Checking assembly and method for checking the outline of a surface of an object

Abstract

Checking assembly (1) and method for checking the outline of a surface (2') of an object (2). The following are included: a support (3) which is configured to support and reference the object; a reference element (4) which defines a reference surface (4') placed in a known position; a measuring head (6) with at least one contactless sensor (8) configured to detect at each acquisition the position of a point (P1) of the surface of the object, and the position of a corresponding point (P2) of the reference surface; a displacement system (5) which is configured to support and displace the measuring head on the surface of the object; and a processing unit (7) which is configured to check the outline of the surface of the object according to the position of the detected points of the surface of the object and of the reference surface.

Description

[0001] CHECKING ASSEMBLY AND METHOD FOR CHECKING THE OUTLINE OF A SURFACE OF AN OBJECT

[0002] Cross-Reference to Related Patent Applications

[0003] This patent application claims priority of the Italian patent application No. 102024000003541 filed on 20 February 2024, the content of which is incorporated by reference herein.

[0004] Technical Field

[0005] The present invention relates to a checking assembly and method for checking the outline of a surface of an object.

[0006] In particular, the present invention relates to checking of an object with a reduced thickness, and it has an advantageous application in checking a windscreen for a vehicle, to which the following description will make explicit reference, without however losing generality.

[0007] Prior Art

[0008] Conventionally, the outline of a windscreen is checked by means of a frame which supports a plurality of contact sensors which, at predetermined checking points, project overhanging from the frame; in use, the windscreen is brought close to the frame or is supported on it, and, at the various checking points any divergence is measured which exists between the actual outline of the windscreen and the ideal (or nominal) outline. However, this solution is particularly cumbersome and inflexible, since, for each different model of windscreen, it is necessary to configure the sensors and place them appropriately in contact on a corresponding frame. In addition, it is normally necessary to calibrate or “reset” the contact sensors, at least before carrying out the measuring operations and after a certain number of measurements carried out, and for this purpose, use is made of a glass or sample part, which, at least at the checking points, has the nominal outline of the windscreen to be checked. In order to carry out the calibration, the sample part must be periodically loaded on / unloaded from the frame, with consequent increases in the times taken, and a need to provide storage and undertake corresponding movements.

[0009] Other known solutions involve the use of a robotic arm which moves a contactless sensor of the optical type; in use, the robotic arm moves the sensor to a series of predetermined checking points, at each of which the sensor detects without contact the position of the surfaces of the windscreen (or, more generally, at least one surface of the windscreen). This solution provides great advantages in terms of size and flexibility, since, even if the frame which supports the part to be checked is in general different for each different windscreen, the same sensor can check an extensive range of windscreens without needing to use multiple sensors, or needing to position them on each occasion according to an appropriate different configuration. However, as far as the calibration is concerned, this solution also requires the use of a sample part, which must be periodically loaded on the frame and unloaded therefrom, with the aforementioned disadvantages. In addition to the error made by the sensor, there is the positioning error made by the robotic arm, and this limits the precision of measuring which can be obtained.

[0010] Description of the Invention

[0011] The objective of the present invention is to provide a checking assembly and method for checking the outline of a surface of an object which makes it possible to carry out very precise measurements, and at the same time is easy and economical to produce.

[0012] According to the present invention, a checking assembly and method for checking the outline of the surface of an object are provided as claimed in the appended claims.

[0013] The claims describe preferred embodiments of the present invention forming an integral part of the present description.

[0014] Brief Description of the Drawings

[0015] The present invention will now be described with reference to the appended drawings, which illustrate some non-limiting examples thereof, in which:

[0016] • figure 1 is a schematic view of a checking assembly for checking the outline of a surface of an object, produced in accordance with the present invention;

[0017] • figures 2 and 3 are two schematic views of a measuring head of the checking assembly of figure 1 during measurement of the outline of the object;

[0018] • figures 4 and 5 are schematic views of two different embodiments of the measuring head of figures 2 and 3; and

[0019] • figure 6 is a schematic view of a different embodiment of the measuring head of figure 4. Preferred Embodiments of the Invention

[0020] In figure 1 , the reference numeral 1 indicates as a whole a checking assembly for checking the outline of (at least) one outer surface 2’ of an object 2 having a reduced thickness, and in particular a windscreen, which has extensive areas of transparency.

