System for recording a trajectory traced by an instrument on a writing surface

Abstract

The present invention relates to a system for recording a trajectory depicted on a writing surface, comprising: an instrument (3) including a tip (4) and equipped with a magnetic object (6); means (10) for locating the magnetic object (6), which is adapted to determine an estimated reference position #imgabs0# on the writing surface (2); and a matrix array touch sensor (20), which is adapted to define a set S of M pixels that at least partially surround the estimated reference position #imgabs1# among N pixels px , and detecting contact of the tip (4) on the writing surface (2) based on electrical signals generated by the set S of the M pixels px .

Description

Technical Field

[0001] The field of the invention is that of recording the trajectory traced by the tip of an instrument manipulated by a user on a writing surface. The trajectory corresponds to all the successive positions of the tip while it is in contact with the writing surface. Background Art

[0002] Electronic systems for recording the trajectory of the tip of an instrument, for example a stylus or pencil, on a writing surface allow, in particular, drawings drawn or writings written by a user manipulating the instrument to be digitized.

[0003] Generally, it is important to be able to accurately detect the contact of the tip of the tool on the writing surface while avoiding or limiting the influence of the detection of parasitic contacts (such as the contact of the thumb or the contact of the palm of the user). In this regard, document EP2811383A1 describes an example of a system for recording the trajectory of the tool on the writing medium by means of a magnetometer array that allows tracking the position of at least one magnet fixed to the tool. Such a system makes it possible to ignore parasitic contacts.

[0004] In order to detect the contact and pressure exerted by the tip on the writing surface, the apparatus of the tracing system comprises a first magnet fixed to the tip, which tip is retractable relative to the body of the apparatus, and a second magnet fixed to the body. The system determines the position and / or orientation of the two magnets, deduces from them their relative spacing, and then detects the contact of the tip on the writing surface when this spacing is less than a predefined threshold. However, it is necessary here to use a specific apparatus comprising at least two magnets, which are mechanically associated with each other. It is therefore not possible to use any apparatus.

[0005] Document WO2013 / 057412 describes another example of a system for recording the trajectory of an instrument, here by means of a matrix array touch sensor, for example of the capacitive or resistive type. Such a matrix array touch sensor comprises a matrix array of different pixels formed by the intersection of wires placed in rows and columns on both sides of a film. The contact of the instrument tip is detected based on the measurement of the amplitude of the electrical signal emitted by the pixels.

[0006] However, in such a system, the resolution associated with the measurement of the contact position of the tip depends mainly on the size and arrangement pitch of the pixels. Moreover, such a system has a certain delay due to the time required to read the pixels of the matrix array. In this document, in order to reduce this delay while optimizing power consumption, a global column measurement is performed and the rows are measured sequentially only when a contact is detected on at least one activated column. This requires suitable electronics that allow providing such control of the pixel activation. Therefore, there remains a need to limit power consumption while reducing the delay associated with pixel readout without complicating the required electronics and connection links.

[0007] Furthermore, document FR 2 988 872 A1 describes a display comprising means for locating a movable magnetic object by means of an array of magnetometers. Summary of the invention

[0008] The object of the present invention is to at least partially remedy the drawbacks of the prior art. To this end, the subject of the present invention is a system for recording a track drawn on a writing surface, said system comprising:

[0009] o an implement intended to be operated by a user, said implement being equipped with a magnetic object and comprising a tip intended to come into contact with a writing surface in order to form the track to be recorded;

[0010] o A positioning device, comprising:

[0011] a magnetometer array affixed to the writing surface and configured to measure magnetic fields emitted by magnetic objects;

[0012] an electronic computing unit configured to determine a state vector X representing at least the position of the magnetic object based on the measured magnetic field a , and based on the state vector X a Determine the estimated reference position on the writing surface

[0013] According to the present invention, the system includes a matrix array touch sensor, and the matrix array touch sensor includes:

[0014] o a matrix array of N distinct pixels affixed to a writing surface and each pixel configured to deliver an electrical response signal representative of contact of the tip with the writing surface;

[0015] o an electronic processing unit connected to the electronic computing unit and configured to: define a reference position at least partially surrounding the estimated A set S of M pixels px , where M is less than N; to the set S px The M pixels transmit electrical command signals and receive their electrical response signals; and based on the set S of the M pixels px The generated electrical response signal detects contact of the tip with the writing surface and when contact is detected, the writing surface is determined based on at least a continuously estimated reference position. Successive positions of the tip are stored to form a track record.

[0016] The following are some preferred but non-limiting aspects of this system for recording the trajectory of an instrument.

[0017] The positioning device can be configured based on the state vector X aDetermine the position P of the tip along an axis normal to the writing surface p,z , the determined position P p,z With the predefined threshold P p,z,th is compared, and when the position P p,z Less than or equal to a predefined threshold P p,z,th The estimated reference position Transmitted to the matrix array touch sensor.

[0018] The positioning device may be adapted to position P p,z Less than or equal to the predefined threshold P p,z,th The matrix array touch sensor is enabled when ON, and remains off in the opposite case.

[0019] By moving the tip position P along an axis perpendicular to the writing surface p,xy Projected in a plane parallel to the writing surface to determine the estimated reference position

[0020] The positioning device is configured to determine the state vector X based on the state vector X determined at multiple measurement times. a to calculate the velocity of the magnetic object and transmit it to a processing unit configured to define a set S of M pixels having a contour elongated along the main axis px , which is parallel to the velocity axis. The length of the principal axis depends on the norm of the velocity.

