The invention relates to a device for measuring a cargo carried by a hoisting frame.

As a result of recent guidelines from the International Maritime Organization (IMO), as of 1 July 2016 the weight of any container which is shipped has to be verified. One of the ways in which this can be realized is by weighing the container when it is lifted by a hoisting frame, a so-called spreader. This could in principle be done by measuring the force which must be exerted by a hoisting mechanism in order to lift the spreader with the container, although the measurement would in that case have to be corrected for the weight of the spreader itself. A more accurate measurement result can be obtained when only the container is weighed, for which purpose the force exerted by the spreader on the container has to be measured. This force is exerted by coupling members, or twist-locks, which engage in receiving spaces at the corners of the container, the so-called corner castings.

A problem which occurs here is that the coupling members or twist-locks of a spreader are heavily loaded, and the immediate vicinity of these coupling members is not very suitable for placing weighing equipment. Placing of the equipment in the vicinity of the coupling members or twist-locks is however important for accurate weighing.

The invention has for its object to provide a device of the above described type wherein this problem does not occur, or at least does so to lesser extent. This is achieved according to the invention with at least one sensor associated with a coupling member of the hoisting frame, which sensor is kept free of loads during use of the hoisting frame. A precise measurement can be performed by making use of sensors which co-act directly with the coupling members. Keeping this/these sensor(s) free of loads during use of the hoisting frame also prevents the sensor(s) being damaged, which could result in failure of the sensor(s), whereby measurement of the carried cargo is no longer possible.

The at least one sensor is preferably a contactless sensor. There is hereby no necessity to form vulnerable physical connections, whereby a relatively robust device is obtained.

The at least one sensor can be a magnetic sensor. Such a magnetic sensor is relatively accurate and very robust.

For an optimal determination of the weight of the cargo the device can be provided with a number of sensors placed distributed in peripheral direction around the coupling member.

In order to be able to detect the loads on the coupling member accurately the at least one sensor can be connected to a force-absorbing housing at least partially enclosing the coupling member.

The at least one sensor is here preferably received free of load in the housing.

This can be achieved for instance in that the housing at least locally has dimensions in a main direction of load which are larger than the corresponding dimensions of the at least one sensor. The sensor protruding in the main direction of load, whereby load could be exerted thereon, is thus prevented.

In a practical embodiment a receiving space for the at least one sensor is formed in the housing, and at least one wall part of the receiving space protrudes in the main direction of load beyond an end surface of the at least one sensor. This protruding wall part can then transmit the forces.

When the at least one sensor has dimensions transversely of the main direction of load which are larger than the corresponding dimensions of the housing, at least one wall part of the housing can have an opening through which the at least one sensor can protrude. The dimensions of the sensor are thus not limited by the dimensions of the housing.

The dimensions of the at least one sensor transversely of the main direction of load can substantially correspond to the dimensions of a widened head of the coupling member in this direction. This widened head of a twist-lock has the largest dimensions of all components, and thus determines the dimensions of the surrounding construction. Linking the dimensions of the sensor to the dimensions of the widened head makes additional operations unnecessary.

For an optimal measurement accuracy it is important that the at least one sensor is fixed in the housing. Unexpected movements which could result in measurement errors are thus prevented.

When the housing has an external shape and an external dimension such that it is interchangeable with a standard bearing bush for the coupling member, it can be retrofitted relatively easily in order to replace a standard bearing bush. The hoisting frame can thus be provided with measurement sensors in simple manner without additional operations being necessary for this purpose.

The coupling member can be pivotable about an axis which is substantially parallel to the main direction of load and about an axis which is substantially perpendicular to the main direction of load. The first pivoting option serves for rotation of the widened head for locking thereof in the oval opening of the corner casting, while the second pivoting option ensures that the coupling member can "float". Deformation of the spreader for instance when loaded by a heavy container can hereby be compensated by pivoting of the coupling member. This is important because the container itself will in principle not deform, whereby the accuracy of fit is adversely affected.

When the hoisting frame comprises a number of coupling members, at least one sensor is associated with each of the coupling members and the sensors of the respective coupling members are connected for signal generation to a central processing unit, a total value of the load acting on the hoisting frame can be calculated on the basis of measurement signals from the different sensors.

