Method and apparatus for monitoring a load condition of a dragline

A dragline includes a boom, a bucket, a hoist rope from which the bucket is suspended from the boom, and a drag rope for dragging the bucket. Data is produced on the alignment, with respect to a vertical plane containing the boom axis, of at least one of the following dragline components:    This data can be used for controlling the load condition on the basis of the dragline.The data can be inputted to a man-machine interface, e.g. a display device, controlled by a human operator, and/or it can be inputted to control the drive of the hoist rope and/or of the drag rope, so as to decrease or cease drive in response to detected misalignment of dragline component(s).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to draglines and electric shovels, such as used in open cast (or open cut) mining, and more particularly to a method and apparatus for monitoring their boom load conditions. In what follows, the teachings are given for a dragline, it being understood that they apply mutatis mutandis to an electric shovel. A dragline is a piece of machinery used for scooping ground material by means of a bucket suspended from a boom.

2. Description of Related Art

FIG. 1is a simplified diagram of a classical dragline1. It comprises a base unit2, a boom4having a proximal end4adepending from the base unit and a distal end4bfitted with a pulley (also known as a sheave wheel)6, from which a bucket8is suspended by a metal (steel) cable, referred to hereafter as a hoist rope10. The base unit2comprises an elevated structure12for passing the hoist rope10to the pulley6. In the example, this structure includes a mast14at the front portion (seen from the pulley) and stays16, from which the hoist rope10connects to a drive point in the base unit2. The hoist rope is thereby driven from a motor drive in the base unit to raise and lower the bucket8as required. The boom4can be driven to swing in an azimuthal (horizontal) plane by an electric swing motor, and thereafter blocked at a set azimuth. In the example, the swing axis SW passes through the base unit2, the latter being mounted on rotary platform.

The bucket8is pulled towards base unit2substantially along the ground (horizontal) plane by another metal (steel) cable, referred to hereafter as a drag rope18, to carry out the scooping action. The drag rope18is attached at one end18ato anchoring points8a,8bof the bucket, so that bucket's opening8cis kept horizontal and facing the base unit2. The other end of the drag rope is connected to an electrically-driven winch (not shown) within the base unit2.

In operation, the distal end4bof boom4is initially positioned over the zone where material20is to be scooped, typically 70-100 m above the ground. The hoist rope10is initially adjusted to suspend the bucket8vertically (dotted lines) with its opening8cconfronting piled material20to be scooped. The drag rope18is then driven to exert a tractive force TF which drags the bucket along the ground plane, thereby picking up material20through the opening8c. At the same time, the portion of the hoist rope10hanging from the pulley6is lengthened to maintain the bucket suspended following along the horizontal path of the ground. After the bucket has been dragged over a certain distance, filled, and lifted at some distance above the ground by hoist rope, the boom4is swung to place the bucket over a dumping zone.

The bucket is then arranged to drop the material, e.g. by tilting the bucket using an appropriate mechanism.

The dragline constitutes a large scale structure, with a boom length of 80 meters or more and a bucket capacity of up to 250 tonnes. The forces exerted on the boom4result from a combination of the tractive force TF exerted by the drag rope18and the suspending force SF exerted on the hoist rope10. In particular, the hoist rope transfers a very high load to the boom, notably during the hoisting phases for lifting and during swinging of the boom.

Under ideal operating conditions, the bucket8, hoist rope10and drag rope18are maintained in azimuthal alignment with the principal axis of the boom BA (boom axis), i.e. the boom, hoist rope and drag rope are kept substantially in the same general plane, in alignment with the horizontal projection of the boom, as shown inFIG. 2. These alignments should ideally be maintained as the bucket8is pulled and the hoist rope10thereby subtends an evolving angle α (FIG. 1) with the vertical in the vertical plane containing the boom4. In this way, the forces TF and SF on the boom are coplanar with the boom and exert a compressive force on its structure. In particular, the lateral stress LS on the boom, which would exert a lateral bending moment, is zero under those ideal conditions.

To meet the load demands, the boom4constitutes a complex mechanical structure made of steel, typically as a trellis box frame. The boom is a major limiting factor in the production rate of the dragline.

If the boom is overloaded, it will crack and cause downtime on the machine. If it is badly overloaded, it will cause complete failure of the structure. This is a major safety issue within a mine and can result in a fatal accident.

The boom4is usually specified for operation under these idealized working conditions, notably as regards its safe working load limits. With a proper control of the stresses within the boom structure, it would be possible to allow for a controlled overload of the dragline. This would give an improvement in output for a very low extra cost. Savings in terms of work efficiency under these circumstances can be typically on the order of hundreds of thousands of dollars per year per dragline.

It is known in the art to equip the boom with strain gauges at critical points to provide the dragline operator with a computer display showing stress-related parameters. This method, however, has the disadvantage of requiring rather complex calculations based on the boom structure characteristics, which may vary from one dragline to another.

SUMMARY OF THE INVENTION

The present invention is based on considering the real working conditions, and more particularly the observation that the aforementioned ideal coplanar alignment conditions of the boom4with the hoist rope10and/or the drag rope18and/or the bucket8are not always maintained.