[0021] The matrix array touch sensor may be a matrix array pressure sensor configured to determine a pressing force applied by a tip on the writing surface.

[0022] The matrix array touch sensor can be configured to determine the location of the contact point of the tip on the writing surface. p|c , based on the estimated position of the reference The position of the contact point with the tip is C p|c to store the position of the tip to form a trajectory.

[0023] State vector X a It can be determined by a Bayesian estimation algorithm or using optimization methods.

[0024] The invention also relates to a method for recording the trajectory of a tip of an instrument on a writing surface by means of a system according to any of the preceding features, said method comprising the following steps:

[0025] - the device is operated by the user without the device coming into contact with the writing surface;

[0026] -Measured by magnetometer matrix array at each continuous measurement time t n Magnetic fields emitted by magnetic objects;

[0027] - Determine the state vector X of the magnetic object based on the measurement results of the measured magnetic field a (t n );

[0028] - Based on the determined state vector X a (t n ) Determine the estimated reference position on the writing surface

[0029] - Determine a reference position for at least part of the surround estimate N pixels (Px i ) px (t n );

[0030] - to the set S px (t n ) pixels transmit electrical command signals and receive electrical response signals;

[0031] - detecting contact of the tip with the writing surface based on the received electrical response signal and based on at least a continuously estimated reference position Successive positions of the tip are stored to form a record of the trajectory.

[0032] The invention also relates to a data storage medium comprising instructions which, when executed by a computing unit, carry out the method of recording a trace according to the aforementioned features. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Other aspects, objects, advantages and features of the present invention will become more apparent on reading the following detailed description of a preferred embodiment of the invention given by way of non-limiting example with reference to the accompanying drawings, in which:

[0034] Figure 1 is a schematic partial cross-sectional view of a system for recording a track traced by a tip of an instrument on a writing surface according to one embodiment;

[0035] Figure 2 yes Figure 1 A schematic partial exploded view of the trajectory recording system shown;

[0036] Figure 3 is a flow chart illustrating the steps of a method for recording a track traced by a tip of an implement on a writing surface according to one embodiment;

[0037] Figure 4A and 4B is a schematic and partial perspective view of a trajectory recording system according to one embodiment at two different measurement times. DETAILED DESCRIPTION

[0038] In the drawings and the rest of the description, the same reference numerals have been used to represent the same or similar elements. In addition, for the clarity of the figures, the various elements are not shown to scale. In addition, the various embodiments and variants are not mutually exclusive and can be combined together. Unless otherwise stated, the terms "substantially", "approximately" and "about" refer to within 10%, preferably within 5%. In addition, unless otherwise stated, the term "comprising between ... and ... " and its equivalents mean including limitations.

[0039] The present invention relates to a system and method for recording a track drawn by a tip of an instrument on a writing surface. The track recording system generally comprises:

[0040] - appliances equipped with magnetic objects;

[0041] - a positioning device adapted to determine the position P of the magnetic object a , and optionally determine its orientation, and determine an estimated reference position on the writing surface and

[0042] - A matrix array touch sensor configured to detect contact of a tip on a writing surface and advantageously measure its bearing force.

[0043] The recording system may also include a graphical interface for displaying the trajectory thus recorded. It is suitable for the digitization of drawings or writings and even for the control of the graphical interface (e.g. selection and movement of digital objects displayed by the graphical interface, etc.). By recording the trajectory traced by the tip of the instrument, this means determining and storing the successive positions of the tip of the instrument when it is in contact with the writing surface. Thus, the trajectory recording system can detect the initial time of the first contact of the tip on the writing surface, which defines the beginning of the trajectory, and the end time corresponding to the interruption of the contact and defining the end of the trajectory.

[0044] An implement is an object intended to be manipulated by a user, for example in his hand. It comprises a rigid structure (body) made of preferably non-magnetic material (e.g. plastic) having a tip intended to come into contact with the writing surface of the track recording system. It may be a pencil in the broadest sense, i.e. a pen, stylus, felt tip, brush or any other writing or drawing instrument. The tip is one end of the implement and may be pointed or rounded, hard or deformable.

[0045] A matrix array touch sensor is called a "touch" sensor because it is suitable for detecting contact of the tip of an implement on a writing surface. Furthermore, it is said to be a "matrix array" sensor because it contains a matrix array of pixels, which are different from each other, formed by conductive tracks placed in rows and columns. Each pixel is configured to transmit an electrical response signal representing a possible contact of the tip of the implement on the writing surface. The matrix array touch sensor can be capacitive or resistive, such as piezoresistive. More broadly speaking, the matrix array touch sensor has a locally varying parameter that depends on the contact of the tip on the writing surface and optionally on the applied bearing force. The parameter can be capacitance, resistance, voltage, etc.

[0046] Figure 1 and 2 Schematic and partial cross-sectional and exploded views, respectively, of a system 1 for recording the trajectory of an implement 3 according to one embodiment. In this example, the implement 3 is a stylus, the tip 4 of which is intended to come into contact with a writing surface 2. Furthermore, the matrix array touch sensor 20 is a resistive matrix array pressure sensor, which is then configured to measure the bearing force (also called pressing force) of the tip 4 in addition to detecting the contact of the tip 4 with the writing surface 2.