[0021] The checking assembly 1 comprises a support 3 which is configured to support and define the position of the object 2 to be checked, i.e. to reference it in a known and predetermined position in which the outer surface 2’ of the object 2 is facing upwards.

[0022] The checking assembly 1 comprises a reference element 4 which is placed in a fixed position in relation to the support 3 (i.e. it cannot carry out displacements in relation to the support 3), it is preferably integral therewith, and defines a reference surface 4’ which is placed in a position. According to a preferred embodiment, the checking assembly 1 comprises a single reference element 4 which has a surface 4’ substantially with the same extent as the surface 2’ of the object 2. According to a preferred embodiment, the reference element 4 is opaque, i.e. it has a coefficient of transparency of zero, and therefore it does not have light radiations passing through it; in particular, the reference element 4 is made of metal material (and can therefore be detected by capacitive or inductive sensors). According to a possible embodiment, the reference surface 4’ reproduces at least partly a nominal form of the outer surface of the object 2 (i.e. the outline of the reference element 4 represents the ideal or desired outline of the object 2 apart from a determined offset, with a known law, along the line normal to each point of the surface). In a different embodiment, the reference element 4 is constituted by different parts which constitute the reference surface 4’, reproducing at least partly the nominal form of areas to be checked of the outer surface 2’ of the object 2 (apart from a determined offset). According to a preferred embodiment, shown in figure 1 , the reference element 4 is placed such that the object 2 is superimposed thereon. In a different form, not shown in the figures, the reference element 4, or at least part of the reference surface 4’ defined by it, is not covered by the object 2.

[0023] The checking assembly 1 also comprises an automatic displacement system 5 which is configured to support, and give rise to displacements of, a measuring head 6 on the outer surface 2’ of the object 2.

[0024] According to a preferred embodiment, herein described and illustrated, the automatic displacement system 5 is a robotic arm 5, for example an anthropomorphic robot.

[0025] More specifically, in the embodiment illustrated in the attached figures, the measuring head 6 is secured on a gripper of the robotic arm 5, such that the robotic arm 5 can give rise to displacements of the measuring head 6 in space in order to follow the outer surface 2’ of the object 2. The measuring head 6 is configured to detect (at each acquisition, typically during the displacements to which the robotic arm 5 gives rise) the position in space of a point P1 (illustrated in figures 2-5) of the surface 2’ of the object 2, and the position in space of a corresponding point P2 (illustrated in figures 2 and 5) or P2’ (illustrated in figures 3 and 4) of the reference surface 4’, and to emit corresponding signals.

[0026] In particular, in the embodiment illustrated in the attached figures, the robotic arm 5 can displace the measuring head 6 by means of translations and rotations with six degrees of freedom.

[0027] Finally, the checking assembly 1 comprises a processing unit 7 which is connected to the measuring head 6, in a manner which in itself is known and is not shown in figure

[0028] 1 , and is configured to check, on the basis of the signals emitted by the measuring head 6, the outline of the outer surface 2’ of the object 2, i.e. to check that the outer surface 2’ of the object 2 has the nominal form (to within the tolerance margins specified). In particular, the processing unit 7 is configured to check the outline of the outer surface 2’ of the object 2, according to the position in space of the point P1 of the surface 2’ of the object 2, and the position in space of the corresponding point P2 (or P2’) of the reference surface 4’. In use, the positions in space are detected of a plurality of points P1 of the outer surface 2’ of the object 2, and of a plurality of corresponding points P2 (or P2’) of the reference surface 4’, such that the processing unit 7 checks the outline of the outer surface 2’ of the object 2 at all the points P1 at which the acquisition has been carried out.

