Boom telescoping mechanism for multi-stage boom

Abstract

In the present invention, a contracting wire rope tensioner (60) of a boom telescoping mechanism (2) of a multistage boom always applies spring force, in the direction in which a state of tension is maintained, to a contracting wire rope (40) via a slider (67), which can slide in the telescoping direction. When the multi-stage boom is elongated such that slack is generated in the contracting wire rope (40), the contracting wire rope (40) can be maintained in a prescribed state of tension without slack. The slider (67) slides along a plurality of guide shafts (64-66) and can apply a large amount of spring force for maintaining the state of rope tension in a limited space by means of compression coil springs (71-73) disposed on the guide shafts. The slider (67) slides without rattling, and the contracting wire rope (40) is stably maintained in the state of tension without slack.

Description

Multi-stage boom telescoping mechanism

[0001] The present invention relates to a boom extension and contraction mechanism for a multi-stage boom used in construction machinery such as cranes, and more specifically to a retraction wire rope tensioner that works in conjunction with a hydraulic cylinder for boom extension and contraction to keep the retraction wire rope, which is used to move the final stage of the boom from an extended position where it is pulled out from the front end of the boom on the previous stage to a retracted position where it is pulled into the boom, in an appropriate tensioned state to prevent slack from occurring in the retraction wire rope.

[0002] A wire rope telescoping boom extension mechanism is known as a multi-stage boom extension mechanism used in construction machinery such as cranes. A wire rope telescoping boom extension mechanism is configured, for example, to extend or retract the second boom stage using a hydraulic cylinder, and then extend or retract each of the boom stages from the third stage to the final stage using multiple wire ropes in conjunction with the extension or retraction of the second boom stage. Such wire rope telescoping boom extension mechanisms are proposed, for example, in Patent Documents 1, 2, and 3.

[0003] In the wire rope telescopic boom extension device described in Patent Document 3, a single wire rope is used exclusively for retracting the boom, and the retraction wire rope is routed within the boom, thereby narrowing the gap between the booms and making the boom smaller and lighter.

[0004] Japanese Patent Laid-Open No. 8-337392 Japanese Utility Model Publication No. 56-17433 Japanese Utility Model Publication No. 6-50460

[0005] In such a wire rope telescoping boom extension mechanism, the wire ropes for extending the boom at each stage and the wire ropes for retracting the boom are adjusted so that they are in a tensioned state. When one wire rope is pulled from this state to extend the boom, the other wire rope, which is not involved in the boom extension, becomes slack. Furthermore, the wire rope for extending the boom is stretched by the lifting load. If the wire rope becomes slack when it is routed inside the boom, the slack portion of the wire rope may interfere with parts inside the boom, potentially causing malfunction.

[0006] In view of this, the object of the present invention is to provide a boom extension mechanism for a multi-stage boom equipped with a retraction wire rope tensioner that can maintain the retraction wire rope, which is not involved in the extension of the boom, at a predetermined tension level to prevent slack when the boom of each stage of the multi-stage boom is extended or when the extension wire rope is stretched due to the lifting load.

[0007] In order to solve the above problems, the present invention provides a boom extension and contraction mechanism for a multi-stage boom having a plurality of booms of three or more stages, which moves each boom from the second stage to the final stage in a multi-stage boom having a plurality of booms in three stages or more to a retracted position retracted into the boom of the previous stage and an extended position extended from the front end of the boom, the mechanism comprising: a fluid pressure cylinder which moves the boom of the second stage to the retracted position and the extended position relative to the boom of the first stage; a retraction wire rope which moves the boom of the final stage from the extended position to the retracted position in conjunction with the movement of the boom of the second stage from the extended position to the retracted position by the fluid pressure cylinder; and a retraction wire rope tensioner which maintains the retraction wire rope in a predetermined tensioned state so that slack does not occur, the retraction wire rope tensioner comprising: a slide guide attached to the boom of the final stage and extending in the retraction direction which is the movement direction of the boom; a slider which is supported by the slide guide so as to be slidable in the retraction direction and to which the retraction wire rope is attached; and an expansion spring that constantly urges the slider in a direction that causes it to slide in the direction of extension of the boom, wherein the slide guide comprises a plurality of guide shafts that extend in the expansion / contraction direction, and the expansion springs are arranged along each of the guide shafts.

