EP1295246A1

EP1295246A1 - Accurate interactive acoustic plate

Info

Publication number: EP1295246A1
Application number: EP01949585A
Authority: EP
Inventors: Fabrice Devige; Jean-Pierre Nikolovski
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-06-29
Filing date: 2001-06-29
Publication date: 2003-03-26
Also published as: FR2811107B1; US20030066692A1; FR2811107A1; WO2002001490A9; US6933930B2; AU2001270711A1; WO2002001490A1

Abstract

The invention concerns a device for acquiring the position co-ordinates of a source of mechanical waves optionally generated by impacting the surface of a plate (PLQ) of finite dimensions comprising a set of acoustic sensors (PZT00 to PZT11) each formed by a pair of piezoelectric transducers (PZTa, PZTb) facing each other on either side of the plate, the device including processing means for determining the co-ordinates of the source by analysing the difference in propagation time of the acoustic waves generated by the source to the different sensors. Said device is characterised in that the processing means comprise combined with each sensor (PZT00 to PZT 11) a respective electronic circuit including means mounted in cascade for digitizing the amplified signal around a predetermined frequency, associated with means for limiting the digitization to a time window starting before the acoustic waves reach a sensor and ending when the acoustic waves have reached said sensor.

Description

PRECISION INTERACTIVE ACOUSTIC PLATE

The present invention relates generally to interactive communication devices between a user and a machine.

More specifically, the invention relates to a device for collecting and processing acoustic waves transmitted by a user or a sensor to a plate serving as an interface with a machine, said device analyzing the propagation times of the acoustic waves in the plate. in particular to measure the coordinates x _r , y _r of impacts on the surface of the plate.

We know from patent wo96 / 11378 a device for acquiring coordinates x _r , y _r of the point of a rigid plate from which a source punctually emits wave packets, by analysis of the propagation time of the waves in the plate in two directions x and y of the plate.

Also known from French patent 9816229 of December 22, 1998 is an acquisition device where two pairs of transducers are associated respectively with each direction x, y, the position of the source in each direction being determined by measuring the time differential d arrival of the wave packets on the two pairs of respective transducers of said direction.

These two acquisition devices are particularly well suited to the selective detection of a Lamb acoustic mode in an isotropic glass plate. In particular, the device of patent 9816229 proposes a method for quantifying the intensity of an impact enabling it to achieve a precision of

1% on the position measurement. The present invention shows how to further improve this result, which is necessary if one wants to be able to reliably point areas the size of one square centimeter on a plate of four to ten square meters. In addition, the devices described in the patents cited above are unreliable when the plate is a laminated glass, that is to say an assembly of two or more panes, simple or annealed or toughened, intimately bonded together by the interposition of one or more polymer films such as polyvinyl butyral.

For safety reasons, the use of laminated glasses is a condition more and more often required in public places. In the event of breakage, the polymer constitutes a frame on which the glass shards remain glued, which allows the laminated glass to provide residual protection before replacement.

The use of laminated glass for the production of acoustic panels operating on the principle of localization of impacts by measuring the propagation time of ultrasonic plate modes requires an improvement of the devices described in the preceding patents.

The object of the present invention is thus to improve the quality and reliability of the reception of acoustic waves in a device suitable for both simple isotropic or laminated plates. In particular, the invention will show how to improve the accuracy of the measurement by making it even more independent of the intensity of the shock.

Another object of the present invention is also to improve the ergonomics of the device in particular by an automated calibration of the plate making it possible to take into account the effects of temperature on the speed of propagation of the acoustic waves and therefore on the precision as well as by establishing a simpler and faster homothetic correspondence between the actual coordinates of an impact on the plate and the screen coordinates of a graphic interface projected directly onto the plate using a video projector, the size of said graphical interface can vary rapidly depending on a desired or accidental movement of the video projector.

The invention also aims to improve the means of communication made available to the user in order to emulate according to the principle of activation by impact, the operation of a pointer of the mouse type or of an alphanumeric keyboard necessary. looking for information on the Internet. The invention finally shows how to mask the impact noises on the display case by a process of superimposing a synthesized sound on the sound resulting from an impact.

To achieve these goals, the invention provides a device for acquiring coordinates of points of interaction of an acoustic source with the surface of the plate, possibly laminated, of finite dimensions, comprising a set of acoustic sensors each formed of a pair of piezoelectric transducers located opposite each side of the plate, the device comprising processing means for determining the coordinates of said interaction point by analyzing the difference in propagation time of the acoustic waves emitted by the source to the various sensors, device characterized in that the processing means comprise, in association with each sensor, a respective electronic circuit comprising in cascade means for carrying out broadband pre-amplification, means for selective amplification centered on a first determined frequency , means for detecting the head of the wave packet and for sampling the signal over a time window including the head of the wave packet as well as means for switching the sensors into transmitter or receiver in order to determine the speed of propagation of ultrasonic waves or else carry out a plate integrity check, as well as means for give the acquisition system in an automated way and therefore simple for the user. Preferred but non-limiting aspects of the device according to the invention are the following:

The sensors are four in number and the piezoelectric transducers of each sensor are piezoelectric ceramic discs glued on either side of the plate, so that four sensors form the vertices of a rectangle whose center constitutes l origin of the coordinates,

The rectangle defined by the sensors is divided into four quadrants, each quadrant being associated with a triplet of sensors closest to the center of the quadrant responsible for detecting the coordinates of an impact in this quadrant with a measurement accuracy better than that which would be obtained with the other triplets,

The piezoelectric ceramic discs have a silver back enabling electrical connections to be made on the same face of the disc, - The piezoelectric ceramics are of the ferroelectric type, The silvering return is preferably cylindrical symmetry. When the silvering return does not respect the cylindrical symmetry, it is positioned so that the sensor has the most omnidirectional sensitivity possible, - The electrical connections of the two piezoelectric transducers of each sensor are connected in parallel, the polarization vectors being mounted symmetrically with respect to the median plane of the plate so that the slower asymmetrical modes are discriminated against and the symmetrical modes faster, preferred, - The location of an impact point with a laminated glass made up of an assembly of 2 identical plates, each of thickness e, linked to each other by a polymer film, consists in extracting the ultrasonic frequency component fc satisfying the rule: f _c . e = 1, 2 MHz.mm, the said frequency being generated by the impact of a hard object such as the dish of the nail of a finger, a metal key, a rod made of hard plastic,

The location of an impact point on a plate in one of the four quadrants defined by the pair of bits (g _y , g _x ) consists in measuring the difference in flight times between two sensors, taken from a triplet of sensors, defining a first direction and two sensors, taken from the same triplet of sensors, defining a second direction perpendicular to the first, so that the Cartesian coordinates of the point of impact (x _r , y _r ) on the plate are given by the formula :

Atxg (qVp ² V ² (4 p ² - v ² Atxg ² ) <4 ² t 4 q ² - v ² (Atxg -. Atvg) ² ) At g ² (4 g ² - irΑtyg ² ) * p ² v ² At g ² (-4 g ² * » ² Atyg (- Atxg + Atyg)) i