[0029] As illustrated in figure 1 , and as illustrated better in figures 2-6, the reference element 4 is placed such that the reference surface 4’ is on the side opposite the object 2 in relation to the measuring head 6, such that the measuring head 6 simultaneously frames the reference surface 4’ and the surface 2’ of the object 2, which object is for example superimposed on the reference element 4. In this case, the measuring head 6 frames both the surface 2’ of the object 2 and the reference surface 4’ through the object 2 with a reduced thickness. The measuring head 6 is configured to detect (at each acquisition, and typically during the displacements caused by the robotic arm 5) simultaneously both the position in space of the point P1 of the surface 2’ of the object

[0030] 2, and the position in space of a corresponding point P2 (or P2’) of the reference surface According to a preferred embodiment, the processing unit 7 determines a difference between the position in space of the point P1 belonging to the outer surface 2’ of the object 2, and the position in space of the corresponding point P2 (or P2’) of the reference surface 4’, thus determining the distance between the point P1 belonging to the outer surface 2’ of the object 2, and the corresponding point P2 (or P2’) belonging to the reference surface 4’. In particular, the measuring head 6 is configured to measure simultaneously a distance Z1 along its own measurement axis Z, between the measuring head 6 and the point P1 of the surface 2’ of the object 2, and a distance Z2 between the measuring head 6 and the corresponding point P2 (or P2’) of the reference surface 4’. Preferably, and as illustrated in figures 2-5, the measurement axis Z has an orientation substantially perpendicular to the surface 2’ of the object 2 at the point P1 , but it can have a different angle of orientation, at the point P1 , in relation to this surface 2’ of the object 2. The distance Z2 is preferably, but not necessarily, measured parallel to the distance Z1 , as illustrated in figures 2-5. Then, the control unit 7 calculates the difference between the distance Z2 and the distance Z1 , in order to determine the distance between the two points P1 and P2 (or P2’), and compares the distance between the two points P1 and P2 (or P2’) with a reference value known for example because it is certified, which value can be constant along the entire extent of the reference surface 4’, or can be variable along the extent of the reference surface 4’; the difference between the distance between the two points P1 and P2 (or P2’) and the reference value indicates the divergence of the form of the outer surface 2’ of the object 2 from the nominal form (optionally represented by the reference surface 4’ of the reference element 4).

[0031] The measuring head 6 comprises at least one contactless sensor, and, in particular, as illustrated in figures 2, 3 and 4, the measuring head 6 comprises two contactless sensors 8 and 9, which are placed at a determined distance from one another, and are both secured on a rigid support 10 which is fitted on one end of the robotic arm 5, in particular on the gripper of the robotic arm 5.

[0032] According to a preferred embodiment, the rigid support 10 is fitted on the robotic arm 5 in order to rotate around an axis of rotation 1 1 (coinciding with the axis of rotation of the gripper of the robotic arm 5, as illustrated in figure 1 ).

[0033] In the particular embodiment shown schematically in figures 2-4, the sensor 8 is fitted coaxially in relation to the axis of rotation 11 , and the sensor 9 is fitted at the determined distance from the axis of rotation 11 ; by means of this particular arrangement, which is however not necessarily present in a checking assembly according to the present invention, the rotation of the support 10 around the axis of rotation 1 1 gives rise to a rotation around itself of the sensor 8, without actual displacement (translation) of the sensor 8, and on the other hand gives rise to displacement of the sensor 9. The rotation of the support 10 around the axis 1 1 of rotation makes it possible to vary the position of the sensor 9 in relation to the sensor 8, such that the measuring head 6 succeeds in framing simultaneously the outer surface 2’ of the object 2, and the reference surface 4’ at the points P1 and respectively P2 (or P2’). In particular, in the case illustrated in figure 1 , where the object 2 is superimposed on the reference surface 4’ of the reference element 4, when the sensor 8 is in the vicinity of an edge of the object 2 (i.e. an edge of the reference element 4), it is always possible to position the sensor 9 further in the interior than the sensor 8, such that the sensor 9 is in the interior of the object 2 (i.e. in the interior of the reference element 4). If however the reference surface 4’ at the point P2 (or P2’) is not covered by the object 2 (for example the reference surface 4’ projects in relation to the edge of the object 2), the sensor 9 will be able to be positioned appropriately on the exterior of the object 2.

[0034] According to an embodiment illustrated in figures 2 and 3, the sensor 8 is configured to detect at each acquisition the position in space of the point P1 of the outer surface 2’ of the object 2, and, when possible, the position in space of the corresponding point P2 of the reference surface 4’. In other words, the contactless sensor 8 is used to detect at each acquisition also the position in space of the point P2 of the reference surface 4’, when the sensor 8 succeeds in “seeing” also the point P2 of the reference surface 4’ through the transparency of the object 2 with reduced thickness (as illustrated in figure 2).