Indeed, the bucket8can be dragged, and then hoisted, while it is out of alignment with the plane of the boom axis BA. This can arise since, even if the bucket's stable equilibrium point is in alignment with the boom axis when placed on the ground, it does not always advance smoothly when being dragged. For instance, the bucket can slide sideways on a slanted ground profile or the swing motors of the dragline can be activated while the bucket still has ground contact. Both—and other—effects can take the bucket some distance to one side or the other of the boom axis. This misalignment is a key issue notably during the hoisting and swinging phases for emptying the bucket8.

This situation is illustrated schematically inFIGS. 3a,3band3c, which illustrate respectively a laterally misaligned bucket8and hoist rope10during the scooping operation (bucket along the ground), during a bucket hoisting operation, and a boom/bucket swing operation. As shown inFIG. 3a, the hoist rope10is laterally misaligned by an angle β with respect to the vertical alignment of the boom axis BA. The force SF on that hoist rope thus creates on the boom4a lateral stress LS proportional to SF*sin β. When the hoist rope is raising the bucket and subsequently swinging it to a dumping point, the full weight BW of the suspended bucket and payload is applied to the distal end of the boom, with a consequently large lateral force component SF.

The risk of dangerous levels of lateral force LF is both of material damage to the boom and its fixtures, e.g. the mast14and stays16of the elevated structure12and to personnel operating in the vicinity should the boom become damaged or break. It is to be noted that a dragline boom4is of considerable cost to repair or replace, owing to its large size and special construction, and moreover the downtime on a dragline is also very costly in terms of lost production.

In view of the foregoing, the present invention seeks to assess the alignment/misalignment conditions of the boom, ropes and bucket, enabling to have at disposal critical information about the out of plane forces being applied to the dragline structure, or equivalently on an electric shovel.

The present invention offers a method and apparatus for automatically monitoring that the aforementioned alignment conditions with the plane of the boom axis, or equivalently on an alignment axis of an electric shovel.

More particularly, the invention provides, according to a first object, a method of monitoring a load condition of a dragline or an electric shovel, the dragline comprising a boom, a bucket, a hoist rope from which the bucket is suspended from the boom, and a drag rope for dragging the bucket, the boom extending substantially along a boom axis in its normal, unstressed state,

characterised in that it comprises the step of:using technical means to produce alignment data indicative of the alignment, with respect to the plane containing said boom axis, of at least one of the following dragline components:i) the hoist rope,ii) the drag rope,iii) the boom,iv) the bucket.

Optional aspects are presented as follows.

The method can be implemented as a method of controlling a load condition of a dragline or electric shovel, by further comprising a step of controlling the aforementioned load condition of the dragline or electric shovel on the basis of the alignment data.

The alignment data can be inputted to a man-machine interface, e.g. a display device, whereby the controlling step is performed via a human operator.

The alignment data can be inputted to automated control means for controlling at least one of:i) the drive motor(s) of the hoist rope,ii) the drive motor(s) of the drag rope,iii) the drive motor(s) of the boom, for swinging the boom,
to perform the controlling step.

The controlling step can be performed substantially in real time using a feedback of the alignment data.

The controlling step can be performed in a combined manner by a human operator via a man-machine interface and by automated control means.

The controlling step can comprises authorizing a controlled overload of the dragline or electric shovel, notably when controlling a maximum structure stress thereon, as a function of the alignment data.

The method can be implemented with a boom having a specified maximum load limit, wherein the controlling step can comprise authorizing a controlled overload of the boom above that specified load limit as a function of the alignment data.

In one embodiment the information on the alignment/misalignment is fed into the dragline or electric shovel control system to automate the response to a thus-detected overload condition, and to control the maximum structure stress. In this way, the controls can be slowed or otherwise modified intelligently to ensure that there is no excessive stress (dangerous level of stress) while applying a controlled overload above standard manufacturers' limits.

The technical means can be used to produce the alignment data as quantitative data indicative of an amount of misalignment in at least one aforementioned dragline component.

The alignment data can be obtained by measurement on a pulley along which the hoist rope passes to hang from a distal end of the boom.

The pulley can be configured to sway (i.e. tilt or lean sideways) in response to a lateral stress from the hoist rope, and the alignment data can be obtained by determining the amount of sway of the pulley.

The alignment data can be obtained by measuring a lateral stress exerted on the pulley, e.g. by strain gauge means on the pulley structure.

The alignment data can be obtained by physical contact with at least one aforementioned dragline component.

The method can comprise physically engaging the hoist rope with an angular or linear displacement sensor device.

The alignment data can be obtained by detecting a lateral deflection of the boom from the boom axis.

The lateral deflection can be detected by producing an optical beam from a source attached to the boom, preferably at or near a distal end, and detecting a displacement of the beam spot where it impinges a target.

The alignment data can be obtained by imaging at least one dragline component.

The method can comprise imaging the hoist rope using camera means.

The alignment data can be obtained by analysing coordinate data from GPS receiver means, at least one GPS receiver being positioned on the boom.