4 p Atvg (q ² ï ² Atxg ² * p ² (-4 q ² ^ Atyg ² )) qv ² ! ιtxj (- p ² (Atxg (Atxg - Atyg)) Atl gp ² v ² (4 p ² - τ ² Atxg ² ) ( ^{! l} * 4 q ² - ï ² (Atxg - Atyg) '(Atvg ² H q ² - - V ² Atyg ² )

4 (g ² v ² Atxg ² tp ² (-4g ² tv≈ At g ² )) - Where, p and q are positive numbers representing respectively the abscissa and the ordinate of the position of the sensors relative to the center of the rectangle defined by the sensors, v the speed of the plate mode detected, that is to say, for a laminated glass, that of the fastest mode, Δt _xg , (respectively Δt _yg ) the difference in propagation times of the wave packet generated by the impact, between the sensors of the first pair located in the half-rectangle g _x (respectively of the second pair located in the half rectangle g _y ), The determination of the triplet of sensors associated with a given impact is carried out according to an algorithm searching for the greatest difference in time of flight available between the sensors in two perpendicular directions, said electronic circuits associated with the sensors cascade a wide-band preamplifier stage, a selective amplifier stage in the ultrasonic band, a square elevator stage, a peak detector stage, an integrator stage, an adaptation stage at a logic level constituting a synchronization signal “S YNC” intended for on the one hand to the approximate calculation of the position of an impact, on the other to order the stopping of the digital recording of the ignal associated with the sensor, on the other hand at the start of the sound enrichment procedure, described below,

The electronic circuits associated with the respective sensors comprise, downstream from said selective amplification means, synchronous digital analog converters associated with FIFO memories.

(first in-first out) of sufficient depth to digitize the equivalent of several acoustic periods of the selected frequency, so as to have a digital recording starting before the arrival of the wave packet, the so-called digitization of the signal being characterized by a sampling frequency of at least 1 MHz,

The difference in flight times between the sensors is deduced, on the one hand, from the time intervals between the synchronization signals, on the other hand, from the time intervals separating the synchronization signals from the heads of the wave packets, The electronic circuits associated with the respective sensors comprise, upstream of said means of selective amplification, a bypass towards means for digitization, analysis and frequency enhancement of the audible acoustic signal generated by the impact on the plate, as well as means to convert the enriched digital signal into an analog signal and send it to speakers so as to mask the discomfort caused by the impact in the form of a more pleasant sound reproducing for example the noise of a percussion instrument at within a symphonic composition, or the sound of an animal or a natural event, said enrichment means being implemented at the very moment when the first of the four synchronization signals is activated,

Measuring the time interval separating a synchronization signal from the head of the associated wave packet consists in determining the instants of zero crossing of the digitized signal by going back in time from the switching instant defined by SYNC , while a test on the sum of the amplitudes between the zero crossings, ie a test on the average value of the signal per half-period, decides on the continuation of the algorithm. When the average value over a half period is equal to the output value of the sampler in the absence of a signal, to within a threshold deviation, the algorithm is stopped, and the average value is considered to be the instant origin I _HD of the packet, at least one of the sensors is capable of being switched into a transmitter of a packet of ultrasonic waves detected by the other sensors whose positions are known in order, on the one hand, to measure automatically the propagation speed of the ultrasound, dependent on the temperature, on the other hand, triggering a plate integrity test, by measuring the difference in propagation time of the wave packet between the different sensors, The management of all steps of measurement, processing and transfer of data by a serial communication interface, either to an LCD display, or to an interface for musical instruments (MIDI interface), or to a more powerful computer such as a microcomputer via its RS232 or USB port is controlled by a microcontroller,

The device constitutes a peripheral interface with a machine which receives the signals from the processing means and which, depending on the said signals, controls the execution of files contained in the computer by various peripherals of known types connected to the computer such as by example without limitation a video projector, light sources, speakers, a printer, or even an automation unit controlling a mechanical action such as closing a protective curtain, The system has software means to emulate the operation of another peripheral such as a mouse or keyboard type pointer and constitutes a peripheral interface with computer which controls, as a function of the signals coming from the processing means, the execution of files contained in the computer or, via a modem or a network card, the execution of files contained remotely on a server, - The computer is associated with a flat screen of large dimensions or, better, to a computer video projector projecting on a portion called screen area of the surface of the plate of which at least one of the faces is in frosted glass, the information available from an Internet portal, - The frosting of the surface can be replaced by the installation of a diffusing film, possibly in combination with a Fresnel lens playing the role of directional magnifier, that is to say of directional light concentrator allowing to use the graphic interface, even in full day, The device has software means making it possible to display, reduce or move a keyboard on the screen area,

The device has software means making it possible to establish, in a rapid and simplified automated manner, a homothetic correspondence between the real physical coordinates in millimeters of an impact and the graphic coordinates in pixels of this impact when it is produced inside the graphics area. The axes of the graphic and real coordinate systems are parallel and the said software means involve the following operations: • Display by the software of a target at various positions of known graphic coordinates and measurement of the corresponding real coordinates. For example, a first target is displayed in

No (i j) where i and j are screen coordinates, close to the screen origin.

This target is displayed on the acoustic plate at the real coordinates No (x _a , y _c ). An impact made at the place where the target appears makes it possible to collect these real coordinates via the acquisition card. A second target of screen coordinates Nι (k, l) is displayed next to the maximum screen coordinates. The corresponding real coordinates Nι (xb, ya) are obtained by an impact opposite the target.

• The graphic coordinates (N _qx , N _qy ) of any point Q with real coordinates (x _r , y _r ) can then be deduced from the formula:

• A reference target is displayed one last time in the center of the graphic screen. The impact made against the target is converted into screen coordinates according to the above formula. The calculated position is compared to the reference position. If the difference is below a certain threshold, the calibration operation is validated. Otherwise it is renewed. The device has software means so that the portion of the plate that does not serve as a screen is nonetheless interactive and is configured as an extension of the screen area, in particular an impact made on the left (respectively, on the right, at the above, below) the screen area moves the screen content to the right (respectively to the left, below, above), thus making it possible to read a document of size much larger than the size of the screen area, - The device has software means so that the portion of the plate which serves as a screen is considered as a special area allowing to leave or switch from any software application managing the execution of groups of programs associated with various areas off the screen. - Conversely, the system has software means so that any impact made on the plate outside the screen area is associated with the execution of a chosen application, manager of the workspace located off screen, such as for example l application where, from the homothetic correspondence established between the pixels of a digital photo of the acoustic plate and the physical coordinates of these pixels on the acoustic plate, groups of programs are executed following an impact on a given area of the plate. Other aim and advantages aspects of the present invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of nonlimiting example and made with reference to the appended drawings, in which:

FIG. 1 is a schematic view of a rectangular plate giving the location and the coordinates of the sensors, the defined real and graphic references, as well as the real and graphic coordinates of three impacts on the plate. The figure 2-a is a screen capture of a dialog window allowing to configure the graphic interface and to define the authorized zone in which the impacts are interpreted as events of a mouse pointer type.

