Hoisting apparatus for a straddle carrier

Abstract: The invention relates to a hoisting apparatus for a straddle carrier, which is provided with a spreader from which hoisting cables (16) used as a hoisting means are passed over cable pulleys (29) to a hoist mechanism situated on a top frame (13) of the straddle carrier. The hoist mechanism comprises a lifting cylinder (21) and a cable pulley set structure mounted on the top frame (13), which cable pulley set structure is driven by the lifting cylinder and comprises first and second cable pulleys (27, 28), and to which cable pulley set structure each hoisting cable (16) is passed. A lifting movement is produced by means of the lifting cylinder (21) by changing the distance between the first and second cable pulleys (27, 28) such that a change in the length of the lifting cylinder (21) produces a lifting movement of equal magnitude for each hoisting cable (16). Regardless of the tilting moment caused by the eccentricity of load, each lifting point of the spreader is arranged to move synchronously an equal distance and hoist the load connected to the spreader substantially in a horizontal position.

Description: The invention relates to a hoisting apparatus for a straddle carrier, which hoisting apparatus is provided with a spreader having a frame part with four separate lifting points from which hoisting cables used as a hoisting means are passed over cable pulleys, or intermediate pulleys to a hoist mechanism situated on a top frame of the straddle carrier, which hoist mechanism comprises a lifting cylinder and a cable pulley set structure mounted on the top frame, which cable pulley set structure is driven by the lifting cylinder and comprises first and second cable pulleys, to which cable pulley set structure each hoisting cable is passed and in which cable pulley set structure a lifting movement is produced by means of the lifting cylinder by changing the distance between the first and second cable pulleys such that a change in the length of the lifting cylinder produces a lifting movement of equal magnitude for each hoisting cable, whereby, regardless of the tilting moment caused by the eccentricity of load, each lifting point of the spreader is arranged to synchronously move an equal distance and hoist the load connected to the spreader substantially in a horizontal position. Conventionally, straddle carriers employ two different techniques for hoisting containers, i.e. chain hoisting and, on the other hand, cable hoisting. In chain hoisting, as a hoisting means four chains are used which run from a hoist mechanism situated on a top frame of a straddle carrier to the corners of a frame part of a spreader. The spreader is a so-called top-lift spreader by which the upper corners of a container are grasped from above. The hoist mechanism comprises two separate lifting cylinders, which are situated on the sides of the top frame of the straddle carrier, and further separate sets of sprockets placed on the sides of the top frame. A lifting movement is produced by displacing the sprocket sets by means of said lifting cylinders in a horizontal direction, whereby the displacement of the sprocket sets produces a lifting movement with a transmission ratio which depends on the number of the sprockets in the sprocket sets. Hydraulic cylinders are generally used as lifting cylinders. The centre of gravity of the container that is being lifted may be situated eccentrically, with the result that this eccentricity of load causes a tilting moment. The tilting moment has been eliminated such that the separate sets of sprockets on either side of the top frame have been connected together by a differential axle mounted between the sets of sprockets. In cable hoisting, a steel cable is used as a lifting means, which is wound round a hoist drum. The cable runs from the hoist drum to each comer of the frame part of the spreader. The drive of the hoist drum may be provided either electrically or hydraulically. The hoist drum may be situated on a top frame or it may be disposed on a base frame on one side of the straddle carrier. One example of such an arrangement is the construction disclosed in published EP application 763 497 . Cable transmission may be selected so as to be appropriate in accordance with the guidelines provided by normal crane standards. As a prior art publication, reference is made to US Patent 2 982 430 , corresponding to the preambles of claim 1, which discloses a hoisting apparatus having a hoist mechanism, which comprises a lifting cylinder and a cable pulley set structure mounted on the top frame. The cable pulley set structure is driven by the lifting cylinder and it comprises first and second cable pulleys. Each hoisting cable is passed to the cable pulley set structure in which a lifting movement is produced by means of the lifting cylinder by changing the distance between the first and second cable pulleys, so that a change in the length of the lifting cylinder produces a lifting movement of equal magnitude for each hoisting cable, whereby each lifting point is arranged to synchronously move an equal distance and hoist the load substantially in a horizontal position. For the operator, there are, among other things, the following differences in the used lifting techniques. From the technical point of view, it is simpler to provide chain hoisting than cable hoisting. The required lifting height is so low, generally less than 