Patent Publication Number: US-2016236043-A1

Title: Device for receiving impacts, comprising inner piezoelectric energy recovery means

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. §371 and claims the benefit of priority of international application no. PCT/FR2014/051951, filed Jul. 28, 2014, which claims the benefit of priority under 35 U.S.C. §119 of French patent application no. 1359232, filed Sep. 25, 2013, and the entire contents of each is hereby incorporated herein by reference, in its entirety and for all purposes. 
    
    
     TECHNOLOGICAL FIELD 
     The present disclosure relates to the functionalization of balls, particularly pressurized deformable balls, especially in the field of sports and/or of physical restoration, such as, for example, tennis balls. 
     BACKGROUND OF THE DISCLOSURE 
     In ball sports and physical restoration based on such objects, it is useful to have statistics enabling the players to analyze their play and the medical staff to assess the quality of the exercises practiced by the patients. Usually, such statistics are manually collected by, for example, counting the number of hits, bounces, or others that a player or a patient exerts on a ball during a determined time period. 
     Further, certain sports consume a large quantity of balls, the latter having a limited life-time, and the balls need to be recycled, which generates a non-negligible cost. The French Tennis Federation thus estimates to more than one million the number of tennis balls consumed yearly in the various tennis clubs and schools on the French territory. 
     It is also advantageous to integrate in balls electronic functions enabling to automatically make statistics and/or to convert into electric energy and store the mechanical energy provided to these objects during the use thereof. 
     Document US 2011/136603 discloses a sports ball comprising a deformable shell defining a pressurized inner space, such as for example a tennis ball, and comprising an energy recovery circuit based on a piezoelectric material, which converts into electric energy part of the mechanical energy received by the shell under the effect of the deformation thereof by an impact, and which stores the electric energy thus generated in a battery internal to the ball. The energy thus recovered and stored is used by a circuit internal to the ball, such as for example, an accelerometer, a pressure sensor, or a GPS system. 
     This document however says nothing of the means for integrating such electric elements into the ball to hinder as little as possible the aerodynamics and the deformations thereof. Indeed, the functionalized ball should be substantially identical to conventional balls in order to be used in their place, particularly in sports, where balls must fulfill very strict criteria to be deemed conformal. Moreover, this document says nothing either of what happens with the circuits embarked in balls once said balls are worn out. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides various embodiments of a device with a deformable shell defining a pressurized inner space which comprises electric circuits implementing at least an energy conversion and storage function, which has an operation substantially identical to that of a device comprising no such circuits, and having easily-recyclable electric circuits once the device is out of use. 
     To achieve this, the disclosed embodiments describe a deformable shell defining an inner space under a gas pressure higher than the atmospheric pressure. A flexible piezoelectric membrane, applied against an inner wall of the deformable shell under the effect of the pressure present in the inner space, is capable of generating electric energy under the effect of a deformation of the shell. An electric circuit electrically connected to the piezoelectric membrane, includes an element for storing the electric energy that it generates and a rigid structure. Longilineal resilient elements for holding the electric circuit according to a predetermined position of the inner space, are each arranged between the rigid structure of the electric circuit and the inner wall of the deformable shell and secured to the piezoelectric membrane and to the rigid structure. 
     “Deformable” here means a shell capable of deforming under the effect of impacts to which it is submitted during a standard use of the shell. Conversely, “rigid” means an element which does not substantially deform during said use. 
     In other words, the piezoelectric material takes the form of a membrane, usually very thin, having a thickness smaller than one millimeter, applied against the shell. As compared with shell thicknesses usually observed for balls, typically a few millimeters, the presence of the piezoelectric membrane thus does not alter the general properties of these objects. 
     Further, the internal electric circuit is held in place, particularly at the center of a spherical ball, by resilient elements exerting pull-back forces towards this position and capable of following the deformation undergone by the outer shell under the effect of impacts. First, the electric circuit held in an appropriate position disturbs as little as possible the operation of the object, particularly by leaving the center of gravity unchanged. Further, by adopting non-rigid holding elements, the shell deformation properties also remain unchanged. Indeed, if rigid holding elements were adopted, the shell would be effectively less deformable, and thus impossible to use in certain sports, such as tennis, for example, for which the significant deformation of the ball is essential for the game. 
