Multi-stage boom extension mechanism

Abstract

To provide a multi-stage boom extension mechanism capable of maintaining a retraction wire rope, which is not involved in the extension of a boom, in a tensioned state without slack, when the multi-stage boom is extended.SOLUTION: A retraction wire rope tensioner 60 of a multi-stage boom extension mechanism applies a spring force to a retraction wire rope 40 in a direction to constantly maintain a tensioned state via a slider 67 that is slidable in an extension / retraction direction, and can maintain the retraction wire rope 40 in a predetermined tensioned state without slack at the time of extension or the like of the multi-stage boom in which the slack occurs in the retraction wire rope 40. The slider 67 slides along a plurality of guide shafts 64 to 66, and compression coil springs 71 to 73 arranged on each guide shaft can apply a large spring force to maintain the rope in the tensioned state in a small space. The slider 67 slides without any rattling, and the retraction wire rope 40 is stably maintained in the tensioned state without slack.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a boom telescoping mechanism for a multi-stage boom used in construction machines such as cranes. More specifically, in conjunction with a hydraulic cylinder for telescoping the boom, a retracting wire rope is used to move the last-stage boom from an extended position pulled out from the front end of the boom on the front stage side to a retracted position retracted into the boom, and the present invention relates to a retracting wire rope tensioner that holds the retracting wire rope in an appropriate tension state so that no slack occurs.

Background Art

[0002] As a boom telescoping mechanism for a multi-stage boom used in construction machines such as cranes, a wire rope telescoping type is known. The wire rope telescoping type boom telescoping mechanism is configured such that, for example, the second-stage boom is telescoped by a hydraulic cylinder, and in conjunction with the telescoping operation of the second-stage boom, each stage of the boom from the third stage to the last stage is telescoped using a plurality of wire ropes. Such a wire rope telescoping type boom telescoping mechanism has been proposed, for example, in Patent Documents 1, 2, and 3.

[0003] In the wire rope telescoping type boom telescoping device described in Patent Document 3, a dedicated retracting wire rope for retracting the boom is made into one, and the routing of the retracting wire rope is performed inside the boom, thereby narrowing the gap between the booms and achieving miniaturization and weight reduction of the boom.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In such a wire rope telescopic boom expansion and contraction mechanism, the wire rope for extending each stage of the boom and the wire rope for contracting the boom are adjusted to be in a tensioned state where they are pulled against each other. From this state, when one wire rope is pulled and the boom extends, slack occurs in the other wire rope that is not involved in the extension of the boom. Also, elongation occurs in the wire rope for boom extension due to the suspended load. When the wire rope is routed inside the boom, if slack occurs in the wire rope, there is a risk that the slack portion of the wire rope will interfere with a part inside the boom, causing problems.

[0006] In view of this point, an object of the present invention is to provide a boom expansion and contraction mechanism for a multi-stage boom equipped with a contraction wire rope tensioner that can maintain a non-slack predetermined tension state for the contraction wire rope that is not involved in the extension of the boom when each stage of the multi-stage boom extends or when elongation occurs in the extension wire rope due to a suspended load.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention provides a boom expansion and contraction mechanism for a multi-stage boom having a plurality of booms of three or more stages, which moves each stage of the boom from the second stage to the final stage to a retracted position drawn into the boom on the previous stage side and an extended position drawn out from the front end of the boom, a fluid pressure cylinder that moves the second-stage boom to the retracted position and the extended position with respect to the first-stage boom, a contraction wire rope that moves the final-stage boom from the extended position to the retracted position in conjunction with the movement of the second-stage boom from the extended position to the retracted position by the fluid pressure cylinder, A wire rope for retraction, and a wire rope tensioner for the retraction that maintains the wire rope for retraction in a predetermined tension state so that no slack occurs. It has The wire rope tensioner for retraction is attached to the boom of the last stage, and includes a slide guide extending in the telescopic direction, which is the moving direction of the boom. A slider that is slidably supported in the telescopic direction by the slide guide and to which the wire rope for retraction is attached. A telescopic spring that always biases the slider in the direction of sliding in the extension direction of the boom. It is provided with The slide guide includes a plurality of guide shafts extending in the telescopic direction. The telescopic spring is characterized in that it is arranged along each of the guide shafts.