Figures 2-b to 2-f are screen captures of the calibration procedure of the graphic interface allowing to establish the homothetic correspondence between the physical coordinates and the screen coordinates of the portion of the plate playing the role of screen.

FIG. 3a is a screen capture of the main keys of an alphanumeric keyboard occupying approximately the entire width of the graphic screen and approximately 1/3 of its height. The keyboard is enriched with 2 additional keys allowing it to be moved or reduced in size to two floating buttons according to Figure 3b.

FIG. 4 is a chronogram of the main steps for measuring the difference in transit time between two sensors.

FIG. 5a is a block diagram of the general architecture of the acquisition card designed on the basis of analog and digital circuits with, in particular, the use of a microcontroller capable of carrying out the data processing for the calculation of the time of arrival of the wave packet and the transfer of data by a serial communication protocol to a microcomputer or another device. FIG. 5b is an electrical diagram of the PMP module of FIG. 5a and representing a generator delivering a high voltage HV using a diode pump, synchronous with the system clock of the microcontroller.

Figure 6 is a schematic sectional view of the symmetrical mounting of the piezoelectric transducers of a sensor intended to detect the mode S ₀ corresponding to the fastest vibrations propagating in a laminated glass.

Figures 7a and 7b show the signals from the transducers of Figure 6 in response to an impact distant from 70 cm (Figure 7a) and 130 cm (Figure 7b), after selective amplification around 100 kHz.

FIG. 7c shows in more detail the loss of symmetry observed in the modes S ₀ detected by the transducers PZTb and PZTa of FIG. 6 in the case of a laminated glass consisting of an assembly of two 6 mm thick plates sandwiching a polymer film.

FIG. 8 is a block diagram of the detection device with 3 sensors glued in the corners making it possible to free the sides of the plate. FIG. 9 shows the uncertainty of localization of an impact at nine places on the plate of the device of the Figure 8 when the detection of the arrival time of the wave packet is known to within 1 μs

FIG. 10 is a schematic view showing the transit times between an impact and the sensors of a detection system with four sensors operating in triplet of sensors each operating on a given quadrant of the plate.

FIG. 11 is a block diagram of part of the internal architecture of the programmed component “wavepro4” in FIG. 5.

Referring firstly to FIG. 1, there is shown a PLQ plate comprising four pairs PZTOO, PZT 10, PZT01, PZT1 1 of piezoelectric transducers which each constitute an acoustic sensor, the two transducers of each pair being fixed visually opposite on the two opposite faces of the plate for example by gluing to collect the acoustic waves circulating in the plate. Unlike the plate described in patent 9816229, the direction of the electrical polarizations and of the electrical connections are respectively symmetrical with respect to the median plane of the plate and antiparallel or antisymmetrical with respect to the median plane and parallel so as to discriminate any mode of antisymmetric propagation and to favor any symmetrical propagation mode.

An orthogonal coordinate system x, y of origin O is associated with the plate PLQ, the center of the plate possibly coinciding with the origin O of the coordinate system. The four sensors constitute the vertices of a rectangle. The x and y axes intersect the midpoints of the sides. PZTOO, PZT 10, PZT01, PZTl 1 have the respective coordinates (-p, -q) and (- p, q), (p, -q), (p, q). Acoustic waves can be generated by the impact of an object on the plate. The plate is an assembly of at least 2 isotropic plates each made of a rigid material constituting a good acoustic conductor isotropic around 100 kHz such as glass. The plates are rigidly connected to each other by a polymer film such as polyvinyl butiral, denoted PVB. The thickness of the polymer film is of the order of one to two millimeters. Its intrinsic acoustic impedance is small compared to that of glass, so we will continue in this talk to assume, as a first approximation, that each of the plates constituting laminated glass is capable of propagating symmetrical and antisymmetric Lamb waves. During the propagation in the laminated glass, the modes propagate in a plate and from one plate to another of the laminated. A shock produced on the surface of the laminated glass gives rise in the plates to coupled symmetrical modes as well as to coupled asymmetric modes. Given the material displacement vectors which characterize them, the asymmetric modes are all the more attenuated by the PVB compared to the symmetrical modes, the lower the acoustic frequency. FIGS. 7a and 7b clearly show this phenomenon of greater relative attenuation for the asymmetric modes: there we see the signals collected independently by the transducers PZTa and PZTb of FIG. 6 after selective amplification at 100 kHz. The signals of figure 7a are a response to a shock generated at 0.7 m distance, while the signals of figure 7b are a response to a shock generated at 1.3 m. Although more efficiently generated than symmetrical modes, the more dispersive propagation of antisymmetric modes combined with attenuation by PVB more rapidly degrade the head of the antisymmetric wave packets. This is why, it is preferable when using laminated glass to favor the detection of symmetrical modes.

In addition, the Applicant has observed that the mounting of the sensors for the detection of the asymmetric modes and the rejection of the symmetrical modes as described in patents 98/16229 and WO / 11378 cannot be used with laminated glasses. Indeed, as can be seen on the curves of FIG. 7C obtained by an impact on a laminated glass made up of 2 glass plates of 6 mm rigidly linked by a PVB film of 2 mm according to the assembly of FIG. 6, the S ₀ modes of the upper and lower plates are no longer totally in opposition phase, so that it is no longer possible to discriminate the mode S ₀ effectively and whatever the intensity of the shock, according to the known methods described in the cited patents.

The aim of the present invention is to show how to detect the symmetrical modes in a reliable manner. For this, the invention proposes to keep a mounting with 2 transducers facing each other according to the symmetrical mounting and the electrical connections in parallel of the transducers PZTa and PZTb of FIG. 6, to ensure this time of the discrimination of the antisymmetric modes of greater amplitude near receivers. In addition, it must also be taken into account that the intensity and phase of the symmetrical modes depend on the angle of impact on the display case. The waveforms recorded by the receivers are therefore highly variable. For the asymmetric modes, they decrease in amplitude and change shape according to the dispersion curves characterizing the Lamb modes, that is to say that the mechanical waves associated with audible frequencies have a lower phase and group speed than mechanical waves associated with higher ultrasonic frequencies. This has the effect of renewing the shape of the head of the wave packet, which makes frequency components appear higher and higher during propagation. This is not the case for the symmetrical modes whose waveform is preserved because they are very little dispersive for the ultrasonic frequencies considered and the thicknesses of plate envisaged.