     Finally, the assembly formed by the membrane, the electric circuit, and the holding elements is easily extractible from the shell. Indeed, once it has been ripped open, for example, to be recycled, the disappearing of the overpressure results in a separation of the piezoelectric membrane from the shell. This assembly can then easily be recovered and may be used again in another shell, the pressurizing of the inner space of the shell pressing of the membrane against the inner wall thereof. 
     According to an embodiment, the holding elements comprise springs compressed between the rigid structure of the electric circuit and the inner wall of the deformable shell. Springs indeed have the advantage of requiring a limited volume of matter to efficiently implement a pull-back force, and thus disturb as little as possible the operation of the device. 
     According to an embodiment, the deformable shell defines a tennis ball, where the predetermined position is the center of the tennis ball, where the electric circuit is inscribed within a spherical volume concentric to the tennis ball and having a diameter smaller than half the inner diameter of the deformable shell, and where the holding elements are deformable with no deterioration over approximately at least one third of the length that they have when the ball is submitted to no deformation. Indeed, during a game, a tennis ball undergoes deformations capable of reaching one third of its diameter. The useful volume of a tennis ball where the electric circuit can be housed with no risk of coming into contact with the deformed shell is thus limited to a very small sphere. By providing an electric circuit contained within this sphere and holding elements capable of significantly deforming, the tennis ball can thus be submitted to the required extreme deformations with no risk of deteriorating or destroying the electric circuit. 
     According to an embodiment, the piezoelectric membrane comprises a polyvinylidene fluoride or lead zirconium titanium. Particularly, the film has a thickness in the range from 10 micrometers to 200 micrometers. The membrane is thus light, flexible, and mechanically robust. 
     According to an embodiment, the electric energy storage element comprises a microbattery formed on a flexible or rigid substrate. This type of electric energy storage means is very light, usually with a low weight and surface area for a large storage capacity. 
     According to an embodiment, the holding elements are formed of springs, particularly made of steel, stainless or not, particularly AlSl302 or AlSl316 stainless steel, of a nickel and chromium alloy, for example, inconel® 600, 625, or 718, of copper, or of beryllium. 
     According to an embodiment, at least two of the holding elements are electrically conductive and form two electric connections between the piezoelectric membrane and the electric circuit for the transmission of the electric energy generated by the membrane to the electric circuit. It is thus not necessary to provide other types of electric connection, such as, in particular, welded wires. Further, such connections are robust. 
     According to an embodiment, the electric circuit is formed of parallelepipedal electric stages arranged in parallel in a rigid frame. This type of configuration provides a compact circuit, which thus only very little disturbs the operation of a ball. 
     According to an embodiment, the electric circuit comprises a circuit for generating data from the electric energy generated by the piezoelectric membrane, 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. The data generation circuit is in particular capable of counting the number of electric pulses generated by the piezoelectric membrane and/or the data generation circuit is capable of determining a wearing state of the device according to the number of counted pulses. Advantageously, the electric circuit comprises a circuit connected to the electric energy storage element and comprising an electric interface for the connection to an external circuit for recovering the energy stored in the element when the device is open. 
     The described embodiments also provide a device intended to be integrated in an inner space of a deformable shell taken to a pressure higher than the atmospheric pressure. The device includes a flexible piezoelectric membrane capable of generating electric energy under the effect of mechanical stress. An electric circuit electrically connected to the piezoelectric membrane includes an element for storing the electric energy that it generates and a rigid structure. Longilineal resilient elements for securing the rigid structure of the electric circuit are secured to the piezoelectric membrane. 
