WO2014138801A1

WO2014138801A1 - Crane load rating system

Info

Publication number: WO2014138801A1
Application number: PCT/AU2014/000261
Authority: WO
Inventors: Glenn JENDRA
Original assignee: Terex Australia Pty Ltd
Priority date: 2013-03-15
Filing date: 2014-03-14
Publication date: 2014-09-18
Also published as: AU2018217205B2; AU2018217205A1; NZ712037A; AU2014231780A1; AU2020202695A1

Abstract

A load rating calculation system for a mobile crane, comprising one or more sensors to measure a spatial position of, and/or an articulation of, a body of the mobile crane; and a signal processor comprising a sensor signal receiver to receive a signal from the, or each, sensor relating to the measurement taken by the respective sensor; and a load rating calculator in communication with the sensor signal receiver to calculate a load rating of the mobile crane based on the signal of the respective sensor.

Description

CRANE LOAD RATING SYSTEM Technical Field

The present disclosure relates to a system for calculating a load rating of a mobile crane .

Background

Mobile cranes are primarily designed to be used on firm, flat, level ground. For each crane, rated capacity manuals are produced that provide load chart tables defining the capacity of the crane when in a particular configuration. The Configuration' of a crane typically includes the extension of the boom, boom angle, load radius, whether there is no articulation of the crane chassis, or whether the chassis is fully articulated, and whether the incline of the ground surface beneath the crane is 0° or otherwise less than 5°.

One such load chart table is the Terex^® pick and carry articulated mobile crane load chart table that defines a capacity based on boom length, load radius and chassis articulation, either straight ahead, or fully articulated. A dynamic safety factor is applied to load ratings to ensure that there is a buffer in the load rating to account for dynamic loads . This is also due to the load ratings being generally calculated using static

calculations . Some crane operators use knowledge of the dynamic safety factor to incorrectly increase the calculated load rating for a crane, by considering the safety factor as an unecessary 'buffer' . This can result in tipping or structural failure of the crane. Further to this, mobile "Pick and Carry" cranes, from their definition, have the ability to operate on varying terrain. Pick and Carry cranes also traverse terrain during a ^carry' operation. Thus a level chassis can be difficult to achieve. Many machines limit how the operator can use the machine to overcome some issues involved with variation in terrain. Such limits may include limiting the angle and length of the boom. Other systems detect the slope of the terrain and warn the operator .

It would be desirable to remove operator error and/or the effects of variation in terrain when calculating the load rating of a mobile crane .

Summary of the Disclosure

As used herein, the terms 'roll' , 'roll angle' and similar will be used to refer to a side angle, incline or slope: in other words, an angular offset of the ground relative to the horizontal when taken about an axis extending generally in the forward direction of the crane (e.g. along a centreline through the cabin and boom of a mobile crane) . To that end, the terms 'roll' , 'roll angle' , 'side incline' , 'side slope' , 'side tilt' and similar will be used interchangeably through the description.

Similarly, as used herein, the terms 'pitch' , 'pitch angle' and similar will be used to refer to a forward angle, incline or slope: in other words an angular offset of the ground relative to the horizontal when taken about an axis extending generally perpendicular to the forward direction of the crane. To that end, the terms 'pitch', 'pitch angle' , 'forward incline' , 'forward slope' ,

'forward tilt' and similar will be used interchangeably through the description. Also, the terms 'slope', 'sloping', 'incline' and similar will be used interchangeably to refer to a gradient of the chassis or body of the crane , or the gradient of the ground on which the crane is positioned. The present disclosure provides a load rating calculation system for a mobile crane, comprising:

one or more sensors to measure a spatial position, and/or an articulation, of a body of the mobile crane; and a signal processor comprising:

a sensor signal receiver to receive a signal from the, or each, sensor relating to the measurement taken by the respective sensor; and

a load rating calculator in communication with the sensor signal receiver to calculate a load rating of the mobile crane based on the signal of the respective sensor. The present disclosure provides a load rating calculation system for a mobile crane, comprising:

one or more sensors to measure a spatial position of a body of the mobile crane ; and

a signal processor comprising:

a load rating calculator in communication with the sensor signal receiver to calculate a load rating of the mobile crane based on the signal of the respective sensor. The load rating calculator may recalculate the load rating upon the, or each, signal indicating a change in the spatial position of the body. The spatial position of the mobile crane may include an incline of the body of the mobile crane . The incline may be measured relative to an horizon. At least one of the sensors may measure a roll angle of the body of the mobile crane . At least one of the sensors may measure a pitch angle of the body of the mobile crane. The load rating may be displayed to an operator of a mobile crane. The load rating, as displayed, may be updated based on a change in spatial position of the body. The change in spatial position of the body, that results in an updated load rating being displayed to the operator, may be an incremental change. The incremental change in spatial position may be a change of about ±5°. The maximum incline of the body may be ±15°. The sensor signal receiver may continuously receive signals from the one or more sensors and recalculates the load rating of the mobile crane based on a most recently received signal . The present disclosure also provides a load rating calculation system for an articulated crane, comprising: one or more sensors to measure an articulation of a body of the crane; and

a signal processor comprising:

a load rating calculator to calculate a load rating of the crane based on the signal of the respective sensor . The load rating calculator may recalculate the load rating upon the, or each, signal indicating a change in the articulation of the body . The load rating may be displayed to an operator of a mobile crane. The load rating, as displayed, may be updated based on a change in articulation of the body. The change in articulation of the body, that results in an updated load rating being displayed to the operator, may be an incremental change . The incremental change may be a change of about ±10°. The maximum articulation in the body may be ±40°. The load rating calculation system described above as including sensors for measuring a spatial position of the crane may also be a load rating calculation system as described above as including sensors for measuring an articulation of the crane. The load rating calculator may calculate the load rating based on a stability of the crane relative to one or more tipping axes . The one or more tipping axes may include one or more of :