If we stick to the signal processing described in French patent 98/16229 reporting a broadband amplification followed by a square rise followed by a peak detection then an integration, it appears that this method bases the detection of the arrival time of the wave packet on obtaining a threshold energy level. However, the further the sensor is from the impact position, the more it decreases in amplitude, which implies a longer integration time before reaching this threshold level. This integration time will then depend on the intensity of the shock, as well as on the nature and shape of the striking object. This will manifest itself at the end of the procedure by uncertainty about the position of the impact. To overcome this drawback, the present invention proposes a modification of the method for detecting the instant of arrival of the wave packet. This modification consists in carrying out a measurement in two stages. The first step is the same as the method known in patent 9816229 and the principle of which has just been recalled. It makes it possible to determine in a first approximation the instant of arrival of a packet and provides synchronization signals for the second step. The second step, new, consists, for each sensor, in continuously sampling the signal at the output of the selective amplifier centered on a high ultrasonic frequency, around 100 KHz, and in saving the samples in a FIFO memory (First in first out ) of sufficient depth to store the equivalent of 10 acoustic periods. Typically, for a sampling frequency of one million samples per second (1 MSPS) and a central filter frequency of 100 kHz, the depth of the FIFO memory will be 128 samples. Continuous sampling is performed independently for each pair of sensors. Signal sampling is stopped by the synchronization signal. The content of the FIFO memory, then frozen, contains a digital recording of the head of the wave packet. The analysis of this content, carried out later in this description, provides the time interval between the synchronization signal and the head of the wave packet making it possible to go up, independently of the amplitude or of the phase of the signal. , at the instant of arrival of the head of the packet. The precision on the measurement of this instant is then imposed only by the sampling frequency, the signal to noise ratio and the number of quantization bits.

During the first step, the receiver which is the quickest to reach the energy threshold for detection of the component at 100 kHz defines the origin of the times and triggers a time count until the arrival of the wave packet on the other receivers.

This dating of events can possibly be called into question during the second stage, in this case when the difference in propagation times is very small. The configuration of Figure 1 is suitable when you want to have a plate with free edges. However, three pairs of sensors are enough to determine the coordinates of an impact. FIG. 8 illustrates this detection principle with three sensors forming a right triangle. The axes of the physical coordinate system as well as its origin remain unchanged compared to the configuration with four sensors of FIG. 1. Unlike the transducers described in the previous patents, the transducers of the present invention have silver returns making it possible to produce the connections on the same face of the sensor and subsequently bonding with a fluid insulating adhesive. The measurements of the transit time differences of a packet of waves are preferably made in two orthogonal directions. Several configurations with 3 sensors forming a right triangle can be extracted from the configuration with 4 sensors in Figure 1. The four configurations described below lead to identical mathematical solutions, except for the sign, for the coordinates of an impact (x _r , y _r ). In addition, each of these configurations is better suited than the others, from the point of view of the accuracy of the measurement, if it is used only on a given quadrant of the plate. To realize this, let's take a configuration with three sensors PZTOO, PZT 10, PZT1 1 corresponding to the diagram in Figure 8 and look at the uncertainty that we obtain on the position of the impact when the uncertainty on the arrival time of a packet of waves is 1 μs for a packet of waves moving at 3350 m s. Figure 9 illustrates this uncertainty by solid rectangles whose size, given in millimeters, is displayed in 9 different places on a plate with dimensions 1400 mm x 800 mm. It is noted that the uncertainty on the position of the impact remains less than 7 mm ² in the quadrant (1.0) while it reaches 80 mm ² in the quadrant (0.1). It is therefore advantageous to restrict the use of the configuration of FIG. 8 to a single quadrant, the quadrant (1,0). However, the same precision can be obtained on the other quadrants if the detection triplet is changed when the impact changes quadrant. Thus, for a given impact, we first determine the quadrant (g _y , g _x ) to which it belongs, then we calculate the coordinates (x _r , y _r ) according to the formula associated with this quadrant.

FIG. 10 shows a rectangular plate with four pairs of silver feedback sensors bonded in the corners, the silver returns being oriented so that the angular response of the sensors is as uniform as possible over an angular reception range of π / 2. The sensors also form a rectangle and make it possible to define a Cartesian coordinate system, the center of which is the center of the rectangle formed by the sensors and the axes of which pass through the middle of the sides, similar to Figure 1. The Cartesian coordinates of the sensors are (-p, -q), (- p, + q), (+ p, + q), (+ p, -q). Acoustic waves travel at speed v. The propagation times to the sensors of a packet of waves generated by an impact at (x _r , y _r ) are too, to, tιo, t _π .

The coordinates (x _r , y _r ) are obtained by solving a system of equations, valid for a given quadrant. The four systems of equations are: • (g _y , g _x ). = (0,0) .x _r <0ety _r <0

• (g _y , g _x ). = (0, l) .x _r <0ety _r> 0

• (gy, gχ). = (l, 0) .Xr> 0ety _r <0

(gy, gχ) - = (U) -x _r > 0ety _r > 0

The following formulas give the position of the impact (x _r , y _r ). It suffices to replace g _x and g _y by the value corresponding to the quadrant concerned.

Atxg jq V ² v ² (4 p ² - v≈ Atxg ² ) (4 p ^! T 4 q> - v ² (Atxg - Atyg) ² ) Atyg ² (4 q ² - v ² Atyg ² ) + p ² v ² Atyg ² (-4 q ² * v ² Atyg (-Atxg + Atyg)) 1

• <-ιp

4 p Atyg (q ² v ² Atxg ² * p ² (-4 q> t ^ Atyg ² )) qv ² Atxg (- 4 p ² t V ^2. Atxg (Atxg - Atyg)) Atj rg p ² v ² ( 4 ² - v ² Atxg ² ) (4 p ^; ¹ * 4 q ² - v ² (Atxg - Atyg) ² ) Atyg ² (4 q ² - tyg ² ) y _r - (-l) 'r

4 (q ² v ² Atxg ² * p ² (-4 q ² t V ² Atyg ² ))

The determination of the measurement quadrant associated with an impact depends on the differences in time of flight between the four sensors. FIG. 4 illustrates the steps for measuring the time of flight difference in the “y” direction from the PZTOO and PZT 10 sensors and the acquisition card described according to the block diagram of FIG. 5. The signals represented are : the signals at the output of the selective filters centered on 100 kHz, FCH00 and FCH10, the contents of the memories FIFO 10 and FIFO00 at the time of low-high switching of the synchronization logic signals SYNC10 5 and SYNCOO the signal at the output of the quadrator SQ00 the INTGR00 signal at the output of the channel integrator associated with PZTOO, the SYNC10 and SYNC00 synchronization logic signals at output 0 of PMOS00 and PMOS 10 the time interval Δtyso separating the synchronization signals from the time intervals TT10 and TT00 separating the heads of the wave packets of the respective synchronization signals SYNC10 and SYNC00 a counting frequency counter identical to the sampling frequency of the signals and trigger by the logic signal

SYNC10 The signals relating to the two other sensors PZT01 and PZT11 are not shown, but provide similar signals on their own acquisition channel.