[0035] However, in some situations, the sensor 8 does not succeed in “seeing” also the point P2 of the reference surface 4’, since in some areas the object 2 is not transparent, because of the presence for example of screen printing 12 (as illustrated in figure 3); in this case, the sensor 8 can not detect at each acquisition also the position in space of the point P2 of the reference surface 4’, and therefore the position in space, in this case of the point P2’ of the reference surface 4’, is detected by the contactless sensor 9 (which replaces the sensor 8 for this task only when necessary). In other words, the contactless sensor 9 is used to detect the position of the point P2’ of the reference surface 4’ only when the contactless sensor 8 cannot detect at each acquisition the position in space of the corresponding point P2 of the reference surface 4’. In other words, when possible, the sensor 8 is used to detect at each acquisition the position in space of both the points P1 and P2, whereas, when the sensor 8 cannot detect the position in space of the corresponding point P2 of the reference surface 4’, the position in space of the corresponding point P2’ of the reference surface 4’ is detected by the sensor 9.

[0036] According to a preferred embodiment, the sensor 8 is of the optical type, for example of the chromatic confocal, or interferometric or laser type. In this respect, it is important to note that, thanks to the transparency of the object 2 with reduced thickness, the sensor 8 can be used to detect at each acquisition only the position in space of the point P1 of the outer surface 2’ of the object 2, or the sensor 8 can be used to detect both the position in space of the point P1 of the outer surface 2’ of the object 2, or a similar point of an inner surface of the object 2.

[0037] The sensor 8 can also be used to determine the thickness of the object 2 in a manner which in itself is known.

[0038] According to a preferred embodiment, the contactless sensor 9 is also of the optical type, for example of the chromatic confocal or interferometric or laser type, and can therefore see the reference surface 4’ only in the areas in which the object 2 is transparent (as illustrated in figures 2 and 3).

[0039] According to an alternative embodiment, the contactless sensor 9 is not of the optical type, and is for example a sensor of the inductive or capacitive type; in this embodiment, the sensor 9 can detect the reference surface 4’ also in the areas in which the object 2 is not transparent, for example because of the presence of screen printing 12 (as illustrated in figure 4).

[0040] The sensor 9 can be of the optical type when the object 2 with reduced thickness has extensive portions of transparency (such as a windscreen which generally is opaque only in peripheral areas with a limited extent), which allow the sensor 9 to see the reference surface 4’ through the transparency of the object 2. When the object 2 is completely opaque (for example a panel of coloured plastic material or a completely screen-printed glass panel) or prevalently opaque, the sensor 9 must be contactless but not of the optical type, for example of the inductive or capacitive type, in order to be able to detect the reference element 4 also in the areas in which the object 2 is not transparent (as illustrated in figure 4).

[0041] In the embodiment illustrated in figure 4, the object 2 which is being examined is completely or prevalently opaque, and therefore the contactless sensor 8 is configured (it is used) to detect at each acquisition only the position in space of the point P1 of the surface 2’ of the object 2, and the sensor 9 is configured (it is used) to detect in the same acquisition and typically simultaneously, only the position in space of the corresponding point P2’ of the reference surface 4’. It will be appreciated that, in the embodiment illustrated in figure 4, only the contactless sensor 8 can be of the optical type, whereas the contactless sensor 9 must be of a different type, as previously stated.

[0042] According to a preferred embodiment, the sensor 9 is an inductive sensor.

[0043] In the embodiment illustrated in figure 4, sensors 8 and 9 are both secured on the rigid support 10, which is fitted on the end of the robotic arm 5, and the inductive sensor 9 is placed at a determined distance from the optical sensor 8.

[0044] According to a different embodiment illustrated in figure 6, the sensors 8 and 9 are both secured on the rigid support 10, which is fitted on the end of the robotic arm 5, and the inductive sensor 9 is an inductive ring sensor which is fitted coaxially in relation to the sensor 8 (figure 6 shows a sectional view of the inductive ring sensor 9).

[0045] In other words, the inductive sensor 9 is of annular shape and the optical sensor 8 is positioned in the central opening of the inductive sensor 9 in such a way that the optical axis of the optical sensor 8 and the magnetic field vector of the inductive sensor 9 coincides substantially.

