and the lower horizontal link member 43. An operating device 51 is provided on the workbench 50, and 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 turning operation of the slewing body 20, the raising and lowering operation of the boom 30, and the swing operation of the workbench 50 can be performed.

[0022] Next, the configuration of the parallel link mechanism 40 and its surroundings will be described with reference to Figures 3 and 4. Here, Figure 3 is a perspective view of the tip of the boom 30 seen from the rear at an oblique angle, and Figure 4 is a side view showing the configuration of the parallel link mechanism 40. In Figure 3, the work platform 50 is not shown. Also, in Figures 3 and 4, the same reference numerals are used for components identical to those in Figure 1, and their detailed explanations are omitted.

[0023] As shown in Figures 3 and 4, the parallel link mechanism 40 consists of 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 consists of a left plate 411L and a right plate 411R that have the same shape as each other and are arranged facing each other at a predetermined distance apart, and an upper flat plate 415 and a lower flat plate 416 that are horizontally provided between the left plate 411L and the right plate 411R.

[0024] As shown in Figure 4, the upper part of the right side plate 411R is provided with an upper pivot hole 412 for passing through the boom-side upper pivot pin 421 (see Figure 3), and the lower part of the right side plate 411R is provided with a lower pivot hole 413 for passing through the boom-side lower pivot pin 431. A fan-shaped opening 414 is provided between the pivot hole 412 and the upper plate 415. Although not shown in the figures, the left plate 411L also has an upper pivot hole 412, a lower pivot hole 413, and an opening 414, positioned opposite to the upper pivot hole 412, lower pivot hole 413, and opening 414 provided on the right plate 411R. Furthermore, a spring lower end receiving portion 417 is formed on the upper surface of the upper plate 415, to which the lower end of the spring 60 shown in Figure 4 is attached.

[0025] As shown in Figure 4, upper pivot holes 521 and lower pivot holes 522 are provided on the left and right sides of the workbench fixing member 52 when viewed from the direction shown in Figure 3. These upper pivot holes 521 and lower pivot holes 522 are located opposite each other on the left and right sides of the workbench fixing member 52. The vertical distance between the upper pivot hole 521 and lower pivot hole 522 is the same as the vertical distance between the upper pivot hole 412 and lower pivot hole 413 provided on the left plate 411L and right plate 411R of the boom-side vertical member 41. Below the upper pivot hole 521, a horizontal plate 523 is provided that extends from the left side to the right side of the workbench fixing member 52, and a spring upper end receiving portion 524 is formed on the lower surface of the horizontal plate 523 to which the upper end of the spring 60 is attached.

[0026] As shown in Figures 3 and 4, the upper horizontal link member 42 is composed of a left upper side plate 420L and an upper right side plate 420R, and a boom-side pivot pin 421 and a workbench-side pivot pin 422. The left upper side plate 420L and the upper right side plate 420R have the same shape, and each is provided with a boom-side pivot pin hole into which the boom-side pivot pin 421 shown in Figure 4 is inserted, and a workbench-side pivot pin hole into which the workbench-side pivot pin 422 is inserted. By aligning the boom-side pivot pin holes provided in the left upper side plate 420L and the upper right side plate 420R with the upper pivot holes 412 provided in the left side plate 411L and the right side plate 411R of the boom-side vertical member 41, the upper horizontal link member 42 is pivotally connected to the boom-side vertical member 41 by passing the boom-side pivot pin 421 through them. In addition, cotter pins SP are attached to both ends of the boom-side pivot pin 421. On the workbench 50 side, the upper horizontal link member 42 is pivotally connected to the workbench fixing member 52 by aligning the positions of the workbench-side pivot pin holes provided in the left upper side plate 420L and the upper right side plate 420R with the positions of the upper pivot hole 521 provided in the workbench fixing member 52, and then passing the workbench-side pivot pin 422 through and fixing it.

[0027] The lower horizontal link member 43, like the upper horizontal link member 42, is composed of a left lower side plate (not shown) and a right lower side plate 430R, and a boom-side pivot pin 431 and a workbench-side pivot pin 432. The left lower side plate and the right lower side plate 430R have the same shape, and each is provided with a boom-side pivot pin hole into which the boom-side pivot pin 431 shown in Figure 4 is inserted, and a workbench-side pivot pin hole into which the workbench-side pivot pin 432 is inserted. By aligning the boom-side pivot pin holes provided in the left lower side plate and the right lower side plate 430R with 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, the boom-side pivot pin 431 is passed through to pivotally connect the lower horizontal link member 43 to the boom-side vertical member 41. In addition, cotter pins SP are attached to both ends of the boom-side pivot pin 431. On the workbench 50 side, the lower horizontal link member 43 is pivotally connected to the workbench fixing member 52 by aligning the positions of the workbench-side pivot pin holes provided in the left lower side plate and the right lower 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 them.

