DEVICE WITH DEFORMABLE SHELL INCLUDING AN INTERNAL PIEZOELECTRIC CIRCUIT

Abstract

A device (10) including a deformable shell (12) delimiting an inner space (14), and: a resilient band (18, 30, 32) suspended in the inner space (14) and including two ends secured to the deformable shell (12), said band (18, 30, 32) including a piezoelectric material (30, 32) to generate an electric voltage under the effect of the deformation of the shell (12) and two electrodes for collecting the voltage; and an electronic circuit (34) for processing the voltage, arranged on the resilient band (18, 30, 32) and connected to the electrodes of the resilient band (18, 30, 32).

Claims

1. A device comprising a deformable shell delimiting an inner space, the device comprising: a resilient band suspended in the inner space and comprising two ends secured to the deformable shell, said band comprising a piezoelectric material to generate an electric voltage under the effect of the deformation of the shell and two electrodes for collecting a voltage; and an electronic circuit for processing the voltage, arranged on the resilient band and connected to the electrodes of the resilient band.

2. The device of claim 1, wherein the resilient band comprises a resilient support layer having two opposite surfaces, and a layer formed of piezoelectric material arranged on at least one of said surfaces.

3. The device of claim 2, wherein the modulus of elasticity of the support layer is substantially identical to the modulus of elasticity of the deformable shell.

4. The device of claim 2, wherein the Shore hardness of the support layer is greater than or equal to 70 and the ratio of the length of the support layer to the thickness thereof is smaller than 2,200.

5. The device of claim 2, wherein the support layer is made of polyurethane or of ethylene-propylene-diene monomer.

6. The device of claim 2, wherein the layer of piezoelectric material is made of piezoelectric polymer, particularly of polyvinylidene fluoride, and is covered with a plastic layer.

7. The device of claim 1, wherein the deformable shell and the resilient band each comprise a plane of symmetry, and wherein the planes of symmetry of the deformable shell and of the resilient band coincide.

8. The device of claim 1, wherein the deformable shell is a sphere, and wherein the resilient band is a cuboid having a width smaller than 50% of the diameter of the sphere.

9. The device of claim 1, wherein the deformable shell is a sphere, and wherein the center of mass of the assembly formed of the resilient band and of the electronic circuit is arranged at the center of the sphere.

10. The device of claim 1, wherein the electronic circuit comprises an electric energy storage element.

11. The device of claim 10, wherein the electric energy storage element comprises a microbattery formed on a flexible or rigid substrate.

12. The device of claim 10, wherein the electronic circuit comprises a circuit for generating data from the electric voltage generated by the resilient band, and a circuit of wireless transmission of said data outside of the deformable shell, said generation and transmission circuits being powered by the electric energy storage element.

13. The device of claim 1, wherein the electronic circuit comprises a circuit for determining the force exerted on the deformable shell according to the amplitude of the voltage generated by the resilient band.

14. The device of claim 1, wherein the deformable shell is a tennis ball.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention will be better understood on reading of the following description provided as an example only in relation with the accompanying drawings, where:

[0031] FIG. 1 is a simplified cross-section view of a tennis ball, exhibiting an upper surface of an energy recovery system according to the invention;

[0032] FIG. 2 is a simplified cross-section view along plane II-II of FIG. 1;

[0033] FIG. 3 is a simplified cross-section view illustrating the bending of a resilient band forming part of the energy recovery system of FIGS. 1 and 2 according to two positions of impact on the tennis ball;

[0034] FIG. 4 is a drawing illustrating the voltages generated by two piezoelectric membranes arranged on either side of the resilient band when the tennis ball receives an impact;

[0035] FIG. 5 is a simplified cross-section view of the tennis ball illustrating the lag between the motion of the tennis ball and the motion of the resilient band; and

[0036] FIG. 6 is a simplified cross-section view of a piezoelectric membrane forming part of the energy recovery system.

DETAILED DESCRIPTION

[0037] A tennis ball 10 according to the invention will now be described in relation with FIGS. 1 and 2. Tennis ball 10 comprises a deformable spherical shell 12 defining a hollow inner space 14. Shell 12 is for example formed of a rubber layer covered with an external felt layer and inner space 14 comprises air under a pressure greater than the atmospheric pressure, particularly a pressure in the order of 2 bars. Tennis ball 10 has a diameter between 6.5 cm and 6.9 cm, and a mass between 56 grams and 59 grams.

