Workbench load detection device

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 platform load detection device for detecting the load on a platform in an aerial work vehicle configured by attaching a platform via a parallel link mechanism to the tip of a boom that is freely raised and lowered on the vehicle body. [Background technology]

[0002] Generally, aerial work vehicles are equipped with a running body that has wheels or a crawler device and can run, a swivel base that is mounted on the running body so that it can rotate horizontally, a boom that is mounted on the swivel base so that it can be raised and lowered and extended, and a work platform that is supported at the tip of the boom so that it can swing. In addition, an operating device is mounted on the work platform, and by operating this operating device, a worker on the work platform can control the rotation of the swivel base, the raising and lowering of the boom, and the swinging of the work platform, etc.

[0003] When using the above-mentioned aerial work platform to work on a work object located at a high altitude, a worker mounts the platform with tools, materials, etc., and operates an operating device attached to the platform to move the platform to the work object at a high altitude. At this time, a moment (hereinafter referred to as "overturning moment") that tends to tip the vehicle body toward the platform is constantly acting on the aerial work platform. Since the overturning moment increases with an increase in the load on the platform or the extension operation of the boom, some aerial work platforms are designed to detect the load on the platform and restrict the operating range of the boom according to the detected load, thereby preventing the stability of the vehicle body from being impaired by the overturning moment that changes with the operation of the boom.

[0004] A conventional device for detecting the load on the work platform described above is an aerial work vehicle that supports a work platform at the tip of a boom via a parallel link mechanism so that the work platform can swing up and down. The device has a support spring disposed between a support arm extending integrally from the work platform and a support member that supports the parallel link mechanism at the tip of the boom, and is equipped with a limit switch that turns on when the support spring is compressed (see, for example, Patent Document 1). In this work platform load detection device, the work platform load is set to be the allowable load when the work platform moves downward due to 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) when the limit switch turns on. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-128497 Summary of the Invention [Problem to be solved by the invention]

[0006] The work platform load detection device described in Patent Document 1 detects an overload on the work platform by turning on a limit switch, so for example, when inspecting before starting work, it is difficult to confirm whether the limit switch is operating normally based on the weight of a single worker alone. Also, the maximum load capacity of the work platform in a specified work area (the area in which the work platform can move) needs to be set to an allowable load capacity when the work platform is in a position where the tipping moment is at its maximum within the range in which the stability of the vehicle body can be maintained. However, when the limit switch is turned on and the movement of the work platform is restricted when the maximum load capacity is exceeded, for example, it is necessary to set the limit switch to a position within the specified work area where the tipping moment is relatively small (the maximum limit determined by the above-mentioned method). Even when moving the work platform to a position where the stability of the vehicle body is not compromised even if the load is exceeded, the movement of the work platform is restricted if the maximum load is exceeded, so although safety can be maintained, the working area is limited.

[0007] Therefore, in order to enable more effective movement of the work platform, it is conceivable to provide a plurality of limit switches that activate with different load weights on the work platform, and to expand or reduce the working area based on the activation of each limit switch (i.e., according to the load weight on the work platform). However, because the number of limit switches that can be provided is limited due to constraints such as installation space, this method makes it difficult to finely set limits on the working range according to the load weight on the work platform.

[0008] The present invention has been made in view of the above-mentioned problems, and has an object to provide a workbench load detection device that is capable of detecting a load in accordance with changes in the load on a workbench. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides a work platform load detection device for detecting the load on a work platform of an aerial work vehicle configured by attaching a work platform via a parallel link mechanism to the tip of a boom that is provided on a vehicle body so as to be able to be raised and lowered freely, the parallel link mechanism comprising a boom side vertical member (for example, boom side vertical member 41) pivotally connected to the tip of the boom and extending in the vertical direction, an upper horizontal link member (for example, upper horizontal link member 42 in the embodiment) whose base end is pivotally connected to the boom side vertical member and extends in the horizontal direction, and a work platform side vertical member (for example, work platform fixing member in the embodiment) pivotally connected to the tip side of the upper horizontal link member and extending in the vertical direction, to which the work platform is fixed. 52), and a lower horizontal link member (e.g., lower horizontal link member 43 in the embodiment) located below the upper horizontal link member and 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, so that the work platform can be displaced in the up and down direction relative to the boom side vertical member, and a spring member (e.g., spring 60 in the embodiment) attached between the boom side vertical member and the work platform side vertical member and contracting in response to the load of the work platform, a transmission mechanism (e.g., transmission mechanism 61R in the embodiment) that transmits the up and down displacement of the work platform due to the expansion and contraction of the spring member, and ... in response to the displacement of the work platform transmitted by the transmission mechanism. continuously changes and a displacement signal output device (for example, potentiometer 62R in the embodiment) that outputs a signal, and the load on the work table is detected based on the signal output from the displacement signal output device.