[0028] The parallel link mechanism 40 described above is equipped with a spring 60, a transmission mechanism 61R, and a potentiometer 62R for detecting the load on the work platform 50. The spring 60 is a compression coil spring and is attached between the lower end receiving portion 417 on the boom-side vertical member 41 and the upper end receiving portion 524 on the work platform fixing member 52 when pivotally connecting the upper horizontal link member 42 and the lower horizontal link member 43 to the boom-side vertical member 41 and the work platform fixing member 52. The potentiometer 62R has a rotating shaft RS with a male thread formed at its tip. This is a rotary-type potentiometer, mounted on the right-side plate 411R of the boom-side vertical member 41. The potentiometer 62R changes its resistance value according to the rotation angle of the rotation axis RS, and by using the potentiometer 62R to form a voltage divider circuit, a voltage signal corresponding to the rotation angle of the rotation axis RS can be obtained.

[0029] The transmission mechanism 61R transmits the vertical movement of the workbench fixing member 52 to the rotation shaft RS of the potentiometer 62R, and as shown in Figure 5, it consists of a crank member 610, an upper spacer 611, a connecting shaft 612, and a lower spacer 613. A mounting hole CH is formed at one end of the crank member 610, and the rotation shaft RS of the potentiometer 62R is passed through this mounting hole CH and fixed to the crank member 610 by a nut NT1 shown in Figure 4. The upper spacer 611 is fixed to the other end of the crank member 610, and the upper spacer 611 is fixed to the upper connecting portion 612a of the connecting shaft 612 so as to be rotatable relative to it. The lower spacer 613 is fixed to the lower connecting portion 612b of the connecting shaft 612 so as to be rotatable. 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 Figure 4.

[0030] Figure 3 shows a potentiometer 62L attached to the left plate 411L of the boom-side vertical member 41. The potentiometer 62L is also fitted with a transmission mechanism (not shown) similar to the transmission mechanism 61R described above.

[0031] Next, with reference to Figure 6, the displacement of each part of the workbench load detection device in response to changes in the load on the workbench 50 will be explained. In Figure 6, components identical to those shown in Figure 4 are denoted by the same reference numerals, and detailed explanations are omitted. Also, in Figure 6, point A is the center position of the boom-side pivot pin 421, point A' is the center position of the workbench-side pivot pin 422, and point B is the position of the potentiometer 62R. Point RS is the center position of the rotation axis, point C is the center position of the lower connecting part 612b, and point D is the center position of the upper connecting part 612a. Furthermore, if the line connecting point A and point A' when no load is applied to the workbench 50 is defined as reference line RL1, and the line connecting point A and point A' when a load of L [kg] is applied to the workbench 50 is defined as line LL1, then the angle between RL1 and LL1 is defined as θ1. In addition, if the line connecting point B and point D when no load is applied to the workbench 50 is defined as reference line RL2, and the line connecting point B and point D when a load of L [kg] is applied to the workbench 50 is defined as line LL2, then the angle between RL2 and LL2 is defined as θ2.

[0032] When a load is applied to the workbench 50, the workbench fixing member 52 moves downward, and this amount of movement is converted by the transmission mechanism 61R into an angle θ2 with respect to the rotation axis RS of the potentiometer 62R. As a result, the potentiometer 62R generates a voltage signal with a voltage value corresponding to the angle θ2, and based on this voltage signal, a controller (not shown) detects the load applied to the workbench 50. One possible method for detecting this load is to pre-measure the characteristics of the magnitude of the voltage value of the voltage signal generated by the potentiometer 62R in relation to the magnitude of the load applied to the workbench 50, and then detect the load based on the measured characteristics.

[0033] As shown in Figure 6, when a load is applied to the workbench 50 and the workbench fixing member 52 moves downward, the angle θ2 is larger than the angle θ1 described above. Therefore, the rotation angle of the rotation axis RS of the potentiometer 62R per unit load increases, and as a result, the accuracy of the detected load can be improved. Furthermore, the magnitude of angle θ2 relative to angle θ1 is determined by the position of the rotation axis RS of the potentiometer 62R, the length between point B and point D (i.e., the length of the crank member 610), the length between point D and point C (i.e., the length of the connecting shaft 612), the position of the mounting hole BH provided in the workbench fixing member 52, the free height of the spring 60, and The spring constant and other parameters can be adjusted as needed.

