Abstract
A spreader (24) comprises a main frame carrying container connector arrangements configured to engage with a transport container (10); a rotator enabling rotation of the main frame in relation to a crane bracket about a substantially vertical rotation axis (A2); a rotation motor configured to, responsive to a rotation control signal, operate the rotator to rotate the main frame; a rotation detector configured to detect rotation of the main frame in relation to the crane bracket; and a control system configured to, based on a discrepancy between the rotation control signal and a rotation detected by the rotation detector, generate a rotation alert signal.
Claims
1-19. (canceled)
20. A spreader system comprising a spreader for lifting a transport container, the spreader comprising a main frame having a first end and a second end, and extending along a longitudinal axis between said first end and said second end, the first end carrying a first container connector arrangement and the second end carrying a second container connector arrangement, each of said first and second container connector arrangements being configured to engage with a transport container; a main frame carrier comprising a crane bracket and a rotator enabling rotation of the main frame, and thereby any container held by the spreader, in relation to the crane bracket about a substantially vertical rotation axis; a rotation motor configured to, responsive to a rotation control signal, operate the rotator to rotate the main frame in relation to the crane bracket; and a rotation detector configured to detect rotation of the main frame in relation to the crane bracket, wherein the spreader system further comprises a control system configured to, based on a discrepancy between the rotation control signal and a rotation detected by the rotation detector, generate a rotation alert signal.
21. The spreader system according to claim 20, wherein the rotation detector is configured to detect a rotation direction of the main frame in relation to the crane bracket.
22. The spreader system according to claim 20, wherein the control system is configured to generate said rotation alert signal based on a determination that a detected rotation direction is opposite to a rotation direction dictated by said rotation control signal.
23. The spreader system according to claim 20, wherein the rotation detector is configured to determine a rotation speed of the main frame in relation to the crane bracket.
24. The spreader system according to claim 23, wherein the rotation detector is configured to generate said rotation alert signal based on said speed exceeding a limit speed.
25. The spreader system according to claim 20, wherein the rotation detector is configured to determine an absolute rotation in relation to a reference position.
26. The spreader system according to claim 20, further comprising at least one rotation brake configured to, based on said rotation alert signal, mechanically brake and/or block a rotation between the crane bracket and the main frame.
27. The spreader system according to claim 20, wherein the control system is configured to, based on the rotation alert signal, stop the operation of the rotation motor and/or generate a warning signal via a user interface.
28. The spreader system according to claim 20, wherein the main frame is connected to the rotator via a main frame suspension arrangement, wherein the main frame is translatably suspended in said main frame suspension arrangement to enable translation along said longitudinal axis.
29. The spreader system according to claim 20, wherein the control system is configured to, based on said rotation alert signal, impose a control constraint limiting a set of permissible operations of the spreader.
30. The spreader system according to claim 29, wherein said control constraint limits side-shifting of the main frame along said longitudinal axis.
31. The spreader system according to claim 20, wherein the spreader comprises a detector for detecting a position along said longitudinal axis of a centre of mass of the container, or of the spreader and any container attached thereto, wherein said control system is configured to, based on a detected position of said centre of mass, brake or block a rotation between the crane bracket and the main frame, and/or impose a control constraint limiting a possibility to tilt the rotator about an axis parallel to the longitudinal axis.
32. The spreader system according to claim 20, wherein the rotation motor is a hydraulic motor.
33. The spreader system according to claim 20, wherein the rotation motor is connected to the rotator via a gear arrangement, wherein the rotation detector is configured to detect rotation based on detection of the presence of at least one gear tooth of the gear arrangement.
34. The spreader system according to claim 33, wherein the rotation detector comprises two gear tooth detectors arranged at a periphery of a gear of the gear arrangement, at mutual positions enabling said gear tooth detectors to sense the presence of gear teeth out of phase with each other.