In general and with reference to what has just been said, the differences in time of flight between the sensors, given in number of XBUF clock periods are determined according to the following formulas and symbols: #, denotes a Logical "or", &, indicates a logical "and", abs, indicates the absolute value,. denotes multiplication,

A bar above a symbol indicates the logical reverse. The symbols SPOO to SP11 are the outputs of flip-flops D associated with the signals SYNCOO to SYNC11 and passing to the high logic state during a low-high transition of the respective signals SYNCOO to SYNC11.

We have :

gx = \ otherwise

or if Δt i≥ Δt o and [r7îι-r7îo + (- l) ^{s & 1} ffiL ^ & Δtoι] <0 gv = \ otherwise The FIFO 10 and FIFO00 memories each contain a digitization of the head of the wave packet detected by the respective sensors PZT10 and PZTOO. The two-step method of determining coordinates here shows the improvement it brings: in fact, it was not possible with the analog detection system using an active integrator to have the precise moment of arrival of the packet of waves, simply by the fact that it is not possible to know the time that the active integrator takes to pass from a positive saturated state close to +10 V, in the absence of signal, to a saturated state negative close to -10 Volts by signal integration. During this transition, the signal passes at a given time below the switching threshold THR of the PMOS transistor responsible for adapting this transition to logic levels compatible with CMOS logic, characterized by a supply voltage VCC which may be 5 Volts. The switching threshold of the PMOS transistor is approximately 1.5 volts below VCC, or 3.5 volts. The integrator TT transition time is thus the switching time from +10 V to + 3.5 V triggered by the arrival of the wave packet. This time depends on the amplitude of the envelope of the quadratic signal SQ, on the gain provided by the active integrator, as well as on the specific characteristics of the operational amplifier used to make the integrator. Although the integration time can be reduced by increasing the gain of the amplifier as well as by reducing the positive voltage of the saturated state, this arrangement is faced with the problem of the compromise that must be found between sensitivity and reliability. . Too high a gain could cause the integrator to switch to a spurious signal, while a too low gain generates a loss of precision due to a more variable integration time between a low intensity impact and a high intensity impact. By proceeding in two steps according to the present invention, the gain of the integrator is kept high enough to keep good immunity to noise and the integration time corresponding to the interval TT is known. The measurement of the interval TT consists for example of rectifying the digitized signal, then of creating an interpolation curve from the peak amplitudes of the rectified digitized signal. The intersection of the interpolation curve with the time axis corresponding to the output value of the sampler in the absence of a signal provides the instant I _HD origin of the packet. Another preferred solution for measuring the TT interval consists in starting from the synchronization instant situated at one end of the window and in searching for the successive moments of zero crossing towards the head of the packet. The instants of zero crossing make it possible to lock onto the period of the digitized signal, while a test on the sum of the amplitudes between the zero crossings, that is to say by half-periods, decides on the continuation of the algorithm. When the average value over a half period is equal to the output value of the sampler in the absence of a signal, to within a threshold difference, the algorithm is stopped and the average value is considered to be the original instant t _HD of the package. Referring now to Figure 5, each sensor is associated with an analog acquisition channel. The channels associated with the PZTOO, PZT01, PZT1 1 sensors are equivalent. The analog channels are characterized by a wideband amplification A1 and A2 followed by a selective FCH amplification in the ultrasonic band, followed by a derivation one channel of which goes to an 8-bit ADC analog digital converter with positive measurement range. The positive input voltages are obtained using high pass filtering and a bias bridge using the Ca, Ra, Rb, Rc components. The converter is controlled by CTA control logic signals from a μC microcontroller. The CAN converter supplies the input of a FIFO memory. The data in the memory is transferred via an 8-bit bus of DATA data and other CTF control signals, controlling the loading, unloading, resetting of the memory pointers, setting the impedance of the output bus, signals indicating the filling state of the FIFO memory, in the μC RAM memory, to be processed there locally and / or to be transferred there to another device or a more powerful computer such as a microcomputer via a parallel or serial communication which can be a USB, MIDI, or RS232 port. The logic levels between the microcontroller and the microcomputer are adapted using an LGCSHF logic level adapter. The other channel originating from the derivation supplies a step-up stage square followed by an envelope detection stage followed by an integrator stage supplying a PMOS transistor for adaptation to a CMOS logic level. The channel associated with the PZT 10 sensor also has a high voltage block for switching in transmission mode. The high voltage is produced by the PMP module explained by the diagram in FIG. 5B and comprising a diode pump D21 to D26 and capacitors C21 to C25 supplied by the logic signal XHT whose high logic level is adapted to the potential +12 V at using transistors T10 and Tl 1 and the logic level low at potential -12 V using transistors T12 and T13. The XHT signal comes from a logic “and” function between the XBUF system clock signal from the microcontroller and the CGPP signal activated at high level when a plate integrity test or propagation speed measurement procedure ultrasound is triggered. Without validation by the CGPP signal, the high-voltage module does not produce the high-voltage HV close to 70 V. The switching block is managed by the programmed logic component wavepro4 responsible for creating the logic excitation burst and counting the time of propagation of acoustic waves between the PZT 10 sensor and the other sensors. The wavepro4 programmed logic component is controlled by the μC microcontroller. The programmed counters are powered by the same XBUF system clock frequency as that of the microcontroller. This frequency is also the sampling frequency of analog-digital ADCs. The burst is obtained using the logic signals SRC and SNK responsible for controlling the opening of the switching transistors SWHTC and SWHTK. The CMRC and CMSH transistors are respectively responsible for putting the sensor in reception mode or for short-circuiting the input of the analog amplification channel to protect it from high voltage.

Part of the internal architecture of the programmed wavepro4 component is described by the block diagram in Figure 1 1. The component has logic flip-flops FFl to FF4 of type D triggered by the synchronization signals SYNCOO to SYNC11. Logical combinations between the outputs of these flip-flops validate flip-flops FF5 and FF6 whose outputs are the signals SSxo and SSxi, while other logical combinations define the logic functions Δtxs ₀ and Δtxsi representing the time intervals used for the calculation of the time of flight difference between the sensors. A logical “and” function between the signal XBUF clock and the Δtxs ₀ and Δtxsi functions respectively supply the 12-bit counters (QOxu..QOxo) and (Qlxu..Qlxo) associated with 3-state output registers, each register being identified and activated by the decoder addresses (A3..A0). The 4 most significant bits of the counters (Q0xn..Q0xo) and (Qlxπ..Qlx ₀ ) share the same output register in the following order most significant on the left: ((QOxn .. Q0x ₈ ), (Qlxι ι ..Qlx ₈ )). The logic flip-flops FF1 to FF4 and FF7, FF8 make it possible to reproduce in the same way the logic functions SSy ₀ , SSyi and Δtyso, Δtysi, which via a logic "and" with the clock signal XBUF respectively supply the 12-bit counters ( Q0yn..Q0y ₀ ) and (Qlyu-.Qlyo) also associated with 3-state output registers. The 4 most significant bits of the counters (Q0yπ..Q0y ₀ ) and (Qlyii-.Qlyo) share the same output register in the following order, most significant on the left: ((QOy,, .. Q0y ₈ ), (Qly,, .. Qly ₈ )).