[0047] The writing surface 2 may be the surface of a protective layer of the matrix array touch sensor 20 described in detail below. It may also be the surface of an additional element placed on the bearing surface of the matrix array touch sensor 20, which element is configured to transmit the pressure applied by the tip 4 of the stylus 3 to the matrix array touch sensor 20. Such an element may be, for example, one or more sheets of paper.

[0048] An orthogonal three-dimensional direct coordinate system OXYZ is defined here and will be referred to in the rest of the description, wherein the X-axis and the Y-axis form a plane parallel to the writing surface 2, and wherein the Z-axis is oriented toward the implement 3. In this example, the origin O is located on the boundary of the track area Zs for tracking the magnetic object 6, but it can be located elsewhere in the track area Zs, for example on the boundary of the writing surface 2.

[0049] The device 3 is equipped with a magnetic object 6, here a permanent magnet, which is fixed here without freedom to the rigid structure 5 of the stylus 3. The magnetic object 6 comprises a material with a magnetization strength (e.g. a remanent magnetism), for which a magnetic moment m is defined. It can be a cylindrical permanent magnet, and for example a toroidal permanent magnet (e.g. as shown in document WO2014 / 053526), ​​or even an electromagnet. It can also be a transponder configured to re-emit the magnetic field emitted by the array of magnetic generators. However, in this example, the magnetic object 6 is a permanent magnet. In this example, the magnetic object 6 is different from the tip 4 and is at a non-zero distance L from it. As a variant, it could be the tip 4.

[0050] The magnetic material is preferably ferrimagnetic or ferromagnetic. It has a non-zero spontaneous magnetic moment even in the absence of an external magnetic field. It may have a magnetic field greater than 100 A.m. -1 or 500A.m -1 The coercive force and the magnitude of the magnetic moment are preferably greater than 0.01Am 2 Or even greater than 0.1Am 2 , for example, equal to about 0.2Am 2 It is considered that the magnetic object 6 can be approximated as a magnetic dipole, but other models can also be used. The magnetic axis of the magnetic object 6 is defined as the axis that is colinear with the magnetic moment m of the magnetic object 6. Preferably, the magnetic axis points towards the tip of the tool.

[0051] like Figure 1 As shown, the magnet 6 can be placed at a non-zero distance L from the tip 4 of the stylus 3. This distance L is known and does not vary with time. It is defined in a digital model representing the instrument 3 used, which is stored in the memory 13 of the positioning device 10. Therefore, knowledge of the position and orientation of the magnet 6 in the coordinate system OXYZ enables the position P of the tip 4 of the stylus 3 to be deduced. p In the case where the magnet 6 and the tip 4 are integral, it is not necessary to determine the orientation of the magnetic moment m of the magnet 6 .

[0052] The stylus 3 is intended to be operated by the user in a track zone Zs. Initially the stylus 3 is not in contact with the writing surface 2 and is at a time varying non-zero distance d from the writing surface. Subsequently, the user moves the stylus 3 so that the tip 4 contacts the writing surface 2. The distance d is then zero and the matrix array touch sensor 20 detects the contact and advantageously the pressure exerted by the tip 4. Next, the user moves the tip 4 of the stylus 3 over the writing surface 2. The successive positions of the tip 4 in contact with the writing surface 2 form a track determined by the track recording system 1.

[0053] The trajectory recording system 1 further comprises a positioning device 10, which is configured to determine the state vector X a , which state vector represents the position of the magnet 6 in the coordinate system OXYZ, and optionally its orientation, and then determines at least one estimated reference position on the writing surface 2 Therefore, the positioning device 10 determines at different consecutive measuring times an estimated reference position on the writing surface 2 before or during contact. The estimated reference position Preferably the position P of the tip 4 p The projection along the Z axis onto the XY plane of the writing surface 2. If it is determined by the positioning device 10 instead of the matrix array touch sensor 20, it is said to be estimated.

[0054] By positioning the magnet 6, it means that the state vector X a and optionally the form of its orientation determine the position of the magnet 6 in the track zone Zs. Here the position P of the magnet 6 a corresponds to the geometric center coordinates of the magnet 6, that is, corresponds to the unweighted center of all points of the magnet 6. In addition, the magnetic moment m of the magnet 6 is a vector whose components (m x ,m y ,m z ) is in the real coordinate system OXYZ. Its norm (also called size or magnitude) is denoted by ||m|| or m.

[0055] The magnet 6 is intended to be moved around in a track area Zs. The track area is a space in which the signal-to-noise ratio (SNR) of at least one magnetometer of the positioning device 10 is higher than or equal to a predefined threshold. For example, the track area Zs may be a space in which the signal (i.e. the norm or at least one component of the magnetic field generated by the magnet 6 and measured by the corresponding magnetometer) is greater than or equal to, for example, 20 times the noise. The noise associated with each magnetometer may be equal to about 0.2 μT. In this case, the track area Zs corresponds to the space in which the signal (i.e. the norm or at least one component of the magnetic field generated by the magnet 6 and measured by the magnetometer M) is higher than or equal to a predefined threshold. i The spatial region in which at least one of the measured magnetic fields is greater than or equal to about 6 μT corresponds to the region along the path passing through the magnetometer M under consideration. i The distance d from the axis of max More simply, the trajectory area Zs can be defined as a space in which each point passes through the nearest magnetometer M i The distance on the axis of the direction is less than or equal to the maximum distance d max , the distance is, for example, equal to 20 cm, or even equal to 10 cm, or even equal to 5 cm.

