Abstract:
A data entry stylus for entering data onto an entry pad. The stylus includes a body having a housing. The stylus includes: a reference element, having two distinct portions, a first portion sitting within the housing and a second portion, including a tip the end of which is at least hemispherical; and a damper forming a cladding around at least a part of the reference element, including an external wall.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is a Section 371 National Stage Application of International Application No. PCT/EP2013/063066, filed Jun. 21, 2013, which is incorporated by reference in its entirety and published as WO 2013/190124 on Dec. 27, 2013, not in English. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention described relates to the field of devices for entering data on to screens and touch pads. More particularly, the present invention pertains to the field of styluses for screens and touch pads. 
       PRIOR-ART SOLUTIONS 
       [0003]    There are known pointing devices in the prior art, called styluses, intended for use on tablets. These may be dedicated tablets such as tablets for drawing. Recently, this type of tablet has undergone major progress. This progress is related chiefly to the fact that portable telephone or smartphone type terminals have undergone major changes, including especially the addition of touch pads enabling direct entry on to the screen of the terminal. 
         [0004]    As a rule, such entry is done by finger. Other modes of entry are also possible, among them the use of a stylus. However, this stylus is a passive element whose function is to imitate the finger to enable selection and/or use on a telephone-type terminal screen. The stylus therefore has a rounded tip that is relatively bulky (of the order of one cubic centimeter). 
         [0005]    Styluses intended for graphic tablets implement other technologies. First of all, the tip of this type of stylus is relatively fine. This is explained by the fact that this type of stylus is intended for the reproduction of precise illustrations, such as for example drawings, graphics or again handwriting. This type of work is fine and therefore requires an instrument offering a high level of precision. Pressure-sensitive styluses have been developed and commercially distributed over the years. These styluses take account of the pressure exerted by the user during use on a surface (whether it is a touch screen or another type of support). Although these styluses are more ergonomical and more precise than the simple non-pressure-sensitive styluses, they are not satisfactory. 
         [0006]    Indeed, one of the problems encountered with styluses relates to the measurement of pressure when the stylus is tilted. The first pressure-sensitive styluses did not accurately take account of the fact that the stylus was tilted, so that for a same pressure exerted, the computed value of the pressure differed according to whether the stylus was tilted or not. Another problem lies in the cost of manufacture of such styluses. Indeed, as shall be seen, these styluses include numerous elements, the assembling of which is a complex process. 
         [0007]    Devices have been designed to overcome at least certain of the problems mentioned here above. 
         [0008]    There is a stylus known from the patent application No. EP0727756 that possesses a pressure-sensitive device used to detect a force of pressure even when this stylus is in an oblique position. The pressure sensor uses modifications of inductance generated by the relative shift between a mobile magnetic body and a fixed magnetic body around which a coil is wound, this coil being positioned at a predetermined distance from the mobile magnetic body. The end of the device, situated at the end of the stylus, has a contact portion receiving a pressure exerted on the stylus. The device also includes an element made out of an elastic material situated between the fixed and mobile magnetic bodies: a first supporting device maintaining the position of the fixed magnetic body despite a depression, and a second supporting device maintaining the depression member in a condition in which the rear plate of the mobile magnetic body and the forward plate of the fixed magnetic body are placed in parallel with each other in receiving the depression. 
         [0009]    In other words, in this prior-art device, two magnetic bodies are positioned inside the stylus. When a pressure is exerted on the stylus, the mobile magnetic body is brought closer to the fixed magnetic body. The magnetic field is therefore modified, thus causing a modification of the inductance at the surface of the tablet or screen on which the stylus is used. As indicated in  FIG. 3  of this patent EP0727756, the surface of the tablet includes a mesh enabling the inductance to be measured. 
         [0010]    This type of stylus nevertheless has a problem. On the one hand it is heavily linked to the technology used by the tablet (i.e. there is a modification of the inductance induced by the modification of the magnetic field inside the stylus), and secondly it is complex and costly to manufacture. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention does not show these problems of the prior art. Indeed, the invention pertains to a stylus for entering data on to an entry pad, said stylus comprising a body comprising a housing characterized in that it comprises:
       a reference element comprising two distinct portions:
           a first portion seated within said housing;   a second portion comprising a tip, the end of which is at least hemispherical;   
           a damper forming a cladding around at least one part of said reference element comprising an external wall, called an external wall of said damper.       