[0008] The retraction wire rope of the boom extension / retraction mechanism is attached to a slider that can slide in the retraction direction along a slide guide attached to the final boom stage, and a retraction spring constantly urges the slider in a direction that pulls the retraction wire rope. The slider slides in the boom retraction direction so that the retraction spring expands or contracts in response to the tensile force acting on the retraction wire rope. When the multi-stage boom is extended, which causes slack in the retraction wire rope, the retraction spring causes the slider to slide in the boom extension direction, maintaining the retraction wire rope in a tensioned state (tensioned state) without slack. When the multi-stage boom is retracted, the tensile force acting on the retraction wire rope causes the slider to slide in the boom retraction direction against the spring force, maintaining the retraction wire rope in a predetermined tensioned state.

[0009] For example, three shafts, a first shaft, a second shaft, and a third shaft, are arranged as the guide shafts. In this case, the second shaft and the third shaft are arranged so that they are located at the left and right corners of an isosceles triangle with the first shaft as the vertex on a plane perpendicular to the telescopic direction. The slider is formed with three shaft holes through which the first shaft, second shaft, and third shaft extend in the telescopic direction so that they can slide. Furthermore, the guide shafts are spanned between a pair of brackets attached to the final boom stage at a fixed interval in the telescopic direction. Three compression coil springs are used as telescopic springs, mounted in a compressed state between the bracket located on the contraction side in the telescopic direction and the slide plate.

[0010] It is also preferable that a stopper for defining the sliding limit of the slider in the direction of compressing the return spring is attached to the final stage of the boom.

[0011] If the retraction wire rope loosens over time, the tension on the retraction wire rope will decrease, for example, when the multi-stage boom is retracted. This will change the slide position of the slider, which pulls the retraction wire rope with spring force (the amount of retraction of the expansion spring). Therefore, it is desirable to provide a slide position confirmation unit that allows the slider slide position to be visually confirmed from outside the final boom stage to which the slider is attached. This allows a worker or other personnel to visually confirm the slider position from outside and, based on this, determine whether the retraction wire rope is properly tensioned.

[0012] In addition, when assembling the retraction wire rope, it is necessary to suspend the retraction wire rope over the slider, which is biased in the pulling direction by the return spring. To facilitate this operation, it is desirable to hold the slider in a position where it is forcibly pushed in the retraction direction, and to suspend the retraction wire rope without the spring force acting. For this purpose, for example, a slider pushing and fixing mechanism that can push the slider against the spring force and fix it in a predetermined position can be attached to the retraction wire rope tensioner.

[0013] Next, the crane of the present invention comprises a multi-stage boom equipped with a plurality of booms of three or more stages, and a boom extension and contraction mechanism that moves the boom of each stage of the multi-stage boom to a retracted position retracted into the boom of the previous stage and to an extended position extended from the front end of the boom, and is characterized in that the boom extension mechanism is equipped with the boom extension mechanism configured as described above.

[0014] According to the present invention, a spring force is always applied to the retraction wire rope in a direction that maintains its tension via a slider that can slide in the extension / retraction direction. When a multi-stage boom is extended, which would otherwise cause slack in the retraction wire rope, the retraction wire rope can be maintained at a predetermined tension without slack, thereby avoiding problems caused by slack. Furthermore, the slider slides along multiple guide shafts, and a large spring force is applied to maintain the tension by expansion springs arranged on each guide shaft. Therefore, the slider slides without rattle, and the retraction wire rope is stably maintained in a tensioned state without slack.

[0015]

[0023] (A) is a schematic side view showing a retracted state of a multi-stage boom equipped with a boom extension mechanism to which the present invention is applied, (B) is an explanatory diagram mainly showing the suspending state of the extension wire rope and the extension wire rope in the boom extension mechanism, and (C) is an explanatory diagram mainly showing the suspending state of the retraction wire rope in the boom extension mechanism. (A) is a schematic plan view of a retraction wire tensioner, (B) is a schematic side view thereof, (C) is a schematic bottom view thereof, and (D) is a schematic cross-sectional view taken along line D-D in (B). (A) is a schematic plan view of a retraction wire tensioner when the multi-stage boom is extended or the extension wire rope is stretched, (B) is a schematic side view thereof, and (C) is an explanatory diagram showing the stopper bolt after adjustment.

[0024] Fig. 1 is an explanatory diagram of a crane to which the present invention is applied.