[0056] The positioning device 10 is able to measure the ambient magnetic field in the coordinate system OXYZ at different measuring times in a tracking cycle of duration T, one contribution being the measurement of the magnetic field generated by the magnet 6, which is then converted from the magnetometer M i The measured values ​​estimate the position of the magnet 6 and optionally its orientation.

[0057] For this purpose, it includes a magnetometer array M i , which is fixed to the back of the matrix array touch sensor 20 without any degree of freedom. i The number of may be, for example, greater than or equal to 2, preferably greater than or equal to 16, and for example equal to about 25, in particular when it comes to the problem of a three-axis magnetometer. i It includes at least three measuring axes which are far from each other and not parallel in pairs.i The magnetometers M may be aligned in rows and columns, or may be positioned relative to each other in a substantially random manner. i The position of is known. For example, the position may be comprised between 1 cm and 10 cm, for example equal to 5 cm.

[0058] Magnetometer M i Each has at least one measuring axis, for example three axes, denoted by x i ,y i 、z i Therefore, each magnetometer measures the ambient magnetic field B i The magnitude and direction of the magnetic field generated by the magnet 6 is measured by one contribution. More precisely, each magnetometer M i Measuring the ambient magnetic field B i Along the axis x of the magnetometer i ,y i 、z i The norm of the orthogonal projection of the magnetometer M i The calibration parameter can be the noise associated with the magnetometer, here about 0.2 μT. The ambient magnetic field B refers to the magnetic field that is not disturbed by any magnetic elements, especially by the ground contribution B of about 50 μT. terr The magnetic field B generated by the magnet 6 is formed a Other magnetic contributions may also be superimposed, such as contributions associated with sensor noise and contributions associated with offset errors, which are neglected here.

[0059] The positioning device 10 further comprises a calculation unit 11 which can calculate the position of the magnetometer M based on the magnetometer M. i The measurement results determine the position of the magnet 6 in the coordinate system OXYZ and optionally its orientation, position and, if appropriate, define the state vector X a Furthermore, the computing unit 11 is able to determine the position P of the tip 4 of the stylus 3 in the coordinate system OXYZ. p The computing unit 11 is further configured to determine an estimated reference position on the writing surface 2 and connected to the processing unit 24 of the matrix array touch sensor 20 to transmit the estimated position to it The calculation unit 11 includes the coordinates of the writing surface 2 in the coordinate system OXYZ. Thus, knowing the position P of the tip p and the coordinates of the writing surface 2 in the coordinate system OXYZ, the calculation unit is able to determine an estimated reference position on the writing surface 2

[0060] To this end, each magnetometer M iThe computing unit 11 is electrically connected via a data bus (not shown). The computing unit 11 comprises a programmable processor 12 capable of executing instructions stored on a data storage medium. It also comprises a memory 13 containing the instructions required to position the magnet 6, as well as a digital model of the apparatus 3 used, making it possible to calculate the position of the magnet 6 based on the state vector X. a Obtain the position P of the tip 4 of the stylus 3 in the coordinate system OXYZ p The memory 13 is also configured to store information calculated at each measurement time.

[0061] The calculation unit 11 executes a mathematical model which relates the position of the magnet 6 in the coordinate system OXYZ and, in this example, the orientation and magnitude of its magnetic moment m to the magnetometer M. i The mathematical model is based on electromagnetic equations, in particular magnetostatic equations, and is parameterized in particular by the position and orientation of the magnetometer in the coordinate system OXYZ. Here, the model is nonlinear. The calculation unit 11 executes an algorithm to estimate its solution, such as a Bayesian filter (e.g. an extended Kalman filter) or an optimization, or even any other algorithm of the same type.

[0062] Preferably, in order to approximate the magnet 6 as a magnetic dipole, the magnet 6 and each magnetometer M i The distance between the magnets 6 is 2 or even 3 times the maximum dimension of the magnet 6. This dimension may be less than 20 cm, or even less than 10 cm, or indeed less than 5 cm. The magnet 6 may be modeled using a dipole model, in particular depending on the relationship between the magnet 6 and each magnetometer M of the array. i The distance between.

[0063] The trace recording system 1 comprises a matrix array touch sensor 20 , here a matrix pressure sensor, which is configured to detect contact of the tip 4 of the stylus 3 on the writing surface 2 based on a measurement of the magnitude of the pressing force applied on the writing surface 2 .

[0064] The matrix array touch sensor includes a pressure detection matrix array, which is composed of a plurality of pixels Px sensitive to the pressure applied on its surface. i The pressure sensing matrix array is a resistive type in this example. This type of sensor is also called a force-sensing resistor.

[0065] It is formed by a film 23 of piezoresistive material, i.e. a film of a material, such as a conductive polymer, whose local resistance varies depending on the applied mechanical stress. The sensitive material of the film can be continuous or pixelated in the XY plane. The conductive tracks 21, 22 are formed in rows on one side of the film 23 and in columns on the opposite side. Seen from above, the pixel Px iThe pixels Px are formed by the intersections between rows and columns of conductive tracks 21, 22. i They may be adjacent to each other or spaced apart from each other (e.g. Figure 2 shown).

[0066] The matrix array pressure sensor 20 includes N pixels Px i , for example approximately equal to 2500. The conductive tracks 21, 22 may have a width of a few millimeters, for example 2.5 mm, so that one pixel here has 2.5×2.5 mm 2 The area of ​​the pixel Px i are different and are spaced apart from one another in the XY plane by a distance of, for example, approximately 1 mm. The diameter of the tip 4 of the stylus 3 that contacts the writing surface 2 can here be around 1 millimeter, and for example approximately 1 mm to 3 mm.

