MEASUREMENTS IN A MINING VEHICLE

TECHNICAL FIELD

The invention relates in general to mining vehicles that are used to carry loads, such as loaders and haulage trucks . In particular the invention relates to making measurements in such vehicles, for example in order to eventually keep track of the weights of carried loads . In this text the concept of weight is used in its everyday meaning, which in exact physical sense is actually mass.

TECHNICAL BACKGROUND

A mine, quarry, or underground tunnel in construction constitutes a very special environment for vehicles, with many characteristics that are seldom or never found to the same extent in other environments. Large, heavy loads of very coarse material such as stone need to be detached, moved, and transported on roads or tracks that may be extremely uneven compared to normal roads. Particulate, gaseous, and liquid contaminants such as dust, sand, fumes, and mud appear in large and widely varying amounts . Temperatures may vary rapidly across even quite short distances, such as along an ascent route for example where the vehicle rises to a significantly different depth in a short time .

These conditions make it very difficult to measure physical loads with sensors installed in the vehicles. As an example, one may consider the task of repeatedly weighing a loader, haulage truck, articulated hauler, or other heavy off-road mining vehicle in order to keep track of how much stone has been transported from one place to another. Setting up a fixed weighing station with scales, through which the vehicle should drive with every load, would be too inflexible so it is generally preferable to install sensors to the vehicle itself. The sensors may comprise e.g. strain sensors fixed to the axles and/or suspension of the vehicle. A load on the bed of the vehicle causes elastic deformations in the axles and suspension, the extent of such deformations being proportional to the weight of the load. In principle it is possible to make a control circuit receive and store the output signal (s) of the strain sensor (s) and calculate the weight of each load based on the received signals .

In practice it has been found that weighing a vehicle of said kind based on integrated strain sensors may give unreliable and inaccurate results.

SUMMARY

It is an objective to present methods, devices, and arrangements for making measurements in a mining vehicle in a reliable and accurate way. Another objective is to ensure that these methods, devices, and arrangements adapt to environmental conditions that are difficult or impossible to predict beforehand. A further objective is to present methods, devices, and arrangements of said kind that are applicable in a wide variety of mining vehicles. Yet another objective is to make such methods, devices, and arrangements advantageous from the viewpoint of manufacturing, installing, and maintenance costs.

According to a first viewpoint, these and further advantageous objectives are achieved by using the sensor data to repeatedly detect moments when a tare of the vehicle can be measured, and by using the tare thus detected to calculate load weights. According to the established meaning of the word, the tare of a vehicle means its empty weight, i.e. weight with- out load . In other words , the sensor data can be used to repeatedly tare the vehicle at moment s that were detected suitable for that .

According to a second viewpoint , these and further advantageous obj ective s are achieved by as sembling the sensor arrangement so that it produces inherent compensation data that can be used to compensate for systematic errors in the original sensor data .

According to a first aspect there is provided a method for measuring the weight of a mining vehicle capable of transporting a load . The method comprises receiving a first load signal from a strain sensor arrangement , said f irst load signal being indicative of a weight of the vehicle , and receiving a first orientation signal from an orientation sensor arrangement , said f irst orientation s ignal being indicative of a relative orientation of at lea st one load-carrying part of the vehicle . The method comprises determining an end of an unloading event using at least said first orientation signal , determining a tare value of said first load signal at or after said determined end of an unloading event , and us ing said tare value to represent the mea sured empty weight of the vehicle .

According to an embodiment said end of an unloading event i s determined as an observed return of the value of said first orientation signal to a transport value range after the value of said first orientation signal has been in an unloading value range .

According to an embodiment said first orientation signal i s indicative of a tilting angle between a bed and a body of the vehicle .

According to an embodiment the method comprises receiving a first movement s ignal from a motion sensor arrangement , said first movement signal being indicative of a movement of the vehicle as a whole , and determining a stand- still event following said determined end of the unloading event us ing at least said first movement signal . The method may then comprise performing said determining of the tare value at or after said determined stand-still event .

According to an embodiment said stand-still event is determined as an observed remaining of the value of the first movement signal within a standstill value range for a predetermined duration of time after said determined end of an unloading event .

According to an embodiment said determining of a tare value comprises low-pa s s filtering a sequence of received values of said first load signal during a period of time after said determined end of the unloading event .

According to an embodiment the method comprises storing a plurality of tare value s , each determined after a respective determined end of a respective unloading event , and determining a baseline drift as a function of time by fitting a curve to said stored plurality of tare values . The method may then comprise using said determined baseline drift as a reference in determining weights of loads carried by the vehicle .

According to an embodiment the steps of receiving said f irst load signal and said first orientation signal and determining said end of an unloading event and said tare value of said f irst load s ignal are executed on board of the mining vehicle .

According to an embodiment the steps of receiving said f irst load signal and said first orientation signal and determining said end of an unloading event and said tare value of said f irst load s ignal are executed in a monitoring system out side the mining vehicle .

According to an embodiment the method comprises receiving a second load signal from said strain sensor arrangement , sard second load signal being indicative of an output value of a similar strain sensor at the same location as one emitting said first load signal but without dependency on the weight of the vehicle ; determining a compensated load signal using the difference between the f irst load s ignal and the second load signal , and using said compensated load signal to represent the weight of the vehicle .