[0008] The wire rope for retraction of the boom telescopic mechanism is attached to a slider that is slidable in the telescopic direction along a slide guide attached to the boom of the last stage. By means of the telescopic spring, the slider is always biased in the direction of pulling the wire rope for retraction. According to the tensile force acting on the wire rope for retraction, the slider slides in the telescopic direction of the boom so that the telescopic spring expands and contracts. When the multi-stage boom extends and slack occurs in the wire rope for retraction, the telescopic spring causes the slider to slide in the extension direction of the boom, and the wire rope for retraction is maintained in a tension state (tensioned state) without slack. When the multi-stage boom contracts, due to the tensile force acting on the wire rope for retraction, the slider slides in the contraction direction of the boom against the spring force, so that the wire rope for retraction is maintained in a predetermined tension state.

[0009] As the guide shaft, for example, three shafts, i.e., a first shaft, a second shaft, and a third shaft, are arranged. In this case, the shafts are arranged such that the second and third shafts are respectively positioned at the left and right corners of an isosceles triangle having the first shaft as its vertex on a plane orthogonal to the telescopic direction. Further, three shaft holes are formed in the slider such that the first, second, and third shafts respectively penetrate therethrough slidably in the telescopic direction. Furthermore, the guide shaft is spanned between a pair of brackets attached to the boom at the final stage with a constant interval in the telescopic direction. As the telescopic spring, three compression coil springs mounted in a compressed state are used between the bracket positioned on the contracting side in the telescopic direction and the slide plate.

[0010] Further, it is desirable that a stopper for defining the slide limit of the slider in the direction of compressing the telescopic spring is attached to the boom at the final stage.

[0011] Here, when slack occurs in the retracting wire rope that is spanned due to changes over time, for example, the tension state of the retracting wire rope when the multi-stage boom is in the contracted state is relaxed. Accordingly, the slide position of the slider (the amount of contraction of the telescopic spring) that pulls the retracting wire rope by the spring force changes. Therefore, it is desirable to provide a slide position confirmation portion that allows the slide position of the slider to be visually confirmed from the outside of the boom at the final stage to which the slider is attached. In this way, an operator or the like can visually confirm the position of the slider from the outside, and based on this, it can be known whether the retracting wire rope is stretched in an appropriate tension state.

[0012] In addition, in the work of assembling the retracting wire rope, it is necessary to pass the retracting wire rope over a slider that is biased in the tensile direction by a telescopic spring. In order to facilitate the work, it is desirable to hold the slider at a position where it is forcibly pushed into the shrinking direction and perform the work of passing the retracting wire rope in a state where the spring force does not act. For this purpose, for example, a slider pushing and fixing mechanism that can push the slider against the spring force and fix it at a predetermined position may be attached to the retracting wire rope tensioner.

[0013] Next, the crane of the present invention has a multi-stage boom having a plurality of booms of three or more stages, and a boom telescoping mechanism for moving each boom of the multi-stage boom to a retracted position retracted into the boom on the front stage side and an extended position pulled out from the front end of the boom. and is characterized in that the boom telescoping mechanism has the boom telescoping mechanism configured as described above.

Effects of the Invention

[0014] According to the present invention, a spring force acts on the retracting wire rope in a direction to always maintain its tension state via a slider that can slide in the telescoping direction. When the multi-stage boom extends and the retracting wire rope loosens, the retracting wire rope can be maintained in a predetermined tension state without loosening, so that problems caused by the occurrence of looseness can be avoided. In addition, the slider slides along a plurality of guide shafts, and a large spring force for maintaining the tension state is applied by the telescopic springs arranged on each guide shaft. Therefore, the slider slides without play, and the retracting wire rope is stably maintained in a tension state without looseness.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0016] Hereinafter, with reference to the drawings, embodiments of a boom extension mechanism of a multi-stage boom to which the present invention is applied will be described. A multi-stage boom equipped with a boom telescoping mechanism is used, for example, when mounted on a crawler-type traveling crane equipped with a crawler-type traveling body.