[0067] The matrix array pressure sensor 20 comprises a processing unit 24, which comprises a microcontroller 25 and a computing unit 26, wherein the microcontroller commands and reads out the various pixels of the pressure detection matrix array, and the computing unit is configured to detect the contact of the tip 4 and determine the magnitude of the applied pressure force based on the electrical response signal generated by the pixel. Therefore, the microcontroller 25 is configured to transmit an electrical command signal to each of the pixels and receive an electrical response signal, which is representative of any contact of the tip 4 of the stylus 3 on the writing surface 2 and, in this case, the magnitude of the pressure force applied by the stylus 3. The processing unit 21 comprises N pixels Px i Coordinates in the coordinate system OXYZ. Thus, the estimated reference position on the known writing surface 2 is and N pixels Px in the coordinate system OXYZ i In the case of coordinates of A set S of M pixels px , wherein M is less than N. M is preferably greater than or equal to 2.

[0068] The computing unit 26 detects whether the tip 4 is in contact with the writing surface 2 based on the received electrical response signal. To this end, the electrical signal generated by each pixel has an amplitude, and when it is higher than a predefined threshold, the amplitude corresponds to the contact of the tip 4 on the writing surface 2. The amplitude of the electrical signal generated by one or more pixels depends on the size of the pressing force applied by the tip 4.

[0069] When a contact is detected, the processing unit 24 stores the continuously estimated reference position on the writing surface 2 determined by the positioning device 10. Thereby forming or participating in forming a track of the implement 3 on the writing surface 2. The magnitude of the pressing force applied makes it possible to quantify additional features of the track of the implement 3 and can be used to, for example, change the width of the track of the implement 3. The processing unit 24 can be connected to the graphical interface 7, for example to display the track recorded by the system.

[0070] The processing unit 24 may thus comprise a microcontroller 25 for controlling the power supply to the pixels associated with the analog-to-digital converter ADC, and a calculation unit 26 thereof comprising at least one processor and at least one memory containing the instructions necessary to perform the contact detection and pressure measurement of the tip 4 and storing the information calculated at each measurement time, as well as the converter here. Of course, the processor and the memory of the calculation unit 26 may or may not be shared with the processor and the memory of the microcontroller 25.

[0071] According to the invention, the processing unit 24 of the matrix array touch sensor 20 is connected to the computing unit 11 of the positioning device 10 and receives from the computing unit the continuously estimated reference position on the writing surface 2. Whether there is contact of the tip 4 on the writing surface 2.

[0072] Preferably, only when the position P of the tip 4 along the Z axis is p,z Less than or equal to a predefined threshold P p,z,th When this is not the case, the matrix array touch sensor 20 may be disabled, ie completely or partially switched off, to limit the power consumption of the track recording system 1 .

[0073] When position P p,z Less than or equal to the threshold P p,z,th When the processing unit 24 is enabled (turned on), it receives the estimated reference position on the writing surface 2 and determine a reference position that at least partially surrounds the estimate A set S of M pixels px , where M is less than N. For example, the total number of pixels N may be approximately equal to 2500, and the set S px The number of pixels M may be approximately equal to 25, for example a square of 5×5 pixels.

[0074] Then, the processing unit 24 only processes the set S px Instead of measuring all the pixels of the matrix array, the electrical command signal is only transmitted to M pixels, the other pixels remain switched off. Next, the processing unit 24 receives the electrical response signal. Therefore, the latency of the pixel command / readout is greatly reduced, since it is a matter of reading 25 pixels instead of 2500 pixels at each measurement time. Therefore, the power consumption is also greatly reduced.

[0075] Finally, the processing unit 24 is configured to calculate the reference position on the writing surface 2 based on the continuously estimated reference position. And here, the trajectory described by the stylus 3 is determined based on the value of the pressing force applied, and then the graphical interface 7 is commanded to display the determined trajectory. As described in detail below, the trajectory can be composed of all consecutive estimated positions However, the continuous position C of the contact determined by the matrix array touch sensor 20 may also be considered. p|c The measurement accuracy of the contacts can then be improved.

[0076] Thus, due to the combination of the device 10 for locating a magnetic object 6 and the matrix array touch sensor 20, the track recording system 1 has many advantages. Thus, a large number of commercially available appliances can be used, as long as the appliance in question allows a magnetic object 6 (e.g. a magnet) to be fixed thereto. In addition, the appliance 3 can be equipped with only a single magnet 6 to be located. Therefore, it does not have to be equipped with a plurality of magnets, even if a plurality of magnets fixed to the appliance can be provided. Thus, the need to use a dedicated and complex appliance 3 as in document EP2811383 is avoided. In addition, it is no longer necessary to integrate a pressure sensor into the appliance.

[0077] Furthermore, the contact of the tip 4 is accurately detected by the matrix array touch sensor 20, and the position of the tip 4 on the writing surface 2 is determined with high resolution by the positioning device 10. Therefore, the position of the tip 4 is not affected by the potential low resolution of conventional matrix array touch sensors, which depends on the size and arrangement of the conductive tracks 21, 22. In addition, the estimated reference position on the writing surface 2 The determination of is not disturbed by any parasitic contact, such as contact by a user's finger or palm on the writing surface 2.

