FR3014186A1 - SYSTEM FOR DETERMINING THE SHAPE AT LEAST PARTIAL OF A THREE - DIMENSIONAL OBJECT AND CORRESPONDING METHOD. - Google Patents

Abstract

The invention relates to a system (1) and a method for determining the at least partial shape of a three-dimensional object (2). It comprises a member (6) for detecting a pressure field arranged to be able to apply the object, elements (5) for connecting the detector member with means (3) for calculating the distribution of the pressures measured for deducing said form, said means (3) calculation and means (9) applicators of the object on the sensor member with a homogeneous pressure. The detector member (6) comprises a part (14) provided with a sheet (15) of flexible plastic material secured to a grid (16) of pressure sensors (17), the grid comprising an intermediate layer of resistivity variable according to the pressure comprising a microcrystalline silicon wafer semiconductor less than or equal to 50 nanometers.

Description

The present invention relates to a system for determining the at least partial shape of a three-dimensional object by means of an external sensor. It also relates to a method implementing such a system. The invention finds a particularly important, although not exclusive, application in the field of complex-shaped physical object modeling, in particular enabling the determination of shapes on a micrometric scale and, for example, applicable to the modeling of the surface of the object. interface between moving parts of complementary shapes, for example in the dental field. By complex form is meant here the shape of an object having an outer surface having many accidents or singular points (inflection points, hollows, bumps, The determination of the at least partial shape of a three-dimensional object is as it is understood here as the obtaining by measurement of a set of digital data corresponding or substantially corresponding to the profile of the interface of the sensor and the object to be determined on a given height. thus be processed by computing means such as a computer.

Impression devices are known, for example by molding. These devices do not make it possible to obtain numerical modeling, in particular in terms of resistance to the constraints of surface data relating to the object. Optical shape recognition devices are also known, but these are not very precise in the small dimensions. They are also very sensitive to the conditions of use such as the brightness, the contrast between the object and its background and only allow a limited modeling of the values, without the possibility of complementary shape appreciation in constraint one with the other. Electronic recognition devices based on particular material resistances are also known. These are manufactured using techniques that do not provide reliable spatial resolutions (US 4,734,034, US 4,856,993, US 5,505,072, US 5,989,700).

The invention proposes to solve these drawbacks by starting from the principle of determining a three-dimensional profile of the space from a set of measurements in two dimensions plus a dimension in pressure, that is to say of measure physical spatial dimensions (length, width, thickness) by measuring pressures at identified locations in space. More precisely, from a sensor, for example a plane, the object is applied to said sensor at a location in x, y determined by exerting a pressure on the opposite side (at the sensor). It is then possible to determine the third dimension (in z) because it is correlated with the pressure existing at the (x, y) level of the sensor. By accepting to replace the measurement of a static datum, such as the length, by a statistical datum such as pressure, which moreover requires a reference surface to be measured, while the finest possible measurement is desired, the invention makes it possible to achieve with a single planar sensor a precise three-dimensional measurement of the order of 10 microns, and this with a system requiring only a small footprint. For this purpose, the invention essentially proposes a system for determining the at least partial shape of a three-dimensional object, characterized in that it comprises a detector member of a pressure field arranged so as to be able to apply the object to it. connecting elements of the detector member with means for calculating the distribution of the measured pressures to deduce said shape, said calculating means and means for applying the object to the detector member with a homogeneous pressure, said detector member comprising a part provided with a sheet of flexible plastics material secured to a pressure sensor grid, said grid 25 comprising an intermediate layer of variable pressure resistivity comprising a half-microcrystalline silicon wafer; conductor of thickness less than or equal to 50 nano meters. The intrinsic flexibility of the sensor and inherent because of its small thickness makes it possible to determine the partial shape of the interface of two objects without disturbing the measurement.

It will be noted that the layers and / or slices which are in general of different thicknesses are, on the other hand, of constant or substantially constant thicknesses.