[0046] The embodiment illustrated in figure 6 is particularly advantageous: as the sensors 8 and 9 are coaxial, errors in the measurement, due for example to Abbe error, are avoided. Moreover, the overall size of the measuring head 6 is reduced remarkably.

[0047] According to a preferred embodiment, when the measuring head 6 comprises sensors of different types, for example an optical sensor 8 and an inductive sensor 9 as described with reference to the embodiments of figures 4 and 6, a linearization of the inductive sensor 9 can be performed.

[0048] The sensor linearization is performed when the checking assembly is assembled for the first time, before checking the outline of the outer surface 2’ of the object 2, and can be repeated periodically.

[0049] The sensor linearization is carried out with respect to the reference element 4 when the measuring head 6 is in a checking position with respect to the object 2.

[0050] Unlike the known techniques providing that the linearization of the inductive sensor is carried out with respect to the displacement system of the sensor, according to the preferred embodiment of the present invention the linearization is carried out with respect to the optical sensor 8.

[0051] In other words, a linearization of the measuring range of the inductive sensor 9 is carried out using the optical sensor 8.

[0052] To carry out the sensor linearization the measuring head 6 is positioned in such a way that the optical sensor 8 and the inductive sensor 9 are coaxial and perpendicular to the reference surface 4’. More specifically, the optical axis of the sensor 8 and the magnetic field vector of the inductive sensor 9 are coaxial and perpendicular to the reference surface 4’.

[0053] After positioning the measuring head 6, an area of the object 2 that is included in the measuring range of both the optical sensor 8 and the inductive sensor 9 is identified, that is an area of the object 2 within the measuring range of both the sensors 8 and 9. The identified area corresponds to the portion of the object 2 at which the measuring ranges of the sensors 8 and 9 intersect. In other words, an area of the object 2 is identified at which both the optical sensor 8 and the inductive sensor 9 can perform a measurement.

[0054] A linearization function of the measuring range of the inductive sensor 9 is obtained by measuring distance values between the optical sensor 8 and the reference surface 4’ at the identified area of the object 2, and relating these distance values, in a manner which in itself is known, with distance values measured between the inductive sensor 9 and the reference surface 4’ at the same points of the identified area of the object 2.

[0055] Such linearization function can be applied to the measurement of further points of the reference surface 4’ provided that the reference surface 4’ has the same curvature at such points.

[0056] The above described sensor linearization allows correcting possible offsets in the distance measurement between the two sensors, due to the features of the support to which the sensors are secured, and also a possible non linearity of the response of the inductive sensor caused by the specific reference surface.

[0057] This applies where the identified area of the object 2 lies in a transparent portion of the object 2, that is the points of the reference surface 4’ with respect to which the sensor linearization is carried out lie in areas in which the object 2 is transparent (for example areas without screen printing) and the optical sensor 8 “sees” the reference surface 4’.

[0058] Where the surface 2’ of the object 2 is at least partly not transparent, that is the object 2 comprises opaque areas, because of the presence for example of screen printing, or is completely not transparent, and the area of the object 2 with respect to which the sensor linearization is carried out lies in not transparent areas of the object 2, the above described sensor linearization comprises an initial zeroing phase.

[0059] As the optical sensor 8 cannot “see” the reference surface 4’ of the reference element 4 at portions of the surface 2’ of the object 2 which are not transparent, it is necessary to correct possible offsets in the distance measurement between the sensors 8 and 9 using an external reference sample.

[0060] The reference sample has to be made of the same material as the reference element 4 and has to be planar, that is the surface of the reference sample facing the sensors 8 and 9 must be plane.

[0061] The zeroing phase provides for relating, in a manner which in itself is known, the distance values detected by each sensor 8 and 9 with respect to the plane surface of the reference sample at a plurality of positions of the robotic arm.

[0062] When the initial zeroing phase is completed, the sensor linearization is performed as described above by measuring in this case distance values between the optical sensor 8 and points of the surface 2’ of the object 2 lying in the identified area of the object 2.

[0063] The zeroing phase is carried out when the checking assembly is assembled for the first time and may be repeated periodically.

[0064] In the embodiments described above and illustrated in figures 4 ad 6, the optical sensor 8 is preferably of the chromatic confocal type.