[0078] Furthermore, the trajectory recording system 1 has a particularly low latency associated with commanding / reading out of the pixel matrix array, since the microcontroller 25 activates only the set S px , rather than N pixels of the matrix. Therefore, the command / readout frequency can be particularly high. Therefore, the power consumption of the track recording system 1 is reduced. In addition, it is advantageous that the matrix array touch sensor 20 remains at least partially disabled when the magnetic object 6 is tracked by the positioning device 10, especially when the position P of the tip 4 along the Z axis is p,z Greater than the threshold P p,z,th hour.

[0079] Furthermore, it is possible to use a matrix array touch sensor 20 whose microcontroller 25 and its electrical connections are simple and conventional. Thus, the need to use a specific microcontroller 25 and specific connections associated with the need to activate rows and / or columns individually, sequentially or in their entirety, as described in document WO 2013 / 057412, is avoided.

[0080] Figure 3 is a flow chart showing a method for recording the trajectory of an appliance 3 according to one embodiment. In this example, the trajectory recording system 1 is connected to the reference Figure 1 and 2 It commands the graphical interface 7 to display the trajectory thus recorded.

[0081] In a first step 11, a digital model of the stylus 3 is stored in the memory 13 of the computing unit 11 of the positioning device 10. As described above, this digital model allows the state vector X of the magnet 6 to be determined. a Derivation of the position P of the tip 4 in the coordinate system OXYZ p This step 11 may also comprise a stage of storing the coordinates in the coordinate system OXYZ of the writing surface 2 and the N pixels Px of the matrix array touch sensor 20 i The coordinate system OXYZ stores the coordinates of the stage.

[0082] In step 21, the user manipulates the stylus 3 in the trajectory area Zs, ie he modifies the position of the stylus and optionally the orientation of the stylus in the coordinate system OXYZ. Initially the tip 4 of the stylus 3 is not in contact with the writing surface 2 and its position P along the Z axis is p,z Greater than the threshold P p,z,th Subsequently, the position P of the tip 4 p,z Less than or equal to the threshold P p,z,th , but still not in contact with the writing surface 2. Finally, thereafter, it comes into contact with the writing surface 2 and the position of the tip 4 on the writing surface 2 is stored and forms the track that is recorded and displayed.

[0083] Steps 22 to 33 are performed at the measuring time t n The iterations are performed at t, and the time is discretized at a certain sampling frequency, for example 140 Hz. Each iteration of rank n is associated with a measurement time t n This time is also called the current time.

[0084] In step 22 , the magnetometer measures the ambient magnetic field at the current time, in particular the contribution to the ambient magnetic field generated by the magnet 6 fixed to the stylus 3 .

[0085] In step 23, the calculation unit 11 receives the measured values ​​of the ambient magnetic field, derives therefrom the magnetic field contribution generated by the magnet 6 and determines the current time t in the coordinate system OXYZ. n The state vector X associated with magnet 6 a (t n ). The state vector X a (t n) includes the position of the magnet 6 in the coordinate system OXYZ and, in this example, its orientation. The state vector can be estimated using an algorithm for estimating the position and orientation of the magnet 6 of the Bayesian type (e.g., an extended Kalman filter), or using an optimization method (gradient descent, etc.), or using any other similar algorithm. An example of estimating the state vector associated with the magnet 6 is described in particular in the patent application WO2018 / 219891.

[0086] In step 24, the computing unit 11 calculates the state vector X based on the state vector X. a (t n ) and the digital model of the stylus 3 to determine the position P of the tip 4 of the stylus 3 p (t n ). The position P of the tip 4 p (t n ) includes a component P along the Z axis p,z (t n ) and the component P in the XY plane parallel to the writing surface 2 p,xy (t n ). In the case where the magnetic object 6 is the tip 4, the position P of the tip 4 p (t n ) and position P a (t n )same.

[0087] In step 25, the computing unit 11 calculates the state vector X based on the state vector X. a (t n ) and the coordinates of the writing surface 2 in the coordinate system OXYZ to determine the estimated reference position on the writing surface 2 The estimated reference position can be equal to the position P of the tip 4 p,xy (t n ) is the projection of the XY plane along the Z axis, where and P p,xy (t n )equal.

[0088] In step 26, the tip 4 is moved to position P along the Z axis. p,z (t n ) value and the predefined threshold P p,z,th When position P p,z (t n ) is greater than the threshold P p,z,th, the positioning device 10 continues to measure the magnetic field (step 22 and following steps). The matrix array touch sensor 20 advantageously remains inactive, i.e. it is not powered, thereby limiting the power consumption of the trajectory recording system 1. If the positioning device 10 is directly connected to the graphical interface 7, the tip 4 can be represented and displayed on the graphical interface 7 without displaying the trajectory. p,z (t n ) is less than or equal to the threshold value P p,z,th When , the method continues to execute step 27.

[0089] In step 27, the matrix array touch sensor 20 is enabled (where appropriate) and the estimated reference position on the writing device 2 is set to The value of is transmitted to the processing unit 24 of the matrix array touch sensor 20. The processing unit then determines a reference position of the pressure detection matrix that at least partially surrounds the estimated The set of pixels S px (t n ). To this end, each pixel Px in the coordinate system OXYZ i The coordinates of are stored in the memory of the processing unit 24. The processing unit 24 determines the pixel selection area Z px (t n ), the region is based on the estimated reference position is centered and has a predefined outline, such as a circle, an ellipse, a square, a rectangle, etc. In this regard, Figure 4A and 4B The trajectory recording system 1 is shown at two different measurement times and the estimated reference position is shown. The area Z is the center px (t n ). In this example, the set S px (t n ) includes an area at least partially located in the pixel selection area Z px (t n ). The set S px (t n ) at each measurement time t n has been redefined.

