EP0913342B1

EP0913342B1 - Method and device for determining the weight of the dumped contents of a refuse receptacle

Info

Publication number: EP0913342B1
Application number: EP98203576A
Authority: EP
Inventors: Paul Jan Bernard Nijdam
Original assignee: EXPL MIJ DE BERGHAAF BV; Exploitatiemaatschappij Berghaaf BV
Current assignee: Exploitatiemaatschappij Berghaaf BV
Priority date: 1997-10-29
Filing date: 1998-10-22
Publication date: 2004-03-17
Anticipated expiration: 2018-10-22
Also published as: ATE261884T1; DE69822398D1; DE69822398T2; EP0913342A1; NL1007388C2

Abstract

Method and device for determining the weight of the dumped contents of a refuse receptacle (33), the receptacle successively being gripped, moved upwards, tilted so as to be emptied and moved back, while the weight and the acceleration of the receptacle with and without contents are respectively measured both during the upwards movement and the downwards movement, in such a manner that, for each of the movements, a first series of values for the weight and a second series of values for the vertical acceleration are measured, a first sum and a second sum of the values from the first series and second series, respectively, are determined, the first sum is divided by the second sum for the purpose of determining a gross mass during the upwards movement and for the purpose of determining a tare mass during the downwards movement, and the tare mass is subtracted from the gross mass for the purpose of determining the mass of the dumped contents of the receptacle. <IMAGE>