In advantageous embodiments, one or more of the following provisions is also used and / or the following: the grid comprises a first layer comprising a first network of metal electrodes 10 called electrodes of line, generally parallel, of said second intermediate layer, and of a third layer comprising a second network of metal electrodes called column electrodes, defining so-called intersecting zones with the line electrodes to form said sensors; the metal of the electrodes is aluminum; the first layer comprises more than one hundred line electrodes and the third layer more than fifty column electrodes; The first layer is of thickness between 150 nm and 500 nm; the intermediate layer is of thickness between 80 nm and 250 nm; the thickness of the wafer being less than 30 nm; the third layer is between 350 nm and 700 nm thick; the grid comprises at least 5000 sensors adjacent to one another, of square section less than or equal to 600 microns; the intermediate layer is formed by plasma deposition of the doped silicon under an insulating layer; the connection elements comprise a connection pin with the support piece; the computing means comprise means arranged for dynamically displaying on a computer screen the shape of the object by integrating complementary data.

The invention also proposes a method for measuring the shape of a three-dimensional object, characterized in that the object is applied to a detector member of a pressure field connected to calculation means, the pressures are measured by the biasing of the detector member provided with a sheet of flexible plastic material glued to a pressure sensor grid comprising at least 5000 sensors adjacent to one another, of square section less than or equal to 600 micro meters, the said grid comprising an intermediate layer of variable resistivity as a function of pressure, said intermediate layer comprising a semicrocrystalline silicon wafer of thickness less than or equal to 50 nanometers, and the shape is calculated from the distribution of the measured pressures. Advantageously, the shape of the object is dynamically displayed on a computer screen by integrating complementary data. The invention will be better understood on reading the following description of an embodiment given hereinafter by way of non-limiting examples. The description refers to the accompanying drawings, in which: FIG. 1 is a general diagram of a measuring system according to the embodiment of the invention more particularly described herein. FIG. 2 is an enlarged fragmentary perspective view of the detector member of the system of FIG. 1 (the proportions between the different elements are not to scale). FIGS. 3A to 3D illustrate the steps of producing a pressure sensor of the detection member of FIG. 2 (in view from above, and in section A-B). Figure 4 is a partial schematic plan view illustrating a sensor array according to the embodiment of the invention more particularly described herein. FIG. 4A shows an experimental curve for measuring the variation of the electrical intensity as a function of the deformation of the sensor for four sensor dimensions. Fig. 5 is a schematic view of the acquisition card belonging to the connecting elements of the system of Fig. 1. Fig. 6 is a simplified flowchart showing the main steps of the method according to one embodiment of the invention. Figs 7A and 7B are diagrammatic representations in section of an object applied at two different pressures on the detector member. FIG. 1 shows a system 1 for determining the at least partial shape of a three-dimensional object 2. The system 1 comprises means 3 for calculating and graphing which are adapted to calculate a distribution of measured pressures and to deduce a shape. The means 3 comprise a computer 4 connected by connection means 5 to a detector member 6 of a pressure field 7.

The detector member 6 is planar and arranged so that the object 2 can be applied to it for example by placing it on its upper plane surface 8. The system 1 comprises means 9 applicators of the object 2 on the sensor member 6, which are arranged vertically above it. These applicator means 9 exert a force F on a side or face 10 of the object, opposite to the one whose shape is desired to be determined. The side 10 is arranged to be of complementary shape to the pressure face of the applicator means, so that there is a homogeneous distribution on the object of the force exerted. The side 10 is for example formed by a flat surface. The means consist for example of a cylinder (not shown) provided with a horizontal plate 11 parallel to the flat surface 8 of the detector member and arranged to cooperate with the flat surface of the side 10. The pressure obtained is resulting from the force F and is applied homogeneously by the applicator means 9 on the object. It is determined and controlled by the calculation means (mixed line 12). The detector member 6 rests on a support table 13 which is fixed and adapted to allow the sensor member to absorb the pressure applied by the applicator means 9, in a measurable way (for example 95%). or in full. The detector member 6 is in the form of a flat plate or part 14, for example of parallelepipedal shape.