[0017] FIG. 1 shows a schematic configuration of a multi-stage boom equipped with a boom telescoping mechanism according to the present embodiment. The multi-stage boom 1 is a five-stage boom including booms 11 to 15 from the first stage to the fifth stage in this example. Each stage of the booms 11 to 15 is, for example, a cylindrical boom having a rectangular cross section, and the base end portion of the first-stage boom 11 is attached to an upper slewing body mounted on a lower traveling body of a traveling crane (not shown). Each stage of the booms 12 to 15 from the second stage to the fifth stage, which is the final stage, can move between a retracted position retracted into the boom on the previous stage side and an extended position pulled out from the front end of the boom.

[0018] Fig. 1(A) is a schematic side view showing the multi-stage boom 1 in a retracted state, with the booms 12 to 15 of each stage being retracted to their respective retracted positions. The multi-stage boom 1 is pivoted by a pivoting hydraulic cylinder (not shown) spanned between the first-stage boom 11 and the upper slewing body of a traveling crane (not shown). Also, by the boom telescoping mechanism described below, the booms 12 to 15 of each stage are telescoped between their respective retracted positions and extended positions.

[0019] Figs. 1(B) and (C) are explanatory views showing the boom telescoping mechanism for telescoping the booms 12 to 15 of each stage in the multi-stage boom 1. In these figures, the multi-stage boom 1 is shown in a state where the booms 12 to 15 of each stage are extended by a predetermined amount from their retracted states. The boom telescoping mechanism includes a hydraulic cylinder 30, a single retraction wire rope 40, a single extension wire rope 51, two telescoping wire ropes 52 and 53, and a retraction wire rope tensioner 60 for maintaining the retraction wire rope 40 in a predetermined tension state without slack. To clearly show the routing state of each wire rope, in Fig. 1(B), the retraction wire rope 40 is omitted and the extension wire rope 51 and the telescoping wire ropes 52 and 53 are shown, and in Fig. 1(C), the extension wire rope 51 and the telescoping wire ropes 52 and 53 are omitted and only the retraction wire rope 40 is shown.

[0020] The hydraulic cylinder 30 of the boom telescoping mechanism is a fluid pressure cylinder for moving the second-stage boom 12 relative to the first-stage boom 11 to the retracted position and the extended position. The extension wire rope 51 moves the third-stage boom 13 from the retracted position toward the extended position in conjunction with the movement of the second-stage boom 12 from the retracted position to the extended position by the hydraulic cylinder 30. The telescopic wire rope 52 moves the fourth-stage boom 14 from the retracted position toward the extended position in conjunction with the movement of the third-stage boom 13 from the retracted position to the extended position. The telescopic wire rope 53 moves the fifth-stage boom 15, which is the final stage, from the retracted position toward the extended position in conjunction with the movement of the fourth-stage boom 14 from the retracted position to the extended position. The retracting wire rope 40 moves the fifth-stage boom 15, which is the final stage, from the extended position to the retracted position in conjunction with the movement of the second-stage boom 12 from the extended position to the retracted position by the hydraulic cylinder 30. The telescopic wire rope 53 moves the fourth-stage boom 14 from the extended position to the retracted position in conjunction with the movement of the fifth-stage boom 15, which is the final stage, moving from the extended position to the retracted position. The telescopic wire rope 52 moves the third-stage boom 13 from the extended position to the retracted position in conjunction with the movement of the fourth-stage boom 14 moving from the extended position to the retracted position.

[0021] More specifically, the hydraulic cylinder 30 is arranged in the center part inside the multi-stage boom 1 in the front-rear direction of the boom, which is the boom telescopic direction, and is spanned between the first-stage boom 11 and the second-stage boom 12. In this example, the cylinder body 31 of the hydraulic cylinder 30 is connected to the rear end portion of the second-stage boom 12 and extends forward inside the fifth-stage boom 15. The telescopic rod 32 of the hydraulic cylinder 30 protrudes rearward from the cylinder body 31 through the rear end opening of the boom 12 and is connected to the rear end portion of the first-stage boom 11.

[0022] Referring to Fig. 1(B), the extension wire rope 51 for extending the third boom 13 has one rope end 51a connected to the rear end of the first boom 11 (in this example, it is connected to the rear end of the telescopic rod 32 of the hydraulic cylinder 30 attached to the boom 11). From here, it is drawn forward, passed over a pulley 33 that moves in the telescopic direction together with the second boom 12 from the front side, and then drawn backward. The other rope end 51b is connected to the inside of the rear end of the third boom 13. The pulley 33 is attached to the front end of the cylinder body 31 of the hydraulic cylinder 30 connected to the second boom 12 and moves back and forth together with the boom 12.