[0016] Hereinafter, an embodiment of a boom extension mechanism for a multi-stage boom to which the present invention is applied will be described with reference to the drawings. A multi-stage boom equipped with a boom extension mechanism is used, for example, by being mounted on a 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 this embodiment. In this example, the multi-stage boom 1 is a five-stage boom equipped with first through fifth boom stages 11-15. Each boom stage 11-15 is, for example, a cylindrical boom with a rectangular cross section, and the base end of the first boom stage 11 is attached to an upper rotating body mounted on, for example, an undercarriage of a mobile crane (not shown). Each boom stage 12-15, from the second stage to the final fifth stage, is movable between a retracted position retracted into the boom of the preceding stage and an extended position extended from the front end of the boom.

[0018] 1(A) is a schematic side view showing the multi-stage boom 1 in a retracted state, with each boom stage 12-15 retracted to its retracted position. The multi-stage boom 1 is raised and lowered by a hoisting hydraulic cylinder (not shown) that is spanned between the first boom stage 11 and the upper rotating body of a traveling crane (not shown). In addition, the boom extension and contraction mechanism 2, described below, allows each boom stage 12-15 to extend and contract between its respective retracted position and its extended position.

[0019] 1(B) and 1(C) are explanatory diagrams showing the boom extension mechanism 2 that extends and retracts each boom stage 12-15 of the multi-stage boom 1. In these figures, the multi-stage boom 1 is shown with each boom stage 12-15 extended by a predetermined amount from its retracted state. The boom extension mechanism 2 includes a hydraulic cylinder 30, one retraction wire rope 40, one extension wire rope 51, two extension wire ropes 52, 53, and a retraction wire rope tensioner 60 that maintains the retraction wire rope 40 at a predetermined tension without slack. To clearly show the laying state of each wire rope, the retraction wire rope 40 is omitted in FIG. 1(B) and only the extension wire rope 51 and the extension wire ropes 52, 53 are shown, while the extension wire rope 51 and the extension wire ropes 52, 53 are omitted in FIG. 1(C) and only the retraction wire rope 40 is shown.

[0020] The hydraulic cylinder 30 of the boom extension and contraction mechanism 2 is a fluid pressure cylinder for moving the second boom stage 12 to a retracted position and an extended position relative to the first boom stage 11. The extension wire rope 51 moves the third boom stage 13 from a retracted position to an extended position in conjunction with the hydraulic cylinder 30 moving the second boom stage 12 from a retracted position to an extended position. The extension wire rope 52 moves the fourth boom stage 14 from a retracted position to an extended position in conjunction with the third boom stage 13 moving from a retracted position to an extended position. The extension wire rope 53 moves the fifth boom stage 15, which is the final stage, from a retracted position to an extended position in conjunction with the fourth boom stage 14 moving from a retracted position to an extended position. The retraction wire rope 40 moves the fifth boom stage 15, which is the final stage, from an extended position to a retracted position in conjunction with the hydraulic cylinder 30 moving the second boom stage 12 from an extended position to a retracted position. The telescopic wire rope 53 moves the fourth boom stage 14 from the extended position to the retracted position in conjunction with the movement of the fifth boom stage 15, which is the final stage, moving from the extended position to the retracted position. The telescopic wire rope 52 moves the third boom stage 13 from the extended position to the retracted position in conjunction with the movement of the fourth boom stage 14 from the extended position to the retracted position.

[0021] More specifically, the hydraulic cylinder 30 is disposed in the boom fore-and-aft direction, which is the boom extension and retraction direction, in a central portion inside the multi-stage boom 1, and spans between the first boom stage 11 and the second boom stage 12. In this example, the cylinder body 31 of the hydraulic cylinder 30 is connected to the rear end of the second boom stage 12 and extends forward inside the fifth boom stage 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 of the first boom stage 11.

[0022] 1(B), as shown by the dashed line, the extension wire rope 51 for extending the third boom stage 13 has one rope end 51a connected to the rear end of the first boom stage 11 (in this example, connected to the rear end of the telescopic rod 32 of the hydraulic cylinder 30 attached to the boom 11), and is pulled out forward from here and hung from the front over a pulley 33 that moves in the extension / retraction direction together with the second boom stage 12, and then pulled out rearward, so that the other rope end 51b is connected to the inside of the rear end of the third boom stage 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 stage 12, and moves in the forward / backward direction together with the boom 12.