According to a second aspect there is provided a method for measuring the weight of a mining vehicle capable of transporting a load . The method comprises receiving a f irst load signal from a strain sensor arrangement , said first load signal originating from a first strain sensor and being indicative of the magnitude of an elastic deformation caused by a weight of the vehicle at a first location in the vehicle where the strain sensor arrangement i s installed . The method comprises receiving a second load s ignal from the strain sensor arrangement , said second load s ignal being indicative of an output value of a second, s imilar strain sensor as the f irst strain sensor but without dependency on the weight of the vehicle . The method comprise s determining a compensated load signal us ing the difference between the first load s ignal and the second load signal , and using said compensated load signal to represent the weight of the vehicle .

According to a third aspect there is provided a system for measuring the weight of a mining vehicle capable of transporting a load . The system comprises receiving means configured to receive a first load signal indicative of a weight of the vehicle and a first orientation signal indicative of a relative orientation of at least one load-carrying part of the vehicle , and proces sing means conf igured to determine an end of an unloading event using at lea st said first orientation signal and a tare value of said first load signal at or after said determined end of the unload- mg event . The system is configured to use said tare value to represent the measured empty weight of the vehicle .

According to an embodiment the receiving means are additionally configured to receive a first movement signal indicative of a movement of the vehicle as a whole . The proces sing means may then be additionally configured to determine a stand-still event following said determined end of an unloading event using at least said first movement signal . The proces s ing means may be configured to perform said determining of said tare value of the first load signal at or after said determined stand-still event .

According to an embodiment said receiving means and proce s sing means are located on board of the vehicle .

According to an embodiment said receiving means and proces sing means are located at a location external to the vehicle .

According to an embodiment said receiving means are configured to remotely receive said first load signal and said first orientation signal .

According to an embodiment the system comprises at least one sensor for generating at lea st one of said first load signal and said f irst orientation signal .

According to a fourth aspect there is provided a system for measuring the weight of a mining vehicle capable of transporting a load . The system comprises at least one proces sor and computer program code that , when executed on said at least one proces sor , cause s the system to at lea st receive a first load signal from a strain sensor arrangement , said first load s ignal being indicative of a weight of the vehicle ; receive a f irst orientation signal from an orientation sensor arrangement , said f irst orientation signal being indicative of a relative orientation of at least one load-carrying part of the vehicle ; determine an end of an unloading event using at lea st said first orientation signal ; determine a tare value of said first load signal at or after said determined end of the unloading event ; and use said tare value to represent the measured empty weight of the vehicle .

According to an embodiment the computer program code causes , when executed on said at least one proces sor , the system to receive a f irst movement signal from a motion sensor arrangement , said first movement signal being indicative of a movement of the vehicle a s a whole ; determine a stand- still event following said determined end of an unloading event using at least said first movement signal ; and perform said determining of said tare value of said first load signal at or after said determined stand-still event .

According to a fifth aspect there is provided a system for measuring the weight of a mining vehicle capable of transporting a load . The system compri ses a strain sensor arrangement that comprises at least a first strain sensor and a second, similar strain sensor . The system comprises attachment means for attaching said strain sensor arrangement to a first location in the mining vehicle such that a first load signal originating from said f irst strain sensor becomes indicative of the magnitude of an ela stic deformation caused by a weight of the vehicle at said first location while a second load signal originating from said second strain sensor remains without dependency on the weight of the vehicle . The system comprise s proces sing means for determining a compensated load signal using the dif ference between the first load signal and the second load signal .

According to a sixth aspect there is provided a system for measuring the weight of a mining vehicle capable of transporting a load . The system comprises at least one proces sor and computer program code that , when executed on said at least one processor, causes the system to at least receive a first load signal from a strain sensor arrangement, said first load signal originating from a first strain sensor and being indicative of the magnitude of an elastic deformation caused by a weight of the vehicle at a first location in the vehicle where the strain sensor arrangement is installed; receive a second load signal from the strain sensor arrangement, said second load signal being indicative of an output value of a second, similar strain sensor as the first strain sensor but without dependency on the weight of the vehicle; determine a compensated load signal using the difference between the first load signal and the second load signal; and use said compensated load signal to represent the weight of the vehicle.

According to a seventh aspect there is provided a measurement unit for measuring the weight of a mining vehicle capable of transporting a load. The measurement unit comprises at least one processor and computer program code that, when executed on said at least one processor, causes the measurement unit to at least receive a first load signal from a strain sensor arrangement, said first load signal being indicative of a weight of the vehicle; receive a first orientation signal from an orientation sensor arrangement, said first orientation signal being indicative of a relative orientation of at least one load-carrying part of the vehicle; determine an end of an unloading event using at least said first orientation signal; determine a tare value of said first load signal at or after said determined end of the unloading event; and use said tare value to represent the measured empty weight of the vehicle.

According to an embodiment the computer program code causes, when executed on said at least one processor, the measurement unit to receive a first movement signal f rom a motion sensor arrangement , said first movement signal being indicative of a movement of the vehicle as a whole ; determine a stand-still event following said determined end of an unloading event using at lea st said first movement signal ; and perform said determining of said tare value of said first load signal at or after said determined standstill event .