All output registers share the same eight-bit DATA data bus. The component also creates the IntHF and IntBF logic functions routed to the output pins of the wavepro4 component and, when they switch high, produces an interrupt request detected by the microController μC having inputs provided for this purpose. The IntBF function is created from the FFBF type D logic flip-flop. The flip-flop clock input comes from a FBF selective amplifier stage centered on 10 KHz or preferably on the upper part of the audible spectrum delivering a signal adapted to CMOS logic by the NMOS10 transistor. The FFBF flip-flop thus validates the presence of spectral energy in the upper part of the audible spectrum. The IntHF logic function is created from a logic “or” between the outputs Q of flip-flops FFl to FF4 validating the presence of spectral energy in the ultrasonic band around 100 kHz. The time interval between IntHF and IntBF interrupts characterizes an impact on the plate. Given the lower frequency spectrum to which it is attached, the IntBF interrupt always occurs after IntHF. When it does not occur or if it occurs after a timeout, the measurement is refused because it is likely to have been caused by an untimely ultrasonic signal having spread to the plate by the ground . The outputs Q of the logic flip-flops FFl to FF4 are routed by means of a logical AND with the signal XBUF to the output pins of the wavepro4 component and form the respective clock signals LDCK00, LDCK01, LDCK10, LDCK1 1 of memories FIFO00 to FIFO1 1. The memories FIFO are thus frozen at the instant for switching SYNCij signals, with i and j being 0 or 1.

The impact intensity is quantified by diverting the output signal from a selective high frequency amplifier, i.e. in the vicinity of 100 kHz, for example that of FCH00 to a 12-bit impact counter , programmed in the component wavepro4 whose clock input CLKi is the signal FCH00 adapted to CMOS logic

The microcontroller is preferably with RISC architecture. Its XBUF system clock is a multiple of the frequency 32768 Hz of the QRTZ quartz. The microcontroller has counters / timers, several input / output ports operating with and without interruption, RAM, PROM or electrically programmable EPROM or reprogrammable FLASH memory, means of in situ programming of the code JTAG-type program, as well as serial communication means to other devices. It has at least four capture / compare functions allowing you to date time events. The synchronization signals SYNCOO, SYNC01, SYNCIO, SYNCl l are in particular connected to the capture / compare ports. The microcontroller has an arithmetic and logic unit allowing it to calculate the Cartesian coordinates of the impact, as well as to quantify the intensity of the impact. This solution is considered when it is necessary to rapidly transmit the intensity and position information relating to the impact. In particular, it is possible to use the acoustic plate as a piano or a two-dimensional percussion instrument. A key then corresponds to a sound or elementary audiovisual event executed in a predefined manner, when a given portion of the plate is struck with a more or less strong intensity. In this type of application, a rapid response time is sought, typically less than ten milliseconds. The acoustic plate is smaller, about 0.25 m ² . The microcontroller is then responsible for all processing and the communication of information (x _r , y _r , impact counters) via the MIDI interface defined for digital musical instruments. According to another aspect which may or may not be considered independently of the aspects mentioned above, the invention proposes to improve the ergonomics and the comfort of use of the display case by addressing the problem of noise annoyance caused by the impact of 'an object on the plate according to a process of masking the sound generated by the impact, by a synthesized sound triggered by IntHF. Indeed, the synchronization signals switch at the beginning of the audible sound generated by the percussion. We can therefore use it advantageously to trigger a recording followed by a processing and a sound synthesis in real time which will be superimposed on the noise of the impact, and which will be able to enrich its frequency content so as to imitate a known sound, such as for example the noise of a percussion instrument, an animal or a natural event or to produce a sound simply different from the sound generated by the impact. The synthesized sound may in certain regions of space oppose in amplitude the sound produced by the impact so as to reduce the intensity of the noise. One can by choice condition the emission of the synthesized sound to the presence of the IntBF interruption occurring in practice less than 1 millisecond after IntHF. The system according to the invention comprises, as has been said, a computer which receives the signals from the electrical processing circuits. The computer can, depending on these signals, emulate the operation of certain peripherals such as a mouse pointer or a keyboard. When the acoustic plate is associated with a large screen such as a plasma screen or a video projector projecting the graphical interface on the surface of the acoustic plate, it is possible to establish a homothetic correspondence between the screen coordinates in pixels and the physical coordinates in millimeters of any impact so that a graphical pointer appears on the screen next to the impact. It must be possible to establish this correspondence knowing that the relative positions of the video projector and the plate may change accidentally. For this, the invention provides a quick and easy interface calibration procedure. The procedure is carried out in five stages with reference to figures 2-b, 2-c, 2-d, 2-e and 2-f. The operator ensures beforehand and by orienting his video projector as necessary that the axes of the Cartesian graphic and physical references are collinear. The actual calibration procedure can then begin. The figure 2-b is a screen of presentation of the procedure. The operator must make an impact on the plate to pass to the stage illustrated in the figure 2-c. During this second step, a target appears on the screen. The screen coordinates N ₀ (iJ) of the target are known and close to the origin of the screen coordinates. The impact on the plate opposite the target provides the software with the corresponding Cartesian physical coordinates N ₀ (x _a , y _c ). We then pass to stage 3 with the figure 2-d. A second target appears with known screen coordinates Nι (k, l) close to the maximum screen coordinates. Here again, the operator is asked to make an impact on the plate opposite the target so that the calibration software determines the corresponding Cartesian physical coordinates Nι (x _t> , yd). The software then has enough information to determine the screen coordinates (N _qx , N _qy ) of any other impact from its physical coordinates (x _r , y _r ) according to the following correspondence formula:

It remains to verify that the calibration is satisfactory. It is the goal of stage 4 illustrated by the figure 2-e: a target appears in the middle of the screen, for example of screen coordinates (400,300) for a screen displaying with a maximum SVGA resolution of (800,600). Here again, the operator is asked to make an impact with respect to the target, which leads to step 5 illustrated in FIG. 2-f. A dialog window appears displaying on one side the expected screen coordinates ATX and ATY, ie (400,300) and on the other the screen coordinates deduced RESX and RESY from the above correspondence formula. When the difference exceeds one certain threshold, in practice of ten pixels, it is advisable to repeat the procedure.

Once the homothetic correspondence between the plate and the graphic screen has been established, any impact at a given location on the plate, located opposite the screen, can be viewed on the screen by a graphic pointer. A software driver then makes it possible to ensure that these impacts are interpreted as events of another pointing device, such as for example a mouse type device. An impact on the plate will thus be interpreted as a click or a double-click of the mouse at the location of the screen coordinates of the impact. If these coordinates correspond to the location of an icon associated with the execution of a program, it will be executed.

The impacts can be interpreted as events associated with other devices, in particular of the keyboard type. This is very useful when browsing the Internet and wanting to communicate information requiring the entry of alpha numeric characters.

