FR2628866A1 - Graphics tablet to convert trace to data set - uses resistive sheets held separate by magnetic sheets which repel each other to restore surface after passage of stylus - Google Patents

Abstract

The graphic tablet (18) includes two resistive films (10a,10b) separated one from the other and has two electrodes on the edges which establish an electric field across the sheet. The stylus causes contact between the sheets and the electric field in one causes a potential to appear in the other corresponding to the coordinates of the point of contact. The two resistive sheets are held separate by two magnetic sheets (22a,22b) attached to the outside of the resistive sheets, the two magnetic sheets being polarised so they generate a magnetic repulsion one to the other. The magnetic sheet on the stylus side of the group is flexible. ADVANTAGE - Graphics tablet which is economically constructed and is of regular thickness and is self-restoring to flatness after stylus has passed.

Description

() FRENCH REPUBLIC Publication No. 2,628,866 (to be used only

  for the NATIONAL INSTITUTE

NATIONAL INSTITUTE

OF INDUSTRIAL PROPERTY

  D N of national registration 88 03379 PARIS

I Int CI ': G 06 K 11/06.

@ APPLICATION FOR PATENT OF INVENTION A1

  ) Filing date March 16, 1988. Applicant (s): NAVEAUFrancis. - FR.

) Priority

) Inventor (s) Francis Naveau.

  Date of the public availability of the

  BOPI "Patents" application No. 38 of 22 September 1989.

  References to other national documents appearing

(n) Holder (s)

  (Agent (s): Cabinet Regimbeau, Martin, Schrimpf.

Warcoin and Ahner.

  (0 Graphic tablet for converting a graphical plot into a set of data representative of said plot.

  A graphic tablet for converting a plot made with a stylus 16 into data, for example numerical data

  comprises two resistive sheets 10a, 10b spaced one of.

  the other and associated with edge electrodes for establishing electric fields thereon. The pressure of the stylus establishes at each instant a point contact between the two sheets and, while the field is established in one sheet, the other 22b. -P '4b takes the representative voltage of a coordinate lOb - the point of contact. According to the invention, means for spacing the two resistive sheets 22 comprise two magnetic sheets 22a, 22b, 10a 'arranged in such a way as to generate a repelling magnetic force therebetween. The resistive sheets are fixed on the surfaces facing the two magnetic sheets and on the

  D minus the write-side magnetic sheet 22b is flexible.

  o eo o Sale of booklets NATIONAL PRINTING. 27. rue de Convention75732 PARIS CEDEX where it sells fascicles to the NATIONAL PARLIAMENT. The present invention relates generally to graphic tablets, intended in particular to convert a graphic trace made by a user.

  on a support in electrical information, analogue

  representative of the said route and

  memory, visualization or processing

  eg in an associated calculator.

  It is already known in the prior art

such graphic tablets.

  They conventionally comprise two resistant sheets

  tives (or a resistive sheet and conductive foil)

  they are kept apart from one another at a short distance

  a plurality of electrodes provided at the edges of at least one of the resistive sheets and intended to establish, alternately, two essentially uniform electric fields and substantially orthogonal directions, and a means for performing the graphical plot, such as a stylus, which establishes an essentially point-like electrical contact between the two sheets, the leaf in which the electric field establishing at this point is established at a given instant. a

  electrical voltage representative of a coordinate of that point and the

  sheet to take this tension for the application

  for example to a calculator or the like.

  A number of solutions have so far been adopted to ensure the required spacing between the two resistive sheets, while enabling their implementation.

  point contact by stylus pressure.

  First, the French utility certificate No. 2,463,955 teaches a graphics tablet in which the two resistive sheets delimit together, and with side walls of the graphics tablet, a sealed volume containing a gas under pressure. , which does not oppose a local deformation of one of the two resistive sheets for the occasional contacting of the

two leaves.

  Such a solution, however, presents a

  major disadvantage: it is essential that the

  graphical blette has a reasonable life, that the closed volume is perfectly gas-tight, and this involves a delicate choice for the materials of the two resistive sheets and particular care in the manufacture of the tablet, with consequent substantial additional cost.