According to an eighth a spect there i s provided a measurement unit for mea suring the weight of a mining vehicle capable of transporting a load . The measurement unit comprise s at least one proce s sor and computer program code that , when executed on said at least one proces sor , causes the measurement unit to at least receive a first load signal from a strain sensor arrangement , said f irst load s ignal originating from a first strain sensor and being indicative of the magnitude of an elastic deformation caused by a weight of the vehicle at a first location in the vehicle where the strain sensor arrangement i s installed ; receive a second load signal from the strain sensor arrangement , said second load s ignal being indicative of an output value of a second, similar strain sensor as the first strain sensor but without dependency on the weight of the vehicle ; determine a compensated load signal using the dif ference between the first load signal and the second load signal ; and use said compensated load signal to represent the weight of the vehicle .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings , which are included to provide a further understanding of the invention and constitute a part of this specification , illustrate embodiment s of the invention and together with the de scription help to explain the principles of the invention . In the drawings : Figure 1 illustrates a known mining vehicle with its bed empty, figure 2 illustrates the known mining vehicle with its bed full , figure 3 illustrates an example of recorded sensor data , figure 4 illustrates an example of recorded sensor data , figure 5 illustrates an example of recorded sensor data , figure 6 illustrates a mining vehicle , figure 7 illustrates a mining vehicle unloading , figure 8 illustrates a method in the form of a state diagram, figure 9 illustrates an a spect of a method, figure 10 illustrates the pos sibility of using multiple sensors for compensating , figure 11 illustrates a system, figure 12 illustrates a system, and figure 13 illustrates a system .

DETAILED DESCRIPTION

Fig . 1 is a schematic cros s section of a mining vehicle , such as a loader , haulage truck , articulated hauler , or other type of vehicle that has a bed 101 for transporting loads and an axle 102 with wheels 103 and 104 . Throughout this text , the designations "mining vehicle" and "vehicle" are used interchangeably to mean an off-road transport vehicle designed for the purpose of transporting loads in demanding environments such as mines , quarries , and underground tunnels under construction . The vehicle does not need to comprise axles in the traditional sense . For example , many electrically driven haulage trucks have a frame that forms a separate support position for each wheel. In such a case the frame (or any other suitable part of the vehicle structure) may be considered in place of the axle 102 schematically shown in fig. 1. In this text, all references to an "axle" must be considered to cover such alternative embodiments also.

A strain sensor 105 is installed in such a way that it can sense any elastic deformation of the axle 102 that takes place in the plane of the drawing. In other words, the strain sensor 105 measures the bending of the axle 102 in the vertical direction. Examples of suitable installation locations include but are not limited to on top of an axle or frame beam as in fig. 1, and below such an axle or frame beam.

Fig. 2 shows, in a somewhat exaggerated way to improve graphical clarity, how the weight of a heavy load in the bed 101 bends the axle 102. The output signal 201 of the strain sensor 105 is proportional to the extent of such bending, so it can be used to calculate the weight of the load filling the bed 101.

For the purposes of this description the exact technology used to implement the strain sensor 105 is not important, although different sensor types may have their own peculiarities that may affect their applicability to the conditions in a mine as well as the way in which their output signals are preferably processed. As an example, the strain sensor 105 may be a vibrating wire sensor, in which the mechanical resonance frequency of a tensioned wire depends on the tensioning force. Such a sensor may be attached to the axle 102 (or to some other part of the transmission or suspension) so that any mechanical deformation caused by the weight of the load either increases or decreases the tension of the wire in a systematic way and in proportion to the magnitude of the deformation. Basically if a vibrating wire sensor is attached on top of the axle as m figs. 1 and 2 by its both ends, any increasing weight of the load decreases the tension of the wire, lowering the resonance frequency. Other types of strain sensors that may be used include but are not limited to resistive strip sensors and piezoelectric sensors.

Fig. 3 shows an example of how the output signal 201 of the strain sensor 105 might look like as a function of time in an ideal case. In fig. 3 it is assumed that the sensor and the signal processing electronics have been calibrated so that when the bed is empty, the strain-indicating output signal of the sensor is zero. Flat sections of the output signal curve at the zero level, like sections 301 and 302 for example, correspond to the vehicle driving empty to haul a new load. The stepwise increasing sections of the curve, like section 303 for example, correspond to the vehicle being loaded by a loader. In this case each load appears to come in four consecutive bucketfuls. Flat sections at non-zero level, like section 304 for example, correspond to the fully loaded vehicle driving from the hauling point to the dumping point. The weight of each load is easy to calculate from the horizontal non-zero level at which each such flat section occurs.

In practice, it has been found that signal distortion appears in multiple forms, one of which is schematically shown in fig. 4. Instead of continuing horizontal, each "flat" section of the output signal curve of the strain sensor exhibits a systematic change, like a steady ascent as in fig. 4, as if the weight of the load increased during transport and as if the weight of the vehicle increased even when driving empty. This makes it more difficult to use the sensor output signal in calculating the weight of each load, for two reasons. First, one does not actually know, at which point in time one should take the read- mg that should indicate the value of the sensor output signal when the vehicle was fully loaded (see section 401 for example) ; there is the uncertainty marked as 402. Second, even if for example some mean value or other statistically representative value would be taken from the duration of such a section in the curve, one does not know how much the baseline (the zero-load value) had diverged from its calibrated value (so- called baseline drift; see arrow 403 in fig. 4) .