10 m, that it is technically more appropriate and easier to use a lifting cylinder than a rotating drum for producing a lifting movement. In this regard, chain hoisting is simpler than cable hoisting, and thus more reliable. In respect of this property, chain hoisting is preferable to cable hoisting. In order to make the service life of the lifting means (chain/cable) sufficiently long, lubrication of chains and greasing of a cable must be taken care of. From the environmental point of view, the greasing of a cable requires considerably less lubricants than the lubrication of chains, and thus the loading to the environment is smaller when cable hoisting is used. In this respect, cable hoisting is preferable to chain hoisting. As a lifting means, the cable is substantially more advantageous in its purchase price than the chain, but, on the other hand, the service life of chains is much longer than the service life of cables. In this regard, the lifting techniques are of equal value. Services, for example, replacement of the hoisting means in the hoist mechanism, can be performed in the cable hoisting technique considerably more easily and more quickly than in the chain lifting technique mainly for the reason that, as a hoisting means, the cable is substantially lighter in weight than the chain. In this respect, cable hoisting is preferable to chain hoisting. An object of the present invention is to provide a novel hoisting system for a straddle carrier, which new hoisting system makes it possible to make use of and combine the advantages of both of the previously known lifting techniques. In order to achieve this, the invention is mainly characterized in that the first cable pulleys of the cable pulley set structure are rigidly mounted to the end of the lifting cylinder on the cylinder side and that the second cable pulleys of the cable pulley set structure are pivotally mounted to the end of the lifting cylinder on the piston side, in which case guidance and support are arranged on the top frame of the straddle carrier for the second cable pulleys in order to receive lateral forces. The new hoisting system in accordance with the invention is based on cable hoisting which, however, makes use of a lifting cylinder in producing a lifting movement so that the structure is uncomplicated, reliable, and advantageous with regard to the environmental loading and the ease of servicing. The cable transmission of the lifting movement can easily be made as desired according to the need in order to provide a sufficient lifting height and lifting speed. The tilting moment caused by the eccentricity of the load being hoisted can be easily eliminated in the system in accordance with the invention. The other advantages and characteristic features of the invention will come out from the following detailed description of the invention. Next, the invention will be described by way of example with reference to the figures of the accompanying drawing. Figures 1 and 2 generally show a straddle carrier to which the hoisting system in accordance with the invention can be applied, Fig. 1 showing the straddle carrier from the side and Fig. 2 showing it from the front in a corresponding way. Figure 3 shows a first embodiment of a hoist mechanism mounted on a top frame of a straddle carrier seen from above. Figure 4A is a schematic and partial sectional view along the line A - A from Fig. 3. Figure 4B is a schematic and partial sectional view along the line B - B from Fig. 3. Figure 5 is an illustration corresponding to that of Fig. 3 of a second embodiment of the invention. Figure 6 is a schematic and partial sectional view along the line A - A from Fig. 5. In Figs. 1 and 2, a straddle carrier is generally designated by the reference numeral 10. The straddle carrier 10 comprises wheels 11 which are situated on both sides of the machine and which support substantially vertical support legs 12. A top frame 13 of the machine is fitted on the upper end of the support legs 12, and a hoist mechanism not shown in Figs. 1 and 2 is mounted on support of said top frame. A spreader 14 is suspended from the hoist mechanism by means of cables 16, which spreader is vertically movable and by which spreader containers are grasped for the purpose of transferring them. The cables 16 pass to a frame part 15 of the spreader, on whose support the spreader 14 itself is fitted. In Fig. 2, the spreader is shown both in its lower position 14 and in its upper position 14'. Figs. 3, 4A and 4B show one embodiment of a hoisting apparatus applied in a straddle carrier. Fig. 3 illustrates the hoisting apparatus from above, Fig. 4A is a partial sectional view along the line A - A from Fig. 3 and, in a corresponding way, Fig. 4B is a partial sectional view along the line B - B from Fig. 3. In said Figs. 3, 4A and 4B, the hoisting apparatus is generally designated by the reference numeral 20. The hoisting apparatus 20 comprises a lifting cylinder 21 mounted on the top frame 13 of the straddle carrier and horizontally disposed on the longitudinal centre axis C of the straddle carrier, which lifting cylinder is fixed to the top frame 13 at its first end, i.e. in the case shown in the figures, at the end 22 on the cylinder side. The second end 23 of the lifting cylinder 21, i.e. the end situated on the piston side, is mounted on a carriage 24, which is provided with rollers 25 or equivalent, which move along guides 26 provided on the top frame 13 