[0023] The telescopic wire rope 52 for extending the fourth boom 14 and contracting the third boom 13 is shown by a fine broken line in Fig. 1(B). One rope end 52a is connected to the outside of the front end of the second boom 12, drawn forward from here, passed over a pulley 55 attached to the front end of the third boom 13 from the front side, then drawn backward through the inside of the front end opening of the boom 13, and the other rope end 52b is connected to the rear end of the fourth boom 14.

[0024] The telescopic wire rope 53 for extending the fifth boom 15 and contracting the fourth boom is shown by a one-dot chain line in Fig. 1(B). One rope end 53a is connected to the outside of the front end of the third boom 13, drawn forward from here, passed over a pulley 56 attached to the front end of the fourth boom 14 from the front side, then drawn backward through the inside of the front end opening of the boom 14, and the other rope end 53b is connected to the rear end of the fifth boom 15.

[0025] Referring to FIG. 1(C), the retractable wire rope 40 is stretched between the first-stage boom 11, the second-stage boom 12, and the fifth-stage boom 15 of the final stage. In this example, pulleys 41 and 41' are symmetrically attached to both sides of the front end of the first-stage boom 11, and a pair of upper and lower pulleys 42 and 43 and upper and lower pulleys 42' and 43' are symmetrically attached to both sides of the rear end of the second-stage boom 12. One of both rope ends 40a and 40a' of the retractable wire rope 40 is connected to a part on one side (left or right) of the front end of the first-stage boom 11, and the other is connected to a part on the other side. In FIG. 1(C), the pulleys 41, upper pulley 42, and lower pulley 43 located on one side (left or right) are shown, and for the pulleys 41', upper pulley 42', and lower pulley 43' located on the other side, only the numbers are shown in parentheses.

[0026] For example, the retractable wire rope 40 is drawn backward from one of its rope ends 40a and is drawn toward the upper pulley 42 attached to one side of the rear end of the second-stage boom 12 (rope portion 40b). After being wound around the upper and rear sides of the upper pulley 42, it is drawn forward from its lower side (rope portion 40c) and is wound around the pulley 41 at the front end of the first-stage boom 11 from the upper and front sides. Also, it is drawn backward from the lower side of the pulley 41 (rope portion 40d) and is wound around the lower pulley 43 on the right side of the rear end of the second-stage boom 12 from the lower and front sides. It is drawn forward from the upper side of this lower pulley 43. The rope portion 40e drawn from the lower pulley 43 is drawn forward through the inside of the third-stage and fourth-stage booms 13 and 14 and through the inside of the fifth-stage boom 15 from the rear-end opening thereof, as shown by the dashed line.

[0027] Here, a retracting wire rope tensioner 60 is attached inside the front end of the fifth-stage boom 15. The retracting wire rope 40 drawn forward inside the boom 15 is wound around the retracting wire rope tensioner 60 (rope portion 40f). In this example, as will be described later, the retracting wire rope tensioner 60 is equipped with a non-rotating semi-circular fixed sheave 70 that can move in the front-rear direction, and the retracting wire rope 40 is wound around the semi-circular fixed sheave 70 so as to be drawn out from the right side, through the front side, and from the other left side to the rear. The retracting wire rope 40 drawn out rearward from the semi-circular fixed sheave 70 is sequentially wound around the lower pulley 43', pulley 41', and upper pulley 42' located on the other side in the left-right direction in a symmetric state, and then its rope end 40a' is connected to the left-side part at the front end of the first-stage boom 11.

[0028] (Configuration of the retracting wire rope tensioner) Figures 2(A), (B), (C), and (D) are a schematic plan view, a schematic side view, a schematic bottom view, and a schematic cross-sectional view of the portion cut along line D-D showing the retracting wire rope tensioner 60. Figures 3(A) and (B) are a schematic plan view and a schematic side view for showing the movement of the slider of the retracting wire rope tensioner 60. In these figures, for the purpose of explaining the slider pushing and fixing mechanism 90, the state in which a bolt shaft 91 for sliding and pushing, which is a component of the mechanism, is attached is shown. As will be described later, normally, instead of the bolt shaft 91, a short adjusted stopper bolt 94 as shown in Figure 3(C) is attached, and the slider 67 can slide between positions 67A and 67B due to its structure.

