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(11) | EP 0 913 342 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and device for determining the weight of the dumped contents of a refuse receptacle |
| (57) 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. |
[0001] The invention relates to a method for determining a weight-dependent quantity for dumped contents of a refuse container, comprising moving the container upwards, tilting it and moving it back in such a way that the container is emptied, measuring the gross weight of the container, including contents, during the upwards movement, measuring the tare weight of the container during the downwards movement, and, depending on the gross weight and the tare weight, calculating the value of the weight-dependent quantity.
[0002] It is known that a method of this nature 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.
[0003] 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.
[0004] 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.
[0005] Furthermore, the known method determines the weight rather than the mass of the refuse container, while the weight is dependent on the geographically different gravitational acceleration.
[0007] This object is achieved, according to the invention, by means of the method as described in claim 1.
[0008] 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.
[0010] Other features and advantages of the invention will emerge from the following explanation given in combination with the appended figure.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0017] 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).
[0018] 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.
[0019] 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.
[0020] 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.
[0022] 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.
[0023] 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.
[0024] When position B is reached, a weighing time window is opened and the movement of the arm 10 in the upwards direction is accelerated.
[0025] 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.
[0026] For the downwards movement of the arm 10, the same weighing time window can be used as for the upwards movement.
[0027] 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.
[0028] At each time ti, or for each sample i, where i = 1, ..., n (500 in this example), the following applies:
or
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.
[0029] 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:
or
[0030] The sum ΣFi (first sum) and the sum Σai (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.
[0031] 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 ΣFi. 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.
[0032] 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).
[0033] 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.
1. Method for determining a weight-dependent quantity for dumped contents of a refuse
container (33), comprising moving the container upwards, tilting it and moving it
back in such a way that the container is emptied, measuring the gross weight of the
container, including contents, during the upwards movement, measuring the tare weight
of the container during the downwards movement, and, depending on the gross weight
and the tare weight, calculating the value of the weight-dependent quantity, characterized
in that both during the upwards movement and the downwards movement a first series
of values for the weight and a second series of values for the vertical acceleration
of the container 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, as
the weight-dependent quantity, the mass of the dumped contents of the container.
2. Method according to claim 1, characterized in that the values from the first series
and from the second series are measured respectively up to and from approximately
the maximum height (C, D, E) to which the container (33) is moved.
3. Method according to claim 1, characterized in that, before the values from the series
are measured 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, and the values from the first series and from
the second series are measured respectively up to and from approximately the maximum
height to which the container is moved.
4. Device for determining a weight-dependent quantity for dumped contents of 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) for measuring the gross weight of the container including contents during the
upwards movement and for measuring the tare weight of the container during the downwards
movement, and calculation means for calculating the value of the weight-dependent
quantity as a function of the gross weight and the tare weight, characterized in that
second measurement means are provided, an acceleration sensor (25) of which is suitable
for measuring the vertical acceleration of the grip means (14), the first measurement
means measure a first series of values for the weight, for each of the directions
of movement, the second measurement means measure a second series of values for the
vertical acceleration of the grip means (14), for each of the directions of movement,
the calculation means calculate a first sum and a second sum of the values from the
first series and the second series, respectively, for each of the directions of movement,
the calculation means divide the first sum by the second sum to obtain a gross mass
value and a tare mass value, respectively, and the calculation means subtract the
tare mass value from the gross mass value in order to obtain the mass of the dumped
contents of the container as the weight-dependent quantity.
5. Device according to claim 4, characterized in that the first and second measurement
means measure the values of the series respectively up to and from approximately the
maximum height (C, D, E) to which the container (33) is moved.
6. Device according to claim 4, characterized in that detection means are provided which,
prior to the measurement by the measurement means, 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, and the first and second measurement means measure
the values from the first series and the second series respectively up to and from
approximately the maximum height to which the container is moved.
7. Device according to claim 4, characterized in that the acceleration sensor (25) is
attached to the load cell (24).