The subject of the present invention is a device for determining the weight of an object. The device according to the invention makes it possible to determine simply and precisely the weight of moving or stationary objects.
It is known practice to measure rolling loads in a static manner with the aid of weighbridges or equivalent systems.
These systems are particularly costly. They may in particular require special routes for gaining access to the weighing areas. The drawback of this is that it causes waste of time associated with the necessities of immobilizing the loads on the weighing area while weighing takes place, and expenditure on personnel assigned to this type of measurement.
The object of the invention is to remedy these drawbacks.
It proposes a device making it possible to measure the weight of objects precisely and economically, in particular the weight of moving objects such as vehicles that can run at high speed and notably at a cruising speed.
The subject of the invention is therefore a device for determining the weight of an object, comprising at least one object support of elongate shape placed on at least a first and a second bearing surface, and processing means capable of computing the weight of the object, irrespective of the position of the object on the object support between a first measurement cross section situated on the side of the first bearing surface and a second measurement cross section situated on the side of the second bearing surface.
According to the invention, the processing means are, capable of determining the weight of the object based on the addition or the subtraction of two values of a physical parameter chosen between the bending moment and the shearing force, the said values being added together if the physical parameter is the bending moment or subtracted if the physical parameter is the shearing force, the distance between the first measurement cross section and the first bearing surface being equal to the distance between the second measurement cross section and the second bearing surface if the physical parameter is the bending moment, the said values being determined at the measurement cross sections using distortion gauges, the distortion gauges being placed in twos symmetrically relative to the neutral plane of the object support.
By virtue of the fact that the addition or subtraction of the values of the physical parameter gives a result proportional to the weight of the object, the assembly makes it possible to easily determine the weight of the object, with the aid of a calibration with reference weights.
The neutral plane is the plane that is situated inside the object support and that is the surface formed by the fibres of the object support which sustain neither shortening nor lengthening and retain a constant length. In the bending phenomena, the shearing stresses due to the shearing force are maximal at the neutral plane and the bending (tension, compression) stresses are maximal in absolute values on the upper and lower faces of the object support, the shearing stresses being zero at this level.
The use of the distortion gauges also makes it possible to obtain particularly precise measurements.
A distortion gauge is a component that makes it possible to monitor the distortions of materials subjected to stresses, by means of the variations in resistance of an electrical conductor.
Each object support is advantageously a beam.
The specific assembly of the distortion gauges into a complete Wheatstone bridge makes it possible to obtain an output electrical signal from the bridge that is proportional to the weight of the object. The distortion gauges may therefore be connected together to form a Wheatstone bridge, so that the potential difference at the output of the bridge is proportional to the weight of the object.
In a first embodiment, the physical parameter is the bending moment. In this case, the distance between the first measurement cross section and the first bearing surface is equal to the distance between the second measurement cross section and the second bearing surface.
For this first embodiment, the distortion gauges advantageously comprise, at each measurement cross section, two upper gauges placed lengthwise above the neutral plane, on either side of the longitudinal vertical plane of symmetry of the object support, and two lower gauges placed lengthwise beneath the neutral plane, the lower gauges being the symmetrics of the upper gauges relative to the neutral plane.
The upper gauges are preferably symmetrical relative to the longitudinal vertical plane of symmetry of the object support and the lower gauges are preferably symmetrical relative to the longitudinal vertical plane of symmetry of the object support.
In a second embodiment, the physical parameter is the shearing force. In this case, the distortion gauges advantageously comprise, at each measurement cross section, two assemblies of two gauges placed on the neutral plane, on either side of the longitudinal vertical plane of symmetry of the object support, each assembly of gauges comprising two gauges that are orthogonal and inclined at 45° relative to the neutral plane.
The two assemblies of two gauges on each measurement cross section are preferably symmetrical relative to the longitudinal vertical plane of symmetry of the object support.
For each physical parameter, the distortion gauges of the measurement cross sections are advantageously connected to form a Wheatstone bridge so as to determine the weight of the object based on a signal that is unique and specific to each physical parameter.
The device according to the invention may comprise at least two object supports. This variant, which may be used with the first or the second embodiment, is particularly suitable for measuring the weight of objects moving at high speed over several object supports, such as for example motor vehicles.
In general, the object supports may be substantially parallel, and preferably parallel.
The device may belong to a pre-existing moving or stationary structure. For example, it is possible to envisage measuring the weight of the object by fitting extensiometer gauges to the cross-beam of a travelling crane provided that this beam fulfils the processing conditions defined above. Similarly, a tipping lorry or a cement-mixer lorry could be fitted with an on-board system of the same principle if there is in its structure a beam fulfilling the conditions of the invention. In general, the device may be fitted to any type of pre-existing structure if there is in this structure one or more beams fulfilling the said conditions.