  Another solution proposed by this same

  utility is to stretch the two

  sistives one above the other. But two disadvantages

  major factors are then observed: on the one hand, the effort to provide with the stylus to bring the two sheets

  resistive in mutual punctual contact increases substantially

  as you get closer to the edges of the leaves,

  because their aptitude for transverse displacement is sensible-

  decreased; on the other hand, the mechanical tension in

  resistive leaves may loosen after a few

  time of use, which limits the life of the tablet, except to provide a system for adjusting the

  complex and expensive tension, or even a particular material

  bind, also expensive, for resistive leaves.

  In addition, French Patent No. 2,181,350 proposes a certain number of other solutions for keeping the two resistive sheets spaced apart from one another in

the lack of effort.

  A first solution is to interpose between the two resistive sheets a grease or a gel

  Deformable and self-regenerating insulation. But some inconveniences

  In this case, the volume defined by the resistive sheets and the lateral edges provided in the tablet must be sealed; in an associated way, the resistive sheets must be chosen non-wettable

  to prevent seepage of the gel. Finally, the characteristics

  Gel ticks can degrade in the more or less long term and in particular its distribution in the thin space between the two sheets can become heterogeneous and thus offer either a pressure resistance too strong for the writing with the stylus with normal pressure causes the correct contact point of the two resistive sheets to be brought into contact, that is to say a resistance to

  pressure low enough that the support of the hand of

  the writer on the writing surface causes contacts

  untimely between the two resistive sheets.

  A second solution described in this patent is to interpose between the two resistive sheets a nylon net, with a wire diameter and mesh size suitably chosen. But the choice of such an insulator has the disadvantage that it can not establish a correct electrical contact to the right son constituting the net. Unwanted "jumps" are

  thus present in the coordinates information collected

  lees. The present invention has the primary object of 2C to overcome the disadvantages of the prior art and of

  to offer a graphic tablet equipped with perfec-

  designed to establish a self-regenerable thin space of uniform thickness between the two resistive sheets,

  and this with an extremely reduced manufacturing cost.

  For this purpose, the present invention proposes a device of the graphic tablet type, intended to convert a graphical plot or the like executed using a stylus

  on a writing area, into a set of data representing

  said trace, and of the type comprising: - two superposed resistive sheets, essentially rectangular and parallel, defining the writing area;

  two pairs of rectilinear electrodes associated

  at the edges of said resistive sheets and

  to generate successively, in one of the two sheets

  the resistive ones or in the two resistive leaves alter-

  natively, two essentially uniform electric fields

my and orthogonal; and

  spacing means for maintaining the

  said two resistive sheets spaced apart from each other by a substantially constant short distance and designed

  so that the stylus can, by the writing pressure,

  blir an essentially punctual electrical contact between

  the resistive sheet in which the electric field reigns

  that and the other resistive sheet, which thus performs the pre-

  the removal of an electrical voltage representative of a

  instantaneous ordinate of said point of contact; characterized in that the spacing means comprise two plates superposed on the inner surface of which the two resistive sheets are respectively fixed and which create

  between them a magnetic force of essential repulsion-

  uniform throughout the entire writing area,

  at least the outer plate being flexible.

  Preferred aspects of the device of the invention

  are shown below: - each magnetic plate consists of parallel bands of alternating North and

  two magnetic plates having the same polarity being

  held side by side, - the one or more flexible magnetic plates consist of a synthetic binder rubber in which magnetized ferrite particles are introduced, - it further comprises a housing comprising a bottom associating the plate lower magnetic, lateral edges having cavities in which the edges of said resistive sheets project to receive the electrodes and stop means for positioning the outer flexible magnetic sheet vis-à-vis the inner magnetic sheet,

  Other aspects and advantages of presenting

  the invention will appear on reading the description

  following detailed description of preferred embodiments thereof, given by way of nonlimiting example and with reference to the accompanying drawings, in which: - Figure 1 is a schematic perspective view of an example of a graphics tablet to which this present invention is applied;

  -. FIG. 2 is a cross sectional view of

  dirty of the graphic tablet of Figure 1; and - Figure 3 is another sectional view

  transverse, on an enlarged and partial scale.

  Diagrammatically shown in the figure

  i the essential mechanical parts of a graphite tablet

  to which the invention applies.