[0010] Furthermore, in the workbench load detection device of the above configuration, 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 be displaced upward, it is preferable to detect the load applied from below to above the workbench based on the signal output from the displacement signal output device.

[0011] Furthermore, in the workbench load detection device of the above configuration, the displacement signal output device is a rotary potentiometer (e.g., potentiometer 62R in the embodiments) that has a rotating shaft and outputs an electrical signal according to the rotation angle of the rotating shaft, and the transmission mechanism is preferably composed of a crank member (e.g., crank member 610 and upper spacer 611 in the embodiments) having one end fixed to the rotating shaft of the potentiometer, and a connecting member (e.g., connecting shaft 612 in the embodiments) 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.

[0012] Furthermore, in the workbench load detection device having the above configuration, the displacement signal output device is a linear type potential which has a slider which can move linearly and outputs an electric signal according to the amount of movement of the slider. It is preferable that the transmission mechanism is a sliding member (for example, a link member that converts the vertical movement of the workbench fixing member 52 in the embodiment into horizontal movement) that is fixed to the workbench side vertical member and slides the slider in response to the vertical displacement of the workbench. [Effects of the Invention]

[0013] According to the work platform load detection device of the present invention, in an aerial work vehicle in which a work platform is attached via a parallel link mechanism to the tip of a boom that is provided on a vehicle body and can be raised and lowered, the device comprises a spring member that is attached between the boom side vertical member and the work platform side vertical member that constitute the parallel link mechanism and that contracts in response to the load of 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 detection device that detects the displacement of the work platform transmitted by the transmission mechanism. continuously changes and a displacement signal output device that outputs a signal, and the load on the workbench is detected based on the signal output from the displacement signal output device. In this way, the load on the workbench is detected based on the signal output from the displacement signal output device in accordance with the displacement of the workbench, so it is possible to detect the load in accordance with changes in the load on the workbench.

[0014] Furthermore, in the work platform load detection device configured as described above, preferably, when a load is applied from below to the work platform, the amount of contraction of the spring member decreases and the work platform is displaced upward, the load applied from below to above the work platform is detected based on the signal output from the displacement signal output device. As a result, when a force pushing up the work platform is applied, for example, when the bottom of the work platform is pressed against the ground or a building when the boom is lowered or retracted, the load reduced by that force can be detected. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a side view showing the appearance of an aerial work platform equipped with a work platform load detection device according to the present invention. [Figure 2] FIG. 2 is a side view showing the configuration of the boom tip, parallel link mechanism, and work platform of the aerial work platform of the vehicle for high altitude work. [Figure 3] FIG. 2 is a perspective view showing the configuration of a boom tip and a parallel link mechanism of the aerial work vehicle. [Figure 4] 3 is a side view showing the configuration and mounting position of the parallel link mechanism of the aerial work vehicle and the work platform load detection device according to the present invention. FIG. [Figure 5] FIG. 2 is a perspective view showing the appearance of a transmission mechanism that constitutes the workbench load detection device. [Figure 6] 5 is an explanatory diagram for explaining displacement of each part of the workbench load detection device in accordance with a change in the load on the workbench. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 shows a self-propelled vehicle for aerial work 1 as an example of a vehicle for aerial work equipped with a platform load detection device according to an embodiment of the present invention. The vehicle for aerial work 1 comprises a running body 10 configured to be able to travel, a rotating body 20 provided on top of the running body 10 and capable of rotating horizontally, a boom 30 provided on top of the rotating body 20 and capable of being raised and lowered, a parallel link mechanism 40 provided at the tip of the boom 30, and a work platform 50. Note that the length of the boom 30 has been partially omitted in Fig. 1.