[0023] The retractable wire rope 52 for extending the fourth boom 14 and retracting the third boom 13 is shown by a thin dashed line in Figure 1 (B), and one rope end 52a is connected to the outside of the front end of the second boom 12, pulled forward from here and hung from the front side on a pulley 55 attached to the front end of the third boom 13, and then pulled rearward through the front end opening of the boom 13 through its interior, and the other rope end 52b is connected to the rear end of the fourth boom 14.

[0024] The retractable wire rope 53 for extending the fifth boom 15 and retracting the fourth boom is shown by a dotted line in Figure 1 (B), and one rope end 53a is connected to the outside of the front end of the third boom 13, pulled forward from here and hung from the front side on a pulley 56 attached to the front end of the fourth boom 14, and then pulled rearward through the front end opening of the boom 14 and its interior, and the other rope end 53b is connected to the rear end of the fifth boom 15.

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

[0026] For example, the retraction wire rope 40 is pulled rearward from one rope end 40a toward an upper pulley 42 attached to one side of the rear end of the second boom 12 (rope portion 40b), wound around the upper and rear sides of the upper pulley 42, and then pulled forward from its lower side (rope portion 40c) and wound around a pulley 41 at the front end of the first boom 11 from the upper and front sides. It is also pulled rearward from the lower side of the pulley 41 (rope portion 40d) and wound around a lower pulley 43 on the right side of the rear end of the second boom 12 from the lower and front sides. It is pulled forward from the upper side of the lower pulley 43. Rope portion 40e pulled from the lower pulley 43 passes through the interiors of the third and fourth booms 13 and 14, as shown by the dashed lines, and is pulled forward through the interior of the rear opening of the fifth boom 15.

[0027] Here, a retraction wire rope tensioner 60 is attached inside the front end of the fifth boom 15. The retraction wire rope 40, which has been pulled forward inside the boom 15, is wound around the retraction wire rope tensioner 60 (rope portion 40f). In this example, as will be described later, the retraction wire rope tensioner 60 is equipped with a non-rotating semicircular fixed sheave 70 that is movable in the front-to-rear direction. The retraction wire rope 40 is wound around the semicircular fixed sheave 70 so that it passes from the right side to the front side and is pulled rearward from the other left side. The retraction wire rope 40 pulled rearward from the semicircular fixed sheave 70 is wound around a lower pulley 43', a pulley 41', and an upper pulley 42' located on the other side in the left-to-right direction in a symmetrical manner, and then the rope end 40a' is connected to the left portion of the front end of the first boom 11.

[0028] (Configuration of the Retraction 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 retraction wire rope tensioner 60. Figures 3(A) and (B) are a schematic plan view and a schematic side view showing the movement of the slider of the retraction wire rope tensioner 60. Note that these figures show the slider push-in bolt shaft 91, a component of the slider push-in and fixing mechanism 90, attached to explain the mechanism. As will be described later, a short post-adjustment stopper bolt 94, as shown in Figure 3(C), is normally attached in place of the bolt shaft 91, and the slider 67 is structurally capable of sliding between positions 67A and 67B.

[0029] First, referring to FIG. 2 , the retraction wire rope tensioner 60 includes a mounting frame 61 attached to the inside of the front end of the fifth and final boom 15, in this example, to the inner ceiling surface of the tip. The mounting frame 61 includes a front end plate 62 and a rear end plate 63 that face each other at a predetermined distance in the fore-and-aft direction of the boom. The front end plate 62 is attached to a front bracket 15a attached to the boom 15, and the rear end plate 63 is attached to a portion 15b of the boom 15. Between the front end plate 62 and the rear end plate 63, multiple cylindrical guide shafts 64, 65, and 66 (three in this example) are suspended in the fore-and-aft direction of the boom as slide guides. When viewed on a plane perpendicular to the fore-and-aft direction, the left and right guide shafts 65 and 66 are symmetrically arranged so that the left and right guide shafts 65 and 66 are located at the opposite 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 so as to be slidable in the fore-and-aft direction of the boom along the guide shafts 64 to 66. The slider 67 includes a slide plate 68 in which guide holes are formed for each of the three guide shafts 64 to 66, and a bushing 69 attached to the front surface of the 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 at a right angle and extending forward from the upper end of the end plate portion 68a. Three guide holes are formed in the end plate portion 68a, and the bushing 69 is attached to the front surface of the end plate portion 68a.