 
         [0016]    Thus, the stylus can be used to carry out a measurement of the pressure exerted on the pad uniformly, whatever the tilt of the stylus. This is made possible by the use of a tip that is at least substantially hemispherical, firstly ensuring that the distance between the pad and the reference element is constant depending on the tilt and, secondly, applying a method for measuring pressure based on this distance. 
         [0017]    According to one particular characteristic, said damper is made out of a flexible and deformable material. 
         [0018]    Thus, the design of the stylus is simple and does not require any complicated and costly construction method. 
         [0019]    According to one particular characteristic, said damper is hemispherical. 
         [0020]    Thus, by using a shape that is also hemispherical for the damper, it is also provided that the distance between the pad and the reference element will not be modified by the shape of the tip of the stylus. 
         [0021]    According to one particular embodiment, said end is substantially spherical. 
         [0022]    Thus, even if the stylus is almost horizontal relatively to the pad, it is ensured that the pressure can always be measured. 
         [0023]    According to one particular embodiment, said damper comprises a cylindrical sleeve comprising a first hemispherical end, the internal diameter of the cylindrical sleeve being substantially equal to the diameter of the at least hemispherical end of the reference element. 
         [0024]    According to one particular characteristic, said damper furthermore comprises a second end comprising a retaining ring for retaining said damper in said housing. 
         [0025]    Thus, it is also possible to implement a mechanical damper in place of a deformable damper. 
         [0026]    According to one particular characteristic, a space left vacant between said first hemispherical end and the at least hemispherical end of the reference element is filled with electrically charged deformable material. 
         [0027]    Thus, the sensitivity of the stylus on the pad is increased. 
         [0028]    According to one particular characteristic, said damper is mobile in translation according to the pressure exerted on the stylus. 
         [0029]    The invention also pertains to a method for measuring a pressure exerted during the entry of data by a user, entered on a pad via a stylus as described here above. According to the invention, such a method comprises:
       a step of acquisition, by said writing surface, at at least one instant of the entry, of at least one piece of data representing a distance d of said stylus relative to said pad, in a zone of proximity of said pad;   a step for computing pressure exerted on said pad taking account of said distance d.       
 
         [0032]    The invention also pertains, in another form, to a computer program product downloadable from a communications network and/or stored on a computer-readable support and/or executable by a microprocessor. According to the invention, such a program comprises program code instructions to execute the method for measuring as presented here above when it is executed on a computer. 
     
    
     
       LIST OF FIGURES 
         [0033]    Other features and advantages of the invention shall appear more clearly from the following description of a preferred embodiment, given by way of a simple illustratory and non-exhaustive example and from the appended drawings, of which: 
           [0034]      FIG. 1  shows a first embodiment of a stylus; 
           [0035]      FIG. 2  shows a second embodiment of a stylus; 
           [0036]      FIG. 3  shows a third embodiment of a stylus; 
           [0037]      FIG. 4  shows a fourth embodiment of a stylus; 
           [0038]      FIGS. 5A and 5B  respectively illustrate an example of a system implementing the method of electronic authentication of a handwritten signature and the main steps of this method of authentication according to one embodiment; 
           [0039]      FIG. 5  schematically illustrates a device for measuring pressure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    6.1 Reminder of the Principle of the Invention 
         [0041]    The object of the present disclosure is to propose a technique that can be used to measure the pressure exerted by the user through a stylus in a simpler and more efficient way than with the previously proposed techniques. More specifically, the proposed invention is based on a computation of a distance (d) between an internal component of the stylus and the pad (which is or is not a touch pad) on which the stylus is used. 
         [0042]    The capacitive touch screens of recent generations enable a precise measurement of the surface of contact between the pad of the screen and any other object to which the touch screen is sensitive (a finger, a hand, a tip of a stylus made out of a conductive material, etc). 