- a tipping axis extending through front wheel assemblies of the crane;

- a tipping axis extending through wheel assemblies on one side of the crane ; and

- a tipping axis extending through at least one wheel assembly of the crane and being parallel to an horizon line. The load rating calculation system may further comprise one or more boom sensors in communication with the sensor signal receiver, the sensor signal receiver receiving a signal from the one or more boom sensors relating to at least one of:

- an extension of a boom of the crane;

- an angle of the boom of the crane;

- a mass of a suspended load; and

- a load radius wherein the load rating calculator calculates the load rating based on the signal from the respective boom sensor . The load rating calculation system may further comprise one or more counterweight sensors in communication with the sensor signal receiver, the sensor signal receiver receiving a signal from the one or more counterweight sensors relating to at least one of:

- a counterweight being present, or not present, on the crane; and

- a mass of the counterweight. The present disclosure also provides a crane including a load rating calculation system as described above. The crane may further include a display for displaying the load rating to an operator of the crane. The present disclosure provides a method for calculating a load rating for a crane, comprising:

measuring a spatial position, and/or an articulation, of a body of the crane; and

calculating a load rating of the crane based on the measured spatial position. The present disclosure further provides a method for calculating a load rating for a crane, comprising:

measuring a spatial position of a body of the crane; and

calculating a load rating of the crane based on the measured spatial position. The method may further comprise recalculating the load rating of the crane when measurement of the spatial position of the crane indicates a change in the spatial position of the crane. In the method, the spatial position may include an incline of the body of the crane . The present disclosure still further provides a method for calculating a load rating for an articulated crane, comprising:

measuring an articulation of a body of the crane; and calculating a load rating of the crane based on the measured articulation. The method may further comprise recalculating the load rating of the crane when measurement of the articulation of the crane indicates a change in the articulation of the crane. The present disclosure further provides a method for calculating a load rating for a crane, including:

calculating a load at which tipping of the crane will occur about each of two or more tipping axes, one of said tipping axes corresponding to a line through a body of the crane, the line having constant height with respect to a horizon ; and

identifying the lowest load of the calculated loads , as the load rating of the crane. The present disclosure provides a computer-readable storage medium containing instructions that, when executed by a processor, cause the processor to:

receive a signal from one or more sensors, the, or each, signal relating to a spatial position, and/or an articulation, of a body of a crane; and

calculate , based on the respective signal , a load rating of the mobile crane . The present disclosure also provides a computer-readable storage medium containing instructions that, when executed by a processor, cause the processor to:

receive a signal from one or more sensors , the , or each, signal relating to a spatial position of a body of a crane ; and

calculate , based on the respective signal , a load rating of the mobile crane .

In relation to the computer-readable storage medium, the spatial position of the body of the crane includes an incline of the body of the crane . The present disclosure further provides a computer- readable storage medium containing instructions that, when executed by a processor, cause the processor to:

receive a signal from one or more sensors, the, or each, signal relating to an articulation of a body of a crane ; and

calculate, based on the respective signal, a load rating of the mobile crane .

Some embodiments of the system disclosed herein may remove operator error in the calculation of the load rating of a mobile crane, by dynamically calculating the load rating of a mobile crane and taking into account the incline or slope of the ground or surface upon which the crane is operating, and/or taking into account the degree of chassis articulation in the crane .

Some embodiments of the system disclosed herein may improve the safety of use of a mobile crane during a carrying operation by intermittently recalculating the load rating of the mobile crane , taking into account the incline or slope of the ground or surface, and the degree of articulation of the chassis , at the time the load rating is recalculated. Some embodiments of the system disclosed herein may calculate the stability of the crane based on any one of three tipping axes. The three tipping axes are (i) about the front tyres of the mobile crane, (ii) about the tyres on one side of the mobile crane, and (iii) about a horizon line through the chassis .

In the present context, the term 'horizon line' is intended to mean a line of constant height or altitude, such as a line across a slope.

Brief Description of the Drawings

The apparatus and methods disclosed above will now be described, by way of non-limiting example only, with reference to the accompanying drawings in which: Figure 1 shows side and plan views of a mobile crane. It will be appreciated that, while Figure 1 shows an example of an hydraulic crane, the description provided herein can apply to other types and models of crane such as lattice boom cranes ; Figure 2 is an example of part of a load rating chart for a mobile crane. It will be appreciated that the load chart and quantities shown on the load chart (i.e.

dimensions, loads and angles) are provided for

illustrative purposes only and other types of load chart, quantities and considerations may apply to particular cranes ; Figure 3 shows a plan view of a mobile crane in an articulated state; Figure 4 is a deration chart for a mobile crane positioned on a surface with an incline of between 0.6° and 5°. It will be appreciated that information provided in the duration chart (e.g. the type of crane and dimensions) are provided for illustrative purposes only, and may be substituted for any information relevant to the particular crane to which the present disclosure is being applied; Figure 5 is a schematic diagram of a load rating

calculation system in accordance with the present disclosure, connected to a display and load moment indicator control system of a crane; Figure 6 is a schematic representation of a crane showing various tipping axes ; Figures 7 and 8 are flowcharts representing examples of methods for calculating a load rating for a crane using the load rating calculation system represented in Figure 5. Detailed Description

In the discussion below, the term Chassis' , referring to the chassis of a crane, may be interchangeably referred to as a 'body' unless context prescribes otherwise. However, it will be understood that the body of a crane in a practical context includes panelling and other features that fit on top of the chassis. It will also be

understood that the body of the crane does not include the boom or boom assembly (e.g. hydraulic supports extending from the chassis to the boom between the centre pin of the crane and head of the boom) , counterweight and wheel assemblies .