The alignment data can be obtained by surveying techniques, to determine coordinate evolutions of a portion of the boom susceptible of deflecting laterally with respect to its boom axis.

The method can comprise surveying a target substantially at the distal end of the boom using a surveying device, preferably a self-tracking total station placed at a known reference point on the dragline.

According to a second aspect, the invention relates to an apparatus for monitoring a load condition of a dragline or an electric shovel, the dragline comprising a boom, a bucket, a hoist rope from which the bucket is suspended from the boom, and a drag rope for dragging the bucket, the boom extending substantially along a boom axis in its normal, unstressed state,

characterised in that it comprises means for producing alignment data indicative of the alignment, with respect to the plane containing the boom axis, of at least one of the following dragline components:i) the hoist rope,ii) the drag rope,iii) the boom,iv) the bucket.

The optional aspects presented above in the context of the method according to the first object can be applied mutatis mutandis to the apparatus according to the second object.

The alignment data can be used to assess/control loads on any component of the dragline or electric shovel, e.g. the boom4, the mast14, stays16, drag and hoist ropes8,18, bucket8, fixtures, mounts, the platform, axles, etc.

The description of the preferred embodiments is based on the dragline already described with reference toFIGS. 1 to 3inclusive. These figures and their description are not repeated for the sake of conciseness. The teachings can be transposed to an electric shovel.

In what follows, the terms lateral misalignment (or more succinctly misalignment), or angle of misalignment, are referenced with respect to the plane containing the axis BA of the boom4in its normal, straight (undeflected) condition. Unless otherwise stated, the boom axis BA refers to the theoretical axis with no lateral distortion.

For the hoist rope10, the lateral misalignment is assessed as an angle β on a vertical plane, transverse to the boom axis BA, subtended by the hoist rope with respect to the vertical.

For the drag rope18, the lateral misalignment is assessed as an angle on a horizontal plane, subtended by the drag rope with the projection of the boom axis BA on that horizontal plane.

For the boom itself, the lateral misalignment expresses a distortion of the boom in a lateral direction, causing the distal end4bof the boom to be laterally displaced in a horizontal plane with respect to its alignment along the (normal) boom axis BA.

The following embodiments of the invention describe a number of different means for detecting one or more among the following conditions:

i) a lateral flexing of the boom4,

ii) a line, or lines, of force having at least a component causing a lateral stress LS on the boom,

iii) a lateral misalignment of the hoist rope10, bucket8or of the drag rope18with respect to the boom axis BA.

The information is used for assessing and controlling the load conditions on the boom4, and/or any other component of the dragline, such as the mast14, stays16, elevated structure12components, anchoring points, linkages, the mounting platform, bearings, fixtures, etc.

First are described embodiments which use the pulley6suspending the hoist rope10at the distal end4bof the boom4as the means for detecting a lateral stress/lateral misalignment of the hoist rope.

FIG. 4illustrates a type of pulley mechanism sometimes used in draglines, in which the pulley6is mounted on bearings22which allow some controlled swaying, i.e. tilting movement of pulley axle24. In the figure, the pulley axle24is also shown in a tilted position (dotted lines) in response to the hoist rope10being laterally misaligned. The swaying force is transmitted by the hoist rope pressing on one of the inner sidewalls of the pulley's guiding groove. Assuming that the general plane of the pulley6sways to follow exactly the angle of the hoist rope's misalignment, the corresponding angular offset β of the pulley axle24when thus tilted is equal to the angle of the rope's misalignment.

FIG. 5shows a first embodiment based on the pulley mechanism ofFIG. 4, in which the swaying motion of the pulley and pulley axle is determined by distance measuring sensors. In the example, two distance measuring sensors26aand26bare provided on the surface portions of the bearing casing that confront respective outer side faces6a,6bof the pulley. The sensors26a,26bare arranged to measure the distance, respectively L1and L2, from their location to a respective outer side face6a,6bof the pulley, this distance being measured along a direction parallel to the unswayed pulley axle24, i.e. perpendicular to the pulley outer side faces when unswayed. The sensors26a,26bcan be of any known suitable technology, e.g. optical (such as laser based) or acoustic, comprising an optical/acoustic source and a sensor analysing the returned laser/acoustic signal to derive the distance measurements S1, S2.

The sensors26aand26bare mounted symmetrically such that when the hoist rope10is aligned with the boom axis, the distances L1and L2measured by the sensors26aand26bare the same. Differences between the distances L1and L2measured by the sensors therefore express the angle of inclination (swaying) of the pulley6, which itself corresponds substantially to the angle of misalignment β of the hoist rope. The values of L1and L2are supplied to an angular offset calculator28, which calculates values of the angle β from the relative values of L1and L2. The output of this calculator28is supplied to a boom strain evaluation unit30, which is programmed to output a boom strain value in response to the angle β, e.g. from a mathematical model or look-up tables, taking into account the forces exerted on the hoist and drag ropes. The boom strain value is then supplied to the controller(s)32for the drive motor(s) of one or several of the different motor drives of the dragline. The latter can be the motor drive for hoist rope10, the motor drive for the drag rope18and the motor drive for the boom swing. In this way, the motor drive(s) can perform a real-time feedback control of the dragline operating parameters to keep the boom stress under proper control, and optionally record the load values for servicing purposes. The controller(s) can be programmed to allow controlled overloads (beyond manufacturer's prescribed limits) of the dragline structure for maximum work output, while remaining below the thresholds of structural damage. The overload can e.g. be controlled to be temporary. The allowed degree of overload can also take into account such factors as: whether the dragline is in a dragging, hoisting or boom swing phase, rope tension values, the elevation angle of the boom, oscillations in the rope or boom, wind speed, state of the boom (e.g. whether repaired) etc. The drive can be controlled in real time in response to the alignment/misalignment information to adapt the drive speed or acceleration accordingly, notably by a reduction in acceleration or speed as a function of load/overload, or to stop the drive.