         [0043]    By using a stylus whose tip is made out of a non-conductive deformable material, the mechanical resistance and hence the deformation of which is known, or else is formed by a mobile rigid case, connected to the sleeve by return means, surrounding a metallic tip, or else again is made of a dielectric material, it is possible, from the distance measured by the entire touch screen between the pad and the metal tip, to deduce the pressure applied by the user throughout his entry operation. 
         [0044]    The non-neutral internal element of the stylus detected by the touch screen can be either made out of a conductive metal in the case of an active pen (the pen constitutes the sensor or the emitter) or else made simply out of a dielectric in the case of a passive pen (the stylus is deliberately interposed as a disturbing element between the emitter and the receiver, both contained in the touch screen). Here below, this internal element which serves as a basis for measuring the distance, is qualified as a reference element. It is either conductive or passive depending on the technology of the stylus used. 
         [0045]    The variations of pressure during the entry are thus an additional biometric parameter to enable various actions such as the authentication or non-authentication of a signature and hence of the person who is in the process of signing. 
         [0046]    6.2 Description of Embodiments. 
         [0047]    As described here above, in order to avoid problems related to the prior-art devices and especially the complexity of manufacture of devices such as those described in the document EP0727756, the inventors had the idea firstly of computing the pressure exerted on the basis of a distance (d) between the reference element (incorporated into the stylus) and the pad on which the stylus is used and secondly of making sure that this pressure (computed from the distance) will be the same whatever the position of the stylus on the pad. More particularly, the technique described makes it possible to ensure that the pressure will be measured in the same way whatever the angle of tilt of the stylus. 
         [0048]    This result is made possible by ensuring that the tilt of the stylus is independent of the distance between the reference element of the stylus and the pad. 
         [0049]    Hitherto, it was not possible to ensure this independence. The technique described offers this result by proposing the combination of two distinct characteristics used to obtain the intended result. 
         [0050]    The first characteristic is the use of a reference element, one end of which is at least hemispherical and at most appreciably spherical, said reference element being fixed and constituting a reference point. In other words, the end of the reference element has a shape ranging from a semi-sphere to a sphere. The reference element is not itself in contact with the surface of the pad. It is integrated into the body of the stylus. The reference element comprises an end having a predetermined shape. This shape is hemispherical in one embodiment. This means that the end of the reference element is hemispherical. The rest of the reference element shaped in order to be integrated into the stylus. However, depending on the embodiments, the rest of the reference element can have a specific shape or a shape between that of a half-sphere and a sphere, which is not solely related to the positioning of the reference element in the body of the stylus, as specified here below. The purpose of this shape (hemispherical or substantially spherical) lies in the fact that whatever the tilt of the stylus, the distance between the surface of the pad and the reference element (more specifically a reference point of the reference element) does not vary. 
         [0051]    The second characteristic is the use of a damper that forms a cladding around the reference element. The external wall of the damper constitutes the point of contact between the stylus and the surface of the pad. The damper acts as a variator of distance between the reference element (and above all the reference tip of the reference element) and the surface of the pad. This damping function makes it possible to vary the pressure exerted on the stylus. Depending on the embodiment, the damper is either mechanical (in this case it is mobile between two positions) or deformable (in this case it can be crushed). 
         [0052]    Here below, three embodiments of the stylus that is the object of the disclosure are presented. Each of these embodiments corresponds to a particular implementation of the principles described here above. 
         [0053]    6.2.1 Hemispherical Reference Element 
         [0054]    This embodiment is presented with reference to  FIG. 1 . In this embodiment, the stylus has a hollow body  100  comprising a housing  101 . Usually, this body has an overall tubular shape. In this housing  101 , a reference element  200  is inserted. This reference element  200  has two distinct portions: a first portion  201  is seated inside the housing  101 . This first portion is shaped for this function. It can be fixed by gluing, fitting together or any appropriate method. 
         [0055]    The second portion  202  comprises a tip  203  having a hemispherical end  204 . The central point  205  of the hemispherical end is the reference point serving to evaluate the distance from the pad. The reference point is defined so that a quasi-absence of pressure exerted on the stylus is interpreted as a quasi-absence of pressure (and therefore gives a line of normal thickness). The pressure exerted is interpreted by means of a component that can be implemented either in the tablet itself or in a terminal to which the tablet is connected. 