[0029] First, referring to FIG. 2, the retractable wire rope tensioner 60 includes a mounting frame 61 attached to the inner top surface of the front end of the fifth boom 15 in the final stage, specifically the inner top surface of the tip in this example. The mounting frame 61 includes a front end plate 62 and a rear end plate 63 facing each other at a predetermined interval in the boom front-rear direction. The front end plate 62 is attached to the front bracket 15a attached to the boom 15, and the rear end plate 63 is attached to the portion 15b of the boom 15. Between the front end plate 62 and the rear end plate 63, a plurality of, in this example, three cylindrical guide shafts 64, 65, 66 are spanned in the boom front-rear direction as slide guides. When viewed in a plane perpendicular to the front-rear direction, the guide shafts 64 to 66 are symmetrically arranged such that the left and right guide shafts 65 and 66 are located at both corners of an isosceles triangle with the central guide shaft 64 as the vertex.

[0030] A slider 67 is attached between the front end plate 62 and the rear end plate 63 of the mounting frame 61 in a state where it can slide in the boom front-rear direction along the guide shafts 64 to 66. The slider 67 includes a slide plate 68 in which guide holes for the three guide shafts 64 to 66 are formed, and a bush 69 attached to the front surface of this slide plate 68 and in which a guide hole for the central guide shaft 64 is formed. The slide plate 68 includes an end plate portion 68a extending in the vertical direction and a top plate portion 68b bent forward at a right angle from the upper end of the end plate portion 68a and extending. Three guide holes are formed in the end plate portion 68a, and the bush 69 is attached to the front surface thereof.

[0031] A semi-circular fixed sheave 70 (rope attachment portion) around which the rope portion 40f of the retractable wire rope 40 is wound is mounted on the upper surface of the top plate portion 68b of the slider 67. Between the slider 67 and the rear end plate 63 of the mounting frame 61, three compression coil springs 71, 72, 73 (telescopic springs) arranged in a compressed state so as to coaxially surround each of the guide shafts 64 to 66 are arranged. The spring forces of the compression coil springs 71 to 73 always act on the slider 67 in the direction of pulling the retractable wire rope 40.

[0032] Here, the slider 67 is pushed out by the compression coil springs 71 to 73 and is structurally movable, for example, to the position 67B shown in FIG. 3(B), but the sliding position is adjusted so that it does not slide to this position 67B and the position before that becomes the sliding limit. Further, on the inner top surface of the tip portion of the boom 15, a stopper 70A made of, for example, a round bar welded to the portion is arranged. When the slider 67 slides in the direction of pushing in the compression coil springs 71 to 73, the semi-circular fixed sheave 70 mounted on the slider 67 hits the stopper 70A, and its sliding is restricted. That is, the sliding limit position 67A in the direction of compressing the compression coil springs 71 to 73 is defined by the stopper 70A.

[0033] In this example, the sliding of the slider 67 in the direction of compressing the compression coil springs 71 to 73 stops when the semi-circular fixed sheave 70 hits the stopper 70A on the inner top surface of the boom 15 at the position 67A. The sliding limit (position 67A) of the slider 67 in the direction of compressing the compression coil springs 71 to 73 is defined by the semi-circular fixed sheave 70 coming into contact with the stopper 70A.

[0034] Thereby, excessive stress due to the large thrust during boom extension can be prevented from deforming the compression coil springs 71 to 73, the mounting frame 61, the guide shafts 64 to 66, etc., which are components of the wire rope tensioner for retraction. Further, since excessive force is prevented from acting on these components, the weight of these components can be reduced. That is, from the viewpoints of ensuring the lifting capacity and stability of the crane, it is important that the boom of the crane is lighter towards the tip of the boom. Using the slide restriction mechanism by the stopper 70A in this example is extremely effective for reducing the weight of the tip side of the boom 15 in which the wire rope tensioner for retraction is incorporated.