35. The spreader system according to claim 20, wherein the first container connector arrangement comprises a first travelling beam, and the second container connector arrangement comprises a second travelling beam, wherein a proximal end of the first travelling beam is guided in the main frame to be telescopically extendable from the main frame in a first direction along said longitudinal axis, and a distal end of the first travelling beam is configured to engage with a first end of said transport container, and wherein a proximal end of the second travelling beam is guided in the main frame to be telescopically extendable from the main frame in a second direction along said longitudinal axis, and a distal end of the second travelling beam is configured to engage with a second end of said transport container.
36. The spreader system according to claim 20, wherein each of said first and second container connector arrangements comprises a respective transversal beam extending in a direction transversal to the longitudinal axis, each of said transversal beams being provided with two respective lifting casting connectors separated along said transversal direction, for connecting to two lifting castings of said transport container.
37. A method of handling a transport container using a spreader, the method comprising: determining a rotation status of the transport container based on a signal from a rotation sensor; comparing the rotation status to an expected rotation status determined based on a rotation control signal; and based on said comparison, generating a rotation alert signal.
38. A spreader for lifting a transport container, the spreader comprising a main frame having a first end and a second end, and extending along a longitudinal axis between said first end and said second end, the first end being provided with a first container connector arrangement and the second end being provided with a second container connector arrangement, each of said first and second container connector arrangements comprising at least one respective lifting casting connector configured to engage with a lifting casting of a transport container; a main frame carrier comprising a crane bracket and a rotator enabling rotation of the main frame, and thereby any container held by the spreader, in relation to the crane bracket about a rotation axis which is substantially perpendicular to the longitudinal axis; a rotation motor connected to the rotator via a gear arrangement and configured to, responsive to a rotation control signal, operate the rotator to rotate the main frame in relation to the crane bracket, and a rotation detector configured to detect rotation of the main frame in relation to the crane bracket, the rotation detector comprising a gear tooth detector configured to detect the presence of at least one gear tooth of the gear arrangement.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:
[0027] FIG. 1 is an illustration in perspective of an intermodal transport container;
[0028] FIG. 2 is an illustration in perspective of a top lifting casting of the intermodal transport container of FIG. 1;
[0029] FIG. 3 is an orthographic projection of a spreader for handling the container of FIG. 1;
[0030] FIG. 4A is a schematic illustration of the spreader of FIG. 3 as seen from below, when in a longitudinally retracted position;
[0031] FIG. 4B is a schematic illustration of the spreader of FIG. 3 as seen from below, when in a longitudinally extended position;
[0032] FIG. 5 illustrates a cross-section of a main frame and a main frame suspension arrangement of the spreader of FIG. 3, the cross-section being taken along the plane V-V of FIG. 3;
[0033] FIG. 6 is a side view of a reach stacker carrying the spreader of FIG. 3, the reach stacker holding the container of FIG. 1 in a first position;
[0034] FIG. 7 is a perspective view, as seen obliquely from below, of a lifting casting connector of the spreader of FIG. 3;
[0035] FIG. 8 is a side view illustrating the spreader of FIG. 3 and the container of FIG. 1 prior to connection;
[0036] FIG. 9 is a side view of the reach stacker and container of FIG. 6, the reach stacker holding the container in a second position which is tilted in relation to the position of FIG. 6;
[0037] FIG. 10A illustrates a cross-section of a rotator of the spreader of FIG. 3, the cross-section being taken along the line X-X illustrated in FIG. 6;
[0038] FIG. 10B is a magnified view of a portion of the section of FIG. 10A, the magnified portion indicated by B in FIG. 10A;
[0039] FIG. 11 is a diagram illustrating exemplary signals from a rotation detector of the spreader of FIG. 3;
[0040] FIG. 12A is a side view of the spreader of FIG. 3, the side view corresponding to the view of FIG. 8, and illustrating the spreader prior to connection to the container;
[0041] FIG. 12B is a side view of the spreader of FIG. 3, the side view corresponding to the view of FIG. 12A, and illustrating the spreader after having side-shifted the container; and
[0042] FIG. 13 is a flow chart illustrating a method of handling a container.