[0017] The running body 10 has a pair of left and right steering wheels 12 rotatably mounted on the running body frame 11, and a pair of left and right drive wheels 13. A slewing mechanism 15 is provided at the center of the upper part of the running body frame 11, and is configured so that the slewing body 20 can be swung in the horizontal direction by the slewing mechanism 15. The slewing mechanism 15 has an outer wheel fixed to the running body frame 11, an inner wheel engaged with the outer wheel and fixed to the slewing body 20, and a rotary center joint (not shown) for supplying hydraulic oil to various actuators provided on the running body 10. A boom 30 is provided on the upper part of the slewing body 20, and the boom 30 swings up and down around a pivot pin 34 as an axis. The boom 30 has a base boom 31 pivotally connected to the rotating body 20, and an intermediate boom 32 and a tip boom 33 that are combined with the base boom 31 in a telescopic manner, and these booms are configured to be able to extend and retract freely.

[0018] Next, the configuration for supporting the work platform 50 at the tip of the boom 30 will be described with reference to Figure 2. Here, Figure 2 is a side view showing the side of the tip of the boom 30 including the work platform 50. In Figure 2, the same components as those in Figure 1 are given the same reference numerals, and detailed description thereof will be omitted.

[0019] 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 work platform support member 38 by a pivot pin 36a. The work platform support member 38 is also 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. The boom-side leveling cylinder 37 is extended and retracted in response to the raising and lowering operation of the boom 30 to perform leveling control of the work platform 50, so that the work platform 50 can be swung up and down relative to the tip of the boom 30 while keeping the floor surface of the work platform 50 horizontal.

[0020] A swing motor SWM is provided at the tip of the workbench support member 38 to swing (swing horizontally) the workbench 50. A vertical post 39 (see Figure 4) is provided inside the swing motor SWM, and the vertical post 39 supports the workbench 50 via a parallel link mechanism 40 so that it can swing horizontally. The swing motor SWM swings the parallel link mechanism 40 in the horizontal direction around the vertical post 39, thereby enabling the swing operation of the workbench 50. The parallel link mechanism 40 also allows the workbench 50 to swing up and down relative to the tip of the workbench support member 38 while keeping the floor surface horizontal.

[0021] The parallel link mechanism 40 mainly comprises a boom-side vertical member 41 fixed to the vertical post 39, a platform fixing member 52 to which the platform 50 is fixed, and 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 platform fixing member 52 to each other via the upper horizontal link member 42 and the lower horizontal link member 43. The work platform 50 is provided with an operating device 51, and by operating the operating device 51, an operator on the work platform 50 can control the travel of the running body 10 shown in Figure 1, the rotation operation of the revolving body 20, the raising and lowering operation of the boom 30, and the swing operation of the work platform 50, etc.

[0022] Next, the parallel link mechanism 40 and its surrounding structure will be described with reference to Figures 3 and 4. Here, Figure 3 is a perspective view of the tip of the boom 30 as seen obliquely from behind, and Figure 4 is a side view showing the structure of the parallel link mechanism 40. The work platform 50 is not shown in Figure 3. In Figures 3 and 4, the same components as those in Figure 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0023] 3 and 4, the parallel link mechanism 40 is made up of a boom-side vertical member 41 for fixing the parallel link mechanism 40 to a vertical post 39 provided on the platform support member 38, an upper horizontal link member 42, a lower horizontal link member 43, and a platform fixing member 52 to which the platform 50 is fixed. The boom-side vertical member 41 is made up of a left side plate 411L and a right side plate 411R that have the same shape and are arranged facing each other with a predetermined distance between them, and an upper flat plate 415 and a lower flat plate 416 that are provided horizontally between the left side plate 411L and the right side plate 411R.