The plate is for example 15 cm x 15 cm in size and in the example chosen here total thickness of the order of 800 pm. More specifically with reference to FIG. 2, the part 14 comprises a support sheet 15 of plastics material, for example flexible polyethylene naphthalate (PEN), glued to a grid 16 of pressure sensors 17. By flexible is meant a plate capable of accepting radii of curvature less than 1.5 mm. The support sheet 15 is substantially parallelepipedal, of dimension of the order of or less than that of the plate. The part 14 comprises a thin layer 18, of ceramic, for example 100 microns thick, bonded to the sheet or PEN 15, for example silicon nitride and of dimensions equal to those of the sheet 15. The assembly thus formed comprises on the top, a first layer 19 comprising a first array of electrodes 20, 20 ', called line electrodes. Each electrode is a metal wire for example of flattened rectangular section, elongate, electrical conductor for example aluminum. The width of the electrodes is less than 2 mm, for example 0.5 mm, and the thickness is for example between 150 nm and 500 nm, for example between 200 and 400, for example 300 nm. The electrode array is thus formed of a bundle of line electrodes substantially parallel to each other and spaced apart by a width of less than 2 mm, for example 0.25 mm.

In the embodiment more particularly described here, the row electrodes are in number greater than 100, for example 120, and operate in pairs 20, 20 '.

Conducting elements 21 and 22 are also provided and will be detailed below. On the first layer 19 of line electrodes is placed an intermediate layer 23. This intermediate layer 23 comprises a semiconductor layer or wafer 24 of piezoelectric material. The piezoelectric material is semicrystalline silicon semiconductor (doped for example with arsenic). The wafer 24 covers with a substantially homogeneous thickness between 30 nm and 100 nm the portions 25 associated with the line electrode array and the space 26 between them, forming an electrical bridge between said parts which will be detailed below.

The space between two pairs of line electrodes 20, 20 'does not have a layer of semiconductor material. The intermediate layer 21 further comprises a layer 27 of electrically insulating material over the semiconductor layer 24. It is of lateral and longitudinal dimensions equal to that of the plastic sheet and a maximum thickness of between 50 nm and 250 nm. nm. It completely covers the first electrode layer 20, 20 'and the semiconductor layer 24 except at specific locations 28 which will be detailed with reference to FIGS. 3A to 3D.

The intermediate layer 27 thus formed is of variable resistivity as a function of the pressure and / or deformation applied thereto. The detector member 6 and more precisely the part 14 also comprises, above the intermediate layer 23, a third layer 29 comprising a second network of metal electrodes called column electrodes 30. The column electrodes 30 are for example 10 similar to the row electrodes but arranged so that the superposition of said row and column arrays form a grid. For example, the two arrays are substantially orthogonal to one another defining zones known as intersections with the line electrodes to form the pressure sensors 17 bonded to the plate. Advantageously, a protective layer 31 (mixed line in Figure 2), neutral (insulating) 20 fills the voids and protect the top of the part 14 so that it has a flat face 32 arranged to cooperate with the measured object. The column electrodes have a thickness of between 400 nm and 600 nm and a number greater than 40, for example 54. The number of sensors 17 being equal to the number of intersections of the grid, in the embodiment more particularly described here, it is greater than 4000 for example 6480. The gate 30 therefore comprises at least 5000 sensors adjacent to each other and, the intersection being orthogonal, the sensor section is square and less than or equal to 600 micro meters .

A method of manufacturing the sensor member according to an embodiment of the invention will now be described with reference to FIGS. 3A to 3D.

This method comprises a first step (FIG. 3A) of providing a first polyimide substrate in the form of a plastic film such as those marketed by DuPont Teijin Films to form the support sheet 15.

This forms a substantially parallelepipedal plate with a rectangular cross section, for example equal to or less than 15 cm by 15 cm and a thickness of less than 125 μm, for example less than 50 μm (for example 10 cm × 10 cm × 10 μm).

