ANDORLINI, Giuseppe (Via Masaccio, 230, Firenze, I-50132, IT)
| Claims 1. Device for verifying and measuring the thickness of structures or manufactured articles (10) comprising: an ultrasound generating probe (34) designed to send ultrasound toward a surface (13) of the article to be verified and measured and for capturing the response signal and transmitting it to a unit for managing and processing the response signal; a support (16) having an axial chamber (20) in which the probe is slidable; first elastic compensation means (42) arranged between said probe (34) and said support (16); means (54, 52, 28, 58, 60) for directing a flow of auxiliary coupling fluid into a containing chamber (64) between said probe and said surface of the article, characterized in that it comprises a sleeve (22) arranged between said probe (34) and said support (16), said sleeve being slidable in said axial chamber (20) for protruding from the support (16) with its free end and forming said containing chamber (64), said probe (34) being slidable in axial direction inside the sleeve (22) and second elastic compensation means (44) being arranged between said probe (34) and said slidable sleeve (22). 2. Thickness verification and measurement device according to Claim 1, characterized in that first and second elastic compensation means (42, 44) are designed to ensure that the surface of the probe is in contact with the said surface of the article via a film of the coupling fluid, said compensation means being opposed to each other and acting simultaneously with means for controlled displacement of said probe for approaching to the surface (13) to be verified and measured, said probe making contact with said surface with interposed film of fluid and generating an resilient contact force able to maintain constant (force/position) contact conditions. 3. Thickness verification and measurement device according to Claim 1, characterized in that it comprises means (54, 52, 28, 58, 60) for directing a flow of cleaning liquid against at least one predetermined area of the surface where the measurement must be performed. 4. Thickness verification and measurement device according to Claim 1, characterized in that the sleeve (22) is slidable over a few tens of millimetres along its axis and the probe is housed slidably over a few millimetres inside said sleeve. 5. Thickness verification and measurement device according to Claim 1, characterized in that said probe is fixed to a bush (36) and said sleeve (22) has at the protruding free end a lip seal (30, 32) which comes into contact with said surface (13) when said probe reaches a measuring position. 6. Thickness verification and measurement device according to Claim 5, characterized in that said first elastic means consist of first compression spring means (42) acting between an upper inner wall (46) of the chamber (20) of said support (16) and a upper end of said bush (36) and said second elastic compensation means (44) consist of second compression spring means (44) arranged between an lower end of said bush (36) and a second bush (50) fixed to the protruding free end of said sleeve (22) and having an axial hole with a diameter such as to allow axial sliding of said probe, said lip seal (30, 32) being fixed to said second bush (50). 7. Thickness verification and measurement device according to Claim 3, characterized in the said means for directing said first washing flow and said second flow of coupling fluid against said at least one area of said surface (13) coincide with each other and comprise ducts (52, 54) formed in said support (16), a cavity (28) formed between the facing surfaces of said support (16) and said sleeve (22), and ending ducts (58, 60) formed in said sleeve (22), said ending ducts (60) being oriented with a predetermined inclination so as to direct the flow of washing fluid or coupling liquid against the said area of said surface (13). 8. Thickness verification and measurement device according to Claim 1, characterized in that said probe (34) is connected by means of a cable (38) to ultrasound generating means positioned inside a management unit (40) which is integral with the support (16) and comprises both the ultrasound generating unit and a receiver/transmitter unit able to dialogue with the control system of the operating unit. 9. Thickness verification and measurement device according to Claim 1, characterized in that said support (16) is provided with connection means (18, 19) for mounting on the terminal end of an operating unit. 10. Thickness verification and measurement device according to Claim 9, characterized in said connection means (18, 19) consist of automatic gripping means for connection, respectively, to a chuck of a machine tool or to a robot gripper quick-change system. 11. Thickness verification and measurement device according to Claim 2, characterized in that said support (16) is provided with connection means (56, 57) for supplying the washing liquid and the coupling fluid onto the surface to be measured (13). 12. Thickness verification and measurement device according to Claim 11, characterized in said connection means for supplying the washing liquid and coupling fluid onto the surface to be measured (13) are quick-action connection means. 13. Thickness verification and measurement device according to the preceding claims, characterized in that said coupling fluid is the actual machining liquid. 14. Thickness verification and measurement device according to Claim 2, characterized in that said washing liquid is the actual machining liquid. 15. Method for verifying and automatically measuring the thickness of a manufactured article (10) by means of an ultrasound generating and receiver probe, in which said probe is moved towards and then brought into contact with a surface (13) of the article, said surface (13) being subject to the action of the ultrasounds emitted by said probe and the signals received by said probe are transmitted for processing to a management unit, in which during the approach movement of said probe, a jet of an auxiliary flux of fluid is directed against at least one area of said surface, and then a containing chamber is created between the probe and the surface for containing a coupling fluid with the thickness of the coupling fluid between the probe and the surface is gradually reduced by first and second opposed elastic means supporting the probe in the chamber in resilient manner. 16. Method according to Claim 15, in which said surface (13) is cleaned beforehand in said at least one area thereof by means of a jet of fluid or liquid. 