when the lifting cylinder 21 is operated. The hoisting system in accordance with the invention is based on cable lifting, and thus the hoisting apparatus comprises a cable pulley set structure, which includes, firstly, first cable pulleys 27 mounted on the top frame 13 and freely rotating on an axle transverse to the length of the lifting cylinder 13. Further, the cable pulley set structure includes second cable pulleys 28, whose axle is mounted on the lifting cylinder 21 in such a way that said second cable pulleys move with the lifting cylinder 21. When the lifting cylinder 21 is operated, the distance between the first and second cable pulleys 27, 28 thus changes. The hoisting cables 16 are attached to each of the four corners of the frame part 15 of the spreader, said hoisting cables being passed over cable pulleys 29 to the cable pulley set structure comprising the lifting cylinder 21 and the first and second cable pulleys 27, 28 such that each hoisting cable 16 passes over the first and second cable pulleys 27, 28. In the structure of Figs. 3, 4A and 4B, the hoisting cables 16 are attached, at one end, specifically to the frame part 15 of the spreader and, at the opposite end, the hoisting cables 16 are attached to the top frame 13. Each hoisting cable 16 passes through an equal number of turns or as an equal number of loops round the cable pulley set structure formed by the first and second cable pulleys 27, 28, thereby providing a desired transmission ratio for the cable transmission. The horizontal movement produced by means of the lifting cylinder 21 is transmitted through the cable pulleys 27, 28, 29 of the cable pulley set as a vertical movement of equal magnitude to each hoisting cable 16. The movement of equal magnitude for the hoisting cables 16 is produced such that all the hoisting cables 16 are passed over the cable pulleys to one and the same cylinder/cable pulley set structure 21, 27, 28, so that each hoisting cable 16 runs the same distance keeping the container in a horizontal position. The balancing problem of the lifting movement is specifically solved such that all the hoisting cables 16 are passed to the same point. A differential axle applied in chain hoisting cannot be employed in connection with cable pulleys, because there may occur slipping between the hoisting cables and the cable pulleys. A suitable transmission ratio of the horizontal movement of the lifting cylinder 21 to the vertical lifting movement is provided by selecting for the cable pulley set structure a suitable number of cable pulleys 27, 28, over which the hoisting cables 16 are caused to run. Figs. 5 and 6 show a second embodiment of the hoisting apparatus in accordance with the invention, Fig. 5 showing the hoisting apparatus seen from above in a way corresponding to that of Fig. 3 and Fig. 6 being a partial sectional view along the line A - A from Fig. 5. In Figs. 5 and 6, the hoisting apparatus is generally designated by the reference numeral 120. In a way corresponding to that shown in Fig. 3, a lifting cylinder is denoted with the reference numeral 121, a piston part of the cylinder with the reference numeral 123, a carriage moving with the piston part with the reference numeral 124, and first and second cable pulleys with the reference numerals 127 and 128. In this respect, the structure of the hoisting apparatus corresponds to that shown in Fig. 3. The guides formed on the top frame 13 for the carriage 124 are denoted, in a similar way, with the reference numerals 126 and the slide parts of the carriage 124 moving along the guides 126 are denoted with the reference numerals 125. The most significant differences of the arrangement shown in Figs. 5 and 6 with respect to the arrangement shown in Figs. 3, 4A and 4B lie in that, first, in the illustration of Figs. 5 and 6, the corners of the frame part 15 of the spreader are fitted with return pulleys 130, over which the hoisting cables 16 run. Thus, the hoisting cables 16 run from the cable pulleys 127 and 128 of the cable pulley set structure over separate cable pulleys 129 to the frame part 15 of the spreader and return over the return pulleys 130 back to the cable pulley set structure over cable pulleys 129. There are thus twice as many cable pulleys 129 as compared with the embodiment illustrated in Figs. 3, 4A and 4B. Thus, in the arrangement of Figs. 5 and 6, one end of the hoisting cables 16 is attached, in the cable pulley set structure, to a rear end of the cylinder 121 on a side of the cylinder 121 that is different, with respect to a longitudinal centre line C, from the side where the opposite end of the hoisting cable 16 is attached. This arrangement thus allows the lifting cylinder 121 to be balanced regardless of the eccentricity of the load hanging on support of the hoisting cables 16. The structure comprising the lifting cylinder 121 and the cable pulley set 127, 128 may be accomplished such that the second cable pulleys 128 of the cable pulley set are attached directly to the end of the piston part 123 of the lifting cylinder, in which case the lifting cylinder 121 itself carries the additional forces caused by the lateral eccentricity of the load. On the other hand, the arrangement may be similar to that shown in Fig. 5 in such a way that the carriage 124 is pivotally connected to the piston part 123 of the lifting cylinder 121, in which case the cable pulley set structure requires external guidance in the form of the