Abstract:
The invention concerns a device comprising an electronic sensor ( 6 ) designed to deliver a compression signal and a shearing signal, and a comparator for comparing the shearing signal to a threshold value, so as to validate, or invalidate, the compression signal. The invention is useful for weighing aircraft.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for weighing an object by lifting it. It applies to the weighing of all kinds of objects, particularly heavy and bulky ones. However, it will be explained hereinafter in the more particular context of the weighing of aircraft. 
     It is known that, in order to weigh an aircraft, weighing devices each provided with an electronic compression sensor, for example arranged at the end of a ram or similar lifting appliance can be arranged under each of the wheelsets, and said airplane is lifted by action of said rams, said sensors being pressed between the corresponding ram and the corresponding wheelset. As a result, the measurement of the compressive load, which measurement is delivered by a sensor, is representative of the mass of that part of the aircraft which has been raised by the corresponding ram. 
     However, such a weighing can be representative of the true mass of the aircraft only if no parasitic transverse force, for example due to deformation of the aircraft, enters into the lifting operation during weighing. Hence, in order to be sure of obtaining a sufficiently precise measurement of the mass of an aircraft, the latter has to be transported to a special weighing site equipped with a fixed-station weighing system. 
     Of course such sites are expensive, and the business of weighing an aircraft is a lengthy one because said aircraft has to be taken to the special weighing site then taken away again. 
     It is an object of the present invention to overcome this drawback. The invention relates to a device allowing an aircraft to be weighed in situ without having to move it. 
     SUMMARY OF THE INVENTION 
     To this end, according to the invention, the device for weighing an object by lifting, comprising:
         a base;   a slide mounted so that it can move vertically on said base;   drive means for moving said slide with respect to said base;   an electronic sensor, secured to said slide in terms of vertical movement and arranged on said slide in such a way as to be inserted between the latter and said object when said drive means operate said slide in order to lift said object, said sensor delivering a first measurement signal representative of the compressive load to which it is subjected; and   means for reading said first measurement signal, is notable:   in that said electronic sensor is able, in a way known per se, in addition to deliver a second measurement signal representative of the shear load, transverse to said object, to which it is subjected; and   in that said device comprises comparison means for comparing said second measurement signal with a threshold value so as to validate, or invalidate, said first measurement signal.       

     It can thus be seen that, by virtue of the present invention, said first measurement signal (that is to say the measurement of the mass of the aircraft in the example above) is validated only if the second measurement signal (that is to say the parasitic transverse force) is below said threshold. 
     Of course, the value of said threshold is chosen so that, when it validates said first signal, the value of the latter corresponds to the mass of said object with sufficient precision and so that, when it does not validate said first signal, the value of said first signal is not representative of said mass with sufficient precision. 
     Said threshold value may be predetermined and correspond to a value of said second measurement signal above which said first measurement signal is no longer representative of the true mass of said object. 
     As an alternative, said threshold value may correspond to a predetermined fraction of said first measurement signal above which the latter is no longer representative fo the true mass of said object. 
     Furthermore, to allow said sensor to center itself spontaneously under said object and limit the parasitic transverse shear loadings, said sensor is mounted on said slide in such a way as to be able, within certain limits, to slide freely in a horizontal direction transversal to said object. 
     As a preference, so as to be able to be moved around and placed under said object with ease, the weighing device according to the present invention is mounted on a mobile carriage. Such a mobile carriage can be moved around in the manner of garage jacks used to jack up automobiles. As an alternative, it may be motorized. 
     The figures of the appended drawing will make it easy to understand how the invention may be embodied. In these figures, identical references denote similar elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows, in perspective from above and the front, one practical embodiment of the weighing device according to the present invention. 
         FIG. 2  is a part view from above of this weighing device, in the direction of arrow II of FIG.  1 . 
         FIG. 3  is the block diagram of the electrical measuring circuit of the device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Device  1  for weighing by lifting, depicted in perspective in  FIG. 1 , comprises a base  2 , a slide  3  mounted so that it can move vertically on the base  2 , as symbolized by the double-headed arrow  4 , and an electric or hydraulic motor  5  allowing the slide  3  to be moved with respect to the base  2 . The device  1  additionally comprises an electronic sensor  6  able to deliver, on the one hand, a signal measuring compression, when subjected to a compressive loading (symbolized by the arrow  7 ) and, on the other hand, a signal measuring transverse shear (symbolized by the arrow  8 ). The electronic sensor  6  is borne by a support  9  connected to said slide  3  by two horizontal pins  10  and  11  parallel to said transverse shear loading  8 . 