         [0056]    The second portion  202  is covered with a non-conductive casing  300 . This casing  300  is made of flexible and deformable material and plays the role of a damper. Since this casing is deformable, according to the pressure exerted by the user on the stylus, the distance between the reference point and the pad varies. This has the effect of modifying the load on the pad and therefore enables the pressure to be deduced for example. 
         [0057]    6.2.2 Substantially Spherical Reference Element 
         [0058]    In this embodiment, presented with reference to  FIG. 2 , the stylus comprises a hollow body  100  comprising a housing  101 . Usually, this body has an overall tubular shape. In this housing  101 , a reference element  200  is inserted. In the housing  101 , in addition to the reference element  200 , there is also a shielding or protective sheath  102 , a shield  103 , an insulating shield  104  and an insulating ring  105 . The reference element  200  comprises two distinct portions: a first portion  201  is seated within the housing  101 , inside the insulators (insulating shield  104 , insulating ring  105 ) and extends so as to come into contact with an electrical contact element  110 , if any, of the stylus (this is true in the case of an active stylus, and this electrical contact element  110  can be absent in the case of a passive stylus). This first portion  201  is shaped for these functions of maintaining and assembling and possibly of contact inside the stylus. 
         [0059]    The second portion  202  comprises a tip  203  having a substantially spherical end  204 . The central tip  205  of the hemispherical end is the reference point used to evaluate the distance from the pad. The reference point is defined so that a quasi-absence of pressure exerted on the stylus is interpreted as a quasi-absence of pressure (and therefore gives a line of normal thickness). The pressure exerted is interpreted by means of a component which can be implemented either in the pad itself or in a terminal to which the pad is connected. 
         [0060]    The second portion  202  is covered with a non-conductive casing  300 . This casing  300 , made of flexible and deformable material, plays the role of a damper. Since this casing is deformable, depending on the pressure exerted by the user on the stylus, the distance between the reference point  205  and the surface of the pad varies. This has the effect of modifying the load on the pad and hence makes it possible to deduce the pressure for example. 
         [0061]    6.2.3 Substantially Spherical Reference Element, Mechanical Damper 
         [0062]    In this embodiment, presented with reference to  FIG. 3 , the stylus comprises a hollow body  100  comprising a housing  101 . Usually, this body has an overall tubular shape. In this housing  101 , a reference element  200  is inserted. In the housing  101 , in addition to the reference element  200 , there is also a screening sheath  102 , a shield  103 , an insulating shield  104  and an insulating ring  105 . 
         [0063]    The reference element  200  comprises two distinct portions: a first portion  201  is seated within the housing  101 , inside the insulators (insulating shield  104 , insulating ring  105 ) and extends to come into contact with an electrical contact element  110 , if any, of the stylus (this is true in the case of an active stylus, and this electrical contact element  110  can be absent in the case of a passive stylus). This first portion  201  is shaped for these functions of maintaining and assembling and possibly of contact inside the stylus. 
         [0064]    The second portion  202  comprises a tip  203  having a substantially spherical end  204 . The central tip  205  of the hemispherical end is the reference point used to evaluate the distance from the pad. The reference point is defined so that a quasi-absence of pressure exerted on the stylus is interpreted as a quasi-absence of pressure (and therefore gives a line of normal thickness). The pressure exerted is interpreted by means of a component that can be implemented either in the pad itself or in a terminal to which the pad is connected. 
         [0065]    The second portion  202  is covered with a non-conductive casing  300 . This casing  300 , made of solid and non-deformable material, plays the role of a damper. This casing  300  has a general shape of a cylindrical sleeve comprising a first hemispherical end  301 . The internal diameter of the cylindrical sleeve is substantially equal to the diameter of the substantially spherical end  204  of the reference element  200 . The hemispherical end  301  is also shaped so that it can receive the substantially spherical end  204  of the tip  203  of the second portion  202  of the reference element  200 . The second end of the casing  300  comprises a ring  302 . This ring  302  blocks the casing  300  in the housing  101 . The casing  300  is mobile in translation depending on the pressure exerted on the stylus. The return of the casing to the initial position is ensured by the use of return means  300  (such as a spring) inserted into the housing  101  and resting on the ring  302 . 
