FR2811753A1 - Portable or pocket personal scales for weighing people or animals has layer covering pressure sensor and surface cap to hold the feet of the user - Google Patents

Abstract

Scales comprise one or more weighing surfaces (2) consisting of a base (4) on top of which a pressure sensor is glued or fixed. The sensor is of polymer surface piezo-sensitive type. A covering layer (5) is glued on top of the sensor for better weight distribution and finally a surface cap (6) is designed to hold the foot or feet of the person being weighed and serve as a cover when the device is carried around. The sensor is linked to an electronic module for analyzing the signal and displaying a weight. The device can be supplied with two or four weighing surfaces for use with a human or an animal.

Description

-

POCKET SCALE

  The present invention relates to an ultra-light and miniaturized bathroom scale intended to measure and clearly display the weight of a person using electronic devices. The technical sector of the invention is the general public domain, but not only, of

  the weight assessment of people traveling.

  The method and device of the present invention can be used in any application, where a determination of the weight, of a person or of an object is sought. However, to simplify the presentation of the prior art, the following will essentially be cited:

  references to the applications of scales and scales.

  The weighing of people is traditionally carried out using mechanical or electronic scales which have relatively large dimensions and weight, thus limiting their use at a fixed station. We have known for a long time, dynamometric mechanical scales whose principle of measurement is based on the deformation of a spring under the effect of weight. By virtue of their principle, as well as their display mode, these devices do not lend themselves to light and compact constructions. Likewise, commercial electronic scales generally consist of two high-stiffness plates, between which there are one or more force sensors, the weight measurement electronics, the supply battery and the display device. weight. The sensors used, whether they are resistive, piezoelectric, capacitive, etc. are sandwiched between two plates which must not bend so that the subject's weight is exerted only in the sensitive axis of the sensors. Furthermore, these sensors generally have a displacement under the action of a force, their thickness cannot therefore be negligible. These requirements imply the use of very rigid trays of sufficient size to receive both feet. These techniques are not suitable for making light scales, of very low

space-saving and inexpensive.

  The subject of the present invention is the production of an ultra light miniaturized bathroom scale which can fit in a handbag or in a pocket. To achieve this objective, it was necessary to design a specific weighing procedure, use other types of sensors

and coating materials.

  The scale which relates to the invention uses according to procedures which will be

  described below, from one to four weighing pads linked together, but not necessarily.

  -2 We will first describe the design and implementation of a weighing pad

according to the invention.

  The force sensor used according to the invention is in the form of a thin sheet. It is a flexible piezo-resistive sensitive surface or a piezoelectric polymer. These two types of technology exist and are marketed. The force sensors are in the form of a plastic sheet less than 0.3 millimeters thick. The piezo-resistive sheet develops a variable ohmic resistance when pinched in its thickness, while the piezoelectric polymer develops an electrical voltage proportional to the pinch force. Although these two technologies are suitable for embodiments according to the invention, we will only speak of piezoresistive sheets which are easier to use and

are of lower cost.

  The commercial piezo-resistive sensor according to the invention consists of a flexible semi-conductor in the form of a plastic sheet of thickness less than 0.3 mm and of variable size on request, integrating one or more cells semiconductor. They are offered in particular by the companies IEE (surfaces FSRTM) in Luxembourg and by TESCAN in the U.S.A. The FSR cell 1, for example, the construction of which is illustrated in FIG. 1, consists of two sheets of polymers laminated together. One of the sheets is covered with a network of electrodes with interleaved areas la, the other with a semiconductor material 1b. When a force is applied to the FSR, the semiconductor material more or less shunts the electrodes with offset ranges. The sensitive surface which comes under this technology is flexible, but does not crash, it can provide the intensity of a force according to a law of variation Resistance-Force if it is sandwiched between two planes subjected to a force of pinch. The sensitive surface which will be designated hereinafter: sensitive surface 2 (FIG. 2) can be composed of one or more cells 1. It should however be noted that such a surface can be delivered in various forms, dimensions and ranges of sensitivity. Although the law of variation of the resistance of the sensitive surface as a function of the force is not linear, it is possible to correctly determine the weight applied to said surface either by calculation if we know the law of variation, or at l 'using a correspondence table established at the construction of the scale by collecting the resistance according to the weight. Said correspondence table will be written in a non-volatile memory of the module

  electronics of the bathroom scale according to the invention.