A further subject of the invention is the use of a device described above for determining the weight of a moving object.
Finally, it has as subject the use of a device described above for determining the weight of several objects supported simultaneously by the object support.
Other features and advantages of the present invention will appear more clearly on reading the following description given as an illustrative and non-limiting example, and made with reference to the appended drawings in which:
The device 1 for determining the weight of an object, as illustrated in
Between the two bearing surfaces, two measurement cross sections α and β are chosen which are situated at an equal distance and preferably at a 25 short distance a from the bearing surfaces. An object of weight Q is situated on the beam 5, between the measurement cross sections α and β, at a distance x from the bearing surface situated at the end A.
The diagram of
Accordingly, as illustrated in
In the same manner, four distortion gauges 3,4,3′,4′ are placed at the cross section 3. The distortion gauges are placed in the same manner as the gauges 1,2,1′,2′ with respect to the beam 5.
A distortion gauge is based on the property that certain materials have wherein their conductivity varies when they are subjected to distortions. Since the variations of resistance are slight, it is preferable to make use of a Wheatstone bridge assembly as illustrated in
Powered by a voltage source, the bridge has, in equilibrium, a zero output differential voltage, but the variation from one to the other of the resistances exhibits a non-zero output differential voltage. This assembly makes it possible to add the electrical resistance variations of the gauges in compression and in tension. Moreover, the complete bridge assembly compensates for the variations of the gauges as a function of the temperature, which means that the resultant measurement is not adversely affected.
Thus, the resistances of the gauges 1,2 and 3,4 on the one hand, and of the gauges 1′,2′ and 3′,4′ on the other hand, the signal of which is desired to be added together, are placed in opposition in the bridge. The output signal from the bridge is consequently proportional to the total of the bending moments Mα and Mβ, and is therefore proportional to the weight of the object. The weight of the object can then be easily determined with the aid of a calibration.
In a second embodiment, as illustrated in
As illustrated in the diagrams of
There is no electrical contact between the gauges which cross mechanically. The gauges 1,2,1′,2′ and 3,4,3′,4′ are symmetrical relative to the vertical axis (mn). The gauges can be grouped into twos in an assembly called a rosette assembly.
The electrical assembly of the gauges is illustrated in
In general, the analogue differential signal output from the Wheatstone bridge is processed by instrumentation that polarizes the bridge, amplifies the analogue signal, makes an analogue-digital conversion and digitally filters the signal. A central processing unit then digitally processes the information and can store it in memory. It is therefore possible to record the values of the measurements and carry out all the processing necessary to exploit them depending on the desired final application, such as for example the display of the weight of a load or the total weight of several loads on a digital display. In this instance, the number of successive loads can be programmed. The measurement protocol can be produced by an operator or a non-specialist user. The operator selects the static weighing mode or dynamic weighing mode. In the case of static weighing, the weight of the load is displayed instantaneously, for example on the display. In the case of dynamic weighing, the operator programmes the number of successive loads, then he selects the cyclicality of the successive loads either manually with the aid of an “on or off” actuator, or automatically by triggering an “on or off” sensor, as the moving load passes. The operator begins measurement with the aid of an “on or off” actuator. When the weighing of the number of programmed loads is complete, the total weight is for example displayed.
In a variant of the second embodiment, as illustrated in
In a variant of the first embodiment, as illustrated in
The device according to the invention therefore makes it possible to weigh vertical, static or mobile loads, such as for example moving loads. The mobile loads can move over one or more horizontal and parallel beams that rest on two or more bearing surfaces. The loads may move either lengthwise over one or more parallel beams, typically over two beams, or perpendicularly to a single beam. The loads that move longitudinally over one or more parallel beams can move at high speed. The device according to the invention is particularly suitable for detecting overloading of heavy goods vehicles and allows enhanced control of this detection.
The invention therefore makes it possible to dispense with the use of multiple sensors of the load cell type or piezoelectric sensors, the use of which involves high cost and often requires the processing of one analogue signal per load cell. By virtue of the device according to the invention, it is also possible to weigh moving loads at high speed with an accuracy of the order of 2%, while the high-speed weighing systems using piezoelectric sensors provide an accuracy of the order of only 20%. This is due to the fact that the beam itself forms the sensor with a constant signal over the whole length of measurement. The device allows multiple usages with various configurations using one or more weighing beams, but requiring only one signal to be processed.
Number | Date | Country | Kind |
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0957871 | Nov 2009 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR10/52356 | 11/3/2010 | WO | 00 | 3/22/2012 |