Fig. 5 shows another example, in which in addition to the systematic change of fig. 4 the sensor output signal contains additional noise at higher frequencies .

It has been found that there are many causes behind the irregularities in the sensor output signal. A systematic change may come for example from changes in temperature. Looking again at fig. 4, we may assume that the sensor output signal curve was taken at the beginning of a shift, before which the vehicle had been standing still for a while. When operation starts and the vehicle begins moving, friction in the transmission causes the axle or other installation location of the sensor to warm up. The natural thermal expansion of all solid materials causes a corresponding change in the tension that affects the sensor. Also the sensor body warms up, probably with a different coefficient of thermal expansion than the axle material, which causes another temperature-dependent systematic change in the sensor output readings. Further issues to consider are the thermal expansion of the wire or other actual sensor element and the thermal effects that occur in the electronic components of the sensor.

Temperature-dependent changes of said kind may be difficult to predict and control, because there are so many possibly affecting factors. A well-oiled transmission will cause smaller losses, and consequently heat up less, than one where the lubrication is not up to date. The mine may have a well-organized ventilation that keeps the temperature in the tunnels at, say, 15 to 17 degrees centigrade, or the ventilation may function poorly so that the ambient temperature varies between 30 and 50 degrees centigrade. The vehicle may be travelling on a flat surface, up a ramp, or down a ramp, with respective consequences to braking and use of engine power and subsequent heating; even the steepness of the ramp plays a role. The vehicle may perform short rides from one level to another, the length of each ride being only some hundreds of metres, or it may travel some 10 kilometres from the bottom of the mine to the surface. The vehicle may haul loads in one direction only and drive empty in the opposite direction, or it may transport loads of different materials in different directions.

Interfering factors as those listed above occur in various combinations that are very hard to predict. They may change by region, by mining method, and by the mine stage where the vehicle is used (like development area, production area, or deep development area) . There are numerous factors that may affect the local temperature within and around the vehicle, even after several hours of continued service when one could otherwise expect every part of the vehicle to have achieved some thermal equilibrium. One commonly encountered and cyclically occurring cause of temperature variations is braking. In particular if the dumping point is lower than the hauling point, the vehicle must travel downhill fully loaded, constantly using its brakes. Suitable installing locations of strain sensors where they react in a clear and consistent way to changes in total load may be close to the brakes, which explains why braking is such an important source of interference of thermal origin.

Other sources of interference, the effects of which are illustrated in fig. 5, may include such fac- tors as random bumps and holes in an uneven road, the vehicle accelerating and decelerating , load items such as large stones being tos sed about on the bed, or even the loader pushing down on the top of the material heap at the end of the loading so that it becomes properly spread in the dumper bed .

Fig . 6 illustrates s chematically a mining vehicle capable of transporting a load, the weight of which mining vehicle should be measured with the ultimate goal of using such a measured weight to derive the weight of transported loads . The vehicle comprises a strain sensor arrangement 105 , which corresponds to the strain sensor 105 des cribed above in that is capable of producing what is called here a f irst load signal indicative of a weight of the vehicle . The concept of weight means here the combined mas s of the vehicle ; any fuels , lubricants , and other consumables present in the vehicle ; the driver of the vehicle if present ; and any load that the vehicle may be carrying at any arbitrary moment . In general , the weight may be a "total" weight and considered to consist of the load weight and the vehicle weight , of which the latter may also be called the empty weight or tare of the vehicle to emphas ize that it means the vehicle with no load on its bed . It should be noted that thi s "empty" weight only refers to the emptine s s of the bed; it still includes the mas s of all consumables held in tanks of the vehicle as well as the ma s s of the driver , if any .

Additionally, the vehicle illustrated in fig . 6 comprises an orientation signal arrangement 601 , which i s capable of producing what i s here called a first orientation signal indicative of a relative orientation of at least one load-carrying part of the vehicle . It i s most illustrative to think here that the orientation signal arrangement 601 tells the orientation of the bed 101 in relation to the main body of the vehicle . In fig . 6 the orientation signal arrange- ment 601 is schematically shown as installed to a hydraulic system 602 that can be used to tilt the bed 101 for unloading (see fig. 7) . In such a case the orientation signal arrangement 601 may measure e.g. the extension of a hydraulic cylinder. For the purposes of this discussion the actual technology of implementing the orientation signal arrangement 601 is not important. As will be seen later, it is not even necessary to produce the first orientation signal at very good accuracy. For example, some simple optical or magnetic sensor could be used that gives one output value when the bed is down (or within a coarse range of normal operating positions) and some other output value when the bed is up (or within a coarse range of unloading positions) . Yet another possibility of orientation sensor technology is an accelerometer (or an accelerometer system comprising two or more acceleration sensors) fixed to the bed 101.

Regarding fig. 7 it must be noted that, just like the other attached drawings, it is highly schematic by nature and only illustrates conceptually the association between unloading and using a corresponding sensor for detection. The unloading can naturally take place otherwise than by tilting the bed to the side; the bed may be tilted towards the back of the vehicle for example. For the purpose of the present text it is sufficient to assume that the unloading involves some kind of mechanical movement which, or at least the end of which, can be detected with a sensor.