17. Method according to Claim 15, in which said ultrasound probe is moved towards said surface (13) starting from a position, still at a distance from said surface, where means for directing against said area of said surface a flow of auxiliary fluid for coupling between the end of said probe and a predetermined area of said surface are activated, said probe being moved towards said surface until it comes into contact with it, from said position, while keeping active said means for directing said flow of auxiliary fluid so that said layer of auxiliary coupling fluid remains between said end of said probe and said area of said surface. 18. Method according to Claim 16, in which, during the approach movement of said ultrasound probe towards said surface (13), prior to said means for directing said flow of auxiliary coupling fluid, means for directing a flow of cleaning liquid against said area of said surface are activated. 19. Method according to Claim 16, in which said probe is associated with a support structure displaceable together with said probe between said positions and said means for directing the flow of fluid or liquid are formed in said support structure and can be connected to respective sources of said fluids or liquids. 20. Method according to Claim 18, in which, during the approach movement of said probe, while said flow of cleaning liquid is directed against said surface (13), said support structure performs a slow rotational movement. 21. Method according to Claim 20, in which said rotational movement is performed at a speed of between 1 and 10 revolutions per minute. 22. Method according to Claim 16, in which coupling fluid is supplied at a low pressure of between 1 and 3 bar. 23. Method according to Claim 18, in which said flow of cleaning fluid is supplied at a pressure of between 10 and 20 bar. 24. Method according to Claim 17, in which said support structure is mounted in the manner of a machining tool on the end of an operating unit and said first and second directing means are connected to the machining fluid ducts. 25. Method according to Claim 24, in which said operating unit is a machine for machining the surface whose thickness is to be measured and said ultrasound probe support structure is taken from and returned to the storage crib of said operating unit. 26. Method according to Claim 25, in which said operating unit is a machine tool for machining the surface whose thickness is to be measured and said ultrasound probe support structure is handled directly by the machining chuck and taken from and returned to the tool crib of said machine tool. 27. Method according to Claim 24, in which said chuck is displaced with a predetermined series of movements into different positions of said surface and the measurements performed in each position are transferred to a management unit comprising both ultrasound generating means and a receiver/transmitter unit. 28. Method according to Claim 25, in which said receiver/transmitter unit is designed to dialogue with the control system of the operating unit. 29. Method according to Claim 28, in which said control system of the operating unit is the numerical control system of a machine tool. 30. Method for verifying and automatically measuring the thickness of a manufactured article (10) by means of an ultrasound generating and receiver probe according to Claim 15, in which said probe, starting from a first position, moves towards the surface 13 to be measured, cleaning said surface by means of a jet of washing fluid and assuming a second position, and from said second position said probe moves towards and is then brought into contact with a surface (13) of the article, which is subject to the action of the ultrasounds emitted by said probe and the signals received by said probe are transmitted for processing to a management unit, characterized in that, during the approach movement of said probe towards said surface, a jet of an auxiliary liquid or fluid for coupling probe and surface is directed against at least one area of said surface so that, when the probe is in contact with the surface, a layer of said auxiliary liquid or fluid is created between the probe and the surface. |
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The present invention relates to the technology for measuring the thickness of structures during machining thereof, such as wing profile structures. More particularly, the present invention concerns a method and a device for measuring the thickness of structures made of compact and homogeneous material, by means of the same unit which performs machining thereof. In the remainder of this description reference will be made to the specific case of measuring the thickness of wing profiles, this reference being understood as being provided solely by way of a non-limiting example.
In order to produce a wing of an aeroplane it is required to manufacture the two wing profiles, i.e. the bottom profile and top profile (also called intrados and extrados), with a very high degree of machining precision. The manufacture of a wing profile requires a high degree of machining precision, both in order to obtain the thicknesses which ensure the required lightness of the profile together with the necessary structural strength of the sections, and in particular when forming the outer profile joining zones where any discontinuity in the joined surfaces would cause turbulence in the air flow streams and therefore serious problems in terms of both lift and resistance to forward movement of the aircraft itself.
At the end of machining the two wing profiles are joined together with other structural parts to form a wing to which the various components, such as the so- called flaps, are then added. In order to manufacture a wing profile which corresponds to the design specifications, it is required to verify already during the machining stage that any variation in the thickness of the walls in the verification zones defined remains within very small tolerances.
In order to achieve this, it is therefore required, before final machining of the surfaces, to measure the thickness at the various points of the profile so as to check that the machining is progressing correctly and, if necessary, take any corrective measures.
Machining of these profiles is performed mainly in two stages: a first stage during which the profile of the outer surface is formed, and a second stage during which the inner structural part is formed, followed by checking of the thicknesses and the joining surfaces.