         [0066]    Depending on the pressure exerted by the user on the stylus, the distance between the central reference point and the pad varies. This has the effect of modifying the load on the pad and therefore enabling the pressure to be deduced. 
         [0067]    6.2.4 Substantially Hemispherical Reference Element, Mechanical and Deformable Damper 
         [0068]    In this embodiment, presented with reference to  FIG. 4 , the stylus comprises a hollow body  100  comprising a housing  101 . Usually, this body has an overall tubular shape. In this housing  101 , a reference element  200  is inserted. In the housing  101 , in addition to the reference element  200 , there is also a screening sheath  102 , a shield  103 , an insulating shield  104  and an insulating ring  105 . 
         [0069]    The reference element  200  comprises two distinct portions: a first portion  201  is seated within the housing  101 , inside the insulators (insulating shield  104 , insulating ring  105 ) and extends to come into contact with an electrical contact element  110 , if any, of the stylus (this is true in the case of an active stylus, and this electrical contact element  110  can be absent in the case of a passive stylus). This first portion  201  is shaped for these functions of maintaining and assembling and possibly of contact inside the stylus. 
         [0070]    The second portion  202  comprises a tip  203  having a substantially hemispherical end  204 . The central point  205  of the hemispherical end is the reference point serving to evaluate the distance from the pad. The reference point is defined so that a quasi-absence of pressure exerted on the stylus is interpreted as a quasi-absence of pressure (and therefore gives a line of normal thickness). The pressure exerted is interpreted by means of a component which can be implemented either in the tablet itself or in a terminal to which the tablet is connected. 
         [0071]    The second portion  202  is covered with a non-conductive casing  300 . This casing  300 , made of solid and non-deformable material, plays the role of a damper. This casing  300  has a general shape of a cylindrical sleeve comprising a first hemispherical end  301 . The internal diameter of the cylindrical sleeve is substantially equal to the diameter of the substantially spherical end  204  of the reference element  200 . The hemispherical end  301  is also shaped so that it can receive the substantially spherical end  204  of the tip  203  of the second portion  202  of the reference element  200 . The second end of the casing  300  comprises a ring  302 . This ring  302  blocks the casing  300  in the housing  101 . The casing  300  is mobile in translation depending on the pressure exerted on the stylus. The return of the casing to the initial position is ensured by the use of return means  300  (such as a spring) inserted into the housing  101  and resting on the ring  302 . 
         [0072]    In addition to the difference of shape of the reference element  200 , this embodiment is also different from the previously described embodiment in that the space  206  left vacant between the reference element and comprising a first hemispherical end  301  of the envelope  300  is filled with an electrically charged deformable material. In one specific embodiment of the invention, this material is charged silicone. This electrically charged deformable material modifies the behavior of the stylus. More particularly, since air is a poor dielectric, it is advantageous to replace the air of the third embodiment by a material which has a better conductive effect. This makes it possible to calibrate and adjust the stylus in a more simple way and improve the sensitivity to pressure. More particularly, the perception of the distance between the reference tip and the pad is improved. 
         [0073]    In other words, in this embodiment, a material that is more or less conductive and compressible is used to fill the vacuum of air between the casing and the end. To this end, a conductive and highly viscous gel can be used in place instead of the silicone-based material. 
         [0074]    Theoretically, if we assume that the work is being done with a flat capacitor, the following formula prevails: capacitance=(permittivity×surface area)/distance. By replacing air with a conductive material, the permittivity and therefore the capacitance (which is the variable measured by the system) is greatly increased as well. In this case, the sensitivity of the system is improved. 
         [0075]    As in the preceding embodiments, depending on the pressure exerted by the user on the stylus, the distance between the central reference point and the pad varies. This has the effect of modifying the load on the pad and hence enabling pressure to be deduced. 
         [0076]    6.3 Method for Obtaining the Distance of The Sensor Relative to the Pad As explained here above, the technique described relies on obtaining the distance from the reference point integrated into the stylus to the pad (whether touch pad or not) on which the stylus is used. 