[0024] As shown in FIG. 4, an upper pivot hole 412 for inserting the boom-side upper pivot pin 421 (see FIG. 3) is provided in the upper part of the right side plate 411R, and a lower pivot hole 413 for inserting the boom-side lower pivot pin 431 is provided in the lower part of the right side plate 411R. A fan-shaped opening 414 is provided between the pivot hole 412 and the upper flat plate 415. Although not shown, the left side plate 411L also has an upper pivot hole 412, a lower pivot hole 413, and an opening 414 at positions facing the upper pivot hole 412, the lower pivot hole 413, and the opening 414 provided in the right side plate 411R. In addition, a spring lower end receiving portion 417 to which the lower end of the spring 60 shown in FIG. 4 is attached is formed on the top surface of the upper flat plate 415.

[0025] As shown in Figure 4, an upper pivot hole 521 and a lower pivot hole 522 are formed on the left and right side surfaces of the work platform fixing member 52 when viewed from the direction shown in Figure 3. These upper pivot holes 521 and lower pivot holes 522 are provided at opposing positions on the left and right side surfaces of the work platform fixing member 52. The vertical distance between the upper pivot holes 521 and the lower pivot holes 522 is the same as the vertical distance between the upper pivot holes 412 and the lower pivot holes 413 formed on the left plate 411L and right plate 411R of the boom side vertical member 41. A horizontal plate 523 is provided below the upper pivot hole 521, extending from the left side surface to the right side surface of the work platform fixing member 52, and a spring upper end receiver 524 to which the upper end of the spring 60 is attached is formed on the lower surface of the horizontal plate 523.

[0026] As shown in FIGS. 3 and 4, the upper horizontal link member 42 is composed of an upper left side plate 420L, an upper right side plate 420R, a boom-side pivot pin 421, and a platform-side pivot pin 422. The upper left side plate 420L and the upper right side plate 420R have the same shape and are each provided with a boom-side pivot pin hole into which the boom-side pivot pin 421 shown in FIG. 4 is inserted and a platform-side pivot pin hole into which the platform-side pivot pin 422 is inserted. As a result, the boom-side pivot pin holes in the upper left side plate 420L and the upper right side plate 420R are aligned with the upper pivot holes 412 in the left side plate 411L and right side plate 411R of the boom-side vertical member 41, and the boom-side pivot pin 421 is inserted through the holes to pivotally connect the upper horizontal link member 42 to the boom-side vertical member 41. In addition, split pins SP are attached to both ends of the boom-side pivot pin 421. On the workbench 50 side, the positions of the workbench side pivot pin holes provided on the upper left side plate 420L and the upper right side plate 420R are aligned with the positions of the upper pivot holes 521 provided on the workbench fixing member 52, and the workbench side pivot pin 422 is passed through and fixed, thereby pivoting the upper horizontal link member 42 to the workbench fixing member 52.

[0027] Like the upper horizontal link member 42, the lower horizontal link member 43 is composed of a lower left side plate (not shown), a lower right side plate 430R, a boom-side pivot pin 431, and a platform-side pivot pin 432. The lower left side plate and the lower right side plate 430R have the same shape and are each provided with a boom-side pivot pin hole into which the boom-side pivot pin 431 shown in FIG. 4 is inserted and a platform-side pivot pin hole into which the platform-side pivot pin 432 is inserted. As a result, the boom-side pivot pin holes in the lower left side plate and the lower right side plate 430R are aligned with the lower pivot holes 413 in the left plate 411L and the right plate 411R of the boom-side vertical member 41, and the boom-side pivot pin 431 is inserted to pivotally connect the lower horizontal link member 43 to the boom-side vertical member 41. In addition, split pins SP are attached to both ends of the boom-side pivot pin 431. On the workbench 50 side, the positions of the workbench side pivot pin holes provided on the lower left side plate and lower right side plate 430R are aligned with the positions of the lower pivot holes 522 provided on the workbench fixing member 52, and the workbench side pivot pin 432 is passed through, thereby pivoting the lower horizontal link member 43 to the workbench fixing member 52.