[0034] As described above, in this embodiment, when the workbench load detection device moves downward due to a load applied to the workbench 50, the workbench fixing member 52 is converted into rotational motion of the rotation axis RS of the potentiometer 62R by the transmission mechanism 61R, and the load applied to the workbench 50 is detected based on the voltage signal output from the potentiometer 62R. This makes it possible to detect a value corresponding to the magnitude of the load applied to the workbench 50, and to detect the load in accordance with changes in the load (increase and decrease), so it is possible to finely set the working range limit according to the magnitude of the load on the workbench. In addition, because a potentiometer is used, costs can be reduced compared to, for example, the case where a load cell is used to detect the load.

[0035] In the embodiment described above, in addition to the potentiometer 62R and transmission mechanism 61R attached to the right plate 411R of the boom-side vertical member 41, a potentiometer 62L (see Figure 3) and its corresponding transmission mechanism (not shown) are also provided on the left plate 411L. This allows the load on the workbench 50 to be detected by the other potentiometer and transmission mechanism even if, for example, one of the potentiometers or transmission mechanism malfunctions. Furthermore, the accuracy of the detected load can be improved by, for example, averaging the voltage values ​​output from both potentiometers. Alternatively, the potentiometer 62L and its transmission mechanism may be removed, and only the potentiometer 62R and transmission mechanism 61R may be provided.

[0036] Furthermore, although a rotary type potentiometer is used for the potentiometer 62R in this embodiment, a linear type potentiometer may also be used, which has a knob (slider) that can move linearly and whose resistance value changes according to the amount of movement of the knob. In this case, for example, a link member that converts the vertical movement of the workbench fixing member 52 into horizontal movement may be used, and the knob of the linear type potentiometer may be attached to this link member so that the knob of the linear type potentiometer is moved horizontally by the vertical movement of the workbench fixing member 52. [Explanation of symbols]

[0037] 40 Parallel link mechanism 41 Boom-side vertical member 42 Upper horizontal link member 43 Lower horizontal link member 50 workbenches 51 Workbench fixing member 60 springs 61R Transmission Mechanism 62R Potentiometer

Claims

1. A work platform load detection device for detecting the load of a work platform in an aerial work vehicle configured by attaching a work platform via a parallel link mechanism to the tip of a boom that is freely raised and lowered on a vehicle body, the parallel link mechanism is composed of a boom-side vertical member pivotally connected to the tip of the boom and extending vertically, an upper horizontal link member whose base end is pivotally connected to the boom-side vertical member and extending horizontally, a work platform-side vertical member pivotally connected to the tip of the upper horizontal link member and extending vertically, to which the work platform is fixed, and a lower horizontal link member positioned below the upper horizontal link member, extending horizontally, with its base end pivotally connected to the boom-side vertical member and its tip end pivotally connected to the work platform-side vertical member, and the work platform is displaceable in the up and down direction relative to the boom-side vertical member, a spring member attached between the boom-side vertical member and the work platform-side vertical member, the spring member contracting in response to a load on the work platform; a transmission mechanism that transmits vertical displacement of the work table caused by expansion and contraction of the spring member; a displacement signal output device that outputs a signal corresponding to the displacement of the work table transmitted by the transmission mechanism, A workbench load detection device that detects the load on the workbench based on the signal output from the displacement signal output device.

2. A workbench load detection device as described in claim 1, characterized in that when a load is applied from below to above the workbench, causing the amount of contraction of the spring member to decrease and the workbench to displace upward, the load applied from below to above the workbench is detected based on the signal output from the displacement signal output device.

3. the displacement signal output device is a rotary potentiometer that has a rotary shaft and outputs an electric signal according to the rotation angle of the rotary shaft, The transmission mechanism includes a crank member having one end fixed to a rotary shaft of the potentiometer; A workbench load detection device as described in claim 1 or 2, characterized in that it is composed of a connecting member having one end rotatably attached to the other end of the crank member and the other end rotatably attached to the workbench side vertical member.

4. the displacement signal output device is a linear potentiometer that includes a slider that is linearly movable and outputs an electric signal according to the amount of movement of the slider; The workbench load detection device according to claim 1 or 2, characterized in that the transmission mechanism is a sliding member fixed to the workbench side vertical member and causes the slider to slide in response to the vertical displacement of the workbench.

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