Additionally, the vehicle illustrated in fig. 6 may comprise a motion sensor arrangement 603, which is capable of producing what is here called a first movement signal indicative of a movement of the vehicle as a whole. In other words, based on the first movement signal it is possible to tell, whether the vehicle is moving or not. In fig. 6 the motion sensor arrangement 603 is schematically shown as installed to the differential gear included m the axle 102, where it could e.g. produce one output value when the gears are rotating and another output value when the gears are stationary. Again, for the purposes of this discussion it is not important what technology is used to implement the motion sensor arrangement 603. Alternatives to the example briefly explained above include, but are not limited to, accelerometers installed anywhere in the vehicle and wireless positioning systems, such as those based on the reception of radio signals from or transmission of radio signals to a network of fixedly installed beacon stations. The methods, systems, and arrangements described here may operate also completely without any motion sensor and without any movement signals produces such a motion sensor.

The way in which the sensors are attached to the respective parts of the vehicle is not important to this discussion. As examples, the sensor, sensor support, or sensor holder can be welded, glued, bolted, or attached with a metallic or non-metallic strap or using a clamp. A sensor support or sensor holder can be also integrated in the axle structure or vehicle structure at the moment it has been casted or fabricated. The sensor support can be also be machined in the axle structure or to other parts of the vehicle structure .

According to a novel insight, at least the first load signal 604 and the first orientation signal 605 may have a role in measuring the weight of the vehicle. In some embodiments also the first movement signal 606 may have a role in measuring the weight of the vehicle.

Depending on the sensor technologies used, these signals may be analogue or digital signals or they may comprise both analogue and digital elements. Each of these signals may be considered to consist of a sequence of consecutive values that keep coming at some predetermined rate whenever the re spective sensor arrangement is operational . In case of analogue sensors the consecutive values are actually a single quantity, the value of which may change continuously over time . In case of digital sensors there are actual , digital values that follow each other at some predetermined sampling frequency . For the purposes of the present discus sion it is not important whether the signals 604 , 605 , and 606 are analogue or digital signals , because analogue signals can be digiti zed and digital signals can be converted to analogue whenever it i s more practical to handle the signals in one form than in the other .

Fig . 8 is a state diagram that illustrates a method for measuring the weight of a mining vehicle capable of transporting a load . Executing the method may be compared to a finite state machine that makes transitions between states at the occurrence of certain criteria . As shown in the top left corner of fig . 8 , the method may comprise receiving the first load signal , the f irst orientation signal , and the first movement signal either continuous ly or whenever such signals are available for reception , irre spective of the state in which the finite state machine is at the moment .

The first state 801 shown in fig . 8 is an operational state . The f inite state machine may be in the operational state 801 whenever it i s not in any of the other states . For the purposes of this di scus sion , the finite state machine may be in the operational state 801 whenever the mining vehicle is moving or waiting , or when it receives a load .

The second state 802 shown in fig . 8 is an unloading state . The f inite state machine may be in the unloading state 802 when the mining vehicle i s unloading . The method may comprise determining the beginning of an unloading event using the orientation signal. As the orientation signal indicates the relative orientation of the bed or other load-carrying part of the vehicle, the finite state machine may perform a transition from state 801 to 802 as a response to noting that the value of the first orientation signal has changed and is now in an unloading value range. In other words, the method may comprise determining a beginning 803 of an unloading event using at least the first orientation signal. As an example, if the value of the first orientation signal is or indicates the tilting angle of the bed, the transition from state 801 to state 802 may take place when the value of the first orientation signal increases to more than 30 degrees (see parameter XI in fig. 8) . In such an example the unloading value range would be synonymous with more than 30 degrees.

The method may also comprise determining an end 804 of an unloading event using at least the first orientation signal. Basically it would be possible to determine the end 804 of an unloading also in other ways, like noting a very sharp and significant reduction in the first load signal. However, fig. 8 suggests an embodiment where the end of an unloading event is determined as an observed return of the value of the first orientation signal to a transport value range after its value has been in the unloading value range. As an example, the transition from sub-state 803 to sub-state 804 may take place when the value of the first orientation signal comes back to below 5 degrees (see parameter X2 in fig. 8) . In other words, the bed which was tilted to dump the load comes back to its horizontal position. In such an example the transport value range would be 0 to 5 degrees.

The method may comprise determining a standstill event following a determined end of an unloading event using at least the first movement signal. In fig. 8 this corresponds to the state machine making a transition from state 802 to state 805. The idea here is to detect a moment where the vehicle has dumped its load and is thus empty in the sense explained above, and does not move so that there are as few interfering factors as possible that could affect a subsequent determining of a tare value. Depending on how the vehicle and in particular its suspension was built, it may be advantageous to wait for a short moment after the end of the unloading event before determining a standstill event. This is because when the empty bed comes down on its supports after unloading, it makes the whole vehicle jolt in a way that continues in a series of damping oscillations for a while. The stand-still event may be determined for example as an observed remaining of the value of the first movement signal within a stand-still value range for a predetermined duration of time after the determined end of an unloading event. As an example, if the first movement signal is an accelerometer value, the transition from state 802 to state 805 may take place when the value of the first movement signal has been between -0.03g and 0.03g for 5 seconds (see parameters X3 and X4 in f ig . 8 ) .