guides 126 and the slide parts 125 as shown in Fig. 5. In summary of the invention the following may be further stated. The feature common to the different embodiments of the invention is that the support forces from the four corners of the frame part 15 of the spreader, i.e. all four hoisting cables 16, are passed over the cable pulleys to one and the same cylinder-operated cable pulley set structure. This accomplishes that each lifting point in the spreader synchronously moves the same distance, and the load that is being hoisted, i.e. the container, remains in a horizontal position regardless of the tilting moment caused by the eccentricity of the load. A desired transmission ratio for the hoisting structure is obtained such that a multiple pulley system, i.e. a necessary number of first and second cable pulleys, is used in the cable pulley set structure. Further, the hoisting cables may be attached either directly to the frame part of the spreader or they may be arranged to be passed over return pulleys back to the cable pulley set structure. The cable pulley set may be mounted rigidly to the end of the lifting cylinder, in which case the lifting cylinder itself carries and receives the additional forces caused by the lateral eccentricity of the container being hoisted. On the other hand, the cable pulley set may be attached to the end of the cylinder by means of an articulation joint, in which case external guidance is required for receiving the additional forces being produced. In the case that the hoisting cables are arranged to run over the return pulleys provided on the frame part of the spreader, the hoisting cables may be attached at one end thereof to the rear end of the lifting cylinder and at the other end to the top frame. On the other hand, both ends of the hoisting cables may be attached to the rear end of the lifting cylinder on different sides of the cylinder with respect to the centre line in order to balance the lifting cylinder regardless of eccentric load.

Claims: A hoisting apparatus (20) for a straddle carrier, which hoisting apparatus is provided with a spreader (14) having a frame part (15) with four separate lifting points from which hoisting cables (16) used as a hoisting means are passed over cable pulleys (29; 129) or intermediate pulleys to a hoist mechanism situated on a top frame (13) of the straddle carrier (10), which hoist mechanism comprises a lifting cylinder (21; 121) and a cable pulley set structure mounted on the top frame (13), which cable pulley set structure is driven by the lifting cylinder and comprises first and second cable pulleys (27, 28; 127; 128), to which cable pulley set structure each hoisting cable (16) is passed and in which cable pulley set structure a lifting movement is produced by means of the lifting cylinder (21; 121) by changing the distance between the first and second cable pulleys (27, 28; 127, 128) such that a change in the length of the lifting cylinder (21; 121) produces a lifting movement of equal magnitude for each hoisting cable (16), whereby, regardless of the tilting moment caused by the eccentricity of load, each lifting point of the spreader (14) is arranged to synchronously move an equal distance and hoist the load connected to the spreader (14) substantially in a horizontal position, characterized in that the first cable pulleys (27; 127) of the cable pulley set structure are rigidly mounted to the end of the lifting cylinder (21; 121) on the cylinder side and that the second cable pulleys (28; 128) of the cable pulley set structure are pivotally mounted to the end (23; 123) of the lifting cylinder (21; 121) on the piston side, in which case guidance (26) and support (24, 25) are arranged on the top frame (13) of the straddle carrier for the second cable pulleys (28; 128) in order to receive lateral forces. A hoisting apparatus as claimed in claim 1, characterized in that the top frame (13) of the straddle carrier is fitted with guides (26; 126) extending in the direction of movement of the lifting cylinder (21; 121) and that a carriage (24; 124) is mounted to the end (23; 123) of the lifting cylinder (21; 121) on the piston side, which carriage is provided with rollers, slides or equivalent (25; 125) which are arranged to move along the guides (26; 126) situated on the top frame (13) in order to receive lateral forces. A hoisting apparatus as claimed in claim 1 or 2, characterized in that , when the hoisting cables (16) are attached directly to the frame part (15) of the spreader, the other end of each hoisting cable (16) is attached, after the hoisting cable (16) has passed round the pulley structure formed by the cable pulleys, to the top frame (13) of the straddle carrier or to the rear end of the lifting cylinder (21). A hoisting apparatus as claimed in claim 1 or 2, characterized in that , when the hoisting cables (16) pass over return pulleys (130) provided on the frame part (15) of the spreader, both ends of each hoisting cable (16) are attached to the rear end of the lifting cylinder (121), i.e. to the end (122) situated on the cylinder side on different sides of the cylinder with respect to the length of the lifting cylinder in order to balance the lifting cylinder (121) regardless of eccentric load.

Inventors: LUKUMAA JUHANI, NURMI JORMA, LUKUMAA, JUHANI, NURMI, JORMA
Applicants: KALMAR IND OY AB, KALMAR INDUSTRIES OY AB
Application year: 1999
Main classification: B66D3
IPC codes: B66C19, B66D3