     The described embodiments further provide a method of manufacturing a device that includes a deformable spherical shell defining an inner space under a gas pressure higher than the atmospheric pressure. The method includes forming a first and a second deformable half-shells, and forming an assembly comprising the piezoelectric membrane, the electric circuit, and the holding elements, the length of the holding elements being selected so that the latter are compressed when the assembly is housed in the deformable shell. The method also includes inserting the assembly into the first half-shell, placing the second half-shell on the first half-shell to form the deformable shell, and pressurizing the inner space of the shell to apply the piezoelectric membrane against the inner wall of the deformable shell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The presently described embodiments will be better understood on reading of the following description provided as an example only in relation with the accompanying drawings, where: 
         FIG. 1  is a simplified cross-section view of a tennis ball; 
         FIG. 2  is a simplified perspective view of a portion of the flexible piezoelectric membrane and of the holding elements of  FIG. 1 ; 
         FIG. 3  is a simplified cross-section view of the piezoelectric membrane of  FIG. 1 ; 
         FIG. 4  is a simplified perspective view of the circuit and of the electric holding elements of  FIG. 1 ; 
         FIG. 5  is a simplified perspective view of the circuit and of the electric holding elements according to an embodiment; 
         FIGS. 6 and 7  are simplified views of the holding elements according to two embodiments; 
         FIGS. 8, 9, and 10  are simplified views of electric connections between the piezoelectric membrane and the electric circuit of  FIG. 1  according to a plurality of embodiments; 
         FIGS. 11 to 14  are simplified cross-section views illustrating a method of manufacturing the tennis ball of  FIG. 1 ; and 
         FIG. 15  is a simplified cross-section view of another embodiment applied to an object having a flexible shell. 
     
    
    
     DETAILED DESCRIPTION 
     A tennis ball  10  according to the present disclosure will now be described in relation with  FIGS. 1 to 8 . Tennis ball  10  comprises a deformable shell  12 , for example, made of rubber, defining a hollow inner space  14  filled with air under a pressure higher than the atmospheric pressure, especially a pressure in the order of 2 bars. 
     More specifically referring to  FIG. 1 , tennis ball  10  comprises in space  14  an energy recovery system  16  comprising: a flexible piezoelectric membrane  18  applied against inner surface  20  of shell  12 , advantageously all over said surface, piezoelectric membrane  18  releasing electric charges when it deforms and thus releasing electric charges when shell  12  deforms, for example, under the effect of a hitting or of a bounce of ball  10 ; an electric circuit  22  comprising an element for converting the electric charges generated by the membrane into a constant current and/or voltage and one or a plurality of elements for storing the electric energy generated by the conversion element, as well as, optionally, an electronic circuit implementing one or a plurality of functions described hereafter; an assembly of holding elements  24  positioning electric circuit  22  at center  26  of ball  10  by implemented pull-back forces towards said position, and capable of deforming in relation with the deformations undergone by shell  12  so as not to oppose them. 
     As illustrated in  FIGS. 2 and 3 , piezoelectric membrane  18  comprises: a piezoelectric film  28 , having a thickness advantageously in the range from 10 micrometers to 200 micrometers, formed in one piece or in a plurality of pieces. Two metal layers  30 ,  32 , having a thickness in the range from a few nanometers to a few tens of micrometers each, deposited on either side of piezoelectric film  28 , for example, made of silver, of copper nitride, of aluminum, and forming two electrodes for collecting the electric charges generated by film  28 ; optionally, a flexible substrate  34 , for example, made of plastic, such as polyethylene terephthalate (“PET”) or polyethylene naphthalate (“PEN”), having the stack of piezoelectric film  28  interposed between metal electrodes  30 ,  32  formed thereon. 
     Advantageously, piezoelectric film  28  is made of polyvinylidene fluoride (“PVDF”) which has the advantage of being both light, flexible, and mechanically resistant, metal electrodes  30 ,  32  being capable of being directly deposited on the film surfaces without using a substrate  34 . As a variation, film  28  is made of lead zirconium titanium (“PZT”), of zinc oxide (“ZnO”), or of a composite material of at least two materials from among these and PVDF. Due to the materials used for membrane  18  and to the thickness thereof, the membrane has substantially no influence on the aerodynamic and deformation behavior of ball  10 . 