In addition, the definition of operating on level ground, in many circumstances is translated into the requirement of a level crane chassis. Various mechanisms and

environmental constraints are used to achieve this . These include outriggers, suspension levelling, axle locking and modifying the supporting ground structure. All of these mechanisms and their use are well known in the art and need not be described in detail herein. A mobile crane 10, as shown in Figure 1, is commonly known as a Pick and Carry crane as it can perform a "picking" operation, namely lifting a load, and a "carrying" operation, namely driving with a suspended load. The mobile crane 10 includes a boom 12, front tyres 14, rear tyres 16, a cabin 18, a counterweight 20 and chassis 22. The counterweight 20 is used to counter a load suspended by the boom 12 , and may be removable . To ensure the mobile crane 10 is stable, and does not undergo structural failure, the mobile crane 10 has a maximum load rating. The maximum load rating is calculated using a number of measurements . The measurements include one or more of :

• extension of the boom 12

• angle of the boom 12

• load radius (i.e. distance of the load from the front axle or front suspension of the crane 10)

• presence and/or mass of any counterweight 20

• incline or slope of a surface on which the mobile crane 10 is positioned, and

• articulation of the chassis 22.

Load ratings are charted for the mobile crane 10 for various extensions of the boom 12, and load radii.

However, the articulation of the mobile crane 10 and the slope of the surface on which the mobile crane 10 is positioned, must be assessed by the operator. Based on the operator's assessment the relevant charted load rating is selected and/or adjusted. Some models of mobile crane 10 provide a switch that triggers when a threshold articulation is reached.

Triggering of the switch results in an indication (e.g. dashboard light) to the operator that the threshold articulation has been reached, and/or results in automatic deration of the load rating to account for the

articulation . To facilitate determination of load ratings the operator is supplied a load chart, such as that shown in Figure 2. The chart is divided into two areas, namely an area above the thick line 23, and an area below the thick line 23. For boom length and load radius combinations that fall within the area above the thick line 23 , failure of the mobile crane 10 will likely be due to structural failure of the mobile crane 10. For boom length and load radius combinations that fall within the area below the thick line 23, failure of the mobile crane 10 will likely be due to potential instability and therefore tipping of the mobile crane 10. Structural failure may still result from boom length and load radius combinations falling below the thick line 23.

Due to the potential instability of the crane for boom length and load radius combinations falling in the area below the thick line, a 66.6% safety factor is applied (i.e. the load rating is derated by one third) . For each boom length and load radius there are three values specified. Two of the values are mass values. The larger of the two mass values (e.g. 13,200 for a 9 m boom length and 2.5 m load radius) is the load rating (in kg) of the mobile crane 10 with less than 10° of articulation in the chassis 22. The smaller of the two mass values (e.g. 12,050 for a 9 m boom length and 2.5 m load radius) is the load rating (in kg) of the mobile crane 10 with greater than 10° of articulation in the chassis 22. The third value (e.g. 58° for a 9 m boom length and 2.5 m load radius) is the boom angle. An articulated crane 10 is shown in Figure 3. The articulation is the amount by which the front of the crane 10 (i.e. the part carrying the boom 12) is angularly offset from the rear of the crane (i.e. the part carrying the counterweight 20) . The two articulation ranges, namely <±10° and >±10°, are indicated by reference numerals ^''A' and 'B' , respectively, in Figure 3. In Figure 3 , the shaded region - the region designated by numerals 'A' - is a region in which there is less than 10° of articulation in the chassis 22. The articulation region outside, and on either side, of the shaded region is where there is greater than 10° of articulation in the chassis 22 and is designated by numerals 'B' . Where the slope of the ground below the chassis 22 is above 1% (or 0.6°) a further deration factor must be applied. This deration factor is calculated based on the maximum slope on which the crane 10 is intended to operate. The maximum slope for crane 10 may be, for example, 5°. Other cranes may have different maximum operating slopes . To facilitate calculation of the further deration factor, a further chart, such as that shown in Figure 4, is used. Figure 4 shows the amount by which the load rating should be derated for a particular configuration of the mobile crane 10. In the chart the 'C_x' reference numerals will typically be expressed as percentages , and represent the amount by which the relevant load rating should be derated. For example, for a boom length of 11 m, load radius of 7 m and chassis articulation of greater than 10°, the load chart in Figure 2 states that the rated capacity of the mobile crane 10 is 3750 kg. The chart shown in Figure 4 then states that for a side slope of between 0.6° and 5°, and for a boom length of 11 m and load radius of 7 m (see "EXAMPLE PT" on Figure 4) , the rated capacity as

determined by the load chart should be derated by C₆. For the present example, C₆ will be 40%. Consequently, the load rating of the crane at a side slope of between 0.6° and 5° is reduced to 2250 kg.