[0038] Tennis ball 10 comprises in space 14 an energy conversion and data processing system 16 comprising: [0039] a support band 18, made of a resilient material, for example, polyurethane, EDPM, rubber, or neoprene. Band 18 for example has the shape of a cuboid, with its two ends 20, 22 secured to shell 12, for example by being housed and glued in respective notches of shell 12, and comprising two opposite surfaces 24, 26;a piezoelectric membrane 30 and 32 arranged on one or each of surfaces 24, 26 of band 18, secured to said surface, for example, by gluing, and comprising two electrodes (not shown) for collecting the voltage generated by the membrane under the effect of the deformation thereof; and [0040] an electronic circuit 34, arranged on one and/or the other of surfaces 24, 26 of band 18, and secured to the band, for example, by gluing, circuit 34 being electrically connected to the electrodes of piezoelectric membranes 30 and 32.

[0041] In operation, as illustrated in FIG. 3, when tennis ball 10 is submitted to an impact or an acceleration, for example, a bounce on the ground, shell 12 deforms, which causes the deformation of resilient band 18, particularly the bending thereof. Piezoelectric membranes 30 and 32 are thus also deformed and thus generate an electric voltage across their respective electrodes.

[0042] FIG. 4 is a diagram of voltages V1 and V2 respectively generated by piezoelectric membranes 30 and 32 when tennis ball 10 has been hit, the voltages being of opposite signs due to the compressive stress of one of the membranes while the other membrane is being stretched. The amplitude of the first peak of the voltage is directly linked to the force exerted on ball 10, the next oscillations corresponding to the oscillation of band 18 until it returns to its idle position, the invention enabling to obtain voltages having an amplitude of several hundreds of volts, as will be described in further detail hereafter.

[0043] System 16 is advantageously optimized so that the ball according to the invention has a mechanical behavior, particularly in terms of deformation and aerodynamic properties, close to the behavior of a conventional tennis ball comprising no such system.

[0044] First, at rest, the center of mass of system 16 is confounded with center 40 of ball 10. System 16 further has at least one plane of symmetry 36, 38, confounded with a plane of symmetry of tennis ball 10 crossing center 40 thereof System 16 thus has a symmetrical weight distribution adapted to the spherical geometry of ball 10.

[0045] Advantageously, the modulus of elasticity of resilient band 18 is selected to minimize the lag between the deformation of shell 12 and the deformation of band 16. As illustrated in FIG. 5, when ball 10 starts taking off at time “t” from the surface that it has impacted, for example, the ground in the case of a bounce, as illustrated by arrow 42, resilient band 18 is submitted to another motion in an opposite direction, such as illustrated by arrow 44, the motion of band 18 and of ball 10 having the same direction after a duration At, as illustrated by arrows 46, 48. Such a lag may significantly impact the ball bounce. Selecting a modulus of elasticity and hardness of resilient band 18 close to the modulus of elasticity of shell 12 enables to substantially decrease this lag, and thus to obtain a behavior close to that of a conventional tennis ball.

[0046] The amplitude of the lag also depends on the total weight of system 16, whereby the modulus of elasticity of band 18 is determined according to this weight. More particularly, it has been observed that a band formed of a material having a D Shore hardness greater than 70 and a thickness greater than 3 mm enables to obtain a bounce close to that of a ball which does not comprise system 16. The same effect has been observed for a D Shore hardness of support layer 18 greater than or equal to 70 and a ratio of the length of support layer 18 to the thickness thereof smaller than 2,200. For example, a band 18 made of polyurethane, having a Shore hardness equal to 80, or made of EDPM, having a Shore hardness equal to 70, a 15-mm width, and a 4-mm thickness enables to obtain a bounce greater than or equal to 80% of the bounce of a ball.

[0047] Preferably, the width of band 18 is smaller than 50% of the diameter of shell 12 to minimize the band volume in the shell and the glue volume used to secure band 18 in shell 12, and to accordingly decrease the impact of the presence of the band on the deformation properties of shell 12.