         [0077]    The technique relies on the acquisition, relative to the surface of the pad itself, of an element representing the distance of a stylus during the entry made by the user. For greater simplicity, this element is here below designated by the letter “d” for “distance”. The piece of data on distance can be acquired by the pad itself. The technique described then requires no special implementation at the stylus (the stylus is passive), few special settings or no settings at all and little maintenance or no maintenance. Referring now to  FIGS. 5A and 5B , we present an example of a system for implementing the technique described and the main steps of the method for measuring the distance implemented in such a system according to one embodiment. 
         [0078]    As illustrated in  FIG. 5A , we consider a measurement module  10  having a pad  101  comprising a capacitive touch zone on which the user of the data  1  (the entered data can be a signature, an illustration, a sentence, etc) with a view to performing a certain function in the system. The function to be performed can for example be an authentication, a drawing, the writing of a sentence, an entry by means of a virtual keyboard, etc). The measurement module  10  is for example integrated into a payment terminal, a mobile phone, a PDA, a touch-screen tablet, a smartphone, etc. The pieces of data  1  are entered via a stylus  11  adapted to an entry on the capacitive touch zone. This stylus is capable of obtaining the distance from the pad. This is a stylus like those described here above.  FIG. 5B  presents the main steps of the method for measuring a handwritten signature, implemented in a system as described here above with reference to  FIG. 5A . 
         [0079]    A step  13  is implemented for acquiring a piece of data representing distance d of the stylus. This step  13  is implemented at at least one instance of the step  12  for entering data, and advantageously throughout the entry of the data. For example, it is possible to acquire  300  samples per second during the entry of the signature to obtain high performance in terms of reliability of measurement. Besides, depending on the type of capacitive touch zone, it is possible to acquire data on distance up to two centimeters above the pad. 
         [0080]    According to one variant of this embodiment, the acquisition step enables the acquisition of a plurality of other pieces of data on the position of the stylus relative to the capacitive touch zone of the pad, such as (x,y) coordinates of the stylus on the pad, at several moments of the data entry operation. It must be noted that the coordinates x, y and d are acquired by the capacitive touch zone of the pad itself without requiring any special implementation of the stylus. Besides, this implementation by the pad itself necessitates no settings or few settings and requires no special maintenance, unlike in the case of use of optical sensors on the stylus for example. After the acquisition step  13 , as and when the data on distance d is acquired, a step  14  for computing pressure is implemented, delivering a pressure computation result that takes account of the way in which the entry is made by the user. 
         [0081]    According to a first variant, the computation step  14  can be implemented after the entry by the user and therefore after the acquisition of all the distance data. This variant is for example implemented when the reference data used for an authentication is available on a remote server, with which communications have to be initiated to enable this reference data to be used. 
         [0082]      FIG. 6  illustrates a simplified structure of a pressure measurement device according to one embodiment of the invention. For example, the pressure measurement device comprises a memory  61  constituted by a buffer memory, a central processing unit  62 , equipped for example with microprocessor and driven by the computer program  63  implementing a method of measurement of the distance of the sensors relative to the pad. 
         [0083]    At initialization, the code instructions of the computer program  63  are for example loaded into a memory and then executed by the processor of the central processing unit  62 . The central processing unit  62  inputs at least one piece of data representing a variation of distance. The microprocessor of the central processing unit  62  implements the steps of the measuring method according to the instructions of the computer program  63  to evaluate the pressure exerted. 
         [0084]    To this end, the multimedia content server comprises, in addition to the buffer memory  61 :
       means  64  for acquiring a piece of data representing distance d of the stylus relative to the surface of the pad,   means  14  for computing pressure.       
 
         [0087]    These means are driven by the microprocessor of the central processing unit  62  to provide a piece of data representing the pressure exerted. 
         [0088]    In a predetermined way, the pressure can be computed from distance alone. In this case, a given distance corresponds to a determined pressure. A table of correspondence is used to this end. According to another embodiment, the pressure measured at a given instant depends on the distance d at this instant t and of the pressure determined at the instant t-1. 
         [0089]    Although the present disclosure has been described with reference to one or more examples, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the disclosure and/or the appended claims.