Advantageously, the plate is freed from its impurities by cleaning in an ultrasonic bath with acetone and rinsed with ethanol or isopropanol in a manner known per se. A second step is then performed, depositing the ceramic layer 18 such as silicon nitride. This is for example a plasma-assisted chemical vapor deposition (acronym PECVD). The gaseous phase of the PECVD consists of a gaseous mixture of silicon tetrahydride (SiH 4), called silane, nitrogen (N 2) and hydrogen (H 2), and carried out at a temperature below 200 °, for example 165 ° C. The desired silicon nitride layer is less than 100 nm thick, for example 50 nm thick. A third deposition step, on the ceramic layer 18, of the network or layer of line electrodes 20, 20 'is then carried out.

The deposition is carried out by electron beam lithography or by Joule evaporation, to create the line metal contacts on a thickness of the order of 300 nm.

The contacts are then etched by wet etching. For example, the sample is immersed in a hot aluminum bath (about 50 ° C) with an etchant such as phosphoric acid (H3PO4) for a specified time. This determined time can be of the order of 2 to 3 minutes. The sample is then rinsed under distilled water and dried under a N2 gas stream. In the embodiment more particularly described here, the metal contacts comprise, a first in-line electrode 20, a second in-line electrode 20 'parallel to the first and a first 21 and second 22 contact pads. The first contact pad 21 is substantially parallelepipedal and orthogonal to the electrodes 20 being connected to the first electrode 20 and extends in the space between the pair 20, 20 'of electrodes. At the end portion of the first pad 21 is the second pad 22 of square shape. Intermediate layer 23 is formed in a fourth step (Fig. 3B and 3C). The manufacturing method consists of a substep of depositing the piezoelectric layer 24 of semiconductors. The piezoelectric layer 24 completely covers the pads 21, 22 of the line electrodes and fills the space between the two electrode pads 21 and 22 of the same pair.

The deposition is carried out by PECVD, for example by depositing a thickness of about 130 nm of microcrystalline silicon nitride doped with Arsenic (AsH4). The process is again followed by photolithography. Etching is done by a method known to those skilled in the art as reactive ion etching (RIE) using plasma sulfur hexafluoride (SF6). The intermediate layer is thus formed by plasma deposition of doped silicon under an insulating layer. The second substep of the formation of this layer consists of depositing the layer of electrically insulating material. This layer has a maximum thickness of 300 nm. This layer will have holes 28 passing through the second pads 22 of the first line electrode array layer. The insulating material is, for example, silicon oxide (SiO 2). It is deposited for example by spraying and is followed by photolithography. Etching is done by reactive ion etching RIE using SF6. In a fifth step (FIG. 3D), the so-called third layer of column electrodes 30, 30 ', for example 500 nm thick, is deposited in aluminum by Joule evaporation, followed by a photolithography for creating the second metal contacts 22 of columns, in a network orthogonal to the network of lines. The array is arranged such that the lines of a pair of column electrodes 30 pass the first and second pads 22 and 22.

One of the column electrodes 30 of the pair overhangs in order an insulating layer 27, a piezoelectric layer 24 and the first contact pad 21.

The other is directly to the right of a piezoelectric layer 24 and the second contact pad 22. Here again a wet etching technique is for example used as previously. In one embodiment of the invention, the previously obtained assembly undergoes thermal annealing at a low temperature (for example less than 200 ° C., for example 180 ° C.) for a determined time, for example 2 hours in an oven. This improves the microcrystalline silicon / aluminum interface, and increases the conductivity by a factor greater than 1.5 or 2. FIG. 4 schematically shows an arrangement of pressure sensors 17 forming part of the detector member 6.

In the embodiment more particularly described here, each line electrode 20 is split by a parallel offset electrode 20 'allowing flexibility of geometry in the formation of the detector member.

The two electrodes 20, 20 'thus form a pair of electrodes. Each line electrode (one per pair) and column is connected to a connection pin 33 known per se and mounted on the support member and forming a connection member. For a given line or column, there is a single pin 33 of electrical connection.