[0065] According to a different embodiment illustrated in figure 5, the measuring head 6 comprises only the sensor 8 (i.e. it comprises a single contactless sensor 8), which is configured to detect at each acquisition, typically during the displacements to which the robotic arm 5 gives rise, both the position in space of the point P1 of the surface 2’ of the object 2, and the position in space of the corresponding point P2 of the reference surface 4’. A single sensor 8 of the optical type can be used when an object 2 with reduced thickness is being examined which has extensive portions of transparency (such as a windscreen which is generally opaque only in peripheral areas with a limited extent), thus allowing the sensor 8 to see the reference surface 4’ of the reference element 4 through the transparency of the object 2. In this case, in a method for checking the outline of the surface 2’ of the transparent object 2, the position of the points P2 of the reference surface 4’ is detected, through the reduced thickness of the object, simultaneously with the position of the corresponding points P1 of the surface 2’ of the object 2 during the displacements on the surface 2’ of the object 2. In order to implement this method, the contactless sensor 8 is preferably of the chromatic confocal type. If the object 2 is not sufficiently transparent, a single sensor 8 can be used only if it is a contactless sensor of a different type, which can detect a plurality of reflections in sequence, for example by means of ultrasound.

[0066] When a measuring head 6 is used comprising only the contactless sensor 8, in the limited parts of the object 2 which are not transparent (for example at the lateral screen printing of a windscreen), the position in space of the point P1 of the surface 2’ of the object 2 is detected directly (i.e. by means of a direct measurement), whereas the position in space of the corresponding point P2 of the reference surface 4’ is obtained by interpolation or extrapolation of the positions in space of a series of points of the reference surface 4’ placed in the vicinity of the point P2, and already previously acquired or detected by displacing the measuring head 6 around the point P1 (and generally placed at areas of transparency of the object 2, but also, optionally, on the exterior of the object 2). In other words, in this embodiment, in some acquisitions the position in space of the point P2 of the reference surface 4’ is detected directly through the transparency of the object 2, whereas in other acquisitions, the position in space of the point P2 of the reference surface 4’ is obtained indirectly by means of interpolation or extrapolation of the positions in space of a series of points of the reference surfaces 4’ placed in the vicinity of the point P2, and already previously acquired, or detected by displacing the measuring head 6 around the point P1 .

[0067] In other words, the processing unit 7 is configured to detect directly (when possible, i.e. at the transparent parts of the object 2 with reduced thickness) the position in space of the corresponding point P2 of the reference surface 4’, or to obtain (at non-transparent parts of the object 2) the position in space of the corresponding point P2 of the reference surface 4’, on the basis of an interpolation or extrapolation of the positions in space of other points of the reference surface 4’ detected directly by the contactless sensor 8.

[0068] In the embodiment illustrated in the appended figures, the object 2 is a windscreen, but according to other embodiments, the checking assembly 1 can check the outline of a surface 2’ of any other object 2 with reduced thickness which can be prevalently (completely) transparent or prevalently (completely) opaque.

[0069] In the above-described embodiments, the sensor 8 is generally of the optical type, but a contactless sensor 8 of another type can also be used.

[0070] In the embodiments illustrated in the attached figures and described above, the displacement system 5 comprises an anthropomorphic robotic arm.

[0071] The robotic arm can also be of different types, for example a Cartesian robot (or linear robot), a SCARA robot (“ Selective Compliance Assembly Robot Arm”), a parallel robot or others.

[0072] If, to perform the measurement, it is necessary to displace the measuring head 6 by means of translations and / or rotations in addition to those permitted by the nature of the robotic arm, it is possible to equip the robotic arm with additional mechanical elements, for example a rotating joint, to integrate the missing degrees of freedom.

[0073] As an alternative, when the checking assembly is incorporated in a machine tool, for example a computerized numerical control machine, the spindle of the machine tool can move and support the measuring head 6 thus implementing the displacement system 5.

[0074] The above-described checking assembly 1 has numerous advantages.