     Electric circuit  22  is designed to also disturb as little as possible the aerodynamic behavior of ball  10 . First, electric circuit  22  is selected to be as light as possible given the functions that it implements. Particularly, the electric power 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 bearing reference “CBC050-M8C” having a 8×8 mm 2  surface area for a 50 μAh capacity, or a Solicore®, Inc. flexible substrate microbattery, for example, a microbattery bearing reference “SF-2529-10EC” having a foldable surface of 25.75×29 mm 2  for a 10-mAh capacity. As a variation, the electric power storage element comprises one or a plurality of capacitors and/or one or a plurality of supercapacitors. 
     Circuit  22  is also advantageously designed to have the highest possible three-dimensional symmetry, circuit  22  ideally having a spherical shape and a uniform density. However, given usual electric and electronic circuit manufacturing methods, the circuits generally have a parallelepipedal shape. Advantageously, circuit  22  takes the shape of a stack of parallelepipedal circuits, such as illustrated in  FIGS. 4 and 5 , to obtain a cuboid shape, advantageously a cube. 
     Circuit  22  thus comprises, in particular: a first stage  36  electrically connected to membrane  18 , and converting the charges that the latter generates, essentially in the form of a non-constant current, into a constant current and/or a constant voltage, currently used to charge a microbattery, such as for example a circuit of “LTC3588” type of Linear Technology Corp., a second stage  38 , electrically connected to first stage  36 , comprising a microbattery charging due to the constant current and/or voltage generated by the first stage, and, optionally, one or a plurality of third stages  40  electrically connected to the battery of second stage  38  for their electric power supply, and implementing one or a plurality of electronic functions as will be described in further detail hereafter, or comprising one or a plurality of additional electric energy storage elements. 
     The stages are further attached by means of a rigid frame  42  having holding elements  24  fastened thereto. 
     Holding elements  24  have an longilineal shape, and each of elements  24  is fastened at a first end to electric circuit  22 , particularly to frame  42  thereof, and is also fastened to piezoelectric membrane  18 . 
     Elements  24  are fastened to the frame of circuit  22  and to membrane  18  by gluing, by welding, by magnetic contact, by screwing, by a self-locking system, or by means of a quickconnect-type system. As a variation, the fastening is performed by means of a polymer material, such as, for example, a polyurethane, an epoxy glue, an anaerobic glue comprising a mixture of glycol dimethacrylate with a minority quantity of peroxide and setting accelerator, a cyanoacrylate, or an MS polymer mastic based on modified silane. As a variation, the fastening is performed by means of nanofibers, for example, of collagen nanofibers, carbon and copper nanofibers, SiC nanowires comprising carbon microtips. 
     Energy recovery system  16  formed of membrane  18 , of circuit  22 , and of holding elements  24  thus forms one and the same object, which facilitates its installation in tennis ball  10  as well as its removal, as will be described in further detail hereafter. 
     Further, the second end of each of elements  24  rests on inner wall  20  of shell  12  without being secured thereto, which here again allows a simplified installation and removal of system  16 . Finally, membrane  18  is fastened to the second end of each of elements  24 , so that the second end rests on inner wall  20  through membrane  18 , or at least an area close to this end, which eases its deployment and its application on inner wall  20  of shell  12  under the effect of the pressure in inner space  14  of ball  10 . 
     As illustrated in  FIG. 4 , holding elements  24  are advantageously formed of springs, a spring having a significant pull-back force while being hollow, and thus light. For example, the springs are made of steel, stainless or not, particularly AlSl302 or AlSl316 stainless steel, of a nickel and chromium alloy, for example, inconel® 600, 625, or 718, of copper, or of beryllium. 
     Further, the springs are selected to be deformable along their main pull-back axis and substantially more rigid perpendicularly to this axis, which eases the placing into contact of their second end with shell  12 . In the context of an electric circuit  22  having a parallelepiped shape, there are advantageously eight springs, one spring being provided for each corner of circuit  22 . As a variation, as illustrated in  FIG. 5 , the holding elements also comprise a rigid rod  44 , positioned between circuit  22  and the springs, to rigidify system  16  and thus make the latter more mechanically robust. According to an embodiment, holding elements  24  also comprise a piezoelectric material, which also enables to recover energy during the deformation thereof. 