It will be appreciated that the controller(s)32can also be suitably programmed to control the motor drive directly in response to the values L1and L2, i.e. without recourse to the angular offset calculator28and/or boom strain evaluation unit30. In the example, the output of the boom strain evaluation unit30is also sent to a man-machine interface34. The latter is a personal computer type of apparatus with a data display screen placed on board the operator's cabin2b. The computer comprises software and firmware modules arranged to process the output from the boom strain evaluation unit30and produce in real time, in response, a synthesised diagram of the boom and with a representation of its distortion along a reference scale, possibly with other data, such as the estimated stress, load on the ropes, position of the bucket, duration of the lateral stress, suggested actions, etc. In addition, or alternatively, the data can sent to an audio and/or visible alarm, alerting the operator of a lateral stress beyond a determined threshold.

FIG. 6shows a first variant of the first embodiment, also based on the pulley mechanism ofFIG. 4, in which the swaying motion of the pulley6is measured by a rotation sensor36having a rotary disk38. The disk is provided with encoded indicia40readable by an optical sensor of the rotation sensor36. The optical sensor can be implemented using a CCD or an LED, according to known technology. The rotation sensor36delivers a signal indicating the instant angular position of a reference point on the disk38. That point can be set to coincide with the angular position of the assembly52,54when the hoist rope10when it is aligned with the boom axis BA.

The rotary disk38of the sensor is joined to the proximal end42aof rigid stem42, whose distal end42bis arranged to be resiliently biased firmly against the outer face of a flange6aof the pulley6to follow its lateral displacement. The distal end42bcontacts the pulley near the circumference and at a point vertically above or below the pulley axle24for maximum translational movement for a given angle of tilt, i.e. sway. Accordingly, the stem42causes the rotary disk38to turn as a function of pulley's swaying motion from its central position (the latter is illustrated in dotted lines). The rotation signal from the sensor36is sent to an angular offset angle detector44, similar to offset calculator28, calibrated to produce an indication of the misalignment angle β in response to the evolution of rotation sensor output as the pulley tilts.

Preferably, a concentric groove (not shown) is provided on the side face6aof the pulley to receive and guide the distal end42bof the stem, allowing it to maintain a fixed radial position with respect to the pulley's axle24, while allowing the pulley to rotate freely.

In the example, stem is generally straight up to the distal end42b, at the region of which it has a bend portion42cto place the contact point with the pulley entering from the side. The proximal end42aof the stem is laterally displaced from the pulley. This configuration of the stem and its positioning allows to follow the swaying motion of the pulley without interfering with the passage of the rope10.

Alternatively, the stem42can be made to divide into two branches at the distal end, forming a fork embracing the pulley with sufficient free space around the sides to accommodate for its tilting motion as it sways. The free ends of the fork are turned inwardly to contact a respective outer face of the pulley flanges6aand6b, again preferable near their circumference and above or below the pulley axle to convert the pulley's swaying or swinging motion into a substantial angular displacement of the stem.

Depending on the dragline, the response of the pulley bearing22, and its operating conditions, the angle of deflection determined by the rotation sensor36may not correspond to the actual misalignment angle β of the rope. In this case, an experimentally-determined scaling or correction factor may be used in the angular offset detector44.

Likewise, a similar correction factor can be applied in the embodiment ofFIG. 5if the swaying angle of the tilted pulley does not properly match the hoist rope's angle of misalignment.

In a further a variant, the rotary sensor and stem can be replaced by a feeler device, such as a spring loaded plunger projecting inwardly from the bearing housing and impinging one of the faces6aor6bof the pulley. Each plunger is associated to a sensor measuring its projection, corresponding to the distance L1or L2(cf.FIG. 4) to determine the amount of sway in the pulley, based on the known value of L1when there is no sway in the pulley. This variant can also be implemented with two feeler devices operating on opposite side faces6aand6bof the pulley, in a manner analogous to the embodiment ofFIG. 5, so delivering the two distance values L1and L2.

Conversely, the embodiment ofFIG. 5could be implemented with just one sensor device26aor26blaser beam, using the fact that the value of L1/L2or L2/L1when the pulley is unswayed (not deflected) is a known constant.