The electrical principle of the measurement will now be described. An electrical voltage is for example applied between a line pin 20 and a column pin 30. The intensity of the current is measured at one of the pins and is according to the ohm function of the electrical resistance on the path of the electrons. When pressure is exerted on a pressure sensor, the geometry of the piezoelectric layer is modified and therefore its electrical properties including its resistivity. The electrical measurement can be connected to a geometrical datum since the electrical contact can be made between line and column only through the piezoelectric layer and through the through holes of the insulating layer. The electrical resistance value of such a material is modified during physical deformation by following the equation: ## EQU1 ## where AR is the variation of electrical resistance between the initial resistance and the final resistance, the initial electrical resistance, FG the gauge factor (constant characteristic of the piezoelectric material) and s (epsilon) the deformation of the material, which makes it possible to make the connection with an external pressure. More precisely, considering the preponderant characters of PEN young modules and silicon nitride (respectively 270 GPa and 6.45 GPa) compared to other layers, the previously described model can relate to a layer of PEN sandwiched between two silicon nitride layers. The layers having for example 125pm, 550nm and 250nm respectively. Thus we obtain a model connecting the deformation and the resistance measured according to the formula: With E: deformation of the material d, df and df2 respective thicknesses of PEN and silicon nitride layers X - Yri ri 1 = ds,, 1 Where Y, and Yf are the Young's moduli of the Substrate (Y5) ie 2,5GPa, and Silicon Nitride (Yf) layers ie 270 GPa. By choosing this limitation, the calculations of association of a pressure with a measured resistance difference are simplified as shown by the linear character of the experimental record of the variation of current as a function of the deformation always having the same slope (FIG. 4A). The abscissa shows the epsilon stress in% and the ordinate the relative variation of the current. The four values obtained are given by varying the width (W) for the same length (L) or vice versa. This limitation makes it possible to obtain a measurement accuracy of the micrometric order. In the embodiment more particularly described here, the device comprises acquisition means 5 (FIG. 5). These acquisition means comprise an acquisition card 34 on which are mounted a module 35 for multiplexing / demultiplexing the information coming from lines 36 and columns 37. The card also comprises means 38 for adapting the electrical signal so that it is provided to a 39/40 analog / digital converter to allow processing by the calculation means 3, and a communication module 41 of the card 15 with the computer 4. Each pressure measurement comprises two resistivity measurements, the first said initial without pressure applied to measure and the second with the pressure to be measured applied to the object. By way of example, the measurement of each sensor 17 can be performed according to the following diagram: - By interrogation (request by applying a voltage to the corresponding pins) random of any sensor present and so on until that all have been questioned. - polling all sensors for a fixed column or row until all columns or rows have been queried. By interrogating a particular area of interest. A measurement and the at least partial determination of the shape of a three-dimensional object according to one embodiment of the invention will now be described with reference more particularly to FIGS. 6, 7A and 7B. In a first step 42, the object whose shape determination is sought is placed on the plate 14 of the horizontal detector member 6 below the applicator means 9. The operator activates, for example via a computer 4, the beginning of the determination of the shape, which sets the cylinder in motion to bring the plate 11 into contact with the object and exert on it a homogeneous pressure. A first pass (step 43) of the measurements of the set of sensors is then made and / or concomitantly at the descent of the jack and the result is introduced into a memory of the computer in the form, for example, of "Line 5 - column 27 - Initial - 28 (MD) Megohms ". Then the jack (step 44) exerts and maintains a homogeneously determined pressure on the side 20 of the object 2 with which it is in contact. The calculation means 3 then control (step 45) a second measurement of all or some pressure sensors. The results of the measurements are also introduced into the computer memory in the form for example "Line 5 - column 27 - measurement 1 - 245 Q ohms". The calculation means having the internal characteristics of the detector member 30 (in particular the thicknesses and the Young's moduli of the materials) previously introduced into the computer and having the differences in resistance between the initial positions and under pressure for a pair of coordinates (row / column) data, they then determine the pressure applied to the plate for each pair of coordinates (step 46).

For each coordinate of the space in the plane, the calculation means then associate at 47 a value of difference of resistance and therefore of pressure and thus establish a field of pressure intensity, before displaying in 48 the results on the computer screen using software means for presenting data known in themselves. Each pressure intensity corresponds to an intensity of deformation and penetration of the object into the thickness of the detection plate.