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

[0029] The transmission mechanism 61R transmits the vertical movement of the workbench fixing member 52 to the rotating shaft RS of the potentiometer 62R. As shown in FIG. 5, the transmission mechanism 61R is composed of a crank member 610, an upper spacer 611, a connecting shaft 612, and a lower spacer 613. A mounting hole CH is formed in one end of the crank member 610, through which the rotating shaft RS of the potentiometer 62R passes. The rotating shaft RS is fixed to the crank member 610 by a nut NT1 (see 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 an upper connecting portion 612a of a connecting shaft 612. A lower spacer 613 is rotatably fixed to a lower connecting portion 612b of the connecting shaft 612. A male thread MC is formed at the tip of the lower spacer 613, and the lower spacer 613 is fixed to a mounting hole BH formed in the workbench fixing member 52 by a nut NT2 (see FIG. 4).

[0030] In addition, FIG. 3 shows the potentiometer 62L attached to the left side plate 411L of the boom side vertical member 41, and a transmission mechanism (not shown) similar to the above-mentioned transmission mechanism 61R is also attached to the potentiometer 62L.

[0031] Next, the displacement of each part of the work platform load detection device in accordance with the change in the load on the work platform 50 will be described with reference to Figure 6. In Figure 6, the same components as those shown in Figure 4 are given the same reference numerals, and detailed description will be 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 work platform side pivot pin 422, point B is the position of the potentiometer 62R. The center position of the rotation axis RS, point C, and point D indicate the center position of the upper connecting portion 612a. Furthermore, if the line connecting points A and A' when no load is applied to the workbench 50 is defined as a reference line RL1, and the line connecting points A and A' when a load of L [kg] is applied to the workbench 50 is defined as a line LL1, the angle formed by RL1 and LL1 is defined as θ1. Furthermore, if the line connecting points B and D when no load is applied to the workbench 50 is defined as a reference line RL2, and the line connecting points B and D when a load of L [kg] is applied to the workbench 50 is defined as a line LL2, the angle formed by 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 the amount of this 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, a voltage signal with a voltage value corresponding to the angle θ2 is generated by the potentiometer 62R, and the load applied to the workbench 50 is detected based on this voltage signal, for example, in a controller (not shown). One possible method for detecting this load is to measure in advance the characteristics of the magnitude of the voltage value of the voltage signal generated by the potentiometer 62R relative 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. The magnitude of the angle θ2 relative to the angle θ1 depends on the position of the rotation axis RS of the potentiometer 62R, the length between points B and D (i.e., the length of the crank member 610), the length between points D and 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 This can be adjusted by appropriately selecting the spring constant, etc.

[0034] In this way, when the workbench fixing member 52 moves downward due to a load applied to the workbench 50, the workbench load detection device of this embodiment converts this movement into rotational motion of the rotation axis RS of the potentiometer 62R by the transmission mechanism 61R, and detects the load applied to the workbench 50 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 (increases and decreases) in the load, making it possible to finely set limits on the working range according to the magnitude of the load on the workbench. Furthermore, because a potentiometer is used, costs can be reduced compared to when detecting loads using, for example, a load cell.

[0035] In the embodiment described above, in addition to the potentiometer 62R and transmission mechanism 61R attached to the right side plate 411R of the boom-side vertical member 41, a potentiometer 62L (see FIG. 3) and a corresponding transmission mechanism (not shown) are also provided on the left side plate 411L. As a result, even if a malfunction occurs in one of the potentiometers or transmission mechanism, the load on the work platform 50 can be detected by the other potentiometer and transmission mechanism. 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 omitted, and only the potentiometer 62R and transmission mechanism 61R may be provided.

[0036] Although a rotary potentiometer is used as the potentiometer 62R in this embodiment, a linear potentiometer having a knob (slider) that can move linearly and whose resistance value changes according to the amount of movement of the knob may also be used. 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 potentiometer may be attached to this link member, so that the knob of the linear potentiometer can be 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 Workbench 52 Workbench fixing member 60 spring 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 that continuously changes in accordance with 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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