The method may comprise determining a tare value of the first load signal at the determined stand-still event. There is no particular criterion shown in fig. 8 for the finite state machine making the transition from state 805 to the tare state 806, which means that this transition may come immediately after the transition from state 802 to state 805. After the tare value has been determined at state 806, the finite state machine may continue with a further transition back to the operational state 801.

As an alternative to going through state 805, the state machine may make a direct transition from sub-state 804 to state 806. In the method this corresponds to determining the tare value of the first load signal at or after determining the end of the unloading event , without having to separately detect a stand-still event in between . This may simplify the method, with corresponding simplif ication in programming because the method is typically performed by one or more computers that execute a computer program code in which the method steps have been def ined .

The tare value determined at state 806 corresponds to the value of the first load signal when there i s no load on the bed ( and pos s ibly after the vehicle has been standing still for a short while after the load was dumped) . In other words , this value can be used to represent the measured empty weight of the vehicle at that moment . Us ing the tare value may comprise e . g . providing the tare value as an input to a further calculating proce s s where the weight of a load (presumably the weight of the most recently dumped load ) i s calculated by subtracting the tare value from a measured weight of the vehicle before unloading . Additionally or alternatively, us ing the tare value may comprise transmitting the tare value to some other system where it can be used e . g . for calculations of said kind, for calculations where the effect of environmental conditions on load sensors are proces sed statistically, and/or for any other purpose s .

As there may be interfering factors remaining that cause some continuous oscillation in the value of the first load signal even when the vehicle is standing still , determining the tare value may comprise low-pas s filtering a sequence of received values of the first load signal during a period of time after the determined stand-still event . In any ca se , and particularly if the method does not comprise separately determining a stand-still event , the reception and storing of value s of the first load s ignal for determining the tare value may begin immediately after determining the end of the unloading event . I f the se re- ceived values show little statistical variation compared to values received after the determined standstill event (if applicable) , these received and stored values may all be taken into account in the sequence that is low-pass filtered. Low-pass filtering is mentioned here as an example of a signal processing step that is used to convert a sequence of slightly varying values into a single most representative value. Additionally or alternatively also other signal processing steps of statistical nature may be taken.

If applicable, determining a stand-still event that is "valid" enough for determining a tare value may depend also on other criteria than just the first movement signal remaining still enough. As an example, if there are one or more general orientation sensors for detecting the orientation of the whole mining vehicle with respect to horizontal, there may be a requirement that this orientation must not deviate from horizontal by more than some allowable maximum value. This is because if the strain sensor arrangement has been designed to measure elastic deformations strictly in the vertical direction, it will not give a completely reliable indication of weight if the vehicle is heavily inclined.

The determined tare value is a reliable indication of the empty weight of the vehicle naturally at that moment only. At least in some cases it may, however, be good enough for at least some purposes. As an example, if the (possibly somewhat filtered or otherwise statistically processed) value of the first load signal immediately before the unloading event was used to represent the measured weight of the vehicle with the load on, the difference between that value and the newly determined tare value gives a quite accurate indication of the weight of the most recently dumped load . However, even more advantageous results can be achieved by performing the determining of a tare value repeatedly during a work shift. Fig. 9 illustrates an embodiment that comprises storing a plurality of tare values determined at or after consecutive determined ends of unloading events . The method may then continue by determining a baseline drift as a function of time by fitting a curve 901 to the stored plurality of tare values. The determined baseline drift can then be used as a reference in determining weights of loads carried by the vehicle quite reliably at arbitrary moments of time.

Fig. 9 also illustrates schematically the mutual timing of the strain, movement, and orientation signals. The movement signal is labeled as acceleration in fig. 9, because in this example case it was taken from an accelerometer. It shows how negative acceleration values were sensed while the vehicle was driving with full load and positive acceleration values when empty, indicating that the dumping point was lower than the hauling point. It also shows how the movement signal may go temporarily to zero when the vehicle must stop somewhere to wait for its turn to move. The movement signal is also close to zero during loading and unloading, with some noticeable interference caused by the loaded material hitting the bed and by the unloading mechanism operating. The vertical dashed lines in fig. 9 show the moments when the criteria for taring are fulfilled: in particular after the orientation signal has returned to zero. If the determining of stand-still events is applicable, the criteria comprise also checking that the movement signal has subsequently remained close to zero.

A mining vehicle such as a loader, haulage truck, or articulated hauler is often used in a cyclical manner throughout its working shift. This is clearly visible in the graphs of fig. 9: the cycle may consist of driving empty, loading, driving full, and unloading, with the track to be driven in each cycle remaining essentially the same. It is advantageous to tare the vehicle always at essentially the same point of the cycle, because in that case the cyclically occurring sources of interference (like the variations in ambient temperature along the track) will also have completed their full, regular cycle. Taring just after unloading is advantageous, because the end of an unloading event can be quite reliably detected from the orientation signal, as was described above. However, there is nothing that would preclude taring additionally or alternatively at some other points of the operating cycle. As an example, it is possible to tare just before loading begins. A suitable moment for such taring could be detected, for example, by noting that there is a relatively long period of no movement, during which the level of high-frequency mechanically originating interference suddenly increases (because the dumper begins to drop load items into the bed) .