The invention provides for this purpose a menu bar, floating and always accessible shown in Figure 3-B. This bar is placed in a corner of the screen. It contains a limited number of icons in order to hide as little graphic area as possible. However, if despite this minimal space requirement, the bar hides a document in the background, it is possible to move it to another corner of the screen indicated by the icon K03 representing a menu bar associated with an arrow indicating the corner in which will be the floating menu bar the next time you hit this icon. Successive impacts on this icon will have the effect of moving the bar in the four corners of the screen, the movement towards another corner being done in an anticlockwise direction.

The second visible icon K04 on the figure 3-B represents a keyboard. An impact made next to this icon triggers the appearance of the alphanumeric keyboard of figure 3-A. In order to maximize the surface occupied by the keys, so that the association of an impact with a key is reliable without however covering the entire surface of the screen, the keyboard contains a number restricted alphanumeric keys according to a configurable format, French QWERTY type or American QWERTY type.

The keyboard occupies the entire width of the screen, but only a third of its height. Again, there is an additional KOI key to move it up or down in case it hides the document of interest located in the background. The key represents a keyboard with an arrow above or below depending on whether the keyboard is respectively in the lower or upper part of the screen.

Another aspect of the invention relates to the addition of a functionality making it possible to limit the portion of the plate on which the impacts emulate the events of the graphic pointer of the mouse type (click; double click, etc.). In fact, it is desirable in a public environment to limit the field of action of unscrupulous users. In particular, the functionality aims to prevent a user from leaving a software application by clicking in the close icons or in the drop-down menus. You just have to define an area of the screen allowing the interpretation of the impacts in events of the mouse device. An impact made outside the authorized zone will possibly trigger the display of a message. The message can be in the form of a graphic window whose contours delimit the authorized zone.

The procedure for defining the authorized zone is illustrated in Figure 2a. It shows a dialog window. The authorized zone is defined either by directly entering the screen coordinates (X, Y) of the upper left corner, followed by the data of the width L and height H of the zone in pixels, or by direct acquisition of these data by successively activating the "acquire" keys and performing the acoustic impacts in the upper left and lower right corners of the zone to be defined. The impacts are then converted into screen coordinates, from which the data displayed in the fields provided for direct input of values are extracted.

This dialog window also contains a schematic image of the plate used to configure the acquisition of the coordinates. The symbols p and q defining the Cartesian coordinates of the sensors throughout this description are replaced in the figure respectively by the symbols CH and CV.

Claims

CLAIMS 1. Device for acquiring the position coordinates of a source of mechanical waves possibly generated by an impact on the surface of a plate (PLQ) of finite dimensions comprising a set of acoustic sensors (PZTOO to PZT1 1) formed each of a pair of piezoelectric transducers (PZTa, PZTb) located opposite each side of the plate, the device comprising processing means for determining the coordinates of the source by analyzing the difference of propagation time of the acoustic waves generated by the source towards the various sensors, device characterized in that, the processing means comprise in association with each sensor (PZTOO to PZTl 1) a respective electronic circuit comprising in cascade means for digitizing the signal amplified around a predetermined frequency, associated with means for limiting the digitization to a time window starting before the arrival of the acoustic waves on a sensor and teasing after the arrival of the acoustic waves on the said sensor.

2. Device according to claim 1 characterized in that the sensors are four in number and the piezoelectric transducers of each sensor are discs or plates of piezoelectric ceramics bonded on either side of the plate, so as to what the four sensors form on the plate the vertices of a rectangle whose center (O) constitutes the origin of the coordinates of a Cartesian coordinate system whose axes x and y are parallel to at least two sides of the rectangle defined by the four sensors.

3. Device according to claims 1 or 2 characterized in that the determination of the position coordinates is done by a triplet of sensors taken from the four sensors, said triplet corresponding to the three sensors closest to the source, each triplet being responsible for the detection of coordinates in a given quadrant of the Cartesian coordinate system defined by the sensors

4. Device according to claims 1 to 3 characterized in that the localization of a point of interaction of the source with the plate consists in extracting the ultrasonic frequency component in the vicinity of 100 kHz generated by the impact of a hard object such as the fingernail, a metal key, a ballpoint pen, a hard plastic 5 in the form of a rod and to determine the largest of the differences in absolute value of the flight times between two sensors of two first pairs (PZTOO , PZT01) identified by gx = 0 or (PZT10, PZT1 1) identified by gx = 1, on the one hand, and two pairs of two sensors (PZT00, PZT10) identified by gy = 0 or (PZT01, PZT1 1) identified by gy = 1, on the other hand, so that the Cartesian coordinates of the point of impact (xr, yr) on the plate are given by the formula:

Atxg jq p ² v ² (4 p ² - î ^ Atxg ² ) (4 p ^2. 4 q ² - v ² (Atxg - Atyg) ² ) Atyg ² (4 q ² - v ² Atyg ² ^ * p ² v ² Atyg ² (-4 g ² * v ² Atyg (-Atxg + Atyg)) J

. (- 1) ⁹

4 p Atyg (q ² v ² Atxg ² * p ² (-4 g ² * ² Atyg ² ))

, qv ² Atxg (-4 p ² * v ² Atxg (Atxg - Atyg)) Atyg * V p ² v ² (4 ² - i ^ Atxg ² ) (4 p ² * 4 q ² - v ² (Atxg - Atyg ) ² ) Atyg ² (4 q ² - v ² Atyg ² ) y. = (- i) ^y ^

4 (q ² v ² Atxg ² * p ² (-4 g ^2. I ^ Atyg ² ))

where p and q denote the position of the sensors relative to the center O of the rectangle, v, 5 the speed of the plate mode selected by the particular assembly of the pair of transducers forming a sensor, Δtxg, (respectively Δtyg) the time difference propagation of the wave packet generated by the impact between the sensors of one of the first two pairs (respectively of one of the following two pairs), selected by the value of the index gx (respectively gy) being 0 if the 0 coordinate yr (respectively xr) is negative and 0 otherwise and written Δtx ₀ if gx = 0 or Δtxi if gx = 1 (respectively Δty ₀ if gy = 0 or Δty _! if gy = 1)

5. Device according to claims 1 to 4 characterized in that said electronic circuits associated with PZTij sensors (i or j equal to 0 or 1) comprise in 5 cascade two stages wideband preamplifier (Alij, A2ij), a selective amplifier stage FCHij centered on a frequency close to 100 kHz, a step-up square (SQij), a peak detector stage (ENVLij), an integrator stage (INTGRij), a stage PMOSij of adaptation to a logic level providing a synchronization signal SYNCij, said triggering SYNCij synchronization signal, by a logical transition, a flip-flop FFij responsible for controlling the stopping of the analog-digital converter CANij and the transfer into memory FIFOij (first in first out) of the digitized value of the signal from the selective filter FCHij rerouted towards the converter CANij.