  -3 A weighing pad 3 according to the invention as shown schematically in Figure 3 consists in its basic principle, of a base 4 formed of a thin plate of one to three mm thick a rigid and light material in aluminum AU4G for example or in plastic reinforced with fibers of the Kevlar type, on which is bonded a sensitive surface 2 composed of one or more cells 1 according to a particular arrangement such as the force to which the said is subjected sensitive surface is the best distributed. To do this, said surface is covered by one or more covering pads 5 of small thickness of a rubber or elastomer material. Said pads serve to improve the response of the sensitive surface by uniformly distributing the force exerted on said surface. The assembly is covered with a sufficiently rigid plate or cover 6 so that the weight exerted via said cover is best distributed over the

surface of the pad (s) 5.

  In an alternative embodiment illustrated in Figure 4, the weighing pad is a parallelepiped of eight centimeters on the side and six to seven millimeters thick. Said pad consists of a base 4 two millimeters thick on which the force sensor 2 is stuck. Said sensor consists of a sensitive surface of dimension slightly smaller than that of base 4 so as to provide a place for the electrical connector 7. Said surface consists of one or more cells of the SFR type for example - for linearity needs and to increase the measurement range, it may indeed be necessary to have several independent cells - . An elastomeric buffer sheet 5 two millimeters thick is bonded to the entire surface of the sensor 2. The cover 6 has the shape of a cover so that when it is placed on the assembly 4, 2.5, it come overflowing without touching the edges of the base 4 or the ground, even when the pad is crushed under the action of a weight. A cutout 8 made on a

  sides of the cover 6 allows the passage of the connector 7.

  In a second alternative embodiment of the weighing pad as illustrated in FIG. 5, four sensitive surfaces of small size, two centimeters in diameter for example, are used, placed at the four corners of the base 4 and on which come to bear. buffers of the same diameter. The whole is covered by

  a cover of the same type as that of the previous embodiment.

  These exemplary embodiments of weighing pads are not limiting and it is possible to design other more suitable shapes such as, for example, pads of circular shape. As mentioned above, the scale according to the invention can consist of one or more weighing pads of the type which has been described. In order to use the information from the weighing pads, the piezo-sensitive sensors of said pads are connected to a box 10 by means of a cord 9 coming out of said box and which is plugged into the connector 7 of the pad. weighing. The length of the cord must be sufficient to go from the ground to the folded hand of a standing subject. The housing 10 contains the weighing module 11 1. The said module has several functions: it incorporates all of the processing and processing electronics, the liquid crystal display 12 which indicates the weight and useful information, the battery d power supply and a switch or push-button 13 for implementing the module 11 and validating the weighing. The case is smaller than that of a remote control and can be shaped like a pen. In a normal weighing procedure, the subject is standing on the scale and holds the box in his hand 10. He actuates the pusher 13 as soon as it stabilizes on the scale. The weight is then immediately indicated in clear by the device 12. The subject can at will trigger a new weighing. Thus with this design of the scale according to the invention, the force sensor represented by one or more weighing pads does not

  contains no mechanical element which allows a miniaturization pushed.

  To clearly understand the interest of the scale according to the invention, it is appropriate to describe the different modes of use according to the number of weighing pads

implemented.

  1) Use of a single weighing pad. In this weighing mode as illustrated in FIG. 6, there is only one measurement axis. the person who wishes to weigh himself, places

  one foot on the weighing pad 3 while keeping the other foot momentarily raised.

  To display the weight, the person activates push-button 13. The weight remains displayed

  for a predetermined time which can be of the order of five seconds.

  2) Use of two weighing pads. In this weighing mode, there are two measurement axes which can be used in two ways:

  - in uni-podal support as illustrated in Figure 7, the person is placed on the scale

  person on one foot so that the heel rests on a pad while the forefoot (metatarsus) rests on the other pad, - in bi-podal support, the person places both feet on the scale placing

  for example its two forefoots on each of the two studs.

