AU2012232994A1 - Weighing system and method of weighing loads - Google Patents

Abstract

WEIGHING SYSTEM AND METHOD OF WEIGHING LOADS 5 The weighing system and method of weighing loads according to the embodiment comprises: a weighing platform having two parallel sides joined at either end to form either a square or oblong shaped platform upon which a load can be placed. The system comprises at least one sensor providing an output proportional to the force applied by the load and a plurality of 10 accelerometers placed at locations around the platform such that the accelerometers are located at or near the centre of gravity of the load on the platform; and a control system for computing the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; ii) determining the position of the centre of mass of the load based on a 15 minimisation technique and the outputs from the accelerometers and the at least one sensor; and iii) calculating a compensated mass of the load using the determined position of the centre of mass of the load. Figure 1 to accompany the Abstract 20 50 30 FIGURE 1 3

Description

1 WEIGHING SYSTEM AND METHOD OF WEIGHING LOADS FIELD OF THE INVENTION 5 The invention relates to a system, and method for weighing loads transported by vehicles. The invention also extends to an apparatus for measuring the weight of load carried in a vehicle such as a truck. The invention has particular but not exclusive application to a system, 10 and method for determining the weight of a load lifted by a lifting apparatus mounted to a vehicle. In further detail, the apparatus, method, and system of the present invention are provided for the weighing of loads collected by refuse vehicles. 15 BACKGROUND TO THE INVENTION Mobile trash or refuse collection systems are well known and are widely utilised to efficiently collect large volumes of trash such as residential and commercial waste. These systems generally utilise on-site trash 20 collection containers of various sizes and shapes typically containing from approximately 200 to 1000 or more litres of capacity. The on-site containers are filled with trash or refuse by the users and periodically the contents of the container are transferred to a mobile collection vehicle and the refuse taken to the dump, landfill, or recycling centre. The term "refuse" as used herein 25 generally refers to all types of residential and commercial trash, garbage and waste. It is often necessary to determine the weight of cargo or refuse that is carried in a vehicle. The common procedure utilised to measure this weight 30 is to drive the vehicle onto a weighing scale, which provides a readout of the combined weight of the vehicle itself along with the weight of the cargo that is carried by the vehicle. There are, however, clear and significant drawbacks to this procedure. The weight that is measured on these scales is the overall 2 or combined weight of the vehicle and the cargo which it carries, and thus does not provide the desired weight of the cargo alone. In order to calculate the weight of the refuse or cargo the weight of the vehicle or tare weight must firstly be determined and then subtracted from the combined weight of the 5 vehicle and cargo. The process of weighing both the combined weight of the vehicle and the load and the tare weight of the vehicle is somewhat time consuming and a better method of determining the weight of a load is needed. 10 A number of weighing systems have been proposed in the past for installation on refuse trucks in order to determine the weight of a load. However, these systems have been subject to various problems, and no system has been provided as yet which is sufficiently accurate and efficient. 15 Conventional refuse trucks have some type of automatic lifting system for lifting a refuse container from the curb, and raising and inverting the container over a collection area in the truck into which the refuse is dumped. The emptied container is then lowered back to the curb. In these systems, the container is weighed as it is lifted and again as it is lowered, with the 20 difference between the two weights providing an indication of the amount of refuse or recyclable material deposited in the truck. However, there are a number of problems in accurately weighing a container as it is lifted by a truck. The truck may be positioned on an incline, which will affect the weight reading. The truck engine is normally running while the container is lifted, 25 and the lifting system itself will affect the weight sensed, due to vibration, acceleration and other variables. Additionally, the contents of the container are liable to shift during lifting, causing more variations in the detected weight. Because of this, some 30 systems in the past have proposed stopping the lifting device while the container is being emptied, once during the up cycle and once during the down cycle. However, this will increase the amount of time needed to collect refuse and decrease efficiency. Additionally, other variables such as truck inclination and engine vibration will still cause variation in the detected load.