[0043] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0044] FIG. 1 schematically illustrates an intermodal container 10 according to the above-mentioned ISO standards. The container 10, which for clarity is illustrated transparent, has a top face 10a, a first longitudinal side 10b, and a first short side or gable side 10c. The container also has a bottom face 10d, a second longitudinal side, and a second gable side 10e, which are located parallel and opposite the top face 10a, first longitudinal side 10b, and first gable side 10c, respectively. Each corner of the container 10 is provided with a respective lifting casting for attaching a respective lifting casting connector, for the purpose of facilitating the handling of the container 10, and for locking the container 10 to other containers or to the deck of a freight ship. Hence, the container top corners which define the corners of the top face 10a are provided with two lifting castings 12a at a first longitudinal end 14a of the container 10, and two lifting castings 12b at a second longitudinal end 14b of the container 10. Similarly, the container bottom corners are provided with four bottom lifting castings 15a, 15b at the four corners of the bottom face.
[0045] FIG. 1 also illustrates the container 10 arranged in a cartesian coordinate system, wherein the bottom face 10d of the container 10 is in the x-y plane, the longitudinal sides 10b of the container 10 are arranged along the x-z plane, and the gable sides 10c, 10e of the container 10 are arranged along the y-z plane. The rotation directions of a container 10 are typically given by reference to the directions of rotation of a container arranged on a cargo ship. Containers 10 arranged on a cargo ship are aligned with the cargo ship having the longitudinal sides 10b along the length of the cargo ship. The rotational motions of the container may therefore be defined by reference to the motions of the cargo ship, i.e. list, trim and skew. List is rotation about the x-axis, and is sometimes also referred to as tilt. Trim is rotation about the y-axis; herein, trim may also be referred to as sideways leaning of the container 10. Skew is rotation about the z-axis.
[0046] FIG. 2 illustrates one of the top lifting castings 12b in greater detail, in the same perspective as that of FIG. 1. It is provided with a top face lock opening 18, a longitudinal side lock opening 20, and a gable lock opening 22, each of which is configured to receive and engage with a male insert of a lifting casting connector, such as a lifting hook or a twist-lock. It will be appreciated that all top lifting castings 12a, 12b may be identical, albeit in a mirror configuration.
[0047] FIG. 3 illustrates a top-lift spreader 24 for handling an intermodal transport container according to the above-mentioned ISO standards. The spreader 24 comprises a main frame 26 extending along a longitudinal axis L between a first end 26a and a second end 26b. The first end 26a carries a first container connector arrangement 28a configured to be connected to the first end 14a of the container (FIG. 1), and the second end 26b carries a second container connector arrangement 28b configured to be connected to the second end 14b of the container (FIG. 1).
[0048] The spreader 24 further comprises a main frame carrier 30 comprising a crane bracket 32, which is configured to be connected to a crane (not illustrated) such as a telescopic boom crane or a wire crane. The crane bracket 32 is connectable to the crane to enable tilting the container about a horizontal tilt axis A1, extending along the longitudinal axis L, for changing the tilt of the container 10 (FIG. 1). For the purpose, a pair of hydraulic tilt cylinders 33 are likewise connectable to the crane. The main frame carrier 30 further comprises a rotator 34 enabling rotation of the main frame 26, and thereby any container(s) 10 held by the spreader 24, in relation to the crane bracket 32 about a substantially vertical rotation axis A2 for changing the skew of the container. A first hydraulic rotation motor 35a and a second rotation motor 35b are configured to, responsive to a rotation control signal from a spreader control system 54a, operate the rotator 34 to rotate the main frame 26 in relation to the crane bracket 32. Even though one rotation motor 35a may be sufficient for rotating the main frame 26, the torqued added by the second motor 35b may increase the spreader’s 24 ability to rotate heavy loads. The total rotation torque applied about the rotation axis A2 by the rotation motors 35a, 35b is indicated by an arrow Tm. The main frame carrier 30 also comprises a main frame suspension arrangement 36 enabling translation of the main frame 26 relative to the main frame carrier 30 along the longitudinal axis L. The main frame suspension arrangement 36 thereby carries the weight of a suspension arrangement load comprising the main frame 26, the container connector arrangements 28a, 28b, and any container(s) 10 attached to the container connector arrangements 28a, 28b. A side-shift mechanism 37, configured as a hydraulic cylinder extending along the main frame 26, is connected to the main frame 26 as well as to the main frame suspension arrangement 36. The side-shift mechanism 37 enables, responsive to a side-shift control signal from the spreader control system 52a, moving the main frame 26 relative to the main frame suspension arrangement 36 along the longitudinal axis L. The side-shift mechanism 37 also comprises a side-shift sensor (not illustrated) enabling determining the mutual positional relationship between the main frame suspension arrangement 36 and the main frame 26. The side-shift sensor may be arranged within the hydraulic cylinder as such, or be provided as a separate sensor.