[0031] A semicircular fixed sheave 70 (rope attachment portion) around which the rope portion 40f of the retraction wire rope 40 is wound is mounted on the upper surface of the top plate portion 68b of the slider 67. Three compression coil springs 71, 72, 73 (expansion springs) are arranged between the slider 67 and the rear end plate 63 of the mounting frame 61, and are positioned in a compressed state so as to coaxially surround each of the guide shafts 64 to 66. The spring forces of the compression coil springs 71 to 73 constantly act on the slider 67 in a direction that pulls the retraction wire rope 40.

[0032] Here, the slider 67 is pushed out by the compression coil springs 71-73 and is structurally movable, for example, to position 67B shown in FIG. 3B. However, the slide position is adjusted so that the slide limit is a position just before position 67B and the slider 67 does not slide to this position. A stopper 70A, made of, for example, a round bar, is welded to the top surface of the interior of the tip of the boom 15. When the slider 67 slides in the direction of compressing the compression coil springs 71-73, the semicircular fixed sheave 70 mounted on the slider 67 hits the stopper 70A, limiting the slide. In other words, the slide limit position 67A in the direction of compressing the compression coil springs 71-73 is determined by the stopper 70A.

[0033] In this example, sliding of the slider 67 in the direction compressing the compression coil springs 71 to 73 is stopped at position 67A when the semicircular fixed sheave 70 abuts against a stopper 70A on the inner top surface of the boom 15. The sliding limit (position 67A) of the slider 67 in the direction compressing the compression coil springs 71 to 73 is determined by the semicircular fixed sheave 70 abutting against the stopper 70A.

[0034] This prevents deformation of the compression coil springs 71-73, mounting frame 61, guide shafts 64-66, and other components of the retraction wire rope tensioner due to excessive stress caused by the large thrust when the boom is extended. Furthermore, preventing excessive force from acting on these components allows for weight reduction. In other words, from the standpoint of ensuring lifting capacity and stability, it is important for a crane boom to be as light as possible, especially toward the boom tip. Using the slide limiting mechanism with stopper 70A in this example is extremely effective in reducing the weight of the tip of boom 15, into which the retraction wire rope tensioner is incorporated.

[0035] (Operation of Retraction Wire Rope Tensioner) The operation of the retraction wire rope 40 associated with the retraction of the multi-stage boom 1 by the boom extension and contraction mechanism 2 will be described with reference to Figures 1, 2, and 3. When the multi-stage boom 1 is retracted, the extension wire rope 51, extension wire ropes 52 and 53, and retraction wire rope 40 of the boom extension and contraction mechanism 2 are wound around a semicircular fixed sheave 70 mounted on a slider 67 that is slidable in the boom extension and contraction direction (the boom fore-and-aft direction) along three guide shafts 64-66 attached to the fifth and final boom stage 15. The slider 67, and therefore the semicircular fixed sheave 70, are constantly biased in the direction of tensioning the retraction wire rope 40 by compression coil springs 71-73 attached to the guide shafts 64-66.

[0036] For example, in the retracted state of the multi-stage boom 1 shown in Figure 1 (A), as shown by the solid lines in Figures 2 (A) and (B) and by the imaginary lines in Figures 3 (A) and (B), the slider 67 (semicircular fixed sheave 70) is positioned at a position 67A pushed rearward in the fore-and-aft direction of the boom by the retraction wire rope 40 which is stretched across under a predetermined tension.

[0037] 1(A) to the predetermined extended state shown in FIGS. 1(B) and 1(C), the hydraulic cylinder 30 is driven to pull the second boom stage 12 forward relative to the first boom stage 11. When the second boom stage 11 is pulled forward, the third boom stage 13 is pulled forward relative to the second boom stage 12 by the extension wire rope 51 stretched between the first, second, and third boom stages 11-13 in conjunction with this. The fourth boom stage 14 is pulled forward relative to the third boom stage 13 by the extension wire rope 52 stretched between the second, third, and fourth boom stages 12-14 in conjunction with this. The fifth boom stage 15 is pulled forward relative to the fourth boom stage 14 by the extension wire rope 53 stretched between the third, fourth, and fifth boom stages 13-15 in conjunction with this.

[0038] During this boom extension operation, slack is generated in the retraction wire rope 40 that is stretched between the first, second, and fifth boom stages 11, 12, and 15 as the second boom stage 12 moves, being pushed out first by the hydraulic cylinder 30. In addition, when a load (hoisting load) is applied to the boom during lifting work or the like, the wire ropes 51, 52, and 53 are stretched, causing slack in the retraction wire rope 40.