3 Prior art techniques for weighing loads lifted by a lifting apparatus have been directed toward measuring the strain (in tension or compression) or deflection of a lift arm of the apparatus. For example, transducers with loadcells have been mounted on forward or rearward arms of a lift apparatus, 5 whereby as a load is lifted the arms experience strain caused by the load. Both beam-type and extensiometer-type of transducers are well-known in the industry, whereby as the lift arms are tensed, or compressed or deflected, the transducers generate an electric signal. The electric signal is calibrated with regard to the particular transducer's properties, so that the loads lifted 10 can be calculated by an on-board computer or other electronic calculation device. Other forms of on-board weighing devices have included measuring the difference in hydraulic pressure in the hydraulic pressure fluid lines of the 15 lift apparatus during lifting. In this way, pressure transducers are utilized, which similarly send out electric signals that can be calibrated to calculate load. The prior art use of transducers for measuring deflection and/or strain 20 provide fair results, but there is a need to improve upon the accuracy of on board weighing systems. Likewise, hydraulic pressure transducer systems offer certain benefits, but there is also a need to improve beyond the accuracy of these types of systems. 25 All of the above systems suffer from considerable error when the load that is being weighed is subjected to vibration. Vibrations can occur from shock loading when heavy material is dumped onto a weighing system, causing forces greater than the system's rated capacity and damaging the system or from process equipment and other sources near the weighing 30 system can cause the load cells to measure the weight of material as well as vibration that's transmitted to them, which the cells sense as mechanical noise.

4 Vibration present in an industrial environment can make observation of weight measurements difficult and because of this it is often necessary for operators to wait until the structural oscillations of the machine have subsided before a weight measurement is taken. 5 Clearly it would be advantageous if a system could be devised that helped to at least ameliorate some of the shortcomings described above. In particular, it would be advantageous if a system could be devised for accurately weighing loads carried in a vehicle or lifted by a lifting apparatus 10 of a vehicle such as a refuse vehicle. SUMMARY OF THE INVENTION According to one aspect of this invention there is provided a system 15 for weighing a load, the system comprising: a weighing platform upon which a load can be placed or contained within; at least one sensor providing an output proportional to the force applied by the load; a plurality of accelerometers placed at locations around the platform such that the accelerometers are located at or near the centre of gravity of the load on the 20 platform; and a control system for computing the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; ii) determining the position of the centre of mass of the load based on a minimisation technique and the outputs from the accelerometers and the at least one sensor; and iii) calculating a compensated mass of the load using 25 the determined position of the centre of mass of the load. Preferably, the at least one sensor may be a load cell and the load cells are placed at predetermined positions around the weighing platform. More preferably, at least two load cells may be placed on either side of the 30 weighing platform. Even more preferably three load cells may be placed on either side of the weighing platform with one load cell located at each end of one side and another load cell placed at the centre of the one side of the weighing platform.