     The collection of elements  2 ,  3 ,  5 ,  6 ,  9 ,  10  and  11  is borne by a carriage  12  provided with wheels  13  and with a pivoting lever  14  (arrow  15 ) allowing said carriage  12  to be guided in the customary way as it moves and allowing the wheels  13  to be prevented from turning when stationary. 
     As can be seen in greater detail in the partial plan view of  FIG. 2 , the slide  3  comprises two parallel vertical walls  16  and  17  projecting toward the support  9 . Likewise, the latter has two vertical walls  18  and  19  which are mutually parallel and parallel to the walls  16  and  17 , projecting toward the slide  3 . In the embodiment depicted in  FIG. 2 , the walls  18  and  19  are arranged on each side of the walls  16  and  17 . 
     Each of the two pins  10  and  11  passes through the four walls  16  to  19  and said pins are mounted with respect to said walls in such a way that the support  3  can slide freely parallel to said pins  10  and  11 , with respect to the slide  3 , as symbolized in  FIG. 2  by the double-headed arrow  20 . Of course, the sliding travel is limited by the collaboration of walls  16  and  18 , on the one hand, and by the collaboration of the walls  17  and  19 , on the other. 
     As is shown in  FIG. 3 , the weighing device  1  comprises a measurement circuit  21 , not visible in FIG.  1 . This measurement circuit  21  comprises a reading and display device  22  receiving, via a link  23 , the compressing measurement signal generated by the electronic sensor  6 . The shear measurement signal, also generated by the electronic sensor  6 , may also be sent to the reading and display device  22  as appropriate, via a link  24 . 
     The measurement circuit  21  additionally comprises a comparator  25  receiving, on one of its two inputs, via a link  26 , said shear measurement signal generated by the electronic sensor  6  and, on its other input, via a link  27 , a threshold value available at a terminal  28 . 
     This threshold value may be predetermined and applied to the terminal  28  by a generator (not depicted). As an alternative, this threshold value may be generated by a divider  29  receiving, via a link  30 , the compression measurement signal and sending a fraction of said signal to said terminal  28  via a link  31 . 
     Furthermore, the electronic sensor  6  bears, on its sensitive upper face, a centering block  32  provided with a centering cavity  33 . 
     The way in which the weighing device according to the present invention works is as follows. 
     An operator brings the carriage  12  under the object for weighing (for example an airplane, not depicted) so that said centering block  32  lies approximately facing a centering block  34 , provided especially for this purpose under said object and provided with a centering projection  35  that complements the centering cavity  33  of said centering block  32 . 
     The operator then operates the motor  5  and the slide  3  rises, moving the sensor  6  nearer to the object for weighing. AS the slide  3  continues to rise, the cavity  33  of the centering block  32  collaborates with the projection  35  of the centering block  34  to improve the transverse centering of the sensor  6  with respect to the object for weighing so that said sensor  6  is able to move in a limited way (arrow  20 ) by virtue of the slide pins  10  and  11 . 
     The rising of the slide  3  is halted when, through collaboration between the blocks  32  and  34 , the object for weighing has been lifted by said slide  3 . 
     The compressive measurement signal (the weight) and possibly the shear measurement signal (the transverse loading) are sent to the read and display device  22  via the links  23  and  24  respectively. 
     In addition, via a link  35 , the comparator  25  sends the read and display device  22  the result of the comparison between said shear measurement signal and the threshold value present on the terminal  28 . 
     As a result, if the transverse loadings  8  are low enough not to adversely affect the precision of the weight (a fact which is represented by said threshold value), said weight is displayed on the device  22 . 
     By contrast, if the transverse loadings  8  are too high and are adversely affecting the precision of the weight, the comparison signal carried by the link  35  inhibits the displaying of said weight or indicates that this weight is not reliable. 
     Of course, to weigh an object as heavy and bulky as an airplane, use may be made of several weighing devices  1 , preferably each arranged under one wheelset and synchronized with the others in terms of operation. 
     Although an embodiment comprising a carriage  12  that can be moved around in the manner of a garage jack used for jacking up automobiles has been described hereinabove, it goes without saying that said mobile carriage could be motorized using any known motorizing means, for example a battery-powered electric motor.