In a second embodiment, the pulley mechanism can also be used as a point of measurement of lateral stress on the boom4even if it not designed to allow the above-described swaying motion of the pulley6and axle24. In this case, the measurement can be effected by means of one or several strain gauges, as illustrated inFIG. 7.

As shown in the example ofFIG. 7, strain gauges46can be placed on the outer side faces of the flanges6a,6bof the pulley6and/or on the pulley axle24. The gauges are connected to a calculation unit (not shown) where the detected distortion is converted to a lateral stress LS value on the boom. This conversion can be established on the basis of prestored conversion tables obtained empirically from test data, or from mathematical modelling.

FIG. 8illustrates schematically a third embodiment of the invention, in which the alignment/misalignment of the drag rope10is also detected by mechanical means48. These comprise a short sleeve50, or alternatively a ring, surrounding the drag rope10, and by which lateral deflections of the rope are detected by angle sensors. The sleeve50is connected to the underside of the boom4by a mechanical assembly comprising two arms52,54which are mutually articulated to allow the sleeve50to follow the variations of the rope angle α in the vertical longitudinal plane as the bucket8is dragged (cf.FIG. 1). The lengths of the arms52,54are set to allow the sleeve50to follow the full amplitude of the evolutions of the angle α of the hoist rope10, without impeding the movement of the latter. The arm assembly52,54is rigid in the lateral direction, i.e. in the direction of lateral stress LS, and joins to a rotary sensor within a housing56fixed to the boom4.

As shown inFIG. 9, arm54of the assembly is attached to a rotary sensor disk38comprising encoded indicia40readable by an optical sensor device36, analogous to the sensor36ofFIG. 6, and which can also be implemented using a CCD or a LED, according to known technology. The sensor36delivers a signal indicating the instant angular position of a reference point on the disk. That point can be set to coincide with the angular position of the assembly52,54when the hoist rope10is aligned with the boom axis BA. The output from the sensor is pre-processed by an angular offset calculator28, which produces the value of the deflection angle β of the rope as the disk38is caused to rotate by the arm assembly52,54.

The calculator28is similar to the one ofFIG. 4used to express the rope angle β. This angle value is inputted to a boom strain evaluation unit30which is also fed with the values of the loads on the ropes10and18to produce monitoring and alarm information to a man-machine interface34. The latter is substantially the same as in the first embodiment, producing equivalent PC display data and audio/visual alarms signals as described above. The boom strain evaluation unit30also delivers signals to one or several motor drive controls32for real time automated control of the dragline load parameters, as described above, notably allowing a controlled overload.

To minimise interference with the natural movement of the rope10, the inside of the sleeve50is equipped with a set of four rollers58whose axes are along respective sides of a square. The rollers surround the rope10, and each one has a concave profile to follow its contour.

In variants of this second embodiment, the rotation angle sensor can be replaced by a linear displacement sensor, with appropriate adaptation of the linkages to the hoist rope10, or drag rope18.

FIG. 10illustrates a fourth embodiment of the invention based on an optical laser60fixedly mounted on the distal end4bof the boom, shown here in a plan view. The laser60is powered to generate a laser beam62which impinges on a target zone64provided on the front face2a(line I-I) of the base unit2, where it creates a detectable beam spot65. The laser is positionally referenced so that its beam62is aligned to follow the boom axis BA when the boom is in its normal state, with no lateral distortion. The beam spot65in this case impinges at a point along a vertical line where the proximal end4aof the boom is centred. The vertical position of the spot depends on the inclination of the boom. Its lateral position along the target zone64depends on a lateral distortion of the boom4: as the boom experiences a lateral stress, its distal end4bis deflected in the direction of stress, and the laser60fixed at that point is no longer directing the beam spot65′ on the vertical centerline, as shown in dotted lines. The displacement SD of the beam spot65′ from the vertical centerline expresses the amount of lateral distortion, and provides a sensitive measurement of that parameter by the virtue of the considerable optical lever effect.

The target zone64is monitored by a video camera66mounted on the base unit2by means of a forwardly projecting bracket68. The raw signal from the camera is supplied to a video signal processor unit70which emphasises the image of the beam spot65,65′. The output from the processor unit70is supplied for display on a monitor72located at the dragline's control cabin2b, where it acts as a man-machine interface for monitoring the lateral stress LS on the boom4. The monitor72, also referred to as video monitor, can be a computer monitor connected to a PC type computer. In this way, it is amenable to display computer generated data. The information can be complemented by markings delimiting limits L on either side of the vertical centerline, beyond which the flexing of the boom has attained a danger threshold. These markings can be painted on the part of the front2aof the base unit that serves as the target zone64, or inserted electronically by the video signal processor70. Other markings can be provided in the same way to indicate e.g. graduations of lateral deflection SD, possibly in units expressing force or percentages of the safe working limit. The contents of the display thus comprise the above reference markings and a real-time representation of the beam spot65,65′.

In this way, the operator OP observing the video monitor72can use this technical information to monitor the lateral distortion of the boom at any time and derive a warning of damaging lateral stresses on the boom.