5 Preferably, the weighing platform may be mounted on a vehicle. The vehicle may be a refuse or waste collection vehicle. More preferably the weighing platform may be formed as a body or container of a vehicle and the load cells and accelerometers are located within the chassis of the vehicle. 5 The plurality of accelerometers may be miniature micro-electro mechanical systems used to sense motion of the weighing platform when a load is placed on the weighing platform. The accelerometers may be embedded or attached to the weighing platform. 10 Preferably, the control system may comprise a first control device for association with at least one sensor and adapted to generate an output representative of a weight sensed by said sensor; a second control device for association with the plurality of accelerometers and adapted to generate a 15 compensation output representative of the acceleration of the load at or near the centre of gravity of the load; a processor for computing the weight of the load by applying the compensated output of the second control device to the output of the first control device; and a storage device for storing the net weight of the load readings. 20 The control system may be located within a vehicle to which the weighing platform is mounted. Preferably, the processor may be located remote from the vehicle to which the weighing platform is mounted and the first and second control devices may transmit their respective output signals 25 to the remote location for processing by the processor. The system for weighing a load may further include a first filter between the load cells and the control system and a second filter between the accelerometers and the control system, the filters comprising means for 30 filtering noise from the sensor output signals. The filters may be digital filters. In accordance with a further aspect, the present invention provides a method of weighing a load, the method comprising the steps of detecting the 6 load carried by a weighing platform using at least one sensor and providing an output from the at least one sensor proportional to the force applied by the load; placing a plurality of accelerometers at a mean location of the centre of gravity acting on the load on the weighing platform; and computing 5 the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; ii) determining the position of the centre of mass of the load based on a minimisation technique and the outputs from the accelerometers and the at least one sensor; and iii) calculating a compensated mass of the load using the determined position of the centre of 10 mass of the load. The method of weighing a load may comprise any one or more of the features of the first aspect. 15 In accordance with a further aspect, the present invention provides a system for weighing a load contained in a container lifted by a lifting arm of a vehicle, the system comprising: a sensor located on the neutral axis of the lifting arm, the sensor being adapted to sense shear stress in the lifting arm and provide an output proportional to the force applied by the load; an 20 accelerometer located on the lifting arm at a location at or near the centre of gravity of the load; and a control system for computing the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; ii) determining the position of the centre of mass of the load based on a minimisation technique and the outputs from the accelerometers and 25 the at least one sensor; and iii) calculating a compensated mass of the load using the determined position of the centre of mass of the load. Preferably, the sensor may be a load cell. The accelerometer may be a miniature micro-electro-mechanical system used to sense motion of the 30 lifting arm when the container and load are placed on the lifting arm. The accelerometer may be embedded or attached to the lifting arm. Preferably, the control system may comprise a first control device for association with the sensor and adapted to generate an output 7 representative of a weight sensed by the sensor; a second control device for association with the accelerometer and adapted to generate a compensation output representative of the acceleration of the load at or near the centre of gravity of the load; a processor for computing the weight of the load by 5 applying the compensated output of the second control device to the output of the first control device; and a storage unit for storing the net weight of the load. The control system may be located within a vehicle to which the lifting arm is mounted. The processor may be located remote from the vehicle and the first and second control devices may transmit their respective output 10 signals to the remote location for processing by the processor. Preferably, the vehicle may be a refuse, waste collection or recycling vehicle. 