  It comprises a first resistive sheet, for example rectangular, resting on a rigid support plate (not shown), and a second resistive sheet 10b, held above the first sheet a and parallel to it, so that there exists between the two leaves a space of height essentially constant, voluntarily exaggerated on the figure for the sake of

clarity.

  In this case, the resistive surface

  10a has two pairs of electrodes, respectively

  11, 12 and 13, 14, the electrodes of the same pair extending parallel to one another along two

  opposite sides of said sheet 10a.

  Finally, a stylus 16 is intended to be used

  se for the realization of a graphical plot, with a determined writing pressure, either directly on the graphics tablet, or preferably on a sheet

  of renewable paper disposed thereon.

  During the course of the plot, the stylus realizes

  every moment a contact is

  between the two resistive sheets.

  If, during this time, the two pairs of

  trodes 11, 12 and 13, 14 are alternately activated, with a relatively high switching frequency determined,

  for example a few kilohertz, so to create alter-

  natively in the resistive leaf 10a two fields elect

  E and E triangles E and E substantially uniform, xy voltages Vx, Vy present on the resistive sheet 10a and representative of the coordinates according to Ox and Oy instantaneous contact point considered are transmitted by said point of contact to the upper resistive sheet 10b, which therefore serves as a means of taking voltages. This avoids the stylet 16 having to play this role, which would require the equipping of a metal tip and a

inconvenient wire binding.

  The voltages (Vx, Vy) are transmitted for example to an appropriate analog / digital converter for processing, storage or subsequent visualization

by a calculator.

  It can be noted here that the top sheet

  10a may be in the present example a conductive sheet

  trice, for example metallic, with essential resistivity

  zero; but it is advantageous to give this sheet substantial electrical resistance because it avoids any risk of overcurrent or short circuit in the

  electrical circuit of the graphics tablet when,

  dentally, there are two points of contact between the two leaves in the respective vicinity of the two electrodes

an activated pair.

  The present invention proposes means permitting

  adapted to maintain the two resistive sheets spaced from each other by a uniform distance, with one-touch capability at substantially constant pen pressure anywhere on the writing surface, and at the same time time considerably minimizing the risk of contacting the two sheets unexpectedly, for example by pressing the user's hand on the writing surface during execution

of the route.

  FIG. 2 shows the detailed physical structure of a graphics tablet according to the invention. In this figure, the respective thicknesses

  various elements have been exaggerated for the sake of clarity.

  On a rigid support plate 20, for example made of plastic and integrated into the casing 18 of the graphics tablet, is fixed a first plate or

  magnetic rubber sheet 22a, for example by collating

  ge. Sheet 22a is designed to display on

  the extent of its upper surface, a network, of not

  as many magnetic poles alternately North and South,

  as will be described in detail below.

  On the magnetic sheet 22a is fixed, preferably also by gluing, the resistive sheet

  10a in which are established the electric fields or-

  thogonaux. The graphics tablet further comprises a second magnetic rubber sheet or sheet 22b extending at a distance, as will be seen later, above the first resistive sheet and having on its lower surface a network of not even that the network of the first magnetic sheet 22a,

  magnetic poles alternately North and South. At the top

  lower face of the magnetic sheet 22b is also fixed, also preferably by gluing, the second

  resistive sheet 10Ob for taking electrical voltages.

  Finally, above the second sheet of paper

  22b is arranged a renewable sheet 24, for example of plain paper, on which the outline

  graph to be analyzed in terms of coordinates shall be

  cut with the stylus 16, which can be an instrument

  writing or conventional drawing.

  In order to better protect the upper surface

  rubbery nature of the magnetic foil.

  22b, one can interpose between the sheet of paper 24 and said magnetic sheet 22b a sheet of material

  plastic with both a good hardness and a certain

  flexibility, that is to say chosen in such a way as to

  sufficient deformability while having good

  resistance to localized penetration by the tip of the

  writing instrument 16. For example, a polycarbonate may be chosen. According to the present invention, the two magnetic sheets 22a and 22b are arranged one

  above each other with relative positions,

  horizontally, such that their North poles and their South poles are respectively facing each other, so as to generate between the two leaves repulsive forces

  of equal amplitude and uniformly distributed over the entire

  due to the useful surface of the tablet.