The output of video signal processor70is also applied to a computerised evaluation unit74programmed to detect automatically the position of the beam spot65,65′ and react accordingly. The reaction can be a warning signal detectable by the human operator OP, or a command to one or several of the motor drive controls32already described, e.g. to reduce or halt the application of the towing force TF on the drag rope18and/or the force SF on the hoist rope10, or again the swinging motion of the boom4.

The evolution of the lateral position of the beam spot can thus be exploited in an automated or human feedback control of the dragline's operating conditions, notably of the load applied to the drag rope and/or the hoist rope, boom swing, as explained above.

FIG. 11illustrates a fifth embodiment of the invention, also based on optical means, which in this case serve to monitor the alignment of the hoist rope10and bucket8. The monitoring is obtained by a video camera76mounted on the boom4, with the lens directed to image the hoist rope10suspended from the pulley6. The camera's field of view is adjusted against a graticule78which serves as a reference for assessing the rope's lateral alignment/misalignment. The graticule can be physical markings78aon a transparent plate in front of the camera lens, or it can be inserted electronically. In the example, the graticule is designed to show a vertical centerline against which the image10I of the hoist rope10coincides when in correct lateral alignment, and a set of inclined lines converging towards the top, associated with indicia78bto enable the operator OP to assess the degree of rope lateral misalignment.

The video output of the camera76is sent to a video signal processor70′, similar to processor70described above, but optimised to enhance the visibility of the rope's image10I and to insert the graticule78when it is created electronically. The output of the video signal processor70′ is sent to a video monitor72at the operator's cabin2b, as in the previous embodiment, where it displays for the operator OP the rope's image10I and graticule78(box79). In this way, the video monitor also provides a man-machine interface producing technical information so as to enable the operator to assess the rope's lateral alignment/misalignment. The video monitor72can be the computer monitor associated to a PC as described with reference to the previous embodiments, or simply a TV monitor.

The video signal processor70′ also extracts and exploits the pixels of the rope's image10I to derive computer exploitable data on the rope's lateral inclination angle β. This data is supplied to an evaluation unit74′, similar to evaluation unit74described above, adapted to use that inclination angle data in conjunction with the instantaneous load values applied on the drag ropes10,18, supplied as input parameters. In this way, it determines the lateral stress LS on the boom4and acts on the motor drive control(s)32as described above to adjust in real time the load on the ropes10,18and if needs be the boom swing dynamics accordingly.

Likewise, the operator OP can exploit the rope inclination data with his knowledge of the instantaneous loads applied to the ropes to assess the risk of boom damage. As in the previous embodiment, the information from the video signal processor70′ or evaluation unit74′ can also be used to trigger an alarm signal detectable by the operator when a certain risk level is detected or to influence the respective drive motors. In certain cases it may be beneficial to only show the derived load characteristics data to the operator.

The camera76can be placed at any suitable point along the length of the boom, based on the following considerations: the closer it is to the pulley6, the closer it will be to the rope10, and hence the better the viewing position, while the further it is from the pulley, the greater the absolute lateral displacement of the rope for a given misalignment—and hence the easier to detect that misalignment.

In a variant, a camera80can be arranged to view the bucket8instead of the rope10, for instance by being placed at the front face2aof the base unit, at a position in vertical alignment with the proximal end4aof the boom4. The video signal processor70′ is then optimised to analyse the contours of the imaged bucket and thereby determine the lateral position of its centerline. This variant has the advantage of placing the camera80at a zone that is relatively more sheltered and stabilised, and of using a larger object (bucket) as the imaging target, compensating for the additional viewing distance.

Naturally, it is possible to implement both cameras76and80, and possibly others, so as to provide the operator OP/evaluation unit with multiple image data for analysing the operating conditions.

FIGS. 12aand12billustrate another variant in which a video camera82is arranged to provide a plunging view of drag rope10. In the example, the camera82is mounted on a bracket84projecting from the distal end4bof the boom4. The camera82is located forward of the vertical from the pulley6and turned at an angle towards the ground zone where the bucket8operates, so as to provide a field of view as shown by the broken lines FOV. The field of view covers both the hoist rope10(foreground) and the drag rope18(background), as well as the bucket8. The vertical centerline of the camera image86coincides with the vertical projection of the boom axis BA when the boom is not deformed, and hence also with the lateral alignment of the drag rope18and hoist rope10under correct working conditions (FIG. 12b). As shown more particularly inFIG. 12b, the camera86can thereby detect a lateral misalignment of the hoist rope10, drag rope18and bucket8(representation in dotted lines). As in the other embodiments, the signal from the camera82is processed as already described with reference toFIG. 11to produce the image86on the operator's video monitor72and/or for exploitation by an evaluation unit74′ controlling the motor drive control(s) in the manner described above.

The camera arrangement ofFIGS. 12aand12bcan be implemented in addition to the camera arrangements described with reference toFIG. 11, providing a further source of visual monitoring information and/or computer data on the alignment conditions.

FIG. 13illustrates a sixth embodiment based on GPS receivers to detect a lateral distortion of the boom4arising from a lateral stress LS. In the example, three GPS receivers GPS1, GPS2and GPS3are positioned along the longitudinal axis of the dragline containing the boom axis BA. A first GPS receiver GPS1is fixed onto base unit2of the dragline, for which it constitutes a fixed reference point. The other two receivers, GPS2and GPS3, are fixed respectively at the proximal and distal ends4aand4bof the boom4.