15 Preferably, two or more accelerometers may be located on the lifting arm at or near or either side of the centre of gravity of the load. Preferably, the container may be lifted by two lifting arms located at either side or end of the container. Two or more accelerometers may be 20 located on the lifting arms at or near or either side of the centre of gravity of the load in the container. Preferably the system may further comprise a first filter between the load cells and the control system and a second filter between the 25 accelerometers and the control system, the filters comprising means for filtering noise from the sensor output signals. The filters may be digital filters. In accordance with a still further aspect, the present invention 30 provides a method of weighing a load contained in a container lifted by a lifting arm of a vehicle, the method comprising the steps of: providing a sensor on the neutral axis of the lifting arm, the sensor being adapted to sense shear stress in the lifting arm and provide an output proportional to the force applied by the load; lifting a container containing the load with the lifting 8 arm; placing an accelerometer at or near the centre of gravity acting on the load on the lifting arm; obtaining readings from the sensor and the accelerometer on the lifting arm; and obtaining a value indicative of the weight of the load in the container by compensating the shear stress in the 5 lifting arm with the acceleration of the load at the mean location of the centre of gravity. The method of weighing a load may comprise any one or more of the features of the previous aspect. 10 In accordance with a still further aspect, the present invention provides a weighing system for a refuse, waste collection or recycling truck, comprising: a lifting arm movably secured to the truck at one end and having lifting forks at an opposite end for engaging a container, the lifting arm being 15 movable between a lower position for engaging a container, a raised position for depositing material from the container into the truck, and back to the lowered position to release the emptied container; a load cell incorporated into each lifting fork for detecting the load carried by the lifting fork and providing an output signal proportional to the force applied by the load; an 20 accelerometer on the lifting fork located at or near the centre of gravity of the load on the lifting forks; and a processing unit including means for compensating the load cell output signals for acceleration forces and inclination of the lifting arm, means for calculating the dynamic gross weight carried by the lifting forks as a container is raised and means for calculating 25 the tare weight as the same container is lowered after emptying for each set of sensor outputs, and means for calculating the net weight of material deposited into the truck from the container based on the calculated dynamic weights. 30 BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of the preferred embodiment of the present invention, which, however, should not 9 be taken to be limitative to the invention, but are for explanation and understanding only. Figure 1 shows a side elevation of a typical front loading refuse 5 collection vehicle incorporating a weighing system in accordance with a first embodiment of the present invention; Figure 2 shows a three dimensional view of the front loading refuse collection vehicle of Figure 1; Figure 3, 3A and 3B show a weighing platform and associated 10 sensors in accordance with the first embodiment of the present invention; Figure 4 shows a weighing system attached to the lifting arm of the vehicle of Figure 1 in accordance with a second embodiment of the present invention; Figure 5 shows a lifting arm and fork in accordance with the second 15 embodiment of the present invention; Figure 6 illustrates a lifting arm and fork in accordance with a third embodiment of the present invention; and Figure 7 shows a pair of lifting arms and associated forks in accordance with the third embodiment of Figure 6. 20 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1 and 2 illustrate a front end loader type of refuse truck 10 incorporating a weighing system according to a preferred embodiment of the 25 present invention. The truck 10 is adapted to pick up a trash can or container (not shown) on lifting arm 14, raise the container upwardly in the direction of arrow A over the top of the truck, and invert the container over an opening in the body 16 of the truck 10 in a conventional manner. The emptied container is then lowered back to the ground. The refuse truck 10 is 30 used by way of an example use of the present invention. The weighing system may be fitted to any type of vehicle which is used for weighing a load or carrying a load which requires the load to be weighed. For example a recycling vehicle which is used to collect recyclable materials including many kinds of glass, paper, metal, plastic, textiles, and electronics.