[0049] FIGS. 4A and 4B illustrate the spreader 24 in a highly schematic manner, and as seen from below. The first container connector arrangement 28a comprises a first travelling beam 38a guided in first travelling beam guide configured as a sleeve 27a within the main frame 26. Similarly, the second container connector arrangement 28b comprises a second travelling beam 38b guided in second travelling beam guide configured as a sleeve 27b within the main frame 26. The travelling beams 38a, 38b are telescopically extendable between a retracted position (FIG. 4A) for connecting the spreader 24 to a 20-foot container, and an extended position (FIG. 4B) for connecting the spreader 24 to a 40-foot container. A proximal end 40a of the first travelling beam 38a is guided in the main frame 26 to be telescopically extendable from the main frame 26 in a first extension direction E1 along the longitudinal axis L, and a distal end 42a of the first travelling beam 38a is provided with a respective first transversal beam 44a extending in a transversal direction T substantially perpendicular to the longitudinal axis L. The first container connector arrangement 28a further comprises a first pair of lifting casting connectors configured as twist-locks 46a arranged at opposite ends of the first transversal beam 44a, which first pair of twist-locks 46a are connectable to the top face lock openings 18 (FIG. 2) of the top lifting castings 12a of the container’s 10 first longitudinal end 14a.
[0050] Similarly, a proximal end 40b of the second travelling beam 38b is guided in the main frame 26 to be telescopically extendable from the main frame 26 in a second extension direction E2 opposite to the first extension direction along the longitudinal axis L, and a distal end 42b of the second travelling beam 38b is provided with a respective second transversal beam 44b extending along the transversal direction T. The second container connector arrangement 28b comprises a second pair of lifting casting connectors configured as twist-locks 46b arranged at opposite ends of the second transversal beam 44b, which second pair of twist-locks 46b are connectable to the top face lock openings 18 (FIG. 2) of the top lifting castings 12b of the container’s 10 second longitudinal end 14b. For the sake of clarity, it is pointed out that FIG. 3 illustrates the spreader 24 with the travelling beams 38a, 38b in the retracted position, such that they are hid within the main frame 26.
[0051] FIG. 5 highly schematically illustrates the main frame 26 and the main frame suspension arrangement 36 in a section along a section plane V-V (FIG. 3) perpendicular to the longitudinal axis L. The main frame comprises a pair of opposite outer side wall faces 56. A respective side-shift rail 58 is welded to the outer face of each side wall 56, the side-shift rails 58 protruding from the side walls 56 and extending along the longitudinal axis L (FIG. 3). Each side-shift rail 58 is vertically supported by and slidingly rests on a respective vertical support 60 of the main frame suspension arrangement 36, to allow sliding the main frame on the vertical supports 60 along said longitudinal axis L. The vertical supports 60 are provided with slide pads 64, which may be made of e.g. plastic such as polyurethane, for reducing the friction for sliding the main frame 26 along the main frame suspension arrangement 36. The slide pads 64 also define a pair of opposite side supports 62 facing the respective outer side wall faces 56, for guiding the main frame 26 along the longitudinal axis L. FIG. 5 also illustrates the travelling beams 38a, 38b within their respective travelling beam guides 27a, 27b. Friction-reducing slide pads 66 are arranged around the circumferences of the travelling beams 38a, 38b.
[0052] FIG. 6 illustrates the spreader 24 attached to a telescopic boom crane 48 of a truck 50, to form a reach stacker 52. FIG. 6 illustrates the reach stacker 52 with a container 10 attached to the spreader 24. The truck 50 is also provided with a truck control system 54b, comprising electronics and/or computer program instructions for controlling the truck 50 and the crane 48, and via the spreader control system 54a (FIG. 3), also the spreader 24. The truck and spreader control systems 54b, 54a together define an overall control system, the functionality of which may be distributed between the truck and spreader control systems 54b, 54a in an arbitrary manner.
[0053] FIG. 7 schematically illustrates a twist-lock 46b comprising a male locking insert 74 configured to be inserted into a top opening 18 (FIG. 2) of a respective container lifting casting 12b (FIG. 2). Once inside the lifting casting 12b, an end portion 76 of the male locking insert 74 is configured to be twisted 90° about a vertical axis R to a lock position, in which it engages with the lifting casting 12b. An abutment face 78 (hatched), flanking the male locking insert 74, corresponds to the size and shape of the top surface 19 (FIG. 2) of the lifting casting 12b, and is configured to rest thereupon once the spreader 24 (FIG. 3) has been lowered onto the container 10.
[0054] FIG. 8 schematically illustrates a situation in which the spreader 24 is lowered onto a container 10 for connection thereto via the container connector arrangements 28a-b. The container 10 and the spreader 24 are seen from the longitudinal side 10b of the container, i.e. from the longitudinal side of the container 10 which faces the truck 50 (FIG. 6). The container 10 is eccentrically loaded with cargo, such that the container’s centre of mass Mc is longitudinally offset from the container’s 10 geometric centre. Thereby, the total vertical load on the spreader will be eccentric in the sense that it is separated from the spreader’s rotation axis A2. In the view of FIG. 8, the weight of the container 10, i.e. the gravitational force on the container 10, is indicated by arrow Gc.
[0055] FIG. 9 illustrates a potentially dangerous situation, in which an operator of the reach stacker 52 has tilted the spreader 24 with the eccentrically loaded container 10 about the tilt axis A1. In the illustrated situation, the tilted container 10 generates, due to the eccentric load and the tilted rotation axis A2, a torque Tc about the rotation axis A2 in the anticlockwise direction, as seen from above. In order to prevent a rotation induced by the torque Tc, and referring back to FIG. 3, the rotator 34 is provided with rotation brakes 39a, 39b, which are engaged to prevent rotation in the rotator 34 whenever the rotation motors 35a, 35b are not operated. The rotation brakes 39a, 39b are configured as disc brakes arranged within the housings of the rotation motors 35a, 35b, and are controlled by the spreader control system 54a. Whenever the operator operates the rotator 34, the rotation brakes 39a, 39b automatically release, and whenever the operator stops operating the rotator 34, the rotation brakes 39a, 39b automatically engage.
[0056] However, and again with reference to the situation of FIG. 9, if the operator attempts to rotate the container 10 in the rotation direction opposite to the torque Tc applied by the container, i.e., in the view of FIG. 9, in the clockwise direction as seen from above, a dangerous situation may occur. If the torque Tc applied by the eccentric load is larger than the opposite torque Tm (FIG. 3) applied by the rotation motors 35a, 35b, the container 10 may start rotating about the rotation axis in the rotation direction determined by the eccentric load-induced torque Tc, instead of the rotation direction determined by the rotation motor-induced torque Tm. It may be intuitive for the operator to keep trying to rotate the container 10 in the intended direction Tm, by keeping operating the rotation motors 35a, 35b, which may in fact worsen the situation.
[0057] In a slightly different situation, the operator may attempt to rotate the container 10 in the same rotation direction as the torque Tc applied by the container 10, i.e., in the view of FIG. 9, in the anti-clockwise direction as seen from above. If the torque Tc applied by the eccentric load is sufficiently large, the container 10 may start rotating about the rotation axis A2 at an uncontrolled speed which is higher than the speed intended by the operator, i.e. higher than the speed dictated by the rotation control signal from the control system 54a to the rotation motors 35a, 35b (FIG. 3).
[0058] In both situations, eventually, the uncontrolled rotation may result in that the container 10 may hit an object, a person, or the truck 50. In particular, for long containers, such as 40-foot containers, the truck 50 may be in the rotation path of a container 10. However, the spreader 24 is provided with an arrangement which addresses those potential risks, and which will be elucidated in the following.
[0059] FIG. 10A illustrates the rotator 34 as seen in the section X-X of FIG. 6. The rotator 34 comprises a gear rim 68, which is rigidly connected to the main frame suspension arrangement 36 (FIG. 3). The rotation motors 35a, 35b are arranged on the crane bracket side of the rotator 34, and are rigidly connected to the crane bracket 32. A rotator bearing 70 journals the gear rim 68 on the crane bracket 32, allowing the gear rim to rotate about the rotation axis A2 (FIG. 3), together with the main frame suspension arrangement 36, the main frame 26, and any containers carried thereby. Output shafts (not illustrated) of the rotation motors 35a, 35b (FIG. 3) carry respective rotation motor pinions 72a, 72b, which drivingly mesh with the teeth of the gear rim. In the illustrated embodiment, each rotation motor pinion 72a, 72b has 12 gear teeth, whereas the gear rim 68 has 124 gear teeth.
[0060] The rotator 34 is also provided with a rotation detector 80 configured to detect the rotation of the first rotation motor pinion 72a, and thereby also the rotation about the rotation axis A2 (FIG. 3) of the gear rim 68 and the main frame suspension arrangement 36 (FIG. 8) with the main frame 26 and container 10 in relation to the crane bracket 32. The rotation detector 80 is further configured to detect the rotation speed and rotation direction of the first rotation pinion 72a, and thereby also the rotation speed and rotation direction of the main frame suspension arrangement 36 (FIG. 8) with the main frame 26 and container 10 in relation to the crane bracket 32.
[0061] The magnified view of FIG. 10B illustrates the rotation detector 80 in greater detail. The rotation detector 80 comprises a first gear tooth detector 82a and a second gear tooth detector 82b, which are arranged at the periphery of the first rotation motor pinion 72a. The gear tooth detectors 82a-b are configured to detect the presence of the gear teeth 84 of the first rotation motor pinion 72a, and may be, for example, inductive sensors. Upon rotation of the first rotation motor pinion 72a, each of the gear tooth detectors 82a-b will generate a periodic signal, wherein the period of the periodic signal indicates the rotation speed. The two gear tooth detectors 82a-b are positioned such that they will provide respective tooth detection signals which are out of phase with each other by 90°. Thereby, the relative phase between the signals from the respective gear tooth detectors 82a-b will indicate the rotation direction of the first rotation motor pinion 72a, and thereby also the rotation direction of the main frame suspension arrangement 36 (FIG. 8) with the main frame 26 and container 10 in relation to the crane bracket 32, which is opposite to the rotation direction of the first rotation motor pinion 72a.