     Advantageously, circuit  22  has dimensions appropriate for the type of deformation to which the tennis ball is likely to be submitted during its use. A tennis ball is known to be able to deform by one third of its diameter when hit by experienced players. Circuit  22  is thus selected to be inscribed within a sphere  48  ( FIG. 1 ), so that shell  12  cannot come into contact with circuit  22 , including when the tennis ball undergoes a significant decrease in its diameter. For example, circuit  22  is inscribed within a sphere having a diameter smaller than half the diameter of tennis ball  10 , for example, a sphere having a 3-cm diameter for a standard tennis ball. 
     Further, holding elements  24  are designed to undergo with no deterioration a compression and an elongation greater than one third of their length when the ball is at rest to follow such extreme deformations. 
     Holding elements  24  further provide a pull-back force when stretched and/or compressed so that circuit  22  can displace in inner space  14  of the ball without ever impacting inner wall  20  under the effect of violent shocks affecting the ball during a tennis match. 
     Advantageously, holding elements  24  each comprise a plurality of springs  24   a,    24   b,  for example, 2, connected in series, as illustrated in  FIG. 6 , or in parallel, as illustrated in  FIG. 7 , which enables to more easily define a different behavior of elements  24  according to the intensity of the impact received by shell  12 . Particularly, by providing a plurality of different springs, it is possible to simply design holding elements  24  which have both a low rigidity, that is, which do not oppose the deformation undergone by shell  12 , and a sufficient rigidity, that is, avoiding the collision of circuit  22  on shell  12  during impacts received by shell  12 . 
       FIGS. 8, 9, and 10  illustrate alternative electric connections between piezoelectric membrane  18  and electric circuit  22  to transmit thereto the electric charges generated by the membrane. 
     According to a first variation illustrated in  FIG. 8 , the two electrodes  30 ,  32  of membrane  18  are connected to circuits  22 , particularly its constant current/voltage conversion circuit  36 , by means of two conductive wires  52 ,  54  welded to said electrodes and to two pads  56 ,  58  of circuit  22 . In this variation, wires  52 ,  54  are free of being positioned independently from elements  24  and frame  42 . 
     According to a second variation illustrated in  FIG. 9 , two of holding elements  24  are electrically conductive and are connected, for example, by welding, to electrodes  30 ,  32  and to conductive portions of circuit  22  forming the electric inputs of circuit  22 , particularly of conversion circuit  36 . 
     According to a third variation, illustrated in  FIG. 10 , elements  24  are hollow, for example, formed of springs, and the connection is formed by two conductive wires  60 ,  62  housed in two of elements  24 , and fastened, for example, by welding, to electrodes  30 ,  32  of membrane  18  and circuit  22 , for example, to pads thereof or to conductive portions of frame  42  forming electric inputs of circuit  22 , particularly conversion circuit  36 . 
     The first variation has the advantage of enabling to select a frame independent from the connection between the membrane and circuit  22 . However, the wires are fully submitted to the accelerations of the ball on impacts thereof, which fragilizes them. 
     The second variation conversely provides connections which are little sensitive to said accelerations, but requires on the other hand a more complex frame for circuit  22 . 
     The third variation show a compromise between the first two variations, where the wires are protected by elements  24  and the connection to circuit  22  may be independent from the frame, for example, by providing a wire portion arranged outside of elements  24  for a connection to pads of circuit  22 . Of course, these variations may be combined. Similarly, more than two connections may be provided. For example, in the case of a piezoelectric membrane  18  comprising a plurality of portions electrically insulated from one another, or “pixelized” membrane, two electric connections may be provided for each of the piezoelectric membrane portions. 