Description

The invention relates to a method according to the preamble of claim 1.
A method of this type is disclosed by EP-A-0402352. With the prior art method, when during an upwards or downwards movement the weight of a load is measured, at the same time the acceleration experienced by the load is measured. Then a measured weight value is divided by a measured acceleration value resulting in a value for the mass of the load at the time of said measurements. During each movement several of such pairs of measurements and related calculations of the mass are carried out. Then an average value for the mass of the load is calculated from the individual calculated mass values corresponding to said pairs of measurements respectively.
The prior art method has the disadvantage that the result, i.e. said calculated average for the mass of the load, is highly dependent on the measurements of each of said pairs of measurements being carried out at exactly the same time. Further, since a means for measuring the weight is not the same means for measuring the acceleration and therefore the weight and acceleration are measured at different locations, a mechanical disturbance at some place of the system will evolve differently towards the different measuring means, so that measuring signals or samples taken therefrom at some specific short moment of time will contain changes which may be caused by the same event but the correlation of which is unknown and time dependent. Since in practice it will be likely that vibrations in the measuring system will occur a mass value calculated from a weight value and an acceleration value measured at a specific time may have a wide range of uncertainty due to disturbances. Uncertainty cannot be ruled out by calculating an average of several individual calculated mass values if the individual values all have such uncertainty range, as is the case in practice.
A method of the above type is employed for emptying containers which contain, in particular, domestic refuse into a loading space of a refuse-collection vehicle. By determining the weight of the contents of the containers, it is possible to determine the degree of loading of the vehicle, so that it is possible to check the value of the net weight of waste in the vehicle, for which an operator of the vehicle may be charged, by means of a weighbridge at a refuse depot. On the other hand, it is possible to charge individuals who present the containers as a function of the net weight of the contents which is measured. Using this method has the drawback that the values of the net weights which are calculated are relatively inaccurate, with the result that only a crudely assessed financial charge can be imposed on the individuals presenting the containers and these individuals have less incentive to produce as little refuse as possible, which in turn is disadvantageous to the environment.
The inaccuracy of the calculated values of the net weights has various causes. Firstly, in the known method it is necessary for the weight to be measured, both during the upwards movement and during the downwards movement, only when the velocity of the movement is steady. However, the mechanical device which has to ensure that this has considerable difficulty doing so. In the case of a hydraulic lifting device, it is necessary, during the steady movement, for example for a constant volumetric flow rate of the medium to lifting cylinders to be achieved, and static friction between the medium and the internal wall of the hoses and the like which convey the medium may cause the movement to jolt. Furthermore, the ends of the lifting cylinders generally engage on points which, under a constant flow of medium, detract from the desired uniformity of the movement, so that the flow of medium for this would have to be compensated as a function of the lifting height. Furthermore, load cells have a preferred measurement direction, i.e. an output signal thereof represents a component of the weight which is resolved vectorially in a specific direction, rather than the total weight. Since the vectorially resolved weight component is dependent on the angle between the preferred measurement direction of the load cell and a vertical line, the result is a measurement error which is dependent on the angle of inclination of the vehicle and on the angle of swing of a lifting arm to which the cell is attached and which is used for lifting the container.
The consequence of the abovementioned drawbacks is that the weight of the container can only be determined during a relatively short section of the total movement height, while the final measurement error is still significant.
The object of the invention is to eliminate the abovementioned drawbacks.
This object is achieved, according to the invention, by means of the method as described in claim 1.
This method makes the calculated mass quantity largely insensitive to changes in the acceleration of the container during the upwards and downwards movements thereof and makes the mass value calculated substantially insensitive to whether or not these movements are purely vertical. Consequently, the measurements and calculations can extend over longer sections of these movements and differences in the measured values can be compensated. Furthermore, as a result, a high level of accuracy of the calculated mass of the contents of the container is achieved.
The invention also relates to a device as described in claim 4.
Other features and advantages of the invention will emerge from the following explanation given in combination with the appended figure.
The figure shows a rear section 1 of a refuse-collection vehicle, in particular for collecting domestic refuse. The rear section 1 of the vehicle is a loading section and has a lower conveying chute 2 having a base 3 and an opening 4 for tipping in refuse and, above these, and separated therefrom, an upper conveying chute 5 with a base 6 and an opening 7 for tipping in refuse.
At the rear side of the vehicle, there is arranged a lifting device which comprises two identical, parallel arms 10, front ends of which can rotate about a common shaft 11 and rear ends of which are coupled to an engagement seat 14 which can rotate about a common pin 12.
A front end of a hydraulic cylinder 15 is coupled to the vehicle in such a manner that it can rotate about a horizontal pin 16, while a rear end of the cylinder 15 is coupled to the arm 10 in such a manner that it can rotate about a horizontal pin 17 and is at a distance from the axis of the arm 10. By means of the cylinder 15, the seat 14 can be moved upwards and downwards with respect to the vehicle along a curved path which is indicated by the double arrow 18.
The seat 14 comprises a front section 21 and a rear section 22, between which a load cell 24 is arranged. An acceleration sensor 25 is attached to the load cell 24. The preferred measuring directions of the sensors 24, 25, i.e. the directions in which they supply the most significant and/or most accurate measurement signals, are preferably parallel to one another.
Between the seat 14 and the rear section 1 of the vehicle, there is arranged a structure which is known per se and a section of a cylinder 26 of which is shown and by means of which the seat 14 can be rotated about the pin 12 in the direction of the double arrow 27 without affecting a measurement signal supplied by the load cell 24.