[0075] Firstly, the above-described checking assembly 1 makes it possible to check the outline of a surface 2’ of an object 2 with a very high level of precision, since the positions of the points P1 and P2 (or P2’) are (at least in most acquisitions) detected simultaneously, without the need to give rise to movements of the robotic arm 5 in order to carry out calibration operations. By comparing the position of the point P1 of the surface 2’ of the object 2 with the position of the corresponding point P2 (or P2’) of the reference surface 4’, it is thus possible to eliminate errors introduced by displacements to which the measuring head 6 can be subjected between the detection of a reference point (in order to carry out a calibration), and a corresponding point of the surface of the object checked, which displacements are obtained for example by means of the movement of the robotic arm 5 (or the positioning error introduced by the robotic arm 5 or by other movements of the measuring head 6 is completely compensated for).

[0076] In addition, the above-described checking assembly 1 provides great advantages in terms of dimensions and flexibility, since the checking assembly 1 can check an extensive range of objects 2, by modifying only the mechanical support part of the object 2, and without any hardware modification.

[0077] Finally, the above-described checking assembly 1 is simple and economical to produce, since it involves the use of components which are commercially easily obtainable, with relatively low costs.

Claims

CLAIMS1 . Checking assembly (1) for checking the outline of a surface (2’) of an object (2) having a reduced thickness, comprising: a support (3) configured to support and define the position of the object (2) to be checked; a measuring head (6) comprising at least one contactless sensor (8, 9); at least one reference element (4) defining a reference surface (4’) adapted to be placed in a known position; a displacement system (5) configured to support the measuring head (6) and cause displacements of the measuring head (6) on the surface (2’) of the object (2), the measuring head (6) being configured to detect the position of a point (P1 ) of the surface (2’) of the object (2) and the position of a corresponding point (P2; P2’) of the reference surface (4’) and emit relevant signals; and a processing unit (7) connected to the measuring head (6) and configured to check, based on the signals emitted by the measuring head (6), the outline of the surface (2’) of the object (2) as a function of the position of the point (P1) of the surface (2’) of the object (2) and of the position of the corresponding point (P2; P2’) of the reference surface (4’); the checking assembly (1 ) being characterized in that: the reference element (4) is placed in a fixed position in relation to the support(3), and the measuring head (6) is adapted to simultaneously frame the reference surface (4’) and the surface (2’) of the object (2) to be checked to detect both the position of the point (P1) of the surface (2’) of the object (2) and the position of the corresponding point (P2; P2’) of the reference surface (4’).

2. Checking assembly (1 ) according to claim 1 , wherein the measuring head (6) is configured to detect simultaneously both the position of the point (P1) of the surface (2’) of the object (2) and the position of the corresponding point (P2; P2’) of the reference surface (4’).

3. Checking assembly (1) according to claim 1 or claim 2, wherein the reference element(4) is placed in such a way that the reference surface (4’) is on the opposite side of the object (2) with respect to the measuring head (6).

4. Checking assembly (1 ) according to any one of claims 1 to 3, wherein the reference surface (4’) reproduces at least partly a nominal form of the surface (2’) of the object (2).

5. Checking assembly (1 ) according to any one of claims 1 to 3, wherein a single reference element (4) is provided, the reference surface (4’) having substantially the same extent as the surface (2’) of the object (2).

6. Checking assembly (1 ) according to any one of claims 1 to 5, wherein the processing unit (7) is configured to: measure, based on the signals emitted by the measuring head (6), a first distance (Z1) between the measuring head (6) and the point (P1) of the surface (2’) of the object (2) and a second distance (Z2) between the measuring head (6) and the corresponding point (P2) of the reference surface (4’); calculate a difference between the second distance (Z2) and the first distance (Z1 ); and check the outline of the surface (2’) of the object (2) as a function of said difference.

7. Checking assembly (1 ) according to any one of claims 1 to 6 for checking an object (2) that is at least partly transparent, wherein said at least one contactless sensor (8) is configured to detect both the position of the point (P1) of the surface (2’) of the object (2) and the position of the corresponding point (P2) of the reference surface (4’).

8. Checking assembly (1 ) according to claim 7, wherein the processing unit (7) is configured to directly detect the position of the corresponding point (P2) of the reference surface (4’), or to obtain the position of the corresponding point (P2) of the reference surface (4’) by interpolation or extrapolation of the positions of other points of the reference surface (4’) directly detected by the sensor (8).