[0039] In this example, the compression coil springs 71-73 expand and contract in response to the tensile force acting on the retraction wire rope 40, causing the slider 67 to slide in the boom extension / retraction direction. When the multi-stage boom 1 is extended, causing slack in the retraction wire rope 40, the compression coil springs 71-73 cause the slider 67 to slide in the boom extension direction (boom forward), maintaining the retraction wire rope 40 in a predetermined tensioned state (pulled state) without slack. Therefore, the retraction wire rope 40, which is wound around the semicircular fixed sheave 70 mounted on the slider 67, is pulled by an amount corresponding to the amount the slider 67 slides forward. As a result, the retraction wire rope 40 is maintained in a predetermined tensioned state without slack even when the boom is extended or when the boom is loaded.

[0040] In this example, three guide shafts 64 to 67 are arranged as guide shafts, which guide the slider 67. Furthermore, three compression coil springs 71 to 73 attached to the guide shafts 64 to 67 apply tension to the retraction wire rope 40. Therefore, the slider 67 slides without rattle, and the retraction wire rope 40 is stably maintained in a tensioned state without slack.

[0041] (Slider Position Confirmation Unit) Next, in the boom extension and contraction mechanism 2, slack may occur in the retraction wire rope 40 that is stretched over time. In this case, the tension on the retraction wire rope will be loosened when the multi-stage boom 1 is in the retracted state. When the tension is loosened, in the retraction wire rope tensioner 60 of this example, the slide position of the slider 67 that pulls the retraction wire rope 40 with spring force (the amount of retraction of the compression coil spring) changes accordingly. Therefore, based on the change in the slide position of the slider 67, it is possible to know that the tension on the retraction wire rope 40 has been loosened.

[0042] Therefore, it is only necessary to provide a slide position confirmation section that allows the slide position of the slider 67 in the boom retracted state shown in Figure 2 to be visually confirmed from the outer side of the final stage boom 15 to which the slider 67 is attached. For example, as shown by imaginary lines in Figures 2(B) and (C), confirmation holes 81 and 82 are formed on the side surface of the final stage boom 15 having a rectangular cross section, as a slide position confirmation section 80, through which the position of the end plate portion 68a of the slide plate 68 of the slider 67 can be visually confirmed.

[0043] The end plate portion 68a functions as an indicator for position confirmation. The position where the end plate portion 68a can be seen through the hole 81 is the adjustment position, and the position where the end plate portion 68a can be seen through the hole 82 is the adjustment limit position. The adjustment limit position is a position within the range that does not exceed the specification limit of the shortening wire rope specifications, and is set as a maintenance reference position. If the end plate portion 68a is not located between the confirmation holes 81 and 82, it is clear that the wire rope needs to be adjusted or replaced.

[0044] In this way, an operator or the like can visually check the position of the slider 67 from outside and, based on this, can determine whether the retraction wire rope 40 is tensioned appropriately. For example, if the position of the slider 67 moves forward away from the hole 82 while the boom is retracted, it becomes impossible to visually check the slider 67, which makes it possible to determine that the retraction wire rope 40 has become loose.

[0045] (Slider Push-in Fixing Mechanism) Meanwhile, in this example, the retraction wire rope 40 is stretched under a predetermined tension by the retraction wire rope tensioner 60. In assembling the retraction wire rope 40, it is necessary to stretch the retraction wire rope 40 over the semicircular fixed sheave 70 of the slider 67, which is biased in the pulling direction by the compression coil springs 71 to 73. To facilitate this work, it is desirable to hold the slider 67 in a position where it is forcibly pushed in the retraction direction, so that the retraction wire rope 40 can be stretched without the spring force acting.

[0046] To achieve this, for example, a slider pushing and fixing mechanism that can push the slider 67 against the spring force and fix it in a predetermined position may be attached to the compression wire rope tensioner 60. The slider pushing and fixing mechanism 90 of this example will be described with reference to Figures 2 and 3.

[0047] The slider push-in and fixation 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 throughout. The threaded hole 92 formed in the front end plate 62 of the mounting frame 61 has internal threads into which the bolt shaft 91 can be threaded. The bolt shaft 91 is threaded into the threaded hole 92, and its tip abuts against the end plate portion 68a of the slide plate 68 of the slider 67. By further threading the bolt shaft 91, the bolt shaft 91 can push the slider 67 to position 67A shown in the figure. The locking nut 93 locks the bolt shaft 91 in this threaded position, allowing the winding operation of the compression wire rope 40 to be performed without the application of spring force.