[0048] Referring to FIG. 6, piezoelectric membranes 30, 32 each comprise: [0049] a piezoelectric film 50, having a thickness advantageously in the range from 10 micrometers to 200 micrometers, formed in one piece or in a plurality of pieces; [0050] two metal layers 52, 54, having a thickness in the range from a few nanometers to a few tens of micrometers each, deposited on either side of piezoelectric film 50, for example, made of silver, of copper nitride, of aluminum, and forming two electrodes for collecting the electric charges generated by film 50; [0051] optionally, two flexible reinforcement layers 56, 58, for example, made of plastic, such as polyethylene terephthalate (“PET”) or polyethylene naphthalate (“PEN”), respectively deposited on electrodes 52, 54.

[0052] Advantageously, piezoelectric film 50 is made of polyvinylidene fluoride (“PVDF”), which has the advantage of being at the same time light, flexible, and mechanically resistant. As a variation, film 50 is made of lead titanium zirconate (“PZT”), of zinc oxide (“ZnO”), or of a composite material made of at least two materials among these and PVDF. For example, the piezoelectric membranes are “DT sensors” manufactured by Measurement Specialties, Inc.

[0053] Electronic circuit 34 implements functions of analysis and processing of the voltages delivered by piezoelectric membranes 30, 32 and comprises an electric energy storage element and a data generation circuit. Circuit 34 is particularly designed to disturb as little as possible the aerodynamic behavior of ball 10.

[0054] First, electronic circuit 34 is selected to be as light as possible given the functions that it implements. Particularly, the electric energy storage element is advantageously formed of a microbattery formed on a flexible or rigid substrate. For example, the storage element is a rigid substrate microbattery from the “EnerChip” range of Cymbet® Corp., for example, a microbattery having reference “CBC050-M8C” with a 8×8 mm.sup.2 surface area for a 50 μAh capacity, or a Solicore®, Inc. flexible substrate microbattery, for example, a microbattery having reference “SF-2529-10EC” with a foldable surface of 25.75×29 mm.sup.2 for a 10-mAh capacity. As a variation, the electric energy storage element comprises one or a plurality of capacitors and/or one or a plurality of supercapacitors.

[0055] The data generation circuit is for example a printed circuit comprising an electronic chip equipped with a microcontroller enabling to process data and a radio transmission module, for example, transmitting according to the ZigBee protocol. The data generation circuit is electrically powered by the electric energy storage element and/or an integrated battery, of “button” cell type.

[0056] For example, the data generation circuit processes the electric pulses generated by piezoelectric membranes 30, 32 and generates data relative to said pulses. Thus, electronic circuit 34 may comprise: [0057] a circuit for counting the number of pulses generated since the putting into service of the tennis ball, [0058] a circuit for determining the average or individual intensity of the pulses, [0059] and/or a circuit for determining the average or individual duration of the pulses, [0060] a radio frequency emitter enabling to locate the ball on a tennis court, which for example enables to know whether a ball is in or out, [0061] an accelerometer enabling to determine the ball speed.

[0062] The data thus generated are for example stored in an internal memory of circuit 34 and/or transmitted by wireless communication outside of the ball in order to be collected.

[0063] Particularly, knowing the number of pulses enables to know, in addition to the number of impacts received by the ball, the state of wear thereof, since this state of wear directly depends, in particular, on this number. The number of impacts, the intensity and the duration thereof further form statistic data useful for a player who can thus know the strength of his/her shots and the type of shots that he/she applies to the ball, etc. It has in particular been observed that there exists a bijective relation between the amplitude of the first pulse following an impact on the ball and the force of this impact. The data generation circuit for example comprises a chart storing force values according to the voltage amplitude and calculates the force exerted on the ball according to the amplitudes of stored voltages.

[0064] Advantageously, circuit 34 is distributed in two portions, arranged on either side of resilient band 18 to distribute its weight and obtain for the center of mass of system 16 to be arranged at the center of the ball and on a plane of symmetry of system 16, which enables to decrease the dependence of the electric power generation to the position of an impact on shell 12 or to the direction of an acceleration undergone by ball 10. For example, the electric energy storage elements are arranged on one side of resilient band 18, and the data generation circuit is arranged on the other side of band 18.

[0065] A tennis ball has been described. Of course, the invention applies to any type of balls, and generally to any object having a deformable shell.

[0066] Applications to sport have been described. Of course, the invention applies to other types of activity, particularly physical restoration activities which use balls or the like, the statistics generated by such objects according to the invention enabling the medical staff to study, for example, the quality of the exercises performed by the patients.