9. Checking assembly (1 ) according to any one of claims 1 to 6, wherein the measuring head (6) comprises: said at least one contactless sensor (8), or first sensor, configured to detect the position of the point (P 1 ) of the surface (2’) of the object (2) and, whenever possible, the position of the corresponding point (P2) of the reference surface (4’); and a second contactless sensor (9) configured to detect only the position of the corresponding point (P2’) of the reference surface (4’) when the first sensor (8) is not able to detect the position of the corresponding point (P2) of the reference surface (4’).

10. Checking assembly (1 ) according to claim 9, wherein said second sensor (9) is an inductive sensor.1 1. Checking assembly (1 ) according to claim 10, wherein said second inductive sensor (9) is of annular shape and is fitted coaxially in relation to said first sensor (8).

12. Checking assembly (1 ) according to claim 9 or claim 10, wherein the measuring head (6) comprises a rigid support (10) on which said first and second contactless sensors (8, 9) are secured and placed at a determined distance from one another.

13. Checking assembly (1 ) according to any one of the preceding claims, wherein said at least one contactless sensor (8, 9) is of the optical type.

14. Checking assembly (1 ) according claim 13, wherein said at least one contactless sensor (8, 9) is of the chromatic confocal type.

15. Checking assembly (1 ) according to any one of the preceding claims, wherein said displacement system (5) is a robotic arm.

16. Checking method for checking the outline of a surface (2’) of an object (2) with reduced thickness, the method comprising the following steps: placing the object (2) on a support (3) configured to support and define the position of the object (2); causing displacements of the measuring head (6) on the surface (2’) of the object (2) by means of a displacement system (5); detecting or obtaining, based on signals provided by the measuring head (6) during said displacements, the position of points (P1 ) of the surface (2’) of the object (2) and the position of corresponding points (P2; P2’) of a reference surface (4’) placed in a known position and defined by a reference element (4); checking, by means of a processing unit (7), the outline of the surface (2’) of the object (2) as a function of the position of the points (P1) of the surface (2’) of the object (2) and of the position of the corresponding points (P2; P2’) of the reference surface (4’); the reference element (4) being arranged in such away that the reference surface (4’) is on the opposite side of the object (2) with respect to the measuring head (6), the measuring head (6) simultaneously framing the reference surface (4’) and the surface (2’) of the object (2).

17. Checking method according to claim 16 for checking the outline of the surface (2’) of a transparent object (2) by means of a measuring head (6) comprising a single contactless sensor (8) of the confocal chromatic type, the position of the points (P2) of the reference surface (4’) being detected, through the reduced thickness of the transparent object (2), simultaneously with the position of the corresponding points (P1 ) of the surface (2’) of the transparent object (2) during said displacements of the measuring head (6) on the surface (2’) of the transparent object (2).

18. Checking method according to claim 16 for checking the outline of the surface (2’) of an object (2) that is at least partly not transparent by means of a measuring head (6) comprising a first contactless sensor (8) configured to detect the position of the point (P1) of the surface (2’) of the object (2) and a second contactless sensor (9) configured to detect the position of the corresponding point (P2’) of the reference surface (4’) at not transparent portions of the object (2).

19. Checking method according to claim 18, comprising the step of performing a linearization of said second sensor (9) with respect to the reference element (4) when the measuring head (6) is in a checking position with respect to the object (2).

20. Checking method according to claim 19, wherein the linearization of the second sensor (9) is carried out with respect to the first sensor (8).

21. Checking method according to claim 20, wherein the linearization of the second sensor (9) comprises: positioning the measuring head (6) in such a way that that the first sensor (8) and the second sensor (9) are coaxial and perpendicular to the reference surface (4’); identifying an area of the object (2) that is within the measuring range of both the first sensor (8) and the second sensor (9); measuring, at the identified area of the object (2), distance values between the first sensor (8) and the reference surface (4’) if said area of the object (2) lies in a transparent portion of the object (2), or distance values between the first sensor (8) and the surface (2’) of the object (2) if said area of the object (2) lies in a not transparent portion of the object (2); measuring distance values between the second sensor (9) and the reference surface (4’) at said area of the object (2); relating the distance values measured in relation to the first sensor (8) and the second sensor (9); and obtaining a linearization function of the measuring range of the second sensor (9).

22. Checking method according to any one of claims 19 to 21 , wherein the linearization comprises an initial zeroing phase with respect to a reference sample, said reference sample having a plane surface and being made of the same material as the reference element (4).

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