The three GPS receivers obtain their coordinate position data from satellites S1, S2, S3, . . . at frequent intervals, say every second. They send these coordinate position data by wire or wireless link to a GPS coordinate comparison unit88, where they are analysed. The GPS coordinate comparison unit initially stores the coordinate position data of the three GPS receivers corresponding to the current location of the dragline and in a condition where the boom is not submitted to a lateral stress. The coordinate data from receivers GPS1and GPS2, respectively at the base unit2and at the proximal end4aof the boom, serve to determine the theoretical orientation of the boom with respect to a fixed coordinate system as the boom axis BA swings (axis SW,FIG. 1). From the coordinate data of receivers GPS1and GPS2, the comparison unit88can thus determine by extrapolation the three-dimensional coordinates of any point lying on the boom axis BA, under a condition of zero lateral stress (theoretical boom axis), and conversely can verify whether a given three-dimensional coordinate lies on that axis or not.

In this way, it verifies whether or not the coordinate data from third receiver GPS3, at the distal end4b, lies on the theoretical boom axis BA. More particularly, it assesses, by standard transformation techniques, the amount lateral deflection of the distal end4bof the boom from the theoretical boom axis BA, resulting from a lateral stress LS. By a similar technique, it can also measure, if needs be, a sag of the boom in the vertical plane.

The calculated value of the lateral deflection of the boom is supplied to a boom strain evaluation unit30as described above, which determines the response to take as a function of the amount of estimated lateral stress, based on the deflection data, as well as possibly other parameters, such as the load on the ropes10,18, motor drive parameters, etc.

The response takes the form of a signal or data sent in adapted form to a man-machine interface34of the type described above.

The boom strain evaluation unit30can also be adapted to supply signals to a feedback loop with the motor drive control(s)32for the hoist rope, drag rope or boom swing drive(s), as already described.

For enhanced accuracy of the GPS coordinate data, the GPS coordinate comparison unit88may be connected to a nearby land-based GPS correction signal station92, if available, e.g. by a radio link94.

Another approach uses 3 GPS units distributed on the boom, e.g. one at its proximal end, one in the middle, one at its distal end, to assess the boom curvature as a consequence of lateral load forces.

FIG. 14illustrates a seventh embodiment of the invention in which a lateral deflection of the boom4resulting from lateral stress LS is detected by surveying techniques. The concept uses a surveying device located at a fixed position with respect to the base unit2or the proximal end4a, adapted to monitor the azimuthal angle of the distal end4brelative a reference axis, suitably the undeflected boom axis BA.

In the example, this technique is implemented by an auto-tracking total station96fixed on the base unit2and positioned in alignment with the boom axis BA. The total station96is trained on a target98, such as an optical prism or mirror, used in surveying. The auto-tracking function of the total station96allows the latter to follow automatically the movements of the distal end4bof the boom and to provide continuous information on the evolution of its azimuthal angle, which is normalized to the deflection angle of boom. The deflection angle data is processed by a boom strain evaluation unit30, analogous to the one described e.g. with reference toFIG. 5, and which sends signals to the motor drive control(s)32and/or to a man-machine interface34as explained above.

Further embodiments of the invention can be implemented by monitoring the torque on the shaft of the swing axis SW of the boom structure (cf.FIG. 1). In this case, a feedback monitor circuit can be placed in the swing motor drive used for swinging the boom structure. The monitor circuit can determine the turning moment on the swing axis SW, e.g. when the bucket8is being dragged, that turning moment resulting from a misalignment of the suspending and drag ropes8and18. The turning moment can be evaluated by various techniques, e.g. by measuring the torque to be applied by the drive motor to compensate for that moment.

FIG. 15illustrates schematically a real-time feedback control system100suitable for the motor drive of any one of the hoist rope drive, drag rope drive, or boom swing drive. This feedback control system, typically in the form of a servo system, can be applied to any of the embodiments having been described. It may, for instance, be functionally integrated with the evaluation unit74or motor drive control32.

The system takes as input the alignment data acquired concerning the alignment/misalignment of the boom structure4, hoist rope10, drag rope18or bucket8, which is assimilated to a low frequency measurement. Typically, that data is delivered in adapted form by the boom strain evaluation unit30, or the evaluation unit74,38′, or the like. The values of the parameters evaluated, which are indicative of lateral boom stress or a risk of lateral boom stress, are submitted to a threshold detector102, which assesses whether one or several graded stress limit values are reached. The output of the threshold detector is applied to a first mixing input104aof a signal mixer or combiner104having a second input104bfor accepting command drive signals from the operator OP. The operator acts through a command interface taking into account the alignment data produced on his man-machine interface34.