It will be appreciated that different deration

percentages, and slopes or conditions under which derating occurs, will vary from crane to crane. Figure 4 is intended to be an illustrative example of a derating chart, and the dimensions and type of crane shown are intended to be an example only. To avoid having to provide a load chart for all extensions of the boom, at all articulations, and at all the various inclines of the ground, threshold values are used. For example , for ground inclines there is a load rating for when the ground is relatively flat (i.e. incline or slope of less than 0.6°) , and a load rating for when the ground has between 0.6° and 5° of incline. Similarly, there is a load rating for when the mobile crane 10 has a chassis articulation of less than 10°, and a different load rating for when the chassis articulation is greater than 10° . As a result of providing a single threshold value (e.g. 0.6° of incline or 10° of articulation) and assessing load ratings as being either above or below that value, a significant under-rating of the crane 10 results in many circumstances . In other words , the underrating of the load rating results from the use of 'worst case' values for inclines and articulations of a magnitude above the relevant threshold values. For example, for a mobile crane 10 with a maximum articulation of 40°, for any articulation the magnitude of which is equal to or in excess of 10° (e.g. ±11°) the crane is load rated as if it were at a maximum 40° of articulation. To improve calculation of the load rating of mobile crane 10, a load rating calculation system 30, as shown in Figure 5, is described. The load rating calculation system 30 comprises one or more sensors 32. The sensors 32 include one or more sensors 34 for measuring a spatial position of a chassis 22 of the mobile crane 10. The load rating calculation system 30 further includes a signal processor 96. The signal processor 96 comprises a sensor signal receiver 38 and a load rating calculator 40 in communication with the sensor signal receiver 38. The signal processor 96 is used for calculating a load rating of the crane 10 based on signals received from the various sensors 32, 34. To that end, the sensor signal receiver 38 receives a signal from each of the one or more sensors 34. The signals relate to a measurement taken by the respective sensor 34 of the spatial position of the chassis 22 of the crane 10. In other words, the sensors 34 measure one or more spatial parameters of the chassis 22 of the crane 10. The spatial parameters may include rotational orientation or 'incline' relative to horizontal axes, at various positions of the mobile crane 10. The rotational orientation may change as the crane 10 traverses over ground. These horizontal axes may include a horizontal, longitudinal axis taken through the chassis 22 and boom 12, and/or a horizontal, transverse axis perpendicular to the longitudinal axis . The sensors thus enable calculation of tipping lines (i.e. axes about which tipping of the crane 10 is likely) as discussed below. To that end, the load rating calculation system 30 takes into account that, while a crane 10 may tip on level ground, it is inherently easier to tip a crane 10 on sloping ground. The load rating calculator 40 then calculates the load rating of the mobile crane 10 based on the signal (s) received by the sensor signal receiver 38. In the present case the load rating calculator 40 also recalculates the load rating upon the respective signal indicating a change in the spatial position of the chassis 22. Changes in spatial orientation may occur as the crane 10 traverses over terrain or drives around a corner . The signal processor 96 may form part of a computing system. The computing system may be capable of being fitted to a crane 10 and connected (e.g. wirelessly or by wires) to sensors 34 mounted at various positions around the crane 10. Alternatively, the signal processor 96 may be programmed into an existing onboard computer of the crane 10, the onboard computer having established connections with the sensors 34. As mentioned above, the spatial position of the mobile crane 10 includes an incline of the chassis 22 of the mobile crane 10. Pre-existing methods for calculating load ratings would have employed load charts that provide one load rating for level ground usage of the crane 10 and another load rating for ground inclined at 0.6° to 5°. Load ratings calculated using pre-existing methods are likely only valid or accurate at the time the load rating chart was consulted. Typically, the load rating will be determined based on the ground upon which the crane 10 was positioned when the load rating was assessed.

In contrast, dynamically measuring the incline of the crane 10 allows the stability of the crane to be determined based on a real-time, actual measurement of the incline of the chassis 22 of the crane 10. The load rating calculation system 30 calculates the load rating of the crane 10 for the particular incline on which the crane 10 is positioned at the time the measurement of the incline is taken. Since it is envisaged that the load rating calculation system 30 will recalculate the load rating a number of times per second (upon receipt of signals from the sensors 32) the load rating calculation system 30, in effect, provides a continuously updated load rating to the operator of the mobile crane 10. To that end, the sensor signal receiver 38 of the load rating system 30, as shown in Figure 5, continuously receives (e.g. a number of times per second) signals from the one or more sensors 34. The load rating system 30 recalculates the load rating of the mobile crane 10 based on a most recently received signal .

The sensors 34 measure the spatial position, or incline, of the chassis 22 of the crane 10 rather than the incline of the ground surface on which the crane 10 is positioned. Although the incline of the ground surface heavily influences the incline of the chassis 22 of the crane 10, the incline of the chassis 22 is further influenced by external factors such as compression and flex in the rubber tyres of the crane 10. Therefore, measuring the spatial position, or incline, of the chassis 22 provides a more accurate indication of the stability of the crane 10 than does measuring the incline of the surface on which the crane 10 is positioned. The incline may be measured relative to any reference datum, but it is generally easiest to measure relative to horizontal. To measure the incline, the sensors 34 include one or more forward incline or forward tilt sensors 42 and/or one or more side incline or side tilt sensors 44. The forward incline or forward tilt sensors 44 measure incline of the chassis 22 of the crane 10 in a forward direction. The side incline or side tilt sensors 44 measure incline of the chassis 22 of the crane 10 in a side direction. It will be appreciated that in some circumstances the one or more forward incline or tilt sensors 42 , or the one or more side incline or tilt sensors 44, may be omitted. The incline or tilt sensors 42 , 44 may each comprise an accelerometer , gyroscope, strain gauge or any other appropriate sensor. The sensors 34, 42, 44 will typically be mounted to a chassis 22 of the crane 10. The sensors 34 , 42 , 44 take direct measurements of the tilt of the chassis 22 relative to an horizon. It will be appreciated that the sensors 34, 42, 44 may be mounted at any appropriate position on the crane 10, provided the requisite tilt of the chassis 22 of the crane 10 can be determined from the mounting position of the sensors 34, 42, 44. A calculated load rating will typically be transmitted to a display 45 for displaying the load rating to an operator of the crane 10. In some cases the displayed load rating may become unclear as a result of being constantly updated based on minor, or practically negligible, changes in spatial position of the chassis 22. To avoid losing clarity, changes in spatial position of the crane 10 can result in an update of the displayed load rating only when a threshold increment of spatial position is exceeded. For example, for incline or tilt sensors 42, 44 the load rating may only be recalculated when an incremental change of 1° is reached. Rounding may be used to categorise measurements into a respective increment of spatial position. For example, if the measured incline of the chassis 22 is 1.7°, then the load rating calculation system 30 may cause the display 45 to display the load rating for the nearest 1° increment (rounded up) , being 2° in the present example. Thus when the crane 10 traverses ground having an incline of greater than 1°, but less than or equal to 2°, the load rating as displayed on the display 45 will remain constant (i.e. at the load rating value applicable to a 2° incline) . For an incline of -1.3° the load rating calculation system will cause the display 45 to display the load rating for the nearest 1° increment (rounded down) , being -2° in the present example. It is useful to round up 'by magnitude' - in other words, round up when above 0° and round down when below 0° - to the next largest relevant increment since rounding down could result in the display of a load rating that exceeds the actual load rating of the crane 10. It will be appreciated that the system 30 is not limited to using rounding increments of 1°.