Finally, the invention further relates to a hoisting frame provided with at least one coupling member and a measuring device as described above.

The invention will now be elucidated on the basis of an embodiment, wherein reference is made to the accompanying drawing, in which:

Figure 1 is a perspective view with exploded parts of an outer end of a hoisting frame with a coupling member and a sensor mounted thereon,

Figure 2 is an end view of the hoisting frame with the coupling member, with beside it a view on larger scale of the detail designated with the letter B, and

Figure 3 is a cross-sectional view along the line A-A in Figure 2.

A device 1 for measuring a cargo (not shown here) carried by a hoisting frame 2 comprises in the shown embodiment two sensors 3A, 3B which are associated with a coupling member or twist-lock 4 of hoisting frame 2. These sensors 3 A, 3B, which are arranged on either side of coupling member 4, detect a deformation (elongation) of coupling member 4 resulting from a tensile force being exerted on coupling member 4 when a container attached to hoisting frame 2 is lifted. By measuring the deformation (and thereby indirectly the tensile force) at each coupling member 4 the overall tensile force exerted by the container, and thereby the weight of the container, can be precisely determined.

Coupling member 4 comprises a shank 5 with a widened head 6 on an end remote from hoisting frame 2. Widened head 6 has chamfered ends so as to allow easy entry thereof into an opening of a corner casting. The opposite end of shank 5 is mounted in a nut 7 received in an outer end 8 of hoisting frame 2 at a position such that a part of shank 5 and widened head 6 protrude below hoisting frame 2.

Shank 5 is inserted through an opening 9 in a receiving body 10. This receiving body 10 has a central part 11, which is substantially cylindrical, and two side wings 12. Receiving body 10 is received non-rotatably in a correspondingly shaped opening 13 in a lower surface of hoisting frame 2. Shank 5 is further inserted through openings 15, 17 of respectively a female part 16 and a male part 18 of a pivot bearing 19. The upper end of the shank, which has two grooves 20, is locked between two co-acting half-collars 21 A, 21B which are each provided with two inward protruding ribs 22. These half-collars 21 A, 21B are in turn received close-fittingly in an opening 29 in nut 7, whereby they are clamped together and shank 5 is locked therein. A groove 23 is formed in an upper surface of shank 5, and corresponding grooves 24 are formed in an upper surface of nut 7. A key 25 can be received close-fittingly in grooves 23, 24 and forms a non- rotatable connection between shank 5 and nut 7. Formed in the upper surface of shank 5 and in the upper surface of key 25 are markings 26 which co-act with a sensor 27 in order to determine the rotation angle of coupling member 4 and thus establish whether coupling member 4 is in its unlocked position or in its locked position. Coupling member 4 is rotated by a drive (not shown here) which is connected to a tongue 42 on nut 7.

Female part 16 of pivot bearing 19 is received in a corresponding recess 28 around an opening 30 in an intermediate wall 31 in end part 8 of hoisting frame 2. An inner surface 32 of female part 16 is chamfered or curved, and an opposite outer surface 33 of male part 18 is chamfered or curved in similar manner so that male part 18 can slide or pivot over female part 16 while co-displacing half -collars 21A, 21B and nut 7 about an axis transversely of a longitudinal axis of shank 5. Openings 13, 15 and 30 have for this purpose a slightly larger diameter than shank 5 so that the part of shank 5 below intermediate wall 31 has some freedom of lateral movement. In order to make the pivoting movement possible there is also some space "d" between an upper surface 34 of receiving body 10 and an underside of intermediate wall 31 (figure 2, detail B).

Because of all these measures coupling member 4 can, as stated, "float". This is important so as to for instance be able to compensate for the fact that the outer ends of hoisting frame 2 bend when loaded, whereby coupling members 4 are not oriented exactly perpendicularly of the upper surface of a container. Other variations, such as for instance due to a non-optimal positioning of hoisting frame 2, can also be compensated by the float capability of coupling member 4. This ultimately prevents coupling member 4 being loaded at only one point, which can result in bending stresses in the coupling member and internal friction whereby the lifespan of coupling member 4 would be shortened.