Fig. 10 illustrates an arrangement that can be used for measuring the weight of a mining vehicle with at least some of the interfering factors inherently cancelled. The arrangement of fig. 10 may be used irrespective of whether any of the methods of figs. 8 and 9 are used also. In the embodiment of fig. 10 the strain sensor arrangement comprises a first strain sensor 105 and a second strain sensor 1001. The second strain sensor 1001 is a similar strain sensor as the first strain sensor 105. Additionally, it is installed at the same location in the mining vehicle, so that all environmental factors like changes in temperature affect the two strain sensors 105 and 1001 as identically as possible. However, the way in which the second strain sensor 1001 is installed makes its output signal independent on any changes in the weight of the vehicle. As an example, we may assume that the strain sensors are vibrating wire sensors and that the first strain sensor 105 i s installed with it s wire parallel to the direction of the axle 102 ( see orientation of the elongate sensor block 105 in the top view of fig . 10 ) . The second strain sensor 1001 may be installed with its wire at a 90 degrees angle to the direction of the axle 102 ( see orientation of the elongate sensor block 1001 in the top view of fig . 10 ) , so that however the axle 102 bends in the vertical direction there is no effect what soever on the output signal of the second strain sensor 1001 .

Compared to fig . 9 , it is likely that the output signal emitted by the second strain sensor 1001 follows more or les s the curve 901 , pos sibly with some superposed high-frequency oscillations caused by the acceleration forces that come f rom the vehicle moving and its wheels hitting random bumps and holes in the road . As the signal of intere st here can reasonably be expected to vary quite slowly, heavy low-pas s filtering may be applied to remove the effect of all such high-frequency interference from the output signal of the second strain sensor 1001 .

I f the strain sensor arrangement has two strain sensors like in fig . 10 , the method may comprise receiving a second load s ignal 1002 from the strain sensor arrangement , which second load signal 1002 is indicative of the output value of a s imilar strain sensor at the same location as the one emitting the first load signal , however without dependency on the weight of the vehicle . The method may then further comprise determining a compensated load signal using the dif ference between the first load signal and (pos sibly a filtered form of ) the second load signal . The method may then comprise us ing said compensated load signal to represent the weight of the vehicle at any arbitrary moment of time . In a strain sensor arrangement like that of fig. 10 there may be more than one additional sensor for producing the signals used for compensation. Using vibrating wire sensors again as examples, if the second strain sensor 1001 has its wire horizontal and orthogonal to the direction of the axle 102 (see orientation of the elongate sensor block 1001 in the top view of fig. 10) , there might be a further similar sensor installed with its wire vertical and orthogonal to the direction of the axle 102. Additionally or alternatively, if the second strain sensor 1001 is installed close to one end of the wire contained in the first strain sensor 105, there might be a further similar sensor installed close to the other end of the wire contained in the first strain sensor 105. By using two or more sensors, none of which reacts in any way to the load weight, to produce the compensating signal it is possible to avoid the nuisance effect of interfering factors such as random accelerations even better than with only one such sensor.

The description above does not take any position concerning where the reception and processing of the various signals should take place. There are numerous alternatives, some of which are discussed next with reference to figs. 11 and 12.

Two basic alternative approaches involve either processing all signals as ready as possible on board the vehicle, or transmitting the signals to an external monitoring system for processing. In the schematic representation of fig. 11 the vehicle 1100 comprises a number of sensors 1101, 1102, and 1103, as well as a control unit 1104 and a wireless transceiver 1105. There is an external monitoring system 1110 with a transceiver 1111, a control unit 1112, and a database 1113. The external monitoring system 1110 may be a dedicated computer at or close to a location where the vehicle 1100 passes by every now and then. Alter- natively, the external monitoring system 1110 may be a system involving one or more computers distant from any location where the vehicle 1100 operate s . The concept of a transceiver 1111 within the external monitoring system 1110 must be understood in a general way so that it covers all neces sary components and connections that are needed to make information transmitted by the wireles s transceiver 1105 of the vehicle available for proce s sing in the control unit 1112 of the external monitoring system 1110 . S imilarly the concept s of a control unit 1112 and a database 1113 within the external monitoring system must be understood in a general way so that one or more computers and one or more data storages may be involved in each ca se , with a wide variety of pos sibilities concerning centralized and distributed computing architectures .

The method that was described earlier comprised steps of receiving the first load signal , the first orientation signal , and the first movement s ignal ; as well a s determining the end of an unloading event , the stand- still event , and the tare value of said first load signal . According to a first one of the two alternative bas ic approaches , these are all executed on board of the mining vehicle 1100 . In such a case the control unit 1104 in the vehicle may use the transceiver 1105 to transmit the determined tare value ( and pos sibly other values , such a s received load values indicative of the weight when loaded) to the external monitoring system 1110 , which may then use the se values to keep track of how much stone or other material the vehicle ha s moved and from where to where .

According to the second one of said two alternative approache s , said steps are all executed in the monitoring system 1110 out side the mining vehicle 1100 . In such a case the control unit 1104 in the vehicle may use the transceiver 1105 transmit "raw data" to the external monitoring system 1110 . It remains then on the re sponsibility of the external monitoring system 1110 to proce s s the raw data it received into tare values and calculated load weights , us ing some of the methods de scribed above .