[0048] After the work is completed, the bolt shaft 91 is removed, returning the slider 67 to a slidable state and applying tension to the retraction wire rope 40. After the work is completed, the bolt shaft 91 is replaced with a shorter, adjusted stopper bolt 94. The adjusted stopper bolt 94 is shown in FIG. 3(C), and in phantom lines in FIG. 3(B). The adjusted stopper bolt 94 also has a male thread so that the shaft portion is fully threaded. As shown in phantom lines in FIG. 3(B), the adjusted stopper bolt 94 is screwed in until its tip 94a reaches position 67B and is fixed in this position with a lock nut 93. During normal work, the adjusted stopper bolt 94 functions as a stopper that limits the forward sliding of the slider 67.

[0049] (Crane) Next, an embodiment of a crane to which the present invention is applied will be described. FIG. 4 is an explanatory diagram of a crane to which the present invention is applied. As shown in FIG. 4, the crane 100 includes the multi-stage boom 1 and boom extension mechanism 2 described above, and a main body 3 on which the multi-stage boom 1 and boom extension mechanism 2 are mounted. The multi-stage boom 1 includes multiple booms 11 to 15 with three or more stages. The boom extension mechanism 2 moves each boom 12 to 15 of the multi-stage boom 1, from the second to the final stage, to a retracted position where the booms 11 to 14 are retracted, and to an extended position where the booms 11 to 14 are extended from the front ends of the booms 11 to 14. The main body 3 is, for example, a crawler-type traveling body. The base end of the first boom 11 is attached to a revolving body 4 provided on the main body 3.

Claims

1. A boom telescoping mechanism for a multi-stage boom having a plurality of booms of three or more stages, which moves the booms of each stage from the second stage to the final stage 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, a hydraulic cylinder that moves the second-stage boom to the retracted position and the extended position with respect to the first-stage boom; a retracting 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 hydraulic cylinder; a retracting wire rope tensioner that maintains the retracting wire rope in a predetermined tension state so that no slack occurs; The retracting wire rope tensioner includes: a slide guide attached to the final-stage boom and extending in the boom telescoping direction, which is the moving direction of the boom; a slider slidably supported in the boom telescoping direction by the slide guide and to which the retracting wire rope is attached; a telescopic spring that always biases the slider in the direction of sliding in the extending direction of the boom; The slide guide includes a plurality of guide shafts extending in the boom telescoping direction, and the telescopic spring is arranged along each of the guide shafts. The boom telescoping mechanism of the multi-stage boom is characterized by this.

2. In the boom telescoping mechanism of the multi-stage boom according to claim 1, as the guide shaft, three guide shafts are provided, the three guide shafts are arranged such that on a plane orthogonal to the boom telescoping direction, 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, the slider is provided with three shaft holes through which the guide shafts respectively slideably penetrate and extend in the boom telescoping direction, the guide shafts are spanned between a pair of brackets attached to the boom of the final stage at regular intervals in the boom telescoping direction, as a telescoping spring, between the slider and the bracket located on the reducing side in the boom telescoping direction, a boom telescoping mechanism of a multi-stage boom having three compression coil springs mounted in a compressed state on each of the guide shafts.

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. A boom telescoping mechanism of a 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. A boom telescoping mechanism of a multi-stage boom.

5. In the boom telescoping mechanism of the multi-stage boom according to claim 4, the slider position confirmation part is provided with one or more holes for confirming the slider position formed on the side surface of the boom of the final stage. A boom telescoping mechanism of a multi-stage boom.

6. In the boom telescoping mechanism of the multi-stage boom according to claim 1, the wire rope tensioner for retraction is provided with a slider pushing and fixing mechanism capable of pushing the slider against the spring force in the reducing direction of the boom telescoping direction and fixing it at a predetermined sliding position. A boom telescoping mechanism of a multi-stage boom.

7. A crane having a multi-stage boom provided with a plurality of booms of three or more stages, and a boom telescoping mechanism for moving the booms of each stage from the second stage to the final stage 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, wherein the boom telescoping mechanism is the boom telescoping mechanism according to any one of claims 1 to 6.

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