  The pressure exerted by the stylet 16 must be sufficient to overcome locally this repulsive force and thus bring the two resistive sheets 10a, 10b, located inside the magnetic sheets 22a, 22b, in essentially point contact, by deformation of the sheet of paper 24, magnetic sheet 22b and sheet

resistive 10b.

  The thickness and magnetization of the magnetic sheets 22a, 22b will be chosen as a function, firstly, of the deformability required to establish a contact whose effective area is as small as possible and, secondly, of the force of the minimum pressure that must be exerted for

establish such contact.

  However, it should be noted that, the magnetic sheet

  lower tick 22a is not intended to deform, its thickness will not be critical, and it can even be rigid.

  FIG. 3 shows a configuration of

  preferred magnetic ration for sheets 22a and 22b.

  The North and South poles of each sheet are in fact constituted by alternating parallel polar lines of constant magnetization. Both leaves are positioned so that the northern polar lines

  two leaves are facing each other, as are the

  South poles, thus creating a set of forces

  homogeneous distribution repulsion determined.

  Preferred numerical values for the magnetic rubber sheets are given below: Thickness of the deformable sheet 22b: 0.5 to 1.0 mm, not alternating polar lines: 1 to 10 mm,

  - Repulsive force: 10 to 100 g / cm2.

  Methods of making such magnetic rubber sheets are well known in the art,

  these sheets being conventionally used for fixing

  magnetism on ferromagnetic boards, etc. For example, European Patent No. 0 080 160, the contents of which are incorporated herein by. reference, discloses flexible compositions with permanent magnetization comprising an elastomeric binder, such as a polyacrylic elastomer, which are incorporated, in relatively large proportions, fine particles of a magnetic compound such as ferrite barium, lead or strontium. The

  particle size may be of the order of 0.5 to 10 Nm.

  Such a composition can be put into

  any form, and in particular in sheet form.

  A suitable magnetic field is applied to the softened formed product to magnetize (orient the ferrite particles according to a predetermined polar pattern,

  and in particular according to the configuration in polar lines

  as described above.

  Also included in this description

  by reference European Patent Application No. 0 176 919 which describes

  an isotropic ferrite powder suitable especially for the production

  magnetic plates, as well as French Patent No. 2,262,856 describing a permanent magnet body in the form of a plate, whose magnetization is present throughout the thickness and which may have

a thickness less than 1 mm.

  With regard to the resistive sheets 10a, 10b, they will advantageously be made from a resistive paper

of commerce.

  Referring again to FIG. 2, one can observe the configuration of the boot 18 of the graphics tablet in the region.

  an edge thereof, corresponding to an edge of the writing area.

  In order to give the user a substantially uniform sensation during writing, even when approaching the boundaries of the writing area, it is expected that the multi-sheet, magnetic and resistive structure, in accordance with the present invention, extends to a certain

  distance beyond the considered limit of the writing area

  ture. Thus, it can be observed that the housing 18 comprises

  an upper horizontal flange 27 extending over a distance

  this substantial inward above the various leaves and delineating the writing area, this being well

heard optional.

  A downwardly projecting portion 26 provides a positioning stop for the upper magnetic rubber sheet 22b so that lines of the same magnetic polarity retain their required vertical alignment. It should be noted in this regard that such a lateral locking system is indispensable because the two magnetic sheets spontaneously tend to align their poles of opposite polarities to stick to one another by the

  magnetic attraction forces. On the contrary, the present

  the invention provides for maintaining the two sheets 22a,

  22b in a laterally unstable equilibrium relation.

  In addition, the resistive sheets 10a, 10b extend laterally outwards beyond the magnetic sheets, into cavities 24a, 24b adapted to receive the electrical connections with said resistive sheets, and in particular the electrodes, as well as the connections Vx, Vy Voltage Sampling

representative of the coordinates.

  A horizontal rib 28, of a thickness substantially equal to the height of the space between the two

  resistive sheets as it is created elsewhere by the

  this repulsive magnet, is provided, projecting from the side edge of the box, to overcome the lack of

  magnetic sheets in this region and ensure the isolation

  electrical connection between the two resistive sheets.