10 The weighing system of a preferred embodiment is best illustrated in Figure 3 which shows a weighing platform or vehicle body 16 having a rectangular or oblong shape having two sets of parallel sides which at their joining corners form four right angles. It should be understood that the shape 5 of the weighing platform or vehicle body 16 is not limited to only a rectangular shape, any shaped platform can be used with the weighing system of the preferred embodiment. For example, the weighing platform 16 may be a square shape or any other oblong shaped platform or container. 10 Typically a garbage truck collects trash in a container or body 16 that usually comprises most of the vehicle's mass, and is commonly known as the hopper 16. Hoppers 16 may consist of a single, large open space or a series of compartments for collecting different types of trash. 15 As illustrated in Figure 3 the body or weighing platform 16 of the truck 10 is placed upon the chassis 17 of the truck 10. Installed on the chassis 17 are six load cell assemblies 18, three on either side of the vehicle chassis 17. The number of load cells used is not limited to any particular number and is typically determined by the distribution of the load on the chassis of the 20 vehicle The load cell assemblies 18 are installed in the vehicle chassis 17. The type of load cell 30 used is not limited to any particular type and are typically distinguished according to the type of output signal generated (pneumatic, hydraulic, electric) or according to the way they detect weight (bending, shear, compression, tension, etc.). Deflection of the load cell 18 25 will occur as a result of load in or on the container or weighing platform 16 on the chassis17, and an output signal proportional to the load will be produced on an output line of the load cell. Given that load cells are well known for converting force into a measurable output, the working of the device will not be described in any further detail here. 30 Figure 3A and 3B show further detail of the installation of the load cell assembly 18 into the vehicle chassis 17. Figure 3A shows the load cell 30 a bending beam type load cell which is installed at the front of the chassis 17. The load cell 30 is mounted at its lower or bottom side to the chassis 17 of 11 the vehicle 10. The upper portion or channel body 32 and bumper pad 31 are mounted on the upper side of the load cell 30 and contacts the vehicle body or weighing platform 16. The resilient bumper pad 31 is preferably mounted on the outwardly facing side of each channel body 32 to reduce the 5 risk of impacts damaging the load cell 30. The load cell assembly 18 and the load cell 30 are fixed to the vehicle chassis 17 of the vehicle 10 by fixing means 33. 10 Figure 3B shows the load cell assembly 18 fitted at the rear end of the side of the chassis 17. The load cell 30 is the same type as fitted on the front and middle of the side of the chassis 17. The rear load cell assembly 18 has a different type of mounting on the chassis 17 and different bracket assembly 34 but performs the same task as the other load cells ie. converts 15 a force into a measurable output using the same load cell 30. In Figure 3B the load cell 30 is mounted to the chassis 17 of the vehicle 10 by a trunnion block 36. The trunnion block 36 is a cylindrical protrusion used as a mounting and/or pivoting point for the load cell 30. The trunnion 36 allows the vehicle frame or chassis 17 on which the trunnion 36 attaches and 20 hinges allowing vertical movement. It should be understood that dependent upon the type of load cell used (bending, shear, compression, tension, etc.) will dictate how the load cell assembly is mounted to the vehicle chassis 17. Vehicle mounted weighing systems suffer from considerable error 25 when the load being weighed is subjected to vibration. In order to overcome this problem and provide a measurement of the net weight of the load placed on or in the weighing platform 16 a number of accelerometers 19 are placed or located at a mean location either side of or at the centre of gravity of the load on the weighing platform 16. Thus we are able to determine the 30 acceleration of the load on the weighing platform 16 at the centre of gravity of the load. The present invention is not limited to any particular type of accelerometer. Typically modern accelerometers are often small micro electro-mechanical systems (MEMS), consisting of a cantilever beam with a proof mass (also known as seismic mass). Under the influence of external 12 accelerations the proof mass deflects from its neutral position. This deflection is measured in an analog or digital manner. It should be understood that a minimum of two accelerometers 19 5 placed either side of the possible range of the centre of gravity of the load will allow the user to determine the net weight of the load on the weighing platform 16 and therefore compensate for any vibration which is introduced into the system. The use of more than two accelerometers 19 increases the accuracy of the measurement of the net weight. In cases where a more 10 accurate reading of the net weight is required more accelerometers 19 are placed at predetermined locations around the weighing platform 16 and therefore on either side or at the centre of gravity of the load. In order to compensate the force output from the load cells 30 a 15 control system in the form of a processor or computer is used to perform the calculations and compensation of the readings. This is further described below. In a further embodiment and as illustrated in Figures 4 to 7, a front 20 end loader refuse truck 10 incorporating a weighing system located within the front forks 20 of the lifting arm 14 is also utilised to overcome the inherent problem of vibration. Once again the use of a load cell 30 to convert a force into a measurable output and an accelerometer 19 to generate a compensation reading to be applied to the force output provides an accurate 25 determination of the weight of a load housed within a container. In Figures 5 and 6 only one of the pair of forks 20 are shown. This embodiment shown in Figure 5 shows a fork 20 has a load cell 30 and a single accelerometer 19 embedded or located on the fork 20. 30 Deflection of the load cell 30 will occur as a result of load on the forks 20, and an output signal proportional to the load will be produced on an output line of the load cell. This embodiment is illustrated in Figure 5 and the computation for this embodiment is described in further detail below.