More specifically, and with reference to FIGS. 7A and 7B, there is shown schematically the measurements making it possible to determine the profile 49 of the object 2 penetrated into the plate 14. If portions 50 of the profile remain outside the thickness of the plate (Figure 7A) then it can be exerted a greater pressure (for example controlled by the means 3 of calculation) so as to penetrate a larger portion 51 of the object to determine the complete shape at the interface (Figure 7B). The pressure exerted (arrow 52) is arranged to remain below a determined limit, particularly with respect to the resistance of the materials of the object and the sensor and the yield stress of the two. In one embodiment of the invention, the computing means comprise means arranged for dynamically displaying on a computer screen the shape of the object by integrating complementary data. The shape of the object appears directly on the user's screen.

Also, the second measurement of the pressure (step 45) can be repeated (test 53), for example with a refresh rate greater than 100 hz so as to have a dynamic determination of the shape of the object.

As is obvious and as also follows from the above, the present invention is not limited to the embodiments more particularly described. On the contrary, it embraces all the variants and in particular those in which the pressure applicator means are designed in a form substantially complementary to the upper face of the object which is not flat, or are formed by a pushing finger (integrating or not a pressure gradient by the calculation means), which is moved on the object by adapting in distance relative to the object portion opposite, those where the layers of the intermediate layer are reversed in their order of stacking, those where the electrodes do not form pairs of electrodes but operates as a single electrode, or that or the plate 14 is manufactured with a different method.

Claims (11)

REVENDICATIONS1. System (1) for determining the at least partial shape of a three-dimensional object (2), characterized in that it comprises a pressure field detector (6) arranged to be able to apply the object, elements (5) for connecting the detector member with means (3) for calculating the distribution of the measured pressures to deduce said shape, said means (3) for calculating and means (9) for applying the object to the detector member, said detector member (6) comprising a part (14) provided with a sheet (15) of flexible plastic material secured to a grid (16) of pressure sensors (17), said grid comprising a intermediate layer of variable resistivity as a function of pressure comprising a microcrystalline silicon wafer semiconductor less than or equal to 50 nanometers. 2. System according to claim 1, characterized in that the gate comprises a first layer (19) comprising a first network of electrodes (20) called generally parallel line electrodes, of said second intermediate layer, and of a third layer comprising a second network of metal electrodes (30) called column electrodes, defining so-called intersecting zones with the line electrodes to form said sensors. 30 3. System according to claim 2, characterized in that the metal of the electrodes is aluminum. 4. System according to any one of claims 2 and 3, characterized in that the first layer comprises more than one hundred line electrodes and the third layer more than fifty column electrodes. 5. System according to any one of claims 2 to 4, characterized in that the first layer is of thickness between 150 nm and 500 nm, the intermediate layer is of thickness between 80 nm and 250 nm, the thickness of the wafer being less than 30 nm, and in that the third layer is of thickness between 350 nm and 700 nm. 6. System according to any one of the preceding claims, characterized in that the grid comprises at least 5000 adjacent sensors of each other, of square section less than or equal to 600 micro meters. 7. System according to any one of the preceding claims, characterized in that the intermediate layer is formed by plasma deposition of the doped silicon under an insulating layer. 8. System according to any one of the preceding claims, characterized in that the connection elements comprise a connection pin with the support part. 9. System according to any one of the preceding claims, characterized in that the computing means comprise means arranged for dynamically displaying on a computer screen the shape of the object by integrating complementary data. 10. A method for measuring the shape of a three-dimensional object, characterized in that the object is applied to a detector member of a pressure field connected to calculation means, the pressures are measured by means of the detector member provided with a sheet of flexible plastics material glued to a pressure sensor grid comprising at least 5000 sensors adjacent to each other, of square section less than or equal to 600 microns, said grid comprising an intermediate layer of variable resistivity as a function of pressure, said intermediate layer comprising a semicrocrystalline silicon wafer of thickness less than or equal to 50 nanometers, and the shape is calculated from the distribution of the measured pressures. 11. The method of claim 9, characterized in that one displays dynamically on a computer screen the shape of the object by integrating complementary data.