Adjacently of the coupling member a stop member 35 is further arranged in an opening 36 in end part 8 of hoisting frame 2. This stop member 35 consists of a pin 37 with a recess 38, a spring 39 and a ring 40 with locking pin 41.

Sensors 3 A, 3B are mounted on a ring 43 arranged around shank 5. Arranged on ring 43 is a guide 44 which leads to a connector 45. Sensors 3 A, 3B are powered via this connector 45 and guide 44 and they generate their measurements signals to a processing unit (not shown here). Sensors 3 A, 3B, ring 43, guide 44 and connector 45 form a sensor unit 46 which in the shown embodiment is received in a force-absorbing housing 47. Because housing 47 absorbs forces, sensor unit 46 is kept free of loads which could affect the measurements and could result in damage to sensors 3A, 3B and other parts of sensor unit 46. In order to guarantee that sensors 3A, 3B do indeed remain free of loads, they are in any case shorter in the main direction of load - which coincides with the longitudinal axis of shank 5 - than the enclosing side wall 48 of housing 47. The upper edge of side wall 48, which also defines upper surface 34 of receiving body 10, protrudes beyond sensors 3A, 3B (figure 2, detail B). Further arranged on either side of sensor unit 46 as seen in the main direction of load are O-rings 50 which lock sensor unit 46 in this direction and prevent the loads which act on housing 47 also being transmitted to sensor unit 46. That the main direction of load coincides with the longitudinal axis of shank 5 comes about because great pressure forces are exerted on coupling member 4 in the direction of hoisting frame 2 when widened head 6 does not enter a corner casting but sets down on an adjacent surface. These pressure forces or impact loads are transmitted by the shank to receiving body 10 which in turn guides the forces via upper surface 34 into intermediate wall 31 and from there further into the construction of hoisting frame 2.

Because sensor unit 46 is received in force-absorbing housing 47, sensors 3A, 3B can be placed very close to shank 5 of coupling member 4 without the risk of measurements being disrupted, or even the sensors being damaged, when coupling member 4 is subjected to an impact load. This is particularly important for contactless sensors, such as the magnetic sensors 3A, 3B applied in the shown embodiment.

In order to make measuring device 1 suitable for retrofitting on existing hoisting frames it is important that the shape and dimensions of sensor unit 46 fit within the existing space in end part 8 of hoisting frame 2. For this purpose the shape and dimensions of housing 47 are adapted in the shown embodiment to the shape and dimensions of a standard bearing bush in which coupling member 4 is normally accommodated. In order to nevertheless create sufficient space for sensors 3A, 3B, and in addition enable connection of sensors 3A, 3B to a processing unit, in the shown embodiment side wall 48 of housing 47 is interrupted at three locations 49A-C. The dimensions of interruptions 49A-C are adapted to the width of respectively sensors 3A, 3B and connector 45 such that sensor unit 46 is locked substantially without clearance in housing 47. Sensor unit 46 thus moves with housing 47 around shank 5 - or more precisely: shank 5 rotates in the assembly of sensor unit 46 and housing 47 which is locked against rotation in opening 13 in hoisting frame 2.

Because the shape and dimensions of receiving body 10 correspond to the shape and dimensions of a standard bearing bush, coupling member 4 with measuring device 1 can also be mounted in hoisting frame 2 in the same way as a coupling member 4 that is movable in a standard bearing bush. The only additional step is that sensor unit 46 must be arranged. This can take place from the underside of hoisting frame 2, through opening 13 as shown here, although it is also possible to envisage sensor unit 46 being arranged through the open side 51 of end part 8 of hoisting frame 2. The choice for one of the two mounting methods depends on the type of connector 45 with which sensor unit 46 is equipped.

The invention thus makes it possible to place a load sensor in the very close vicinity of a coupling member without the risk of measurements being disrupted or the sensor being damaged. This makes it possible to determine in accurate manner, as it were directly at source, to determine the weight of a cargo being lifted by the hoisting frame.

Although the invention is elucidated above on the basis of an embodiment, it will be apparent that it is not limited thereto and can be varied in many ways within the scope of the following claims.