  Preferably, the case 18 of the tablet

  chart and the various leaves with a configuration

  analogous along the other three edges of the writing area. Preferably, each electrode 11, 12, 13, 14 is constituted by a chain of weak resistors 30.

  predetermined values which are connected in series, the diver-

  its connections between two successive resistances being fined in electrical contact with the associated edge of the

  resistive sheet 10Oa or 10Ob at regular locations.

  spaced apart. The four electrodes are further connected

  electrically between them at the four corners of the sheet 10a.

  The means for selectively short-circuiting

  The ends of an electrode may comprise a relay, a semiconductor switch or a diode. For more details on the constitution of the electrodes and the electrical operation of such a graphics tablet, reference will be made on the one hand; French Patent No. 2,181,350 and, on the other hand, French Patent Application No. 86/16246 in the name of the Applicant, the respective contents of these two documents being incorporated.

here by reference.

  Of course, the present invention is not

  in no way limited to the embodiment described above.

  and shown in the drawings, but those skilled in the art will be able to make any variant or modification thereof

to his mind.

  In particular, as indicated, the

  The resistivity of the sheets 10a, 10b is to be considered in a relative sense, one of the sheets may be of substantially zero resistivity (and be constituted for example by a thin aluminum foil) in the case o

  the other leaf carries the four electrodes.

  In this respect, it will be understood that the invention

  advantageously applies not only to

  in which the orthogonal electric fields are established in one of the two sheets, which then carries four electrodes while the other sheet performs the sampling of the tensions (coarme described above), but also

  to those in which the electric fields are established alternately

  in both sheets, their roles thus permuted at each half-cycle of the sampling cycle. In the latter case, the two sheets are preferably of equal resistivity. and each carry a set of two opposing electrodes. In addition, in the first case, the surface which takes the voltages by point contact in P created

  by the stylet 16 can be located indifferently above

  above or below the sheet in which the orthogonal fields are alternately established. In addition, the diagram of the North and South poles of the magnetic rubber sheets may be

different from that described.

  In addition, as already indicated, the inner magnetic sheet 22a need not be flexible. In one embodiment, it can even be

  consisting of magnetized particles incorporated in the

  port 20 (Figure 2), which will then preferably be

plastic.

  Finally, although in the description which pre-

  the resistive leaves are attached to the

  of nature, it is understood that said sheets resist

  can be integrated directly into the master sheets

  for example by incorporation into the latter

  a thin layer of electrical resistivity given or

core by surface treatment.

Claims (5)

  1. Device of the graphic tablet type, des-   to convert a graphic or analogous   using a stylus (16) on a writing area, in one   data representative of said plot, and of the type comprising:   - two resistive sheets superimposed essen-   tually rectangular and parallel (10a, 10b), defined   the writing area; - - two pairs of rectilinear electrodes (11 and   12, 13 and 14) associated with the edges of said resilient sheets   and likely to generate successively, in one   two resistive sheets or in both   alternatively, two electric fields   uniform and orthogonal (Ex, Ey); and   spacing means for maintaining the   said two resistive sheets (10a, 10b) spaced apart from each other by a substantially constant small distance   and designed so that the stylus can, by the pressure of writing,   ture, establish a substantially punctual electrical contact (P) between the resistive sheet in which the electric field reigns and the other resistive sheet, thereby performing the sampling of a voltage representative of an instantaneous coordinate of said point of contact; characterized in that the spacing means comprise two superposed plates (22a, 22b) on the inner surface of which the two resistive sheets (10a, 10b) are respectively fixed and which create between them a substantially uniform magnetic repulsion force (F). throughout the writing area, at least the plate outer being flexible.   2. Device according to claim 1, characterized   in that each magnetic plate (22a, 22b) comprises parallel strips of alternating North and South polarities, the strips of the two magnetic plates having the same polarity   being kept in relation to each other.   3. Device according to claim 2, characterized   characterized in that the one or more flexible magnetic plates are constituted by a synthetic rubber forming   binder into which iron particles are introduced. magnetized rite.   4. Device according to one of the claims   2 and 3, characterized in that it further comprises a housing   tier (18) comprising a bottom (20) associating the plate   lateral edges having cavities (24a,   24b) in which the edges of said sheets protrude   the resistives for receiving the electrodes (11, 12, 13, 14) and stop means (26) for positioning the outer flexible plate (22b) opposite the inner magnetic sheet.   5. Device according to claim 4, characterized   in that the bottom (20) and the lower plate constitute a single element.   -. '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '