WO2015181368A1

WO2015181368A1 - Electronic sensor of an electronic writing instrument

Info

Publication number: WO2015181368A1
Application number: PCT/EP2015/062003
Authority: WO
Inventors: Marcus Schwertfeger
Original assignee: Stabilo International Gmbh
Priority date: 2014-05-30
Filing date: 2015-05-29
Publication date: 2015-12-03
Also published as: DE102014107657A1; DE102014107657B4

Abstract

Electronic sensor for measuring forces, especially bearing forces of an electronic writing instrument on a surface, comprising a first resistor being coupled to a current supply and a second resistor being movable with respect to the first resistor, wherein the first resistor comprises an electrically conducting contact surface and the second resistor is movable in the direction of the contact surface, characterized in that the second resistor comprises an electrically conductive elastic element which can be deformed by a force effect and the total resistivity of the first and second resistor is changeable by the size of the contact area of the elastic element on the contact surface and a method for measuring bearing forces of an electronic writing instrument on a surface.

Description

Electronic sensor of an electronic writing instrument

The present invention relates to an electronic sensor for measuring forces, particularly bearing forces that act upon an electronic writing instrument when loaded onto a surface.

Prior Art

Cheap and robust force sensors with easy evaluation are not yet known. For this reason, for manufacturing staple articles, for example electronic writing instruments, known sensor technology has to be applied that is often too complex and, therefore, expensive for such fields of application.

Electronic writing instruments are usually used in combination with touch screens for example, wherein a ball pen refill analog (for example a plastic pallet or a plastic refill) in an electronic writing instrument is placed on a corresponding surface, like a tablet computer, and by movement of the hand with the electronic writing instrument, a drawing or writing is applied. For measuring the bearing forces acting on the electronic writing instrument, strain gauge strips, but also piezo-resistive sensors are most commonly used. Therein, force conditioned bending of a carrier material is translated into a change in resistivity.

Further, geometric changes of a corresponding sensor body due to application of force can be evaluated capacitively in order to determine the acting force. Although all of these sensor systems have high quality with respect to gathering bearing forces also in sufficiently large ranges, they require much space and are usually badly protected against exceedingly strong pushing. Further, these sensors are quite expensive due to the materials used (for example, silicon bodies or printed thick films), which is disadvantageous for producing a mass product, like an electronic writing instrument. Additionally, they provide a measure signal too low or signal range too low for this field of application, therefore making evaluation of the gathered sensor signals difficult.

Problem

Therefore, starting from the prior art, the problem of the present invention is to provide an electronic sensor for measuring forces, especially bearing forces of an electronic writing instrument on a surface, which has a high resolution and linearity, as well as high signal range with respect to measurement of the acting force, while, at the same time, being highly robust and having small space requirements and further being inexpensively producible. Solution

This problem is, according to the invention, solved by the electronic sensor according to claim 1 , and the method for measuring bearing forces acting on an electronic sensor of an electronic writing instrument according to claim 10. Advantageous embodiments of the invention are comprised in the dependent claims.

The inventive electronic sensor comprises a first resistor being coupled with a current supply and a second resistor being movable with respect to the first resistor, wherein the first resistor comprises an electrically conductive contact surface and the second resistor is movable in the direction of the contact surface, and is characterized in that the second resistor comprises an electrically conductive elastic element, which can be deformed by a force effect and the total resistivity of the first and second resistor is changeable by the size of the contact area of the elastic element on the contact surface. This electronic sensor can be produced much smaller than known sensors, and therefore a corresponding electronic writing instrument can be very similar or identical in form and size to common writing instruments. Further, the required materials for producing the electronic sensors are much more cost-effective, since it is not necessary to use printed systems based on silicon here.

In one embodiment, the elastic element comprises an elastic polymer. Utilization of an elastic polymer can prove as inexpensive alternative to other materials.

In a further embodiment, the first resistor comprises copper pathways or thick film resistance pathways comprising a conductive glass matrix. These components are, likewise, cheap and can be produced in a technically easy manner even with small dimensions.

In one embodiment, the inventive electronic sensor is characterized in that the elastic element has a pyramid-shaped, hemisphere-shaped, cone-shaped, paraboloide, hyperbolical or prismatic form. Utilization of different forms of the elastic element can support assigning of clearly measurable different total resistivity values to different applied forces.

It can be provided that the elastic element is tapered along one direction, wherein the elastic element is arranged with the taper in the direction of the first resistor. It can thus be ensured that a greater force corresponds to a greater contact area, wherein an increase in force by this realization of the elastic element also results in a strictly monotonically increasing contact area. Thus, evaluation of the measured signal can be significantly simplified.

Further, a force transmitting element, that can transfer an applied force onto the second resistor, can be arranged on a side of the second resistor opposing a contact side area of the second resistor. This force transmitting element can, for example, be a ball pen refill analog or a movably mounted ball, which can transfer the applied force onto the elastic element.

In one modification of this embodiment, the force transmitting element is arranged in a guide, wherein the force transmitting element is movable within the guide perpendicular to the contact surface. This guide allows for a well-defined movement of the force transmitting element, and thus of the elastic element and the second resistor, respectively, whereby the measurement accuracy can be improved.

The electronic sensor, according to the invention, can be integrated into an electronic writing instrument. A correspondingly adapted electronic writing instrument is much easier to produce, as well as less expensive, and can further be formed such that it equals common writing instruments in form, size and weight.

In a modification of this embodiment, the electronic sensor is coupled to a current supply that is arranged in the electronic writing instrument or connected thereto. In case the current supply is provided in the writing instrument, the writing instrument can be used independently. An external current supply that can be coupled to the electronic writing instrument, however, provides the advantage that the electronic writing instrument can also be used long-term without occurrence of failures due to lack of current supply, like, for example, an empty battery.

The inventive method for measuring forces acting on an electronic sensor, especially bearing forces acting on an electronic writing instrument, provides that a second resistor is moved relative to a conductive surface of a first resistor of the electronic sensor, depending on a force acting on the electronic sensor, and the total resistivity of the first and second resistors is changed by a change of the contact area of an elastic element of the second resistor, being deformable by the force effect, on the contact surface. This method is technically significantly simplified and cheaper, as compared to previous methods for measuring forces acting on electronic sensors, especially in the application in an electronic writing instrument.

In one embodiment, the method is characterized in that a force acting on a force transmitting element being connected to the second resistor is transmitted to the second resistor. Thus, the actual force effect can occur at the force transmitting element, which is then directly or indirectly, for example by means of a spring or the like, transferred to the second resistor, for example for protecting the second resistor from environmental influences. Thereby, durability of the electronic sensor can be increased. Here, it can be provided that the force transmitting element is moved perpendicular to the first resistor in a guide, depending on an applied force. In that way, measurement accuracy of the applied force to be measured can be significantly increased.

In one embodiment, the contact area of the elastic element on the contact surface is strictly monotonically increasing with an increasing applied force. This simplifies the evaluation of the measured resistivity values.

In a further embodiment, the first resistor is carrying a current either continuously or in time intervals. The continuous measurement allows capturing with high accuracy, such as during writing, whereas current carrying of the first resistor in defined time intervals is energetically more economical, which can result in longer service life, especially when using, for example, the internal current supply of the electronic writing instruments.

It is advantages when, by changing the contact area of the elastic element on the contact surface, applied forces reaching between ON and 10N are uniquely assigned to a total resistivity. Thus, all common forces when writing with electronic writing instruments can be captured and unique measure values can be associated therewith.

Brief description of the drawings

Figures 1 a+b Schematic depiction of a sensor according to the invention with equivalent circuit diagram.

Figures 2a+b Schematic top view of a sensor according to the invention at different forces.

Figures 3a-e Schematic depiction of possible embodiments of the contact surface.

Figures 4a-f Schematic depiction of different embodiments of the elastic element.

Figures 5a+b Schematic depiction of two embodiments of an electronic writing instrument with the electronic sensor according to the invention.

Detailed description

Figure 1 shows a schematic depiction of an electronic sensor according to one embodiment of the invention, as it could, for example, be applied in an electronic writing instrument. The electronic sensor 100 comprises a first resistor 101 and a second resistor 102. The first resistor 101 comprises a contact surface on which the second resistor 102 can rest. This contact surface is electrically conductive. The second resistor 102 further comprises an electrically conductive elastic element. This is shown synonymous to the resistor 102. The electrically conductive element is movable or deformable, respectively, in the direction of the contact surface of the first resistor 101 , depending on a force F acting on the element. Thereby, depending on the force F acting on the elastic element, the size of the contact area of the elastic element on the contact surface of the first resistor 101 changes due to a change of the form of the elastic element.

If a current flows through the first resistor 101 , for example from the power supply 103, a change in the size of the contact area of the second resistor 102 on the contact surface of the first resistor 101 causes a change of the total resistivity of the arrangement. This change can be captured by a corresponding evaluation unit 104, and thus the force F acting on the second resistor 102 can be determined.

For this purpose, figure 1 b shows the electric equivalent circuit diagram of the arrangement of the electronic sensor 100, according to Figure 1 a. The first resistor 101 can be subdivided into three partial resistivities. The resistivities R₂ and R₄ left and right of the contact zone of the second resistor 102 respectively and to the elastic element respectively are arranged outside of the contact area of the elastic element on the contact surface. The resistivity R₃ is given by the resistivity of the first resistor in the range of the contact area. The resistivity R-i is the resistivity of the conductive volume of the elastic element.

In case the force acting on the elastic element is small, the resistivities R-i , R₂ and R₄ are large, whereas the resistivity R₃ is comparably small. If the force acting on the second resistor 102 increases, the resistivity R₃ increases. The resistivities R₂, R4 and Ri however decrease. Since the resistivity R-i is connected parallel with the resistivity R₃, the resistivity R, which can be considered to be the total resistivity of R₃ and R-i , is given by 1

/R₃. The total resistivity

R2⁺R₄ ⁺R- The resistivity R depends on the contact area of the elastic element on the contact surface of the first resistor 101 in Figure 1 a. If the contact area increases, the volume available for conducting a current in the elastic element increases, because of which the resistivity R of the parallel connection of the elastic element and the first resistor decreases. The resistivities R₂ and R₄ likewise decrease with increasing contact area, since a great area on the first resistor 101 is available for current propagation, whereby the resistivity is reduced. It, therefore, becomes apparent that the total resistivity of the arrangement decreases when the applied force increases.

The measure or the rate, respectively, with which the total resistivity R_lola] decreases with increasing force depends essentially on the change in the contact area of the elastic element on the contact surface of the first resistor. Figure 2a shows a top view of the elastic sensor according to Figure 1 a and shall further illustrate this correlation. In Figure 2a, the first resistor 101 is shown. The contact surface 210 is electrically conductive. A border 21 1 of the contact surface 210 can, especially for simplifying implementation of the electronic sensor and for arranging current carrying conduits, be provided at least partially insulated. The elastic element 102 is preferably centrally arranged on the contact surface 210 or above it, respectively. At the applied force F-i shown in Figure 2a, only a small part 221 of the area of the elastic element 102 rests and, thus, only a small current flow or a small volume for current flow through the elastic element 102 results. The resistivity of the elastic element 102 is therefore high.

In Figure 2b, the identical arrangement of Figure 2a is shown, but the force F₂, acting from above on the elastic element 102 is greater, as in Figure 2a. Therefore, the contact area 221 ' of the elastic element 102 on the contact surface 210 is greater, as compared to Figure 2a. Compared with this, the area 222' of the elastic element that is not connected with the contact surface 210 is significantly smaller than the corresponding area 222 in Figure 2a. Due to the greater contact area 221 ' on the contact surface 210, more current paths through the elastic element are available for the current, because of which the resistivity of the elastic element decreases.

By manipulating the structure of the contact surface 210 and the form of the elastic element, a corresponding resistivity curve dependent on the force acting on the elastic element can be changed in such a way that a bijective assignment of measured resistivities to acting forces is possible. This ensures that with increasing force, the contact area of the elastic element on the contact surface increases strictly monotonically. It is also thereby ensured that the total resistivity of the arrangement decreases strictly monotonically.

In this regard, Figures 3a-d show different embodiments of the contact surface 310 of the first resistor 301. In principle, the contact surface or the first resistor 301 respectively can be realized by interdigiting structures comprised of low impedance material, like, for example, copper pathways. However, in order to increase the measurement accuracy, it is advantageous if the structures consists of higher impedance printed and/or burnt in thick film resistance pathways without protective cover. If the protective cover is omitted, electric contact with the electrically conductive elastic element is made possible. Usually, a thick film technique is realized by means of a conductive glass matrix with a high chemical and mechanical durability, because of which this embodiment is preferred, since, thereby, a highly durable electronic sensor can be provided at low price.

From the borders 31 1 and 314 of the first resistor 301 , electrically conductive pathways 312 can be provided on insulating material 313. In Figure 3a, these are pathways being in parallel and separated from each other that have their origin in an alternating manner either in the left border 31 1 or in the right border 314 and that do not reach to the opposite border, such that current flow without the elastic element resting on is not possible and the total resistivity in such a state would theoretically be infinite. This alternating arrangement is not mandatory and, for example, also three pathways can originate from the left border 31 1 and only one pathway can originate from the right border 314. Further, other combinations are possible. In particular, the density of the pathways can, starting from the middle of the first resistor 301 , vary perpendicularly to the borders 31 1 and 314. Thus, for example, approximately in the middle of the borders 31 1 and 314, a great number of pathways can be provided in order to realize a preferably high sensitivity to a change of the contact area on the contact surface 310, whereas, towards the outer limitations of the borders 31 1 and 314 (here, on the top or the bottom of the picture), the density of the pathways can decrease.

Since, in the embodiment shown in Figure 3a, no direct connection of the pathways 312 originating from the left border 31 1 and from the right border 314 exists, the resistivity of the complete arrangement without the elastic element resting on is infinite. The greater the contact area of the elastic element on the contact surface is with increasing force, the more connections between the respective pathways of the left border 31 1 and the right border 314 result and the lower the total resistivity of the arrangement.

A corresponding realization of the contact surface 310 in such a way, that no current flow exists if the elastic element is not in contact, is, however, not mandatory. Accordingly, Figures 3b-3d show realizations of the contact surface in which the pathways 312'-312"' provide for a connection of the left border 31 1 and the right border 314 of the first resistor, such that if the elastic element is not in contact, a current flow is always possible. Since such a current flow is only possible through the pathways 312'-312"' and no current flow can result in the insulating areas 313'-313"', the resistivity of this arrangement is also very high if the elastic element is not in contact.

If the elastic element rests on the contact surface 310 in Figure 3b, connections of the pathways 312' also parallel to the hypothetical connection line between the borders 31 1 and 314 are created, such that the total resistivity of the arrangement decreases with increasing contact area.

The analog is valid for Figure 3c. Here, due to the contact with the elastic element, current pathways parallel to the borders 31 1 and 314 occur, such that a current flow from the bottom of the first border 31 1 to the top of the second border 314 is more efficiently possible, and thus the total resistivity of the arrangement is reduced. Figure 3d can be considered to be a combination of Figure 3b and Figure 3c, such that the pathways 312"' are arranged in a kind of checkered pattern. The insulating area 313"' is small compared to the previous figures, such that the total resistivity of the arrangement is smaller, even if the elastic element is not in contact. The arrangement according to Figure 3d, however, provides the advantage that the density of pathways from the center of the contact surface 310 outwards can be easily varied. The realization of the pathways 312"' as checkered pattern thereby allows, compared to the embodiment according to Figure 3a, a significantly more sensitive gathering of the contact area of the elastic element, such that the embodiment according to Figure 3d allows for a high accuracy with respect to the resistivity measurement and the acting force deduced therefrom.

The embodiments according to Figures 3a to 3d provide a further advantage. If an elastic element is used, which maximum contact area (at the maximum intended force acting on the sensor) is smaller, preferably much smaller, than the contact surface shown in Figures 3a to 3d, for example 1/10 of the contact surface 310, then the measured resistivity value is always independent of the actual position at which the elastic element rests on the contact surface 310. Three different positions of the elastic element 102-102" on the contact surface 310 are, therefore, shown in Figure 3e.

The influence of an elastic element slightly shifting during use, for example in a writing instrument, can thereby be neglected, since it does not have any influence on the measured resistivity. It is thus ensured that with the resistivity measurement, only the size of the contact area, and thereby the force acting on the elastic element, is measured. This is, of course, only valid as long as the overall contact area of the elastic element is completely on the contact surface and the elastic element 102 indeed changes its position on the contact surface, but the alignment of the elastic element 102 with respect to the contact surface remains the same. This allows filtering shearing forces that can occur on a ball pen refill connected with the elastic element when loaded on a surface for example, already due to the special mechanical arrangement.

Further, the sensor according to the invention is insensitive of minor deviations of the positioning of the elastic element during manufacturing of the sensor. This can further reduce the costs for producing, since a highly precise positioning of the elastic element 102 with respect to the contact surface 310 (for example exactly in the middle of the contact surface) is not necessary and a significant allowance of error is given.

As already explained above, the measurement accuracy of the electronic sensor does not only depend on the realization of the contact surface 310, but also further depends on the form of the elastic element. For this reason, in Figures 4a-4f, different embodiments of the elastic element are shown.

In Figure 4a, the elastic element is formed as a cone. The apex of the cone shows, when being arranged in the electronic sensor, preferably in the direction of the contact surface, such that, with increasing applied force, the apex initially contacts the contact surface and allows for a current flow and with further increasing force, the contacted surface is increased due to deformation of the cone. By forming the elastic element as a cone, certain symmetry of deformation through application of force can be ensured, such that the total area of the elastic element contacting the contact surface of the first resistor is evenly increased, which can increase the measurement accuracy. Due to the circular profile of the cone 401 , torsion can occur, which can possibly have influence on the resistivity of the elastic element.

In Figure 4b, the elastic element 402 is formed as a pyramid. Likewise, here the advantages as described with respect to Figure 4a are achieved, but the rectangular or even quadratic base of the elastic element 402 allows for a more accurate fixation of the elastic element, for example with the aid of guides inside the electronic writing instrument. Further, when utilizing the elastic element 402 in the shape of a rectangular pyramid (pyramid with a rectangular base) with different side lengths already during manufacture of the electronic sensor, a specific alignment of the elastic element with respect to the contact surface, as is exemplarily shown in Figure 3, can be realized. Depending on the choice of the material from which the elastic element is manufactured, different resistivities in different directions in space can thus be realized for example, that can be used by purposeful arrangement of the rectangular pyramid, in order to configure the resistivity measurement of the electronic sensor in a more accurate manner.

Figure 4c shows an embodiment in which the elastic element 403 is hemisphere-shaped or shaped as a half ellipsoid. Compared to Figure 4a, this embodiment has the advantage that due to the greater material thickness, damages due to strong pushing or sudden movements when using the electronic sensor in an electronic writing instrument can be avoided already for the apex, and the durability of the electronic sensor can thus be increased.

In Figure 4d, a further embodiment of the elastic element in the form of a prism is shown. While, in Figure 4d, the prism results from a parallel shift of a rectangular base, prisms having a hexagonal, octagonal or polygonal base may be used. The prism may rest on the contact surface of the first resistor, either with the corner or the edge. Due to the form of the prism, comparable advantages as were described with respect to realization of the elastic element as a pyramid can be used in order to increase the accuracy of the electronic sensor. Figure 4e shows a further embodiment of the elastic element 405. Here, a geometric shape resulting from the rotation of a defined function around the axis of rotation R is concerned. Here, some functions are especially suitable in order to significantly increase the increase of the contact area of the elastic element on the contact surface of the first resistor just when reaching a defined force. The embodiment shown in Figure 4e allows, for example in the upper region, distant from the apex 451 , a significant increase of the contact area with slightly increasing force due to the significant broadening of the elastic element 405 in this area. Suitable functions that form a corresponding body when rotated around the axis of rotation R are, for example, hyperbolic functions or functions like f(x)=x^"1 or g(x)=e^"x.

Figure 4f shows a further embodiment that results from a combination of Figure 4e and Figure 4c. The elastic element 406 can, in this case, be considered to be assembled from a hemisphere in region 461 and a surface or body 462, respectively, that is formed by a rotation of a function around the axis of rotation R. In this way, the different advantages of the elastic elements described in the individual Figures 4a-4e can be combined with each other, in order to realize specific aims with respect to the sensitivity of the electronic sensor. The combination of embodiments according to Figures 4e and 4c, as shown in Figure 4f, is only exemplary. Other geometric forms can be combined with each other as well.

Figure 5a shows an embodiment in which the electronic sensor, according to one of the described embodiments, is integrated in an electronic writing instrument 550. The electronic writing instrument 550 can comprise a body 551 , in which the electronic sensor is arranged. The body can have the form of a usual pen or can be akin to this form.

The electronic sensor itself that is arranged within or fixed at the body 551 , respectively, can be connected to a force transmitting element 520. Here, it is preferred if the force transmitting element 520 is directly connected with the elastic element 502 forming the second resistor. In this context, it can be provided that the force transmitting element 520 and the elastic element are manufactured as one work piece, or are connected with each other by means of connecting elements. If the connection by the connecting elements is detachable, the force transmitting element and/or the elastic element 502 can be exchanged if necessary, as in case of damage. If the force transmitting element is provided exchangeable, a specific force transmitting element can be used, depending on the surface on which the writing instrument is to be used. Hence, with sensitive surfaces, a particularly low friction force transmitting element, for example from glass or plastic, can be used. If the writing instrument is meant to also be usable for operating a touch display, a force transmitting element that is electrically conductive, at least at the apex resting on the surface, can be used (when used with capacitive displays). The force transmitting element can be provided in analogy to a ball pen refill and is preferably suitable to be positioned on a surface 552 on which the electronic writing instrument is to be used. The force F transmitted during positioning on the surface 552 then retroacts at the same strength on the force transmitting element 520.

For transmitting this force to the elastic element 502, the force transmitting element 520 is preferably arranged in a guide 521. In this, the force transmitting element 520 can be moved in accordance with the provided direction of arrow, whereby the elastic element 502 can likewise be moved in the direction of the contact surface of the first resistor 501 . By means of the power supply 103, which can be arranged in the body 551 of the electronic writing instrument, a current supply takes place, by which the evaluation unit 104 can then determine, from the measurement of the resistivity, the force transmitted from the force transmitting element 522 to the elastic element 502. By means of the obtained data, a stroke thickness can, for example, be determined based on the bearing force, whereby a stroke with a corresponding thickness can be displayed on a display, for example.

Alternatively to the described force transmitting element 520, it can also be provided that, instead of the force transmitting element 520, a commonly used writing instrument refill can be used (for example ball pen refill).

Here, the writing instrument refill can comprise a paste container, in which the writing paste is included. The electronic writing instrument can thus be used for normal writing on paper and, at the same time, to digitalize the strokes applied to the paper. The writing refill can, for example at the end of the paste container, comprise a connection element that can be connected with a complimentary connection element at the elastic element, such that the writing instrument refill can transmit a force acting upon it to the elastic element. Here, the writing instrument refill adopts the force transmitting effect of the force transmitting element 520.