[0062] FIG. 11 illustrates an example of the signals from the gear tooth detectors 82a, 82b as a function of time t, wherein a high signal indicates the presence of a gear tooth in front of the respective gear tooth detector 82a-b, and a low signal indicates the absence of a gear tooth in front of the respective gear tooth detector 82a-b. The phase of the signal from the first gear tooth detector 82a is 90° ahead of the signal from the second gear tooth detector 82b, which indicates that the first rotation motor pinion 72a rotates in a rotation direction Rp (FIG. 10B), corresponding to the direction of the torque Tc (FIG. 10A) generated by the eccentrically loaded container 10 (FIG. 9). In the opposite rotation direction, the phase of the signal from the second gear tooth detector 82b would instead have been 90° ahead of the signal from the first gear tooth detector 82a. Each transition from high signal to low signal, or from low signal to high signal, of any of the gear tooth detectors 82a-b is also detected. The transitions ω are illustrated in the lowermost chart, and their frequency is indicative of the rotation speed. Each gear tooth 84 generates, during each full turn of the rotation motor pinion 72a, two transitions at each gear tooth detector 82a, 82b. Thereby, a full 360° turn of the rotator 34 would correspond to 124*2*2=496 transitions ω, which results in an angular resolution of the rotation detector 80, with regard to rotation of the main frame 26 (FIG. 3) about the rotation axis A2, of 360°/496, i.e. about 0.7°. Based on each transition ω, the control system 54a may update a transition counter which, based on the detected rotation direction, either adds or subtracts the detected transitions ω from the transition counter. Thereby, the control system 54a (FIG. 3) may keep track of a total rotation relative to a start position. The rotation counter may be kept in a non-volatile memory, such that its value may be recovered upon loss of electric power. Referring back to FIG. 10A, the rotator 34 may also be provided with a reference position sensor 86 configured to detect at least one absolute angular position of the rotator 34, in order to provide a reference position for resetting the transition counter. By way of example, the reference position sensor 86 may be configured as an inductive sensor attached to the crane bracket 32, and be configured to detect metallic detection bodies 88a-c rigidly connected to the gear rim 68. The detection bodies 88a-c may comprise a centre detection body 88a, representing when the main frame’s 26 longitudinal axis L extends parallel to the tilt axis A1, and two rotator end position detection bodies 88b, 88c, representing a maximum permitted rotation in each direction. The spreader control system 54a may be configured to re-set the rotation counter to a respective predetermined value each time the reference sensor 86 is positioned in front of a respective detection body 88a, 88b, 88c.
[0063] Returning to the situation illustrated in FIG. 9, and assuming that the operator makes an attempt to rotate the main frame 26 clockwise, as seen from above, the spreader control system 54a (FIG. 3) will generate a rotation control signal to the rotation motors 35a, 35b to rotate the rotation motor pinions accordingly, to apply a rotation torque to the main frame 26 in the direction indicated by Tm in FIG. 3. If the spreader control system 54a receives, in response to applying the torque in the intended rotation direction, the gear tooth detector signals illustrated in FIG. 11, this is an indication that the rotator 34 rotates in the rotation direction opposite to the intended rotation direction, i.e. in the direction indicated by Tc in FIG. 9. Based on the discrepancy between the rotation control signal and the rotation detected by the rotation detector 80 (FIG. 10A), the spreader control system 54a will issue a rotation alert signal. The rotation alert signal may serve as a basis for directly and automatically engaging the rotation brakes 39a, 39b (FIG. 3) and stopping the rotation motors 35a, 35b, or for prompting the operator to stop the attempt to rotate the spreader 24, such that the rotation brakes 39a, 39b may automatically engage. The control system 54a may also impose other control constraints, such as limiting further lifting of the container 10 from the ground, and/or preventing further tilting of the container about the tilt axis A1.
[0064] Similarly, if the signal from the rotation detector rotation speed exceeds a limit speed, corresponding to a limit frequency of transitions ω (FIG. 11), the spreader control system 54a may be configured to, regardless of the detected rotation direction, automatically engage the rotation brakes 39a, 39b (FIG. 3) and stop the rotation motors 35a, 35b.