While the load rating calculation system 30 will provide similar results to the load charts when a mobile crane 10 is traversing level ground in a straight line, the load charts only provide a single deration percentage for inclines of between 0.6° and 5° . Consequently , when the slope or incline of the ground exceeds 0.6° a load rating is used that corresponds to a maximum angle of ground on which the mobile crane 10 can travel. In other words, if the maximum incline of ground over which the crane 10 can travel is 5° , then the load charts will use the load rating of the crane 10 at 5° of incline for all uses of the crane on ground slopes of 0.6° or more . In other words , the load charts provide only a 'level ground' load rating and a 'worst case incline' load rating. Therefore, the load rating calculation system 30 will usually result in a greater calculated load rating than that specified by the load charts as it can take into account the actual slope of the ground. For example, for a slope of 0.6° the load rating calculation system 30 will calculate the load rating of the crane at 0.6°, rather than at 5° . Moreover , during 'carrying' operations of a mobile crane 10 the load rating calculation system 30 will recalculate the load rating of the crane 10 to account for variations in incline of the chassis 22 of the crane 10 as the lift progresses . Particularly when the crane 10 is carrying heavy loads, the front tyres will compress . This makes the slope of the chassis 22 of the crane greater than the slope of the ground beneath the crane 10 for declines in the forward direction of movement of the crane 10, and less than the slope of the ground beneath the crane 10 for inclines in the forward direction of movement of the crane 10.

Consequently, even if the load rating as calculated from load charts is accurate for a particular ground slope, it may underrate or overrate the load rating of the crane 10 since the incline of the ground is used by the load charts as a proxy for the incline of the chassis 22. By using sensors 32 mounted to the crane 10 as described herein, a direct measurement of the incline of the chassis 22 can be taken . The load rating calculation system 30 provides further benefits when used in conjunction with cranes that can vary their speed during a ^''carrying' operation. It is noted that some models of crane are speed limited, or have advisory speed limits imposed, particularly when under load (i.e. during a carrying' operation). For those cranes that have variable speed when under load, the following advantage may become evident. For 'pick and carry' operations the incline or slope used in conjunction with the load charts should be the maximum incline over which the crane 10 is expected to travel during a lift. The crane 10 is therefore given a single, potential artificially low, load rating for an entire pick and carry operation. A load rating for a lift must be based on the maximum incline of a surface over which the crane 10 is expected to travel. Where a single load rating is determined for the entire lift, the crane 10 may need to travel more slowly than is strictly necessary when traversing ground of a lesser incline than the maximum incline over which the crane 10 is expected to travel during the operation.

In contrast, since the load rating calculation system 30 recalculates the load rating dynamically, the load rating for the 'lesser inclined' portions of a pick and carry operation will be high when compared with the load. The crane 10 may therefore travel faster over ground of a lesser incline than the maximum incline for the lift, and only slow down when approaching the maximum incline. For the above reasons, the load rating calculation system 30 can :

• improve the load rating of a crane 10 by taking into account the actual slope of the ground over which the crane 10 is intended to travel, when compared with a single 'worst case incline' load rating; and

• increase the speed with which pick and carry

operations are performed.

Such a load rating calculation 30 system, when applied to an articulated crane 10, may include one or more sensors 46 to measure an articulation of the chassis 22 of the crane 10. These sensors 46 may be supplied in addition, or as an alternative, to the one or more spatial position sensors 34 described above. Similar to use of the load rating calculation system 30 when comprising spatial position sensors 34 , when the load rating calculation system 30 includes one or more sensors 46 for measuring an articulation of the chassis 22. The sensor signal receiver 38 receives a signal from each sensor 46 relating to the articulation of the crane 10 (e.g. the angular offset between front and rear portions of the chassis of the crane 10) . The load rating calculator 40 calculates the load rating of the crane 10 based on the signal received from the respective sensor 46. The load rating calculator 40 of the present embodiment will recalculate the load rating once the signal (s) from the sensors 46 indicate there has been a change in the articulation of the chassis 22.

Since the load rating is transmitted to a display 45 within the operator cabin 18 of the crane 10, the display 45 will become unclear if it updates continuously with each consecutive reading or measurement received from the one or more articulation sensors 46. To preclude the display 45 becoming unclear due to constant updates in the load rating based on minor, or practically negligible, changes in articulation of the chassis 22 , the load rating calculation system 30 only causes an update of the display 45 when a threshold or incremental change in articulation is exceeded. For example, for articulation sensors 46 the load rating may only be recalculated when an

incremental change of 5° is reached. In other words, if the measured articulation of the chassis 22 is 17°, then the load rating calculation system 30 will round up to the nearest 5° increment, being 20° in the present example. The load rating of the crane 10 for an articulation angle of 20° is then displayed until a different increment (e.g. 15° or 25°) is reached. For an articulation of -17° the load rating calculation system will round down to the nearest 5° increment, being -20° in the present example. For reasons discussed above in relation to sensors 42, 44, it is useful to round to the next largest 5° increment, by magnitude .