13 Figure 6 illustrates an embodiment which includes a fork 20 having a load cell 30 fitted to the fork 20 and two accelerometers 19 located either side of the range of the centre of gravity for the load. The computations for this embodiment are also described below in further detail. 5 Figure 7 shows the embodiment of Figure 6 but showing both forks 20 located on either side of the lifting arm 14 and projecting forward of a beam 24 located at the end of the lifting arm 14. Figure 7 shows the location of the two load cells 30 in each fork 20. Each fork 20 also has either embedded or 10 attached to the fork 20 two accelerometers 19 located either side of the range for the centre of gravity of the load which would be contained within a container 31 which would be suspended from the forks 20. For each of the above embodiments the output of load cells 30 is 15 connected via an analog to digital converter and a filter for removing vibration to the input of the control system or central processing unit or computer. The output of the accelerometers 19 is also connected to an analog to digital converter the output of which is connected via filter to the control system. The control system also has a display output connected to a display unit 20 which is preferably located in the driver's cab 50, as best illustrated in Figures 1, 2 and 4. The computer includes a memory unit on which computed weights from each collection site can be stored. Alternatively, or additionally, each refuse truck 10 may be linked to a host computer via a wireless communication system, in which case the collected weights can be 25 transferred to the host computer via the wireless communication system. The installation of each load cell 30 on the respective lifting fork 20 is best illustrated in Figures 4 to 7. Each load cell 30 is secured between the cross bar mounting brackets and the inner end of the respective fork 20. A 30 first mounting plate is secured to the end of each fork 20, and a second mounting plate is secured to mounting brackets. The mounting plates are bolted to the opposite ends of each load cell 30 as illustrated. A mounting plate is secured to a plate by bolts and associated fixing means, while the mounting plate is also secured with bolts and associated fixing means. The 14 load cell 30 is of the bending beam type with relatively thin metal beams spanning an internal cavity, which may house additional beams or shear beams. 5 In use as a refuse can or container 31 is engaged by the forks 20 and as the container 31 is lifted, the total weight of the can and trash will be computed based on the outputs of the load cells 30 and the accelerometers 19. The can 31 is then inverted over the trash receiving opening in the top of the truck 10, and the trash will fall out of can 31 and into the body or 10 container 16 of the truck 10. The empty can 31 is lowered to the ground, and while it is being lowered the weight of the empty can is measured. The weight of material dumped is then computed by subtracting the second weight from the first weight and the truck control system records the weight of material dumped. 15 At the end of the day, the data collected is transferred to the host computer, either via a memory card or disk or by a wireless communication link. The weight collected at each location can be used to bill the customer according to weight of trash collected, which is preferable since landfills 20 typically charge waste collection companies based on the weight of trash dumped. The load sensing and computation of the actual weight of trash collected from each customer will now be described in more detail. 25 The invention described within provides a means of compensating for vibrations and eliminating the need for the operator to pause, thereby speeding up weighing operations. Without any form of compensation the mass measured by a standard beam load cell is as follows: 30 Indication (kg) = Loadcell (kg) * ay (g) Where: Indication = measured mass 15 Loadcell (kg) = scaled output of load cell ay (g) = acceleration in the y axis Note that ay (g) = 1g when the load platform is level and stationary. 5 From this equation we see that the indicated weight will be affected in proportion to the magnitude of the acceleration experienced by the mass to be measured. The embodiment shown in Figure 5 shows a fork 20 has a load cell 30 10 and a single accelerometer 19 embedded or located on the fork 20. Deflection of the load cell 30 will occur as a result of load on the forks 20, and an output signal proportional to the load will be produced on an output line of the load cell 30. 15 Figure 5 shows an improvement to the standard uncompensated measurement system. Note that for simplicity, only one half of the system is shown; typically this will be repeated for the second fork used to support the other side of the bin requiring weighing. 20 A miniature MEMS based accelerometer 19 is embedded or attached to the forks and is located at or close the centre of mass of the bin to be measured. Each measurement of weight is compensated as follows: 25 Loadcell (kg) Indication (kg) = e I accely Typically however these compensated values would be applied to some form of a filter to further reduce the effect of any mechanical vibrations. Filter rates and terms will be chosen according to the nature and frequency 30 of the anticipated vibrations.