In order to ensure the return of the force transmitting element and the elastic element connected therewith accordingly, if no force acts on the force transmitting element 520, it can be provided that the force transmitting element 520 is connected with a spring 522 that ensures, in its relaxed state when no force is acting on the force transmitting element 520, that the elastic element 502 that is connected with the force transmitting element 520, is arranged in its initial position opposite to the first resistor 501 , such that the contact area on the contact surface is small or even zero. This embodiment is shown in Figure 5b. If a force is applied to the force transmitting element, the spring 522 is compressed and the force transmitting element moves along the guide, whereby the contact area of the elastic element 502 on the contact surface of the first resistor 501 is increased. Therein, the spring can be advantageously used in order to compensate part of the occurring force in order to avoid damage to the electronic sensor and/or in order to limit increase of the contact area with increasing bearing force. In order to allow for reliably considering the compensation of the force acting on the elastic element 502 by provision of the spring 522 when measuring the bearing force by means of the change in resistivity, it is preferable if the compression of the spring is within the linear-proportional range when ordinary forces act on the electronic writing instrument. This means that the spring behaves according to hook's law and a force F acting on it causes a compression by -F/k=x, as compared to the relaxed spring, wherein k is the spring constant. If, additionally, a sensor is provided that can measure the compression x of the spring, the determined force acting on the spring can thus be used in determining the total force acting on the force transmitting element.

In principle, it is provided that with the help of such an electronic sensor in an electronic writing instrument, forces between 0 and 10N can be measured, such that these can be associated with stroke thicknesses corresponding to common bearing forces while writing.

Claims

1 . Electronic sensor for measuring forces, especially bearing forces of an electronic writing instrument on a surface, comprising a first resistor being coupled to a current supply and a second resistor being movable with respect to the first resistor, wherein the first resistor comprises an electrically conductive contact surface and the second resistor is movable in the direction of the contact surface, characterized in that the second resistor comprises an electrically conductive elastic element which can be deformed by a force effect and the total resistivity of the first and second resistor is changeable by the size of the contact area of the elastic element on the contact surface.

2. Electronic sensor according to claim 1 , characterized in that the elastic element comprises an elastic polymer.

3. Electronic sensor according to claim 1 or 2, characterized in that the first resistor comprises copper pathways or thick film resistance pathways comprising a conductive glass matrix.

4. Electronic sensor according to any of claims 1 to 3, characterized in that the elastic element has a pyramid-shaped, hemisphere-shaped, cone-shaped, paraboloide, hyperbolical or prismatic form.

5. Electronic sensor according to any of claims 1 to 4, characterized in that the elastic element is tapered along one direction, wherein the elastic element is arranged with the taper in the direction of the first resistor.

6. Electronic sensor according to any of claims 1 to 5, characterized in that on a side of the second resistor opposing a contact side area of the second resistor a force transmitting element is arranged that can transfer an applied force onto the second resistor.

7. Electronic sensor according to claim 6, characterized in that the force transmitting element is mounted in a guide, wherein the force transmitting element is movable within the guide perpendicular to the contact surface.

8. Electronic sensor according to any of claims 1 to 7, characterized in that the electronic sensor is integrated into an electronic writing instrument.

9. Electronic sensor according to claim 8, characterized in that the electronic sensor is coupled to a current supply that is arranged in the electronic writing instrument or connected thereto.

10. Method for measuring forces acting on an electronic sensor, especially bearing forces acting on an electronic writing instrument, wherein a second resistor is moved relative to a conductive contact surface of a first resistor of the electronic sensor, depending on a force acting on the electronic sensor and the total resistivity of the first and second resistors is changed by a change of the contact area of an elastic element of the second resistor being deformable by the force effect on the contact surface.

1 1. Method according to claim 10, characterized in that a force acting on a force transmitting element being connected to the second resistor is transmitted to the second resistor.

12. Method according to claim 1 1 , characterized in that the force transmitting element is moved perpendicular to the first resistor in a guide depending on the applied force.

13. Method according to any of claims 10 to 12, characterized in that the bearing surface of the elastic element on the contact surface is strictly monotonically increasing with an increasing applied force.

14. Method according to any of claims 9 to 13, characterized in that the first resistor is current carrying, either continuously or in time intervals.

15. Method according to any of claims 9 to 14, characterized in that by changing the contact area of the elastic element on the contact surface, applied forces reaching between ON and 10N are uniquely assigned to a total resistivity.