It should be noted that, while update of the display 45 as discussed above has been based on reaching an incremental or threshold change in incline or articulation of the chassis 22, it is likely in practice that the displayed load rating will also be updated, or in the alternative will only be updated, when a threshold or incremental change in load rating is reached. For example, where the display 45 shows a load rating of 3550kg, and the relevant increment is 50kg, then the display will display 3550kg for all calculated load ratings between 3550kg and 3599kg.

If the load rating changes to 3549kg or 3600kg, then the displayed load rating will be 3500kg and 3600kg

respectively .

With regard to the clarity of the display in each circumstance described above, it will be appreciated that the "incremental" or "threshold" changes may represent "ranges" of a particular parameter (e.g. spatial position or articulation of the body or chassis 22) . For example, where the display is updated using an "incremental" change of ±5° for the articulation in the chassis 22 of the crane 10, the display will have a particular value when the articulation is 0°, a different particular value when the articulation is between 0° and less than or equal to 5° (i.e. 0° < articulation ≤ ±5°), a different value when the articulation is between than 5° and less than or equal to 10° (i.e. -5° < articulation < -10° or 5° < articulation < 10°) , and so on. In this sense the increments represent ranges such that the displayed values change when a relevant parameter (e.g. articulation) moves between increments (e.g. from 4° articulation to 6° articulation, and thus from the 0° < articulation ≤ 5° range into the 5° < articulation ≤ 10° range) , and the displayed values remain unchanged with changes of the respective parameter within a particular range or increment (e.g. between 0° < articulation ≤ 5°) . As with the dynamic calculation of load rating based on an actual incline of the chassis 22 of the crane 10, using the actual articulation of the crane 10 in load rating calculations avoids the need to use a single 'worst case' value for any articulation of the crane in excess of 10°. Thus the load rating calculation system 30 should provide a more accurate, and higher, load rating of the crane 10 for operations requiring a maximum articulation (e.g. during travel of the crane 10 over the ground) of between 0° and the maximum articulation of the crane 10.

It will be appreciated that sensors 42, 44, 46 may be provided individually or in any combination, and are intended to be a subset of sensors for determining a spatial position of a mobile crane 10. Using signals from the sensors 42, 44, 46 an indication of the stability of the crane 10 can be derived relative to various tipping lines as discussed below, and can be used to specify a more accurate load rating than would otherwise be achievable using load rating charts .

When used on a typical mobile crane 10, the sensors 42, 44, 46 will typically be used in conjunction with further sensors such as :

- load sensors 48 (e.g. pressure transducers) that determine the mass of a load and tackle suspended from the boom 12 ;

- load radius sensors 50 that determines the radius of the suspended load relative to the front axle of the crane 10, the front axle being the likely axis of tipping of the crane 10 as a result of, for example, too heavy a load being suspended on the boom. It will be appreciated that some mobile cranes will not include a load radius sensor and the load radius will instead be calculated from the boom extension and boom angle;

- boom extension sensors 52 (e.g. a reeling drum sensor) that determine an extension of the boom 12 ; and

- boom angle sensors 54 (e.g. an angle sensor mounted in the reeling drum) that determine an angle of the boom 12. The load rating calculation system 30 further comprises one or more counterweight sensors 56 in communication with the sensor signal receiver 38. The sensor signal receiver 38 receives a signal from the one or more counterweight sensors 56 relating to one or both of:

- in the case of counterweight presence sensors 58, the presence or otherwise of the counterweight 20 on the crane 10 ; and

- in the case of counterweight mass sensors 60 , the mass of the counterweight 20.

When calculating a load rating, the load rating

calculation system 30 uses signals from all available sensors 42 - 60, but particularly spatial sensors 34 and articulation sensors 46, to determine a load rating for the crane 10 based on the stability of the crane 10 about 3 tipping axes , described below as a :

- Mode A tipping axis (reference A in Figure 6) , being a tipping axis about the front wheel assemblies {e.g. about the front suspension, tyres or similar position) , since the load is typically suspended from the front of a mobile crane 10. If the mobile crane 10 carries a load somewhere other than over the front then a different Mode A tipping axis will be used, as will be apparent to the skilled person.

- Mode B tipping axis (reference B in Figure 6) , being a tipping axis generally through the wheel assemblies (e.g. about the suspension, tyres or similar position) on one side of the crane, being the side that crane is most likely going to tip over ; and

- Mode C tipping axis (reference C in Figure 6) , being an azimuthal axis, or axis parallel to the horizon, generally defined by the lines of roll (side tilt) and pitch (forward tilt) , or the plane of the slope of the chassis and generally through one wheel assembly (e.g. suspension or tyre) of the crane. The exception is that, when on level ground or when there is no roll (side incline) in the chassis, the Mode C tipping axis and Mode A tipping axis will coincide, and when there is no pitch (forward incline) in the chassis the Mode C tipping axis and Mode B tipping axis will coincide. The load rating calculation system 30 then takes the lowest load rating necessary to tip the crane 10 about the respective tipping axis A, B, C, and uses this lowest load rating as the load rating of the crane 10. There are many methods to calculate the load rating about a particular axis . One such method is to sum the load moments about the respective axis to identify a loaded centre of gravity. The weight of the load is then theoretically increased until the weighted centre of gravity falls on, or just over, the respective tipping axis .