16 This scheme is limited however by the requirement of the accelerometer to be located close to the centre of mass of the load, which may not be constant due to differing bin types, and or load distributions. 5 A further improved embodiment of the Invention is illustrated in Figure 6 which shows an improvement to the invention in which for each fork 20 a pair of accelerometers 19 are embedded in or attached to the forks 20. These accelerometers Al and A2 need to be located on either side of the anticipated range of the centre of mass of the bin. 10 The acceleration at the centre of mass of the bin is determined by the vector sum of the y axis outputs of accelerometers Al and A2: accely = (P * accelly) + ((1 - P) * accel2y) 15 Where: P = the relative position of the centre of mass of the bin, ranging from 0 to 1 20 ..Indication (kg) Loadcell (kg) (p* acce1y )+ ((1-p)* accel2y) It is probable that the accurate position of the centre of mass is unknown however this may be determined iteratively using many weight and acceleration samples and altering P until the variation in the indicated weight 25 is minimised. For a given collection of N samples ranging from [0..N-1], the values Yn , accel1n and accel2n are stored, where Yo = the loadcell output for that sample instance, and accelln and accel2n are the values of acceleration in 30 the Y axis for that same instance.

17 For each iteration a value p ranging from 0 - 1 is selected, and the following equation is evaluated: Yn (P * accel1n) + ((1 - P) * accel2n) 5 Then the N samples, the sum of the deviations squared from the mean Q is evaluated: N-1 v= (Qn- Q)2 n=O Finally the position value is chosen based on the minimisation of v 10 based on p. This value will be the optimum choice of centre of mass which results in the least variation of the compensated mass value. Note that many other methods are available to calculate this position (p), the concept based on this invention is the evaluation of the position of 15 the centre of mass based on a minimisation technique rather than the actual choice of computation method. In a practical system, two forks 20 would typically be employed, along with four accelerometers 19. The readings from the left and right sides of the 20 system may then be summed to determine the total weight of the unknown mass. Such a system is depicted in Figure 7. Prior to use the system will require a calibration procedure which includes but is not limited to calibration and compensation for such variables as the mounting angle and position of accelerometers, and may also include the application of a static load to the 25 load cells to calibrate the load cell. The embodiments described above all permit accurate measurement of the weight of trash dumped while operating either the lifting forks normally, without having to stop while readings are taken or by a weighing platform 18 with associated load cells and accelerometers. Compensations are made for the acceleration forces at or around the centre of gravity, and unwanted vibration and noise is filtered from the signal prior to computing the weight. 5 The present invention provides an accurate measurement of the weight of a load even under conditions where the contents of the container are liable to shift during lifting, causing more variations in the detected weight. The compensated net weight is an accurate and quick method of measuring the weight of a load. There is no requirement for the vehicle to 10 stop its operation in order to allow vibrations to stop and enable a reading of the weight of the load. This ensures that the speed of operation is continuous and uninterrupted. There is no need for the operator to wait until the structural oscillations of the machine have subsided before a weight measurement is taken. 15 The technique described above is suitable for vehicle mounted or other non-stationary weighing platform. This includes front loading trucks and any chassis mounted load cell system or any other system that involves the weighing of a load on a sprung platform. 20 In the specification the term "comprising" shall be understood to have a broad meaning similar to the term "including" and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or 25 steps. This definition also applies to variations on the term "comprising" such as "comprise" and "comprises".

Claims (29)

1. A system for weighing a load, the system comprising: a weighing platform having two parallel sides joined at either end to 5 form either a square or oblong shaped platform upon which a load can be placed; at least one sensor providing an output proportional to the force applied by the load; a plurality of accelerometers placed at locations around the platform 10 such that the accelerometers are located at or near the centre of gravity of the load on the platform; and a control system for computing the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; 15 ii) determining the position of the centre of mass of the load based on a minimisation technique and the outputs from the accelerometers and the at least one sensor; and iii) calculating a compensated mass of the load using the determined position of the centre of mass of the load. 20

2. A system for weighing a load according to claim 1, wherein the at least one sensor is a load cell and the load cells are placed at predetermined positions around the weighing platform. 25

3. A system for weighing a load according to claim 2, wherein at least two load cells are placed on either parallel side of the weighing platform.

4. A system for weighing a load according to claim 2 or claim 3, wherein three load cells are placed on either parallel side of the weighing platform 30 with one load cell located at each end of one parallel side and another load cell placed at the centre of the one side of the weighing platform.

5. A system for weighing a load according to any one of the preceding claims, wherein the weighing platform is mounted on a vehicle. 20

6. A system for weighing a load according to claim 5, wherein the vehicle is a refuse or waste collection vehicle.

7. A system for weighing a load according to claim 1, wherein the 5 plurality of accelerometers are miniature micro-electro-mechanical systems used to sense motion of the weighing platform when a load is placed on the weighing platform.

8. A system for weighing a load according to claim 7, wherein the 10 accelerometers are embedded or attached to the weighing platform.

9. A system for weighing a load according to claim 1, wherein the control system comprises: a first control device for association with at least one sensor and 15 adapted to generate an output representative of a weight sensed by said sensor; a second control device for association with the plurality of accelerometers and adapted to generate a compensation output representative of the acceleration of the load at or near the centre of gravity 20 of the load; a processor for computing the weight of the load by applying the compensated output of the second control device to the output of the first control device; and a storage unit for storing the net weight of the load. 25

10. A system for weighing a load according to claim 9, wherein the control system is located within a vehicle to which the weighing platform is mounted.

11. A system for weighing a load according to claim 9 wherein the 30 processor may be located remote from the vehicle to which the weighing platform is mounted and the first and second control devices may transmit their respective output signals to the remote location for processing by the processor. 21

12. A system for weighing a load according to any one of the preceding claims, further including a first filter between the load cells and the control system and a second filter between the accelerometers and the control system, the filters comprising means for filtering noise from the sensor output 5 signals.

13. A system for weighing a load according to claim 12, wherein the filters are digital filters. 10

14. A method of weighing a load, the method comprising the steps of: detecting the load carried by a weighing platform using at least one sensor and providing an output from the at least one sensor proportional to the force applied by the load; placing a plurality of accelerometers at a mean location of the centre 15 of gravity acting on the load on the weighing platform; computing the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; ii) determining the position of the centre of mass of the load 20 based on a minimisation technique and the outputs from the accelerometers and the at least one sensor; and iii) calculating a compensated mass of the load using the determined position of the centre of mass of the load. 25

15. A method of weighing a load according to claim 14 and comprising any one or more of the features of the system of claims 1 to 13.