The output of mixer/combiner104produces the motor drive commands. In this example, the command is a weighted or equal combination of inputs from both the operator and an automated analysis of the alignment conditions. The system can thus allow a manual override to a certain degree, or e.g. produce automatically an operational stress limit envelope within which the operator is free to fix the values. In variants, the mixer104can be omitted, whereby the control is entirely manual, based on the operator's information produced on the man-machine interface indicating the acquired alignment/misalignment conditions, or alternatively entirely automated. In the latter case, the alignment data is sent directly to the motor drive(s)32, if needs be via the threshold detector32. The latter can be omitted in variant embodiments.

The control means100is in a feedback loop, with the detection of the alignment/misalignment condition feeding back information in real time to implement the control performed by the motor drive command. The alignment/misalignment data can be sampled at a suitable frequency to ensure a real-time or quasi real time control of the drive and load conditions.

The implementation of the command system can be based on any suitable servo control loop using standard engineering practice.

The operator and/or automated control may be provided with limit stress values corresponding to maximum boom load limits, typically standard manufacturers limits. This maximum load data can be presented in the form of graphical charts, or indicia on a load indication scale presented on the man-machine interface, or it can be in the form of stored machine readable data in look-up tables or a database.

The experience of the human operator allows him to determine if and when an indicated overload can be tolerated, for instance in certain phases, or for certain periods, taking various parameters into account.

For an automated feedback control of drive motors, the maximum load values can be exploited similarly to command intelligently an overload under specific programmed conditions, taking into account other parameters, e.g. based on fuzzy logic techniques.

In this way, the human operator and/or the automated feedback control can control the operation of the dragline with substantially no excessive stress while being under conditions at—or controllably exceeding—standard manufacturer's limits for the boom and possibly other critical components such as the mast14, stays16, ropes10,18, bucket8, platform, anchoring points, etc.

It will be appreciated that the above-described alignment monitoring and human or automated control of the hoist rope and/or drag rope and/or boomswing drive motor(s), as a function of that monitoring, can take place at all times or whenever judged necessary. The above-described monitoring and human or automated control can be carried out notably during:a dragging operation for loading the bucket,a hoisting operation for raising or lowering the bucket,a swinging operation for moving the bucket to a dumping zone,any other phase of operation of the dragline.

In the example ofFIG. 15, the signals from the mixer/combiner104are used to command respective motor drive controls32for:a hoist rope motor106, which is provided at the base unit2to wind/unwind the hoist rope10from the base unit2. The command can serve here e.g. to establish the appropriate wind/unwind speed, acceleration/deceleration, stoppage of the hoist rope;a drag rope motor108, which is provided at the base unit2to wind/unwind the drag rope18from the base unit2. The command can serve here e.g. to establish the appropriate wind/unwind speed, acceleration/deceleration, stoppage of the drag rope; anda boom swing motor110, which is provided at the base unit2to swing the boom4laterally e.g. to position the bucket8from a drag zone to a dumping zone, the swinging being around the swing axis SW at the base unit as shown inFIG. 1. The command can serve here e.g. to establish the appropriate swing speed, acceleration/deceleration, stoppage of the boom4, in either direction.

It also possible to adapt the above-described embodiments of the invention to analyse the alignment of the drag rope18and/or the bucket8, instead of or in addition to the alignment of the hoist rope10.

Thus, for the embodiment ofFIG. 11, the camera76, or an additional camera, may also be arranged to monitor the alignment of the drag rope18, e.g. by being placed at some point along the boom4and directed towards the ground, with a field of view covering the zone occupied by the drag rope and bucket. The electronic image can be referenced and processed in the same manner as described for the camera image46, but to determine the angle subtended by the drag rope18with respect to the boom axis BA.

In a similar manner, in the embodiment ofFIGS. 12aand12b, the camera50, or an additional camera, may be arranged at some point along the boom and directed to focus more particularly on the alignment of the drag rope18.

Also, the embodiment ofFIG. 9can be implemented on the drag rope18in addition to, or instead of, being implemented on the hoist rope. The sleeve50would in that case surround the drag rope18at some point between the bucket8and the base unit2, and be coupled to the rotary sensor unit56by an adapted arm and bracket device.

The measuring/analysing devices (lasers, cameras, sensors, GPS receivers gauges, etc.) and the functional hardware and software units described in the above embodiments can be powered by any suitable means (power cable, battery pack, solar cells, etc.), and can likewise communicate by any suitable means (wire data link, optical data transmission, radio link, wireless communications protocol (WiFi, Bluetooth, . . . ), etc.).

From the foregoing, it will be understood that the invention can implemented in numerous ways and with numerous techniques, e.g. laser and optical lever, electronic image acquisition, telemetry by radio signals, such as GPS receivers, mechanical sensing on the rope and/or pulley, surveying, etc.

The measurements can be of the actual lateral distortion of the boom, the stresses applied to the boom and their lateral force component, or the angle of misalignment of the hoist and/or drag rope(s) with respect to vertical projection of the boom axis, etc.

It will be apparent that the different embodiments described accommodate for transpositions of means and/or techniques from one embodiment to other. Also, a number different embodiments can be implemented together in a dragline or electric shovel to provide respective complementary sources of alignment data.

Also, the hardware and software aspects of embodiments can be implemented in many different equivalent forms in addition to those described in the examples.