[0035] (Operation of the wire rope tensioner for retraction) Referring to FIGS. 1, 2, and 3, the operation of the retracting wire rope 40 accompanying the telescoping operation of the multi-stage boom 1 by the boom telescoping mechanism will be described. In the retracted state of the multi-stage boom 1, the extending wire rope 51, the telescoping wire ropes 52 and 53, and the retracting wire rope 40 of the boom telescoping mechanism are stretched in a predetermined tension state without slack. The retracting wire rope 40 is wound around a semi-circular fixed sheave 70 mounted on a slider 67 that is slidable in the boom telescoping direction (front-rear direction of the boom) along three guide shafts 64 to 66 attached to the fifth-stage boom 15 of the final stage. By compression coil springs 71 to 73 attached to the guide shafts 64 to 66, the slider 67, and thus the semi-circular fixed sheave 70, are always biased in the direction of pulling the retracting wire rope 40.

[0036] For example, in the retracted state of the multi-stage boom 1 shown in FIG. 1(A), as shown by the solid line in FIGS. 2(A) and (B) and by the imaginary line in FIGS. 3(A) and (B), the slider 67 (semi-circular fixed sheave 70) is located at the pushed-in position 67A on the rear side in the front-rear direction of the boom by the retracting wire rope 40 stretched in a predetermined tension state.

[0037] When extending the retracted multi-stage boom 1 shown in FIG. 1(A) to the predetermined extended state shown in FIGS. 1(B) and (C), the hydraulic cylinder 30 is driven to perform an operation of pulling out the second-stage boom 12 forward with respect to the first-stage boom 11. When the second-stage boom 11 is pulled out forward, in conjunction with this, the third-stage boom 13 is pulled out forward with respect to the second-stage boom 12 by the extending wire rope 51 stretched between the first, second, and third-stage booms 11 to 13. In conjunction with this, the fourth-stage boom 14 is pulled out forward with respect to the third-stage boom 13 by the telescoping wire rope 52 stretched between the second, third, and fourth-stage booms 12 to 14. In conjunction with this, the fifth-stage boom 15 is pulled out forward with respect to the fourth-stage boom 14 by the telescoping wire rope 53 stretched between the third, fourth, and fifth-stage booms 13 to 15.

[0038] In this boom extension operation, the retraction wire rope 40 stretched between the first-stage, second-stage, and fifth-stage booms 11, 12, and 15 becomes slack as the second-stage boom 12, which is first pushed out by the hydraulic cylinder 30, moves. Also, when a load (lifting load) is applied to the boom during a load-lifting operation or the like, the wire ropes 51, 52, and 53 stretch, causing the retraction wire rope 40 to become slack.

[0039] In this example, according to the tensile force acting on the retraction wire rope 40, the compression coil springs 71 to 73 expand and contract, and the slider 67 slides in the boom expansion and contraction direction. When the multi-stage boom 1 extends and the retraction wire rope 40 becomes slack, the compression coil springs 71 to 73 cause the slider 67 to slide in the boom extension direction (the front direction of the boom), and the retraction wire rope 40 is maintained in a predetermined tension state (tension state) without slack. Therefore, the retraction wire rope 40 wound around the semicircular fixed sheave 70 mounted on the slider 67 is pulled by an amount corresponding to the forward sliding amount of the slider 67. As a result, the retraction wire rope 40 is maintained in a predetermined tension state without slack even during boom extension and when a load is applied to the boom.

[0040] Here, in this example, three guide shafts 64 to 67 are arranged as guide shafts, and the slider 67 is guided by these. Also, a tensile force is applied to the retraction wire rope 40 by the three compression coil springs 71 to 73 attached to the respective guide shafts 64 to 67. Therefore, the slider 67 slides without rattling, and the retraction wire rope 40 is stably maintained in a tension state without slack.

[0041] (Slider position confirmation section) Next, in the boom telescoping mechanism, the retracting wire rope 40 that is stretched may become slack due to changes over time. In this case, when the multi-stage boom 1 is in the retracted state, the tension state of the retracting wire rope will be relaxed. When the tension state is relaxed, in the retracting wire rope tensioner 60 of this example, accordingly, the slide position (the amount of reduction of the compression coil spring) of the slider 67 that pulls the retracting wire rope 40 by spring force changes. Therefore, based on the change in the slide position of the slider 67, it is possible to know that the tension state of the retracting wire rope 40 has become slack.