An external monitoring system may be understood to be a system that is offboard the vehicle , for example a part of the mine computer system . There may be a plurality of external monitoring systems , and/or there may be a plurality of computers connected to the external monitoring system . The external monitoring system can also be implemented so that there is a data logger unit onboard the vehicle and the external monitoring system receive s the data from the data logger unit at a network server .

I f the first alternative approach discus sed above is chosen , then the s ignal generating , collecting , and proces sing system on board the vehicle 1100 can be said to constitute a system for measuring the weight of a mining vehicle capable of transporting a load . The system comprise s receiving means configured to receive a f irst load signal indicative of a weight of the vehicle , a first orientation s ignal indicative of a relative orientation of at least one loadcarrying part of the vehicle , and a first movement signal indicative of a movement of the vehicle as a whole . In the crude block diagram model of fig . 11 , these are all located in the control unit 1104 of the vehicle . Additionally the control unit 1104 comprises proces sing means configured to determine an end of an unloading event us ing at lea st the first orientation signal , a stand- still event following the determined end of an unloading event using at lea st the first movement signal , and a tare value of the first load signal at said determined standstill event . The system on board the vehicle may even be configured to use said tare value to represent the measured empty weight of the vehicle . Thus all bookkeeping of transported loads may take place on board the mining vehicle 1100 , with only some quite refined and complete reports sent to the external monitoring system 1110 when needed .

I f the second alternative approach di scus sed above i s chosen , then only the signal generating takes place within the vehicle while the s ignal collecting and proces s ing system in the external monitoring system 1110 can be said to constitute a system of the kind described above .

Hybrid embodiments are pos sible where some of the signal proce s sing is performed on board the vehicle 1100 , while the proces s ing is only completed in the external monitoring system 1110 . As an example , the control unit 1104 on board the vehicle 1100 may perform the method up to determining each tare value , while the external monitoring system 1110 may be responsible for storing a plurality of tare value s that the vehicle determined at consecutive determined stand-still event s and determining a baseline drift as a function of time by f itting a curve to said stored plurality of tare values . Any or both of the onboard and external systems may then use said determined baseline drift as a reference in determining weights of loads carried by the vehicle in the continuation .

Even if the sensors have been des cribed above as features of the vehicle , this is not an es sential requirement . Fig . 12 illustrate s an alternative embodiment in which at least some sensors 1201 and 1202 are part of the external monitoring system 1110 . Sensors that are located in the external monitoring system 1110 may be for example such sensors that are only needed for relatively crude measurements . As an example , an unloading station may comprise optical sensors that are accurate enough to determine when the bed of an unloading mining vehicle comes down after unload- mg. Such a measurement can then be used as an indication of an end of an unloading event.

Also other quantities than those discussed above can be measured with sensors, and the output signals of such sensors can be taken into account in the calculations. One factor that could be accounted for by properly entering output signals from such other kinds of sensors into the processing is fuel consumption. If the vehicle has a combustion engine, its weight will sharply increase every time when the fuel tank is filled and thereafter slowly decrease as the fuel is consumed until the next filling. Vehicles with fuel tanks typically have a fuel level gauge and an associated fuel level indicator anyway in order to inform the operator of the need to fill up. If the signal from such a fuel metering system is available in a form suitable for processing in the same system as the strain, orientation, and movement signals, it is easy to configure the processing so that it takes into account the continuous gradual decrease in weight caused by the consumption of fuel.

Fig. 13 illustrates a system for tracking the transporting of loads with a plurality of mining vehicles 1301, 1302, 1303 and 1304. These may all be mining vehicles of a kind described in at least one of the examples earlier in this text. The system comprises an external monitoring system 1305 which is external in the sense that it is not contained in any of the tracked mining vehicles. The external monitoring system 1305 may be for example the computerized control and supervision system of a mine or a quarry, a part thereof, or a subsystem interfaced therewith.

The external monitoring system 1305 may be equipped with sensor systems 1306 of its own. As an example, there may be one or more cameras, laser scanners, RFID readers, digital optical code readers, optical motion sensors, magnetic sensors, thermal imag- ing sensors, and/or other remote sensing sensors installed at various locations in the mine or quarry. The external monitoring system 1305 may use the output signals from such sensor systems, possibly pre- processed by suitable algorithms like image processing and feature recognition algorithms for example, in order to monitor all activity in the area. This way the external monitoring system 1305 may for example keep track of where in the area each vehicle 1301, 1302, 1303, or 1304 is located at any given time.

Combined with information received from the vehicles, in accordance with at least one of the methods described earlier in this text, the information available to the external monitoring system 1305 allows it to keep track of how much material has been transported, from where, and to where in the mine or quarry. The external monitoring system 1305 may transmit such information further through any external interfaces 1307 that it may have, for example to human operators through audiovisual interfaces; to production control systems of ore refining and valuable material extraction arrangements where the material is to be transported further; and/or to financial management systems that benefit from accurate knowledge of what kind of valuable materials may be available for processing, where, and in which quantities.

The invention is not limited to the example embodiments described above but can be varied and extended in multiple ways. Features and embodiments that have been described in isolation above can be combined with each other in any way unless explicitly otherwise stated .