A receiving comb 28 is arranged on the top of the rear section 22 of the seat 14.
On the bottom, the rear section 22 of the seat 14 has a flexible suction cup 29, a suction chamber of which is open at the rear and is in communication with evacuation means (not shown).
In the vicinity of a bottom position of the seat 14, a casing 31 is arranged on the vehicle, in which casing optical detection means (not shown in more detail) are arranged for the purpose of detecting one or more properties of an object on which the receiving comb 28 and the suction cup 29 engage.
The load cell 24, the acceleration sensor 25 and the detection means in the casing 31 are electrically connected to a computer device (not shown) which is arranged in the cab of the vehicle.
The seat 14 is suitable for engaging on and holding various types of containers with various dimensions and contents, such as the container 33 illustrated, by means of its receiving comb 28 and suction cup 29. The container 33 comprises a barrel 34 and a lid 35 which, at the rear side of the container 33, can rotate about a horizontal pin. At the top, the barrel 34 has a collar or rim 37 which is folded downwards and into which the receiving comb 28 can be inserted at the front for the purpose of suspending the container 33 therefrom. A label 38 is arranged on the front of the container 33, which label includes a code area 39, for example comprising dots, which determines one or more properties of the container 33. Some of the properties, which can be derived from the code area 39 either directly or by consulting a data file, indicate the type of container, i.e. the size of the container 33, and/or the type of contents for which the container is intended. With regard to the latter, it can be noted that a container may be intended only for compostible waste, only for noncompostible waste or for both types of waste. In the latter case, the container 33 may be provided with a vertical partition 42 which divides the container 33 into a front compartment 43 for, for example, compostible material and rear compartment 44 for, for example, noncompostible material.
The device operates as follows:
From a bottom position A, which is shown by dashed lines, of the lifting and tilting means 10-17, the arm 10 is moved upwards, so that the receiving comb 28 engages on the bottom of the collar 37 of the container 33 and the suction cup 29 bears against the container 33 and is sucked onto the container 33 by means of the evacuation means.
Between the height positions A and B, the arm 10 moves relatively slowly upwards and the detection means arranged in the casing 31 detect the code area 39 of the container 33 which is held by the seat 14.
When position B is reached, a weighing time window is opened and the movement of the arm 10 in the upwards direction is accelerated.
Depending on the type of container 33 detected, the arm 10 is moved to the height position C, the higher position D or the even higher position E. On approaching the maximum height intended for the particular type of container 33, the movement of the arm 10 is decelerated. When the maximum height has been reached, or a short time before it is reached, the weighing window is closed. When the maximum height is reached, the cylinder 26 is actuated, so that the seat 14, together with the container 33, will rotate about the pin 12 sufficiently far for the container 33 to be emptied via the opening 4 and/or the opening 7. If the container 33 is tilted into position C, the entire contents of the container are tipped into the chute 2. If the container 33 is tilted into position D, the top edge of the partition 42 will bear against the top edge of the inclined section of the base 6 of the top conveying chute 5, with the result that refuse from the compartment 43 of the container 33 can be tipped into the chute 2 and refuse from the compartment 44 of the container 33 is tipped into the chute 5. If the container 33 is tilted into position E, the entire contents of the container are tipped into the chute 5.
For the downwards movement of the arm 10, the same weighing time window can be used as for the upwards movement.
During each weighing window, the computer device takes successive samples of the output signals which are transmitted by the load cell 24 and the acceleration sensor 25. For each of the upwards and downwards movements, from each output signal, by way of example, 100 samples are taken per second, in particular more than twice the highest vibration frequency (Nyquist frequency) of the container 33 in the seat 14. Then, for each of the movements, a first series of samples for the weight and a second series of samples for the acceleration are obtained, each comprising approximately 500 samples.
At each time t_i, or for each sample i, where i = 1, ..., n (500 in this example), the following applies: Fi = ai·m or ai = Fi/m where F is the force measured by the load cell 24 and m and a are respectively the mass and the acceleration of the mass as measured by the acceleration sensor 25 and causing the force F.
Since mass is a constant, nondirectional variable, while the sensors 24, 25 cannot move with respect to one another, the following applies to the sum of n acceleration samples: Σai = F1/m + ... Fn/m = (ΣFi)/m or m = (ΣFi)/Σai.
The sum ΣF_i (first sum) and the sum Σa_i (second sum) can be obtained simply by adding up the relevant samples, so that the mass m can also be calculated simply by dividing the first sum by the second sum.
Although the contents of the container 33 and the fact that the container is suspended from the receiving comb 28 may cause a variation in the measurement of the weight, owing to the short duration of the vibration and the compensation by adding up a relatively large number of samples of the measurement signal for the weight, this has no effect, or scarcely any effect, on the first sum ΣF_i. Furthermore, because the acceleration sensor 25 is arranged on the seat 14 and not on the container 33, the acceleration sensor 25 will not experience the said vibration. As a result, the mass calculated according to the formula given above is independent of the said vibration.
Since a mass rather than a weight is determined, the result is independent of the local gravitational acceleration, independent of any slope on which the vehicle is standing and independent of a distance over which measurements are carried out during the movements of the container 33. As a result, it is also possible to carry out measurements over a great distance and to successfully compensate for variations in the measured values (lower than the Nyquist frequency).
For the upwards movement, a value of the gross mass of the seat 14 and the container 33 with contents is obtained. For the downwards movement, a value of the tare mass of the seat 14 and the container 33, which may or may not have been completely emptied, is obtained. By subtracting the value of the tare mass from the value of the gross mass, the desired value of the net mass of the refuse which has been tipped into the vehicle from the container 33 is obtained.
It should be noted that various types of sensors which are known per se and which may or may not have a preferred measuring direction can be used for the sensors 17 and 18.