[0042] Therefore, in the boom retracted state shown in FIG. 2, a slide position confirmation portion that allows visual confirmation of the slide position of the slider 67 from the outer side of the final-stage boom 15 to which the slider 67 is attached may be provided. For example, in FIGS. 2(B) and (C), as shown by the imaginary lines, as the slide position confirmation portion 80, confirmation holes 81 and 82 that allow visual confirmation of the position of the end plate portion 68a of the slide plate 68 of the slider 67 are formed on the side surface of the final-stage boom 15 having a rectangular cross section.

[0043] The end plate portion 68a functions as an indicator for position confirmation. The position where the end plate portion 68a can be confirmed from the hole 81 is the adjustment position, and the position where the end plate portion 68a can be confirmed from the hole 82 is the adjustment limit position. The adjustment limit position is a position within a range that does not exceed the specification limit of the retracting wire rope, and is set as the maintenance reference position. When the end plate portion 68a is not positioned between the confirmation holes 81 to 82, it can be understood that wire rope tension adjustment or replacement is necessary.

[0044] In this way, an operator or the like can visually confirm the position of the slider 67 from the outside, and based on this, it is possible to know whether the retracting wire rope 40 is stretched in an appropriate tension state. For example, in the boom retracted state, when the position of the slider 67 deviates forward from the hole 82, the slider 67 cannot be visually confirmed, and thus it is possible to know that the retracting wire rope 40 has become slack.

[0045] (Slider Pushing and Fixing Mechanism) On the other hand, in this example, the reduction-use wire rope 40 is spanned in a predetermined tension state by the reduction-use wire rope tensioner 60. In the assembly operation of the reduction-use wire rope 40, it is necessary to span the reduction-use wire rope 40 over the semi-circular fixed sheave 70 of the slider 67 that is biased in the tensile direction by the compression coil springs 71 to 73. In order to facilitate the operation, it is desirable to hold the slider 67 at a position where it is forcibly pushed in the reduction direction and perform the spanning operation of the reduction-use wire rope 40 in a state where the spring force does not act.

[0046] For this purpose, for example, a slider pushing and fixing mechanism that can push the slider 67 against the spring force and fix it at a predetermined position may be attached to the reduction-use wire rope tensioner 60. With reference to FIGS. 2 and 3, the slider pushing and fixing mechanism 90 of this example will be described.

[0047] The slider pushing and fixing mechanism 90 is composed of a bolt shaft 91, a threaded hole 92 formed in the front end plate 62 of the mounting frame 61, and a locking nut 93. The bolt shaft 91 is a fully threaded bolt shaft with external threads cut over the entire length. The threaded hole 92 formed in the front end plate 62 of the mounting frame 61 has internal threads cut to allow the bolt shaft 91 to be screwed in. The bolt shaft 91 is screwed into the threaded hole 92, and its tip is brought into contact with the end plate portion 68a of the slide plate 68 of the slider 67. By further screwing in the bolt shaft 91, the slider 67 can be pushed by the bolt shaft 91 to the position 67A in the figure. The bolt shaft 91 is locked at this screwed-in position by the locking nut 93, and the winding operation of the reduction-use wire rope 40 is performed in a state where the spring force does not act.

[0048] After the work is completed, if the bolt shaft 91 is removed, the slider 67 returns to a slidable state, and the tensile force acts on the retracting wire rope 40. Also, after the work is completed, the bolt shaft 91 is replaced with an adjusted stopper bolt 94 having a short length. FIG. 3(C) shows the adjusted stopper bolt 94, and FIG. 3(B) shows the adjusted stopper bolt 94 by an imaginary line. The adjusted stopper bolt 94 also has a male thread cut so that the shaft portion is a full thread. As shown by the imaginary line in FIG. 3(B), the adjusted stopper bolt 94 is screwed in until its tip 94a reaches the position 67B and is fixed at this position by the locking nut 93. During normal work, the adjusted stopper bolt 94 functions as a stopper that restricts the forward slide of the slider 67.