[0090] Furthermore, the matrix array touch sensor 20 may have been initialized by measuring the "background noise" associated with the pixel matrix without any contact (stylus tip, finger, palm, etc.) on the writing surface 2. px (t n ) is systematically removed from the measured values ​​of the electrical response signals of the pixels of the set, thereby allowing any drift as a function of time and / or offset errors to be removed.

[0091] In step 28, the microcontroller 25 of the processing unit 24 only enables the set S px (t n ), while leaving the other pixels that are not selected (i.e. not powered) in an inactive state. px (t n ) pixels transmit electrical command signals and receive their electrical response signals.

[0092] In step 29, the processing unit 24 determines a parameter κ (t n ) value. This parameter can be a set S px (t n ), or even optionally the set S px (t n ) is an optional weighted average of the amplitudes of the electrical response signals of the pixels of the set S. px (t n ) is a question of the resistance of at least one pixel or any other equivalent parameter.

[0093] In step 30, the processing unit 24 sets the parameter κ(t n ) is equal to the predefined threshold κ th For comparison, and when the parameter κ(t n ) is higher than or equal to the threshold κ th When , it is detected that the tip 4 is actually in contact with the writing surface 2. th This enables fluctuations related to the measurement noise to be filtered out. If this is not the case, the trace recording method continues with the magnetic field measurement (step 22 et seq.) and when a contact is detected, the method continues with step 31 .

[0094] In step 31, assuming that the matrix array touch sensor 20 detects contact of the tip 4 with the writing surface 2, the processing unit 24 stores the estimated reference position transmitted by the positioning device 10 The continuously estimated reference positions stored by the processing unit 24 Forms or participates in forming a record of the track traced by the stylus 3 .

[0095] As a variant, the position of the tip 4 in contact with the writing surface 2 (for example stored by the processing unit 24) may depend on an estimated reference position transmitted by the positioning device 10. and the position C transmitted by the matrix array touch sensor 20 p|c (t n ). Therefore, position C p|c (t n ) may correspond to the pressure applied by the tip 4 on the writing surface 2 and by the set Spx (t n ) is the centroid position (weighted centroid) of the pressing force measured by the pixels of the tip 4. The position of the tip 4 stored by the processing unit 24 may be the position and C p|c (t n ), optionally a weighted average.

[0096] In step 32, when the matrix array touch sensor 20 is configured to measure pressing force, that is, when it includes a pressure detection matrix array, the processing unit 24 measures the pressing force applied by the tip 4 to the writing surface 2. px (t n ) is used to determine the pressing force. n , the pressing force makes it possible, for example, to modify the characteristics of the track, such as the width of the track displayed on the graphical interface 7 .

[0097] In step 33 , processing unit 24 constructs a trajectory based on the successively stored positions of tip 4 , taking into account the pressing force exerted by tip 4 on writing surface 2 . It then commands the display of the trajectory thus recorded on graphical interface 7 .

[0098] Steps 22 to 33 are repeated with a defined sampling frequency, which may or may not remain constant over time, depending mainly on the speed of the magnet 6 or the tip 4, which is determined by the positioning device 10 according to the state vector X a (t n ) is calculated. In particular, the sampling frequency associated with the position of the magnet 6 (eg 140 Hz) can be combined with the command / readout set S px (t n ) have the same or different frequencies of pixels.

[0099] Figure 4A and 4B are perspective views of an implement 3 being operated by a user over a writing surface 2 of a matrix array touch sensor 20 at two different times.

[0100] In both examples, the position P of the tip 4 along the Z axis p,z (t n ) is less than the threshold value P p,z,th , and thus the matrix array touch sensor 20 is enabled and the estimated reference position on the writing surface 2 is transmitted to the matrix array touch sensor. Then determine the value The circular selection area Z is centered px (t n ).

[0101] exist Figure 4A In the example shown in FIG. 1 , the stylus 3 is located on the edge of the writing surface 2. Then select the area Z px (t n ) across the writing surface 2 and across the writing surface. A pixel is completely within the selection area Z px (t n ) and is partially located in the selection area Z px (t n ). Therefore, the set S px (t n ) includes at least partly located in the selected area Z px (t n ). Thus, the selected pixels at least partially surround the estimated reference position on the writing surface 2.

[0102] exist Figure 4B In the example shown, the stylus 3 is located in the center of the writing surface 2. Then select the area Z px (t n ) is completely located on the writing surface 2. In this example, a single pixel is completely located in the selection area Z px (t n ) and is surrounded by 8 adjacent pixels that are partially located in the selected area. Therefore, the set S px including at least partly located in the selected area Z px (t n ). Thus, the selected pixels at least partially surround the estimated reference position on the writing surface 2.

[0103] Of course, select Area Z px (t n ) may have other shapes. For example, it may have an elongated shape, and then the main axis is oriented in the direction of movement of the tip 4, which is determined by the positioning device 10 based on the state vector X a (t n ). The size of the spindle can also depend on the speed of the tip or magnet, which is estimated by the calculation unit 11 based on the state vector X at a plurality of measurement times. a is determined and transmitted to the processing unit 24. In addition, the area Z is selected px (t n ) may depend on the type of instrument 3 used and, optionally, on the characteristics of the tip 4.