Claims

Method for determining a mass quantity of refuse which is dumped from a refuse container (33), comprising moving the container upwards, tilting it and moving it back in such a way that the container is emptied, sensing the weight and the acceleration of the container during the upwards and downwards movements for providing a weight measurement signal and an acceleration measurement signal respectively, taking a series of samples from each of said measurement signals, calculating a gross mass from said samples taken during the upwards movement, calculating a tare mass from samples taken during the downwards movement and subtracting the calculated tare mass from the calculated gross mass for providing the mass of the dumped refuse, characterized in that for each of said movements samples taken from the weight measurement signal are summed for providing a first sum for a gross weight and samples taken from the acceleration measurement signal are summed for providing a second sum for the acceleration, and for each of said movements the first sum is divided by the second sum to provide a value for said gross mass and a value for the tare mass respectively.
Method according to claim 1, characterized in that the taking of samples during the upwards movement is carried out until a maximum height (C, D, E) to which the container (33) is moved is reached, and the taking of samples during the downwards movement is started from said maximum height.
Method according to claim 1 or 2, characterized in that, before taking samples during the upwards movement a property of the container (33) is measured, which property represents the type of container and prescribes the maximum height (C, D, E) for the upwards movement.
Device for determining a mass quantity of refuse which is dumped from a refuse container (33), comprising grip means (14), lifting means (15) and tilting means (27) for gripping the container (33), moving it upwards, tilting it and moving it back, for the purpose of emptying the container, first measurement means having a load cell (24) which provides a weight measurement signal for measuring the gross weight of the container including the refuse during the upwards movement and for measuring the tare weight of the container during the downwards movement, second measurement means having an acceleration sensor (25) for providing a second measurement signal for measuring the vertical acceleration of the grip means (14), the first means being suitable for taking a first series of samples from the first measurement signal for each of said movements, the second measurement means being suitable for taking a second series of samples from the second measurement signal for each of said movements, and calculation means for calculating a gross mass from samples taken during the upwards movement, a tare mass from samples taken during the downwards movement and for subtracting the calculated tare mass from the calculated gross mass for providing the mass of the dumped refuse, characterized in that for each of said movements the calculation means sums the samples taken from the first measurement signal, the calculation means sums the samples taken from the second measurement signal for providing a second sum, and for each of said movements dividing the first sum by the second sum for providing a value for the gross mass and a value for the tare mass respectively.
Device according to claim 4, characterized in that the taking of samples during the upwards movement is carried out until a maximum height (C, D, E) to which the container (33) is moved is reached, and the taking of samples during the downwards movement is started from said maximum height.
Device according to claim 4 or 5, characterized in that detection means are provided which, prior to taking samples, detect a property of the container (33) which represents the type of container and prescribes the maximum height (C, D, E) for the upwards movement.
Device according to claim 4, characterized in that the acceleration sensor (25) is attached to the load cell (24).