ό.Device according to claims 1 to 5, characterized in that the processing means comprise downstream of said electronic circuits associated with the respective sensors a programmable logic module (wavepro4) controlled by a microcontroller μC of an arithmetic and logic unit, of ports inputs / outputs operating on interrupt, random access memory RAM, ROM type program memory, a real time clock, ports for capturing the switching times of SYNCij signals, communication ports, data bus and address bus.

7. Device according to claims 1 and 6 characterized in that the microcontroller μC has software means for measuring the time interval TTij separating the head of a wave packet t _HD ij from the rising edge of the synchronization signal SYNCij, the said software means consisting in determining the instants of zero crossing of the digitized signal from the end of the digitization window starting on the rising edge of SYNCij, while a decay test on the successive sum values of the amplitudes between the crossings at zero, that is to say a test on the average value of the signal by half-period, decides on the continuation of the algorithm of search for the instant t _HD i _j - When the average value on a half period is equal to the sampler output value in the absence of a signal, except for a threshold deviation, the algorithm is stopped, and the average value is considered to be the original instant t _H Dij of the pack and.

8. Device according to claims 1 to 7 characterized in that the values of the bits gx and gy are determined by the following formulas: gx = \ otherwise

g _y - \ otherwise

9. -Device according to claims 1 to 8 characterized in that the acoustic plate is a laminated glass consisting of an assembly of plates of the same thickness, glued to each other by a polymer film.

10. Device according to claims 1 to 9 characterized in that the piezoelectric transducers of a sensor are ferroelectric ceramics whose polarization vectors are oriented symmetrically with respect to the thickness of the plate and the electrical connections are in parallel.

1 1.Dispositif according to claims 1 to 9 characterized in that the piezoelectric transducers of a sensor are ferroelectric ceramics whose polarization vectors are oriented asymmetrically with respect to the thickness of the plate and the electrical connections are antiparallel.

12. Device according to claims 1 to 11 characterized in that the piezoelectric ceramics are discs or plates whose lower electrode, at contact of the plate, is brought back on a small portion of upper face, remaining isolated from the upper electrode by an electrical insulating guard strip.

13. Device according to claims 1 to 11 characterized in that one of the sensors for example PZT 10 is capable of being switched into a transmitter of a packet of ultrasonic waves in order to trigger a measurement of the speed of propagation of the acoustic waves in at least two different directions given by the positions of the other sensors.

14.-Device according to one of the preceding claims constituting a peripheral interface with a computer provided with a screen.

15. Device according to claim 14 characterized in that the acoustic plate also serves as a display screen by diffusion of the projected light, either by frosting at least one of the faces of the glass plates, or by using a film possibly colored translucent polymer, possibly combined with a light concentration effect by means of a Fresnel lens.

lό.Dispositif according to claims 14 and 15 characterized in that the axes of the screen mark and the acoustic plate are collinear.

17. -A device according to claims 14 to 16 characterized in that a homothetic correspondence between a pixel (N _qx , N _qy ) of the screen marker and a physical point (x _r , y _r ) of the plate opposite the graphic pixel is established by an automated calibration according to the following operations:

• display by the software of a target in various positions of known screen coordinates and measurement of the corresponding physical coordinates. For example, a first target is displayed at N ₀ (ij) where i and j are screen coordinates, ready for the origin of the graphic coordinates. This target is displayed on the acoustic plate at the real coordinates N ₀ (x _a , y _c ). An impact made against the target allows collect these real coordinates via the acquisition device. A second target is then displayed in Nι (k, l) near the maximum coordinates of the graphic interface. The corresponding real coordinates Nι (x _t ,, y _d ) are obtained by an impact opposite the target. The graphic coordinates (N _qx , N _qy ) of a pixel of real coordinates (x _r , y _r ) can then be deduced from the formula

• A reference target is displayed one last time in the center of the graphic screen. The impact made against the target is converted into screen coordinates according to the above formula. The calculated position is compared to the reference position. If the deviation is below a certain threshold, the calibration operation is validated. Otherwise it is renewed.

18. Device according to claims 1 to 17 characterized in that the acoustic plate constitutes a graphic pointing device capable of emulating another pointing device such as for example a mouse type device, an impact on the plate in a given position being then interpreted according to a particular coding, like a click or a double click made on the corresponding screen coordinates and triggering the execution of programs associated with an icon located next to the impact.

19. Device according to claims 1 to 18 characterized in that the emulation area for mouse events (click, double click, etc.) is limited to an authorized portion of the screen area in the form of a rectangle defined by the coordinates X, Y in pixels of one of its corners as well as its width L and its height H in pixels, these values can be entered directly with the keyboard or can be deduced by acquiring the coordinates of the impacts in the corners of the area authorized to define.

20.A device according to claims 1 to 19 characterized in that it is provided with software means making it possible to produce a floating toolbar, permanently accessible, consisting of several icons K03, K04 ensuring during an impact which is their carried: “the appearance (K04) on the screen of an alphanumeric keyboard, two of its keys KOI and K02 respectively provide for its movement from bottom to top as well as its reduction to the floating menu bar,

• the rapid and circular movement (K03) of the toolbar in one of the four corners of the screen, designated by the direction of the arrow represented on the icon.

21. Device according to claims 1 to 20 characterized in that it has software means so that the portion of the plate which does not serve as a screen is also interactive and is configured as an extension of the screen area, in particular a impact made to the left (respectively, to the right, above, below) of the screen area moves the screen content to the right (respectively to the left, below, above), thus making it possible to read a document much larger than the size of the screen area.

22.Device according to claims 1 to 21 characterized in that it has software means so that the portion of the plate which serves as a screen is considered as a special zone making it possible to leave or switch from any software application managing the execution of program groups associated with various areas of the plate located off screen. Conversely, the system has software means so that any impact made on the plate outside the screen area is associated with the execution of a chosen application, manager of the workspace located off screen, such as for example the application where, from the homothetic correspondence established between the pixels of a digital photo of the acoustic plate and the physical coordinates of these pixels on the acoustic plate, groups of programs are executed following an impact on an area data from the plate.

23. Device according to claims 14 to 22 characterized in that it is provided with software means such as client-server type protocols allowing the graphical interface to be connected, via a modem or a network card, to a Internet service provider.

24. Device according to claims 14 to 22 characterized in that it contains software means making it possible to update the multimedia content (image, sound, video) available on the host computer of the graphical interface from a remote computer.

25. Device according to claims 1 and 24 characterized in that the electronic circuits associated with the respective sensors PZTij comprise downstream of said wideband amplification means A2ij a bypass towards means of frequency enrichment of the audible acoustic signal generated by the impact on the plate, as well as means for converting the enriched signal into an analog signal and sending it to speakers so as to mask the discomfort caused by the impact in the form of a different sound reproducing for example the noise of '' a percussion instrument within a symphonic composition, or the sound of an animal or a natural event, said enrichment means being implemented at the same instant IntHF where the first of the four synchronization signals SYNCij switches from logic level.