[0104] While specific embodiments have just been described, various changes and modifications will be apparent to those skilled in the art.

[0105] Thus, the tracking system 1 may comprise a plurality of utensils 3, each equipped with at least one magnetic object 6 and intended to be in contact with the same writing surface 2. Thus, the positioning device 10 may determine the state vector of each magnetic object 6, and the matrix array touch sensor 20 may determine the contact of the tip 4 of each of the utensils 3.

Claims

1. A system (1) for recording a trajectory traced on a writing surface (2), said system comprising: o An instrument (3) intended to be operated by a user, said instrument being equipped with a magnetic object (6) and comprising a tip (4) intended to come into contact with said writing surface (2) to form said trajectory to be recorded; o A positioning device (10), which comprises: · Magnetometer array (M i ), which is fixed to the writing surface (2) and configured to measure the magnetic field emitted by the magnetic object (6) at each successive measurement time t n ​ · A computing unit (11) configured to determine a state vector X representative of at least the position of the magnetic object (6) based on a measured magnetic field, and to determine an estimated reference position on the writing surface (2) based on the state vector X a , and based on the state vector X a determine the estimated reference position on the writing surface (2) o Characterized in that the system comprises a matrix array touch sensor (20), the matrix array touch sensor comprising: · A matrix array composed of N different pixels (Px i ), where the different pixels are fixed to the writing surface (2), and each pixel is configured to transmit an electrical response signal representing the contact of the tip (4) on the writing surface (2); · A processing unit (24), which is connected to the computing unit (11) and configured to: determine a set S of M pixels that at least partially surround the estimated reference position ; where the set S of M pixels at least partially surrounds the estimated reference position px , wherein M is less than N; transmitting an electrical command signal to M pixels of the set S px and receiving their electrical response signals; and detecting contact of the tip (4) on the writing surface (2) based on the electrical response signals generated by the set S px of the M pixels, and when contact is detected At least based on a continuously estimated reference position Store successive positions of the tip (4) to form a record of the trajectory.

2. The system (1) according to claim 1, wherein, The positioning device (10) is configured to be based on the state vector X a Determine the position P of the tip (4) along an axis orthogonal to the writing surface (2) p,z , the determined position P p,z With the predefined threshold P p,z,th is compared, and when the position P p,z is less than or equal to the predefined threshold P p,z,th The estimated reference position Transmitted to the matrix array touch sensor (20).

3. The system (1) according to claim 1, wherein, The positioning device (10) is configured to determine the position P of the tip (4) along an axis orthogonal to the writing surface (2) based on the state vector X a and compare the determined position P p,z with a predefined threshold P p,z and, when the position P p,z,th is less than or equal to the predefined threshold P p,z enable the matrix array touch sensor (20), which remains off otherwise. p,z,th ​ 4. The system (1) according to claim 1, wherein, The estimated reference position is determined by projecting the position P of the tip (4) along an axis orthogonal to the writing surface (2) p,xy onto a plane parallel to the writing surface (2).

5. The system (1) according to claim 1, wherein, The positioning device (10) is configured to calculate the velocity of the magnetic object (6) based on a state vector X determined at a plurality of measurement times and to transmit the velocity to the processing unit (24), which is configured to define a set S of M pixels having a profile extending along a main axis, a the main axis being parallel to the axis of the velocity. px ​ 6. The system (1) according to claim 5, wherein, The length of the main axis depends on the norm of the velocity.

7. The system (1) according to claim 1, wherein, The matrix array touch sensor (20) is a matrix array pressure sensor configured to determine the pressing force applied by the tip (4) on the writing surface (2).

8. The system (1) according to claim 7, wherein, The matrix array touch sensor (20) is configured to determine the position C of the contact point of the tip (4) on the writing surface (2). p|c , based on the estimated reference position and the position C of the contact point of the tip (4) p|c to store the position of the tip (4) to form a trajectory.

9. The system (1) according to claim 1, wherein, The state vector X a is determined by a Bayesian estimation algorithm or by using an optimization method.

10. A method for recording the trajectory of the tip (4) of an instrument (3) on a writing surface (2) by means of the system according to claim 1, said method comprising the following steps: o Operating the instrument (3) by the user, the instrument initially not being in contact with the writing surface (2) and subsequently coming into contact with the writing surface (2); o Measuring the magnetic field emitted by the magnetic object (6) at each successive measurement time t through a magnetometer matrix array (M i ) n ; o The state vector X of the magnetic object (6) is determined by the calculation unit (11) based on the measurement result of the measured magnetic field a ; o based on the determined state vector X by the computing unit (11) a determine an estimated reference position on the writing surface (2) o Characterized in that the method further comprises the following steps: o Determine, by means of the processing unit (24), a set S of M pixels (Px ) that at least partially surround the estimated reference position i ; px ; o Transmit an electrical command signal to the pixels of the set S through the processing unit (24) and receive an electrical response signal; px ​ o The processing unit (24) detects the contact of the tip (4) on the writing surface (2) based on the electrical response signal generated by the set S of the M pixels, and when contact is detected, stores the successive positions of the tip (4) at least according to the successively estimated reference positions px to form a record of the trajectory. ​ 11. A data storage medium comprising instructions which, when executed by a computing unit, execute the method according to claim 10.

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