16. A system for weighing a load contained in a container lifted by a lifting arm of a vehicle, the system comprising: 30 a sensor located on the neutral axis of the lifting arm, the sensor being adapted to sense shear stress in the lifting arm and provide an output proportional to the force applied by the load;; an accelerometer located on the lifting arm at a location at or near the centre of gravity of the load; 22 a control system for computing the weight of the load by: i) receiving the outputs from the accelerometers and the at least one sensor; ii) determining the position of the centre of mass of the load 5 based on a minimisation technique and the outputs from the accelerometers and the at least one sensor; and iii) calculating a compensated mass of the load using the determined position of the centre of mass of the load. 10

17. A system for weighing a load according to claim 16, wherein the sensor is a load cell.

18. A system for weighing a load according to claim 16, wherein the accelerometer is a miniature micro-electro-mechanical system used to sense 15 motion of the lifting arm when the container and load are placed on the lifting arm.

19. A system for weighing a load according to claim 18, wherein the accelerometer is embedded or attached to the lifting arm. 20

20. A system for weighing a load according to claim 16, wherein the control system comprises: a first control device for association with the sensor and adapted to generate an output representative of a weight sensed by the sensor; 25 a second control device for association with the accelerometer and adapted to generate a compensation output representative of the acceleration of the load at or near the centre of gravity of the load; a processor for computing the weight of the load by applying the compensated output of the second control device to the output of the first 30 control device ; and a storage unit for storing the net weight of the load. 23

21. A system for weighing a load according to claim 20, wherein the control system is located within a vehicle to which the lifting arm is mounted. 20. A system for weighing a load according to claim 18 wherein the 5 processor may be located remote from the vehicle and the first and second control devices may transmit their respective output signals to the remote location for processing by the processor. 21. A system for weighing a load according to any one of claims 14 to 20, 10 wherein the vehicle is a refuse, waste collection or recycling vehicle.

22. A system for weighing a load according to any one of claim 14, 16 or 17, wherein two or more accelerometers are located on the lifting arm at or near or either side of the centre of gravity of the load. 15

23. A system for weighing a load according to claim 14, wherein the container is lifted by two lifting arms located at either side or end of the container. 20

24. A system for weighing a load according to claim 23, wherein two or more accelerometers are located on the lifting arms at or near or either side of the centre of gravity of the load in the container.

25. A system for weighing a load according to any one of claims 16 to 24, 25 further comprising a first filter between the load cells and the control system and a second filter between the accelerometers and the control system, the filters comprising means for filtering noise from the sensor output signals.

26. A system for weighing a load according to claim 25, wherein the filters 30 are digital filters.

27. A method of weighing a load contained in a container lifted by a lifting arm of a vehicle, the method comprising the steps of: 24 providing a sensor on the neutral axis of the lifting arm, the sensor being adapted to sense shear stress in the lifting arm and provide an output proportional to the force applied by the load; lifting a container containing the load with the lifting arm; 5 placing an accelerometer at or near the centre of gravity acting on the load on the lifting arm; obtaining readings from the sensor and the accelerometer on the lifting arm; obtaining a value indicative of the weight of the load in the container 10 by compensating the shear stress in the lifting arm with the acceleration of the load at the location of the centre of gravity.

28. A method of weighing a load according to claim 27 and comprising any one or more of the features of the system of claims 16 to 26. 15

29. A weighing system for a refuse, waste collection or recycling truck, comprising: a lifting arm movably secured to the truck at one end and having lifting forks at an opposite end for engaging a container, the lifting arm being 20 movable between a lower position for engaging a container, a raised position for depositing material from the container into the truck, and back to the lowered position to release the emptied container; a load cell incorporated into each lifting fork for detecting the load carried by the lifting fork and providing an output signal proportional to the 25 force applied by the load; an accelerometer on the lifting fork located at or near the centre of gravity of the load on the lifting forks; and a processing unit including means for compensating the load cell output signals for acceleration forces and inclination of the lifting arm, means 30 for calculating the dynamic gross weight carried by the lifting forks as a container is raised and means for calculating the tare weight as the same container is lowered after emptying for each set of sensor outputs, and means for calculating the net weight of material deposited into the truck from the container based on the calculated dynamic weights.