In the system shown in Figure 6 the following apply:

- reference 80 is the front axle of the crane 10;

- reference 82 is the rear axle of the crane 10;

- the chassis of the crane is articulated and

therefore comprises a front chassis portion 84 and rear chassis portion 86, pivotally joined at an articulation point 88;

- reference 90 denotes the boom of the crane 10; and

- reference 92 denotes the load suspended by the boom.

In Figure 6 the roll angle or slope of the chassis 84, 86 tends downwardly toward the top of Figure 6 (i.e. the side of the chassis 84, 86 towards the top of the page is lower than the side towards the bottom of the page) and so the Mode B tipping line (generally designated ^¾B' in Figure 6) extends through the respective front and rear wheel assemblies towards the top of the page. The pitch angle of the chassis shifts the centres of gravity (discussed below) further forwards (i.e. to the right of Figure 6) if the pitch is negative: in other words chassis tends downwardly towards the front. The converse is true for positive pitch. In the present example, the pitch is negative. The centres of gravity should be found to make summing moments about each tipping axis easy. This can be done by traditional methods and need not be discussed herein. The centre of gravity of the load 92 will be at the load 92. In other words it is treated similar to a point load at the point of attachment of the load to the boom 90.

Similarly, the other centres of gravity are calculated as point loads . In the present example :

- point 94 is the centre of gravity of the rear body (i.e. the rear chassis portion 86, and the counterweight and other equipment supported on the rear chassis portion 86)

- point 96 is the centre of gravity of the front body (i.e. the front chassis portion 84, along with the cabin and other equipment, but exclusive of the boom 90) ; and

- point 98 is the centre of gravity of the boom 90.

If the load moments applied by the respective centres of gravity are applied about the Mode A tipping line (i.e. a tipping line extending through the front wheel assemblies of the crane 10 and generally designated 'A' in Figure 6) we note that the overall load moment is 'restorative' . A load moment is ^restorative' if the overall moment arm applied by the total mass of the system extends into the wheelbase of the crane. In other words, the centre of gravity of the system as a whole (point 100) is on the same side of the Mode A tipping line as the chassis of the crane and is on the opposite side of the Mode A tipping line relative to the position of the load 92. Where a load is restorative, the crane 10 is stable with respect to the relevant Mode.

In order to tip the crane about the Mode A tipping line, the load 92 will need to be (theoretically) increased until the centre of gravity of the system 100 coincides with the Mode A tipping line. The load 92 required to move the centre of gravity of the system 100 to the Mode A tipping line is the Mode A load rating of the crane, or the load rating of the crane about tipping line A. In this regard, if the centre of gravity of the system 100 is to the right of the Mode A tipping line (i.e. is on the opposite side of the Mode A tipping line to the chassis 84, 86) then the crane will be unstable and in danger of tipping, and the load thus exceeds the Mode A load rating. Similarly, the Mode B tipping line will typically be a line through each of a front and rear wheel assembly that is downhill relative to the other front and rear wheel assembly respectively (generally designated 'B' in Figure 6) . The load moments and load rating for the Mode B tipping line can be calculated in the same manner as described above in relation to the Mode A tipping line and need not be reiterated.

Since the centre of gravity of the system 100 is on the same side of the Mode B tipping line as the chassis 84, 86 (i.e. the centre of gravity of the system 100 is within the wheelbase of the crane) , the crane is unlikely to tip about the Mode B tipping line with the load 92 as shown. To determine the load rating for the Mode B tipping line the load 92 is (theoretically) increased until the centre of gravity of the system 100 coincides with the Mode B tipping line. The Mode C tipping line is the one azimuthal or horizontal tipping line, of all possible azimuthal or horizontal tipping lines, through the chassis about which the crane is most likely to tip. The Mode C tipping line will usually extend through one of the front wheel assemblies .

If the front wheel assemblies are therefore considered, and it is assumed the crane is most likely to tip downhill, then the downhill front wheel assembly

(generally designated 102 in Figure 6) is selected. An azimuth or horizontal line in the plane of the slope or incline of the chassis 84, 86 is then drawn through the relevant wheel assembly 102 , thereby defining a Mode C tipping line (generally designated 'C in Figure 6) .

In the same manner as mentioned above in relation to Mode A, the Mode C load rating can be calculated. As mentioned above, when the crane is on level ground or when there is no roll (side incline) in the chassis 84, 86, the Mode C and Mode A tipping lines will coincide. Similarly, when there is no pitch (forward incline) in the chassis 84, 86, the Mode C and Mode B tipping lines will coincide. Also, with reference to Figure 6, if the pitch is made positive instead of negative then the Mode C tipping line will extend through the wheelbase of the chassis 84, 86 (see broken line ^λ0' ' in Figure 6). The wheel on the same side of the Mode C tipping line as the load 92 will therefore serve to counteract any tipping force about the Mode C tipping line (i.e. the crane is stable for all relevant loads 92 about the Mode C tipping line) . Once each of the Mode A, Mode B and Mode C load ratings has been determined, the lesser of the three load ratings is taken to be the load rating of the crane. This load rating can then be further derated to account for a slope or incline in the chassis 84, 86. Dnder Australian

Standard AS1418.5, the load rating is derated by multiplying the calculated load rating by 66.6%. This load rating can be further derated depending on boom extension and other measurements in accordance with traditional load rating deration techniques .

In the example shown in Figure 6, the likely tipping line will be the Mode B tipping line , as the centre of gravity of the system 100 is much closer to the Mode B tipping line than either of the Mode A and Mode C tipping lines . This visual analysis will not always be definitive but in the present case, because of the relative closeness of the centre of gravity of the system 100 to the Mode B tipping line when compared with the Mode A and Mode C tipping lines, a reasonable assumption would be to assume the lowest load rating to be the Mode B load rating. Making deductions from visual analysis will often not be acceptable, particularly under the standards of the relevant jurisdiction, and in any case all three load ratings should be calculated.