  3) use of four weighing pads. In this bi-podal weighing mode, there are four measurement axes. The person places himself on the scale on his two -5 feet so that each heel and each forefoot rests on a stud. This arrangement is the more comfortable but the more expensive of the two arrangements described above. This design of the scale according to the invention makes it possible to arrange the measurement pads at convenience where there is a need to carry out the measurements since the electronics which centralize them are not embedded in the pads. One can for example realize with four measurement pads a device which informs about the postural asymmetries of the subject by providing the podal distribution of the supports front-back and left-right. To do this, the treatment program provides, in addition to the weight resulting from the sum of the measurements of the four studs, the measurements made on each of the studs as well as the differences in the weights collected between the studs of each foot. It is also possible with four pads, to make an animal scale by placing said pads under each of the legs of the animal. Veterinarians will be able to take advantage of such a device to determine the weight and postural asymmetries of quadruped animals. In certain embodiments, it may prove necessary to link the studs: FIGS. 8 and 9 give an example of integration of the studs on a flexible and foldable support the size of an A4 format sheet. Another embodiment of a particularly compact scale is illustrated in FIG. 10. In this embodiment, the two weighing pads have a half-moon shape. A sliding device 14 makes it possible, in the measurement position, to spread the studs 3 conveniently so as to arrange them under the heel and the metatarsus. After use, the slide 14 is retracted inside the housings 15 formed in the studs which are then folded using the hinge 16 as illustrated in FIG. 11. FIG. 12 shows the half-moon shape of the sensitive cells 2 In one of the embodiments of an electronic interface, the box 10, FIG. 13 contains the electronic weighing module 11 which allows the acquisition and the processing of the signals coming from the sensor (s) 2. Said module contains the battery which supplies it (battery not shown here), the display 12 and the implementation device 13. FIG. 14 gives an exemplary embodiment of the electronic interface in schematic form. The sensitive element 2 is used as a potentiometric divider. It is connected in series with a resistor 17 of known value, the assembly is supplied by the

  DC voltage generator 22 whose value E can be that of the battery.

  Knowing the value of 17 and E, it is easy to determine the ohmic value of 2. If R17 is the ohmic value of element 17, the voltage V across R17 is given -6 by: V = ExR17 / ( R2 + R17) from which R2 = R17 ((W / V) -1) is taken. This example of an electrical interface for determining the value of 2 is not limiting and one can conceive of other assemblies where 2 is for example mounted in a branch of an oscillating circuit whose frequency it would modify as a function of the pressure. Voltage V is digitized by circuit 18 which is an analog-digital converter well known to electronics engineers. In

  the case where we would have to determine the values of several sensitive elements 2 (weighs

  person with several studs), circuit 18 must be multichannel. The digital output of circuit 18 attacks the digital input of a microcontroller 19. This type of microcontroller is capable of executing a program placed in non-volatile memory which is represented here by element 20. Part of the memory 20 contains the correspondence table between resistance R2 and weight, as it was noted during the construction of the scale according to the invention. Element 21 is a volatile memory necessary for the proper functioning of the microcontroller. The results of the various calculations are presented on the display 12 which is connected at the output of the circuit 19. The device 13 makes it possible to initiate a measurement by connecting for example the general power supply to the electronic weighing module as it has just be described. In the case where the device 13 is a push-button, one could advantageously provide a circuit, not shown, which simulates a self-adhesive time relay well known to electronics engineers, in order to continue to supply the electronic module for a certain time even after having released the push-button. It should be noted that the sensitive element 2 is connected to the electronic module by its two terminals via the cord 9. The length of the said cord is not detrimental to the quality of the signal which is large compared to the noise which could be picked up by the connecting electrical wires -7

Claims (2)

  1 - Device for evaluating the weight and its distribution, characterized in that it comprises at least one weighing pad 2 consisting of a base 4 on which is disposed or bonded at least one pressure sensor of the "piezo polymer surface" type -sensitive 2 "on which is disposed or glued a covering pad 5 intended to better distribute the pressure, on which is disposed or glued a plate or a cover 6 intended to receive and carry the object or the foot (s) ( s) of the person to be weighed and an electronic weighing module 1l 1 capable of measuring and displaying the weight 2 Device for evaluating the weight and its distribution according to claim 1 characterized in that the weighing module 1l 1 is included in a remote housing 10, capable of being held in the hand and electrically connected to the weighing pad (s) 2 by means of the cord 9 and containing all the weighing electronics, the supply battery and the display 12, 3 - Evaluation device the weight and its distribution according to claim 1 or 2, characterized in that it comprises four weighing pads for the evaluation of   posture asymmetries in humans or animals.   4 - Device for evaluating the weight and its distribution according to the claims   previous characterized in that the electronic weighing module comprises a microcontroller 19 capable of supplying the sum of the weights measured by the different   weighing pads and their combinations to assess postural asymmetries.   - Device for evaluating the weight and its distribution according to claim 4 characterized in that the microcontroller 19 contains in its non-volatile memory 20 the means for establishing the relationship between the resistance weight of the sensitive elements 2 in order to better linearize the measurements.