[0065] Based on the detected rotation direction about the rotation axis A2, the spreader control system 54a may determine an eccentricity of the load of the container 10. FIG. 12A illustrates, in a view corresponding to that of FIG. 8, a situation in which the spreader 24 has connected to the container 10, and initiated a lift along the arrow of FIG. 12A as well as a tilt about the tilt axis A1, resulting in the position of FIG. 9. If rotation is attempted, the spreader control system 54a (FIG. 3) can, by comparing the rotation control signal with the detected rotation, get an indication of the direction and magnitude of the load eccentricity-induced torque Tc generated by the container 10. Based on the direction and magnitude of the detected torque Tc, the spreader control system 54a may determine a preferred side-shift direction D along the longitudinal axis L, in which preferred side-shift direction the main frame 26 should be side-shifted relative to the main frame suspension arrangement 36 in order to compensate for the eccentric load. The spreader control system 54a (FIG. 3) may, for example, prevent the operator from side-shifting the main frame 26 in a direction opposite to the preferred side-shift direction D. The spreader control system 54a may also prompt the operator of the reach stacker 50 (FIG. 9) to operate the side-shift mechanism 37 to side-shift the main frame 26 in the preferred direction D, or automatically operate the side-shift mechanism 37 to translate the main frame 26 in the direction D, in order to bring the container’s centre of mass Mc closer to the rotation axis A2. A side-shift of the main frame 26 in the direction D brings us from the situation of FIG. 12A to the situation of FIG. 12B, in which the risk of uncontrolled rotation of the main frame 26 and the container 10 about the rotation axis A2 is substantially reduced, since the container’s 10 centre of mass Mc is closer to the rotation axis A2.
[0066] A rotation attempt is not needed for determining an eccentricity of the load of the container 10. According to a further example, the position of the container’s 10 centre of mass Mc may be detected based on load sensors (not illustrated) in the container connector arrangements 28a, 28b, the load sensors determining the vertical load carried by the respective container connector arrangements 28a, 28b, The spreader control system 54a may thereafter determine a preferred side-shift position based on the determined position of the centre of mass Mc. The preferred side-shift position may be compared to the present side-shift position, for obtaining a preferred direction D (FIG. 12A) in which to side-shift the main frame 26 with the container 10. Based on the position of the centre of mass Mc, the spreader control system 54a may also apply control constraint based on the detected eccentricity, such as engaging the rotation brakes 39a, 39b, limiting tilt about the tilt axis A1, and/or preventing a side-shift of the main frame 26 in the direction opposite to the preferred side-shift direction D (FIG. 12A).
[0067] FIG. 12B also illustrates the possibility of determining a total weight Gt, and a combined centre of mass Mt, of the entire system consisting of the spreader 24 and the container 10. The total weight Gt and centre of mass Mt may be determined based on the container weight Gt and centre of mass Mc as determined by the load sensors, combined with à prior knowledge of the spreader’s 24 centre of mas Ms and weight Gs.
[0068] FIG. 13 illustrates a method of handling a transport container 10 (FIG. 1) using a spreader, such as the spreader 24 (FIG. 3) described in detail hereinabove, the method comprising: [0069] 1301: determining a rotation status of the transport container 10 based on a signal from a rotation sensor, such as the rotation sensor 80; [0070] 1302: comparing the rotation status to an expected rotation status determined based on a rotation control signal; and [0071] 1303: based on said comparison, generating a rotation alert signal.
[0072] The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.
[0073] For example, an absolute or relative rotation of the main frame 26 about the rotation axis A2 can be determined using many different types of sensors, and the scope is not in any way limited to the use of inductive sensors or sensors detecting the presence of gear teeth. Moreover, even though the spreader 24 described in detail hereinbelow is a top-lift spreader, the teachings are equally applicable to side-lift spreaders configured to attach to a transport container at only one single longitudinal side thereof. The rotation alert signal may be used in many different ways for mitigating the consequences of an eccentrically loaded container. Moreover, any rotation brake need not be of a disc-brake type; it may be any type of brake suitable for braking or blocking a rotation of the main frame 26 relative to the crane bracket 32. It is pointed out that the teachings herein may be applicable also to a spreader which does not enable side-shifting of the main frame in relation to the crane bracket.
[0074] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.