It may be that other support equipment (e.g. outriggers) can be used to reduce the number of modes of tipping of the crane . In general , a method for calculating a load rating for a crane in accordance with the discussion in relation to the tipping modes above , will include :

calculating a load at which tipping of the crane will occur about each of two or more tipping axes , one of said tipping axes corresponding to a line through a body of the crane, the line having constant height with respect to a horizon (i.e. a Mode C tipping line); and identifying the lowest load of the calculated loads , as the load rating of the crane . The method of calculation can be any relevant method. The load rating calculation system 30 described above may comprise part of a crane 10. Alternatively, the load rating calculation system 30 may be retrofitted into an existing crane 10 by interfacing sensors 34 for measuring spatial positions of the chassis 22, 46 (e.g. inclines of the chassis 22) and/or an articulation of the chassis 22 with an existing computing unit of the crane 10, reprogramming a computing unit of the existing crane 10 to accept inputs from the newly interfaced sensors 34, 46, and calculating a load rating based on the inputs from the newly interfaced sensors 34, 46. The load rating calculation system 30 communicates with a Load Moment Indicator (LMI) control system 56 to limit motion of the boom 12. For example, when the load is approaching, or has reached, the load rating of the crane 10 as calculated by the load rating calculation system 30 , the LMI control system 56 may limit the extent to which the boom 12, load winch for lifting the load towards the boom 12, and hydraulic boom lift cylinders for lifting the boom 12, can respond to luff up and luff down, extend and retract, and winch up and winch down commands issued by the operator of the crane 10. A typical method for calculating the load rating for a crane 10 in a particular configuration of the crane 10 (i.e. tilt, articulation, boom extension etc), as shown in the flowchart in Figure 7 , will comprise :

measuring a spatial position of a body of the crane (at 58) ; and

calculating a load rating of the crane based on the measured spatial position (at 60) . In the present embodiment when a further measurement of the spatial position of the crane 10 is taken (at 62) , and that measurement indicates a change in the spatial position of the crane 10 the load rating is recalculated when (at 64) .

Similarly, for calculating a load rating for an

articulated crane 10 , taking into account a degree of articulation, the method will comprise:

measuring an articulation of a body of the crane (at 66) and

calculating a load rating of the crane based on the measured articulation (at 68) . Again, in the present embodiment when a further

measurement of the articulation of the crane 10 is taken (at 70) , and that measurement indicates a change in the spatial position of the crane 10 the load rating is recalculated when (at 72) . The step of calculating the load rating (at 60, 64, 68 and 72) , includes calculating a load rating based on summing load moments as discussed above, about three tipping axes and taking the lowest load required to cause the crane 10 to tip as the load rating. A factor of safety will typically be built into the load rating so that the actual load rating of the crane 10 as displayed on the display 45 is proportionally less than the absolute load rating as determine by summing load moments. Further static or dynamic calculation methods for determining load ratings and tipping axes may be used, such as methods for calculating the tipping angle of the loaded centre of gravity and other methods as specified in jurisdictional and international standards and

conventions . The method may include further steps as would be evident from the formulae described above, such as summing load moments, and all such further steps are intended to fall within the scope of the present disclosure.

Persons skilled in the art will also appreciate that the method could be embodied in computer program code. The program code could be supplied in a number of ways , for example on a tangible computer-readable medium, such as a disc or a memory (for example, that could replace part of the memory of the processor) or as a data signal (for example, by transmitting it from a server) . For example, there may be provided a computer-readable storage medium containing instructions that, when executed by processor, cause the processor to receive a signal from one or more sensors, the, or each, signal relating to a spatial position of the body of a crane, and calculate, based on the respective signal , a load rating of the mobile crane in the manner described above. Similarly, there may be provided a computer-readable storage medium containing instructions that, when executed by processor, cause the processor to receive a signal from one or more sensors , the, or each, signal relating to an articulation of a body of a crane, and calculate, based on the respective signal, a load rating of the mobile crane in the manner described above . In each case , the load rating may be recalculated upon receipt of a signal indicating a change in the spatial orientation or articulation of the crane as the case may be. As mentioned above, the spatial orientation of the crane can include an incline of the body of the crane .

It will be understood to persons skilled in the art of the present disclosure that many modifications may be made without departing from the spirit and scope of the present teachings. For example, any quantities, measurements and dimensions specified herein and given by way of example, for illustrative purposes only. It will be appreciated that other such quantities, measurements and dimensions may be used. Similarly, not all sensors specified herein will form part of each crane. Instead, various

combinations of sensors may be used. For example, some cranes will have no counterweight sensors .

In the claims which follow and in the preceding

description of the present disclosure, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense , i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the systems and methods described herein.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country .

Claims

What is claimed is: 1. A load rating calculation system for a mobile crane, comprising:

one or more sensors to measure a spatial position of, and/or an articulation of, a body of the mobile crane; and a signal processor comprising:

a load rating calculator in communication with the sensor signal receiver to calculate a load rating of the mobile crane based on the signal of the respective sensor.

2. A crane including a load rating calculation system according to claim 1.

3. A method for calculating a load rating for a crane , comprising:

calculating a load rating of the crane based on the measured spatial position and/or articulation .

4. A method for calculating a load rating for a crane , including :

calculating a load at which tipping of the crane will occur about each of two or more tipping axes , one of said tipping axes corresponding to a line through a body of the crane, the line having constant height with respect to a horizon; and

identifying the lowest load of the calculated loads , as the load rating of the crane .

5. A computer-readable storage medium containing instructions that, when executed by a processor, cause the processor to :

receive a signal from one or more sensors , the , or each, signal relating to a spatial position, and/or an articulation, of a body of a crane; and