     Electric circuit  22  may for example comprise one or a plurality of electronic circuits supplied with electric energy by the microbattery of circuit  22  and processing the electric pulses generated by the piezoelectric membrane and generating data relative thereto. Thus, circuit  22  may for example implement a circuit for counting the number of pulses generated since the tennis ball has been put into service, a function of determination of the average or individual pulse intensity, and/or of determination of the average or individual pulse duration. The data thus generated are for example stored in an internal memory of circuit  22  and/or transmitted by a wireless transmission circuit, for example, by radiofrequency, from circuit  22  to the outside of the ball so that they can be collected. Particularly, knowing the number of pulses enables to know, in addition to the number of impacts received by the ball, the wearing state thereof, since this wearing state particularly directly depends on this number. The number of impacts, their intensity and their duration further are statistical data useful for a player who can then know the strength of its strokes and the type of impact that it applies to the ball, etc. Further, by processing the pulses generated by each portion of a pixelized membrane, it is possible to specify the characteristics of the impacts, their shape, and their mark on the ball. 
     On recycling of the ball, the electric power storage means of circuit  22  may be discharged to recover the stored energy. Usually, used balls are collected in large numbers and transformed into a rubber lining by means of transformation machines. The electric energy stored in the recycled balls can thus be recovered for the operation of said machines. 
     A method of manufacturing the tennis ball just described with now be described in relation with  FIGS. 11 to 14 . 
     The method starts by the manufacturing of two hemispherical deformable half-shells  12   a  and  12   b  which form shell  12  of ball  10  when they are put together ( FIG. 11 ) and the manufacturing of energy recovery system  16  having holding elements  24  in the form of springs and secured to both piezoelectric membrane  18  and electric circuit  22  ( FIG. 12 ). 
     Recovery system  16  is then placed in one of half-shells  12   a  ( FIG. 13 ), after which the other half-shell  12   b  is fastened to half-shell  12   a,  particularly by gluing, springs  24  being compressed ( FIG. 14 ). 
     Finally, inner space  14  of the tennis ball is pressurized, particularly to a  2 -bar pressure, which results in deploying the flexible piezoelectric membrane and in applying it against inner wall  20  of ball  10  ( FIG. 1 ). 
     It should be noted that the manufacturing of the two half-shells and the pressurizing of the ball are for example conventional tennis ball manufacturing steps, the manufacturing of a tennis ball differing from conventional methods by the insertion of energy recovery system  16  into ball  10 . 
     Once the tennis ball is deemed worn out, it is sufficient, in order to recover system  16 , to open the ball, the resulting pressure drop being sufficient to separate piezoelectric membrane  18  from shell  12 . Since, further, holding elements  24  are not fastened to shell  12 , it is then sufficient to grab system  16  to remove it from the ball. 
     An application of the contemplated embodiments with respect to a tennis ball has been described. Of course, the contemplated embodiments apply to any type of balls having deformable shells, such as for example soccer balls, basketballs, handballs, rugby balls, etc. 
     An embodiment applying to an object having a deformable shell is illustrated in simplified cross-section view in  FIG. 15 . 
     Such an object  100  comprises a deformable shell  102  defining an inner space  104 . Inner space  104  is for example naturally present in the object, for example, a ball. Inner wall  106  of shell  102  is further optionally provided with spikes  108 , advantageously regularly distributed on said wall. Finally, an internal object  110 , for example, spherical, is provided in inner space  104  and may displace therein. 
     The internal object comprises a shell  112  defining an inner space  114  under pressure having an energy recovery system  116 , similar to previously-described recovery system  16  and especially comprising a piezoelectric membrane such as previously described and placed against the inner surface of shell  110 , inserted therein. Shell  112  of object  110  is deformable so that object  110  forms an assembly similar to the above-described tennis ball. 
     Preferably, spikes  108  are flexible elements or springs, to avoid mechanically damaging the flexible piezoelectric wall. 
     Object  110  is further fastened to shell  102  by means of resilient holding elements  118 , particularly springs, for example, three or four. Holding elements  118  enable to decrease the impact of the presence of internal object  110  on the aerodynamic properties of object  100 . 
     When object  100  receives an impact, it is submitted to an acceleration, and internal object  110  hits shell  102 , which thus deforms its shell  112 . The piezoelectric membrane applied against the shell thus generates electric charges which are then stored and/or processed in circuit  22  as described hereabove. 
     Applications to sport have been described. Of course, the described embodiments apply to other types of activity, particularly physical restoration activities which use balls or the like, the statistics generated by such objects enabling the medical staff to study, for example, the quality of the exercises performed by the patients.