Explanation of Signs

[0049] 1 Multi-stage boom 11, 12, 13, 14, 15 Boom 15a Bracket 15b Portion 30 Hydraulic cylinder 31 Cylinder body 32 Telescopic rod 33 Pulley 40 Retracting wire rope 40a, 40a´ Rope end 40b, 40c, 40d, 40e, 40f Rope portion 41 Pulley 42 Upper pulley 43 Lower pulley 51 Extending wire rope 51a, 51b Rope end 52 Telescopic wire rope 52a, 52b Rope end 53 Telescopic wire rope 53a, 53b Rope end 55, 56 Pulley 60 Retracting wire rope tensioner 61 Mounting frame 62 Front end plate 63 Rear end plate 64, 65, 66 guide shafts (slide guides) 67 slider 67A, 67B positions 68 slide plate 68a end plate portion 68b top plate portion 69 bush 70 semi-circular fixed sheave 71, 72, 73 compression coil springs 80 slide position confirmation part 81, 82 holes 90 slider pushing and fixing mechanism 91 bolt shaft 92 threaded hole 93 locking nut 94 adjusted stopper bolt 94a tip

Claims

1. A boom telescoping mechanism for a multi-stage boom having a plurality of booms in three or more stages, which moves the booms of each stage from the second stage to the final stage to a reduced position retracted into the boom on the front stage side and an extended position pulled out from the front end of the boom, comprising: A hydraulic cylinder that moves the boom of the second stage to the reduced position and the extended position with respect to the boom of the first stage; A retraction wire rope that moves the boom of the final stage from the extended position to the reduced position in conjunction with the movement of the boom of the second stage from the extended position to the reduced position by the hydraulic cylinder; A retraction wire rope tensioner that maintains the retraction wire rope in a predetermined tension state so that slack does not occur; And having; The retraction wire rope tensioner, Is attached to the boom of the final stage and includes a slide guide extending in the boom telescoping direction, which is the moving direction of the boom; A slider that is slidably supported in the boom telescoping direction by the slide guide and to which the retraction wire rope is attached; A telescopic spring that always biases the slider in the direction of sliding in the extending direction of the boom; And comprising; The slide guide includes a plurality of guide shafts extending in the boom telescoping direction; The telescopic spring is arranged along each of the guide shafts, and is characterized by a boom telescoping mechanism for a multi-stage boom.

2. In the boom telescoping mechanism for a multi-stage boom according to claim 1, As the guide shaft, three guide shafts are provided, The three guide shafts are arranged such that each of the other two guide shafts is located at the left and right corners of an isosceles triangle having one of the guide shafts as a vertex on a plane orthogonal to the boom telescoping direction; The slider includes three shaft holes through which the guide shafts slideably penetrate and extend in the boom telescoping direction; The guide shaft is spanned between a pair of brackets attached to the boom of the final stage at regular intervals in the boom telescoping direction; As a telescopic spring, three compression coil springs mounted in a compressed state on each of the guide shafts are provided between the slider and the bracket located on the reduction side in the boom telescoping direction, and is a boom telescoping mechanism for a multi-stage boom.

3. In the boom telescoping mechanism of the multi-stage boom according to Claim 1, a stopper that defines the sliding limit of the slider in the direction of compressing the telescoping spring is attached to the boom of the final stage, the boom telescoping mechanism of the multi-stage boom.

4. In the boom telescoping mechanism of the multi-stage boom according to Claim 1, a slider position confirmation part for visually confirming the sliding position of the slider from the outside of the boom of the final stage to which the slider is attached is provided, the boom telescoping mechanism of the multi-stage boom.

5. In the boom telescoping mechanism of the multi-stage boom according to Claim 4, the slider position confirmation part includes one or more holes for confirming the slider position formed in the side surface of the boom of the final stage, the boom telescoping mechanism of the multi-stage boom.

6. In the boom telescoping mechanism of the multi-stage boom according to Claim 1, the wire rope tensioner for contraction is provided with a slider pushing and fixing mechanism that can push the slider against the spring force in the direction of reduction in the boom telescoping direction and fix it at a predetermined sliding position, the boom telescoping mechanism of the multi-stage boom.

7. A crane having a multi-stage boom including a plurality of booms of three or more stages, and a boom telescoping mechanism that moves the booms of each stage from the second stage to the final stage of the multi-stage boom to a contracted position drawn into the boom on the front stage side and an extended position drawn out from the front end of the boom, wherein the boom telescoping mechanism is the boom telescoping mechanism according to any one of Claims 1 to 6, a crane characterized by this.

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