During this second stage, for example, the workpiece is positioned on a jig which reproduces perfectly the outer profile (as shown in Fig. 1) and to which a vacuum is applied in order to generate a suction cup effect which locks the workpiece onto this surface.
Once the workpiece has been fixed on the jig, the machine tool starts machining of the inner part and, before performing the final machining operations, the verification measurements must be performed. Since the machined part adheres perfectly to its machining jig, in order to perform measurement of the thicknesses at the bottom of the profile it is not possible to use conventional mechanical feelers with a feeler arm, used for the measurements during the working cycle both on machine tools and on measuring machines, since it is not possible to access the rear of the surface to be measured, while using other surfaces of the jig as a reference point could result in unacceptable errors.
In fact, measurement of the thickness must always be performed in a direction perpendicular to the surface measured which, being constantly variable, does not ensure perfect adhesion to the jig support surface relative to which measurement must be performed. At present measurement is therefore performed manually by an operator using manual ultrasound thickness meters (thickness gauges), i.e. devices provided with an ultrasound generating probe able to emit and capture the response signal, and a management unit which acquires the data recorded. By means of the response signal it is possible to determine with great precision the thickness thereof. The operating principle of this type of thickness gauge is the same as that of the sonar: an ultrasonic sound pulse is emitted and the delay in the return echo is recorded; knowing the velocity of sound in the medium, it is possible to calculate the distance from the surface which reflected the sound pulse. In the specific case the thickness gauge detects the return echo generated by the surface opposite the point where the ultrasonic transducer has been positioned.
A critical aspect during use of the ultrasound thickness gauge is the definition of the velocity of sound in the material of the part to be measured. In fact each material has a specific sound propagation velocity (for metals this may range between 1500 and 6000 m/s). Errors in the definition of this velocity directly affect the measuring precision.
There exist, therefore, two ways of using the instrument:
• Determine in advance the sound propagation velocity (certified by the material supplier). In this case it is sufficient to set the instrument correctly.
• Carry out tests to calibrate the instrument on the part to be measured. In fact, having access to a free edge on the part, it is possible to adjust the instrument on it, after performing beforehand the measurement using a conventional instrument (e.g. a micrometer). Another critical aspect during use of the ultrasound thickness gauge is that correct readings may be carried out only on homogeneous thicknesses; the presence of layers of different material, interstices or blow holes generate false echoes and create reading errors. In order to obtain a reliable measurement, however, it is required to ensure perfect continuity of contact between probe and machined part, which contact may be adversely affected by the following factors: presence of machining waste, such as swarf, dust or the like; roughness of the workpiece which results in discontinuous contact between the surface of the probe and the surface of the workpiece; - curved form of the workpiece since, even if the probe is small in size, if the workpiece is curved (as in the machining of wing profiles) there necessarily exist points of the probe which remain separated from the surface of the workpiece. In the existing process, in order to overcome the first problem, it is obviously required to clean well the surface of the workpiece manually, while in the case of the second and third problems an auxiliary coupling substance, i.e. a liquid or gelatinous (gel-like) substance, is applied manually, this allowing continuous contact to be established between probe and workpiece to be measured, so as to ensure perfect transmission of the ultrasounds from the probe to the workpiece without altering the signal. In particular, the measuring device is composed as follows:
(i) a probe which transmits ultrasound signals and records their response signals;
(ii) a cable for connecting together probe and management unit, which must ensure a continuous connection so as not to alter the signal;
(iii) a management unit containing the ultrasound generating device, the acquisition unit which acquires the signals recorded by the probe and the unit for processing the signals and processing the recorded data. In order to perform measurement, the operator must therefore proceed manually as follows:
(a) firstly clean thoroughly the machined surface, removing the swarf and any other residue which may have been deposited on the workpiece, flushing it with water, an emulsion or other suitable substances; (b) after ensuring that the surface is properly cleaned, apply onto the surface to be measured the auxiliary substance which ensures continuity of contact;
(c) then perform actual measurement by placing the probe on the workpiece and checking that there is perfect contact;
(d) activate the ultrasound device which starts to emit the signal directed towards the surface of the workpiece and receive the response signal;
(e) then manually move the probe to other predetermined points in order to perform other measurements;
(f) after terminating the measuring operation at all the predetermined points, interrupt the measurement and transfer via cable the data recorded by the probe management unit to the numerical control system of the machine;
(g) compare the data recorded by the probe with the theoretical data and check whether there exists any deviation between the two types of data;
(h) in the event of any differences, the operator introduces into the working program the appropriate corrective values in order to resume machining of the workpiece and obtain final machining within the required tolerances.
From the above description it is clear that the entire verification and measurement operation is performed manually. This results in long operating times and consequently a not insignificant machine downtime, during which the numerical control machine is entirely unproductive and in particular the process may not be performed during an unsupervised cycle, namely without the intervention of the operator, this further complicating the process.
Intervention by a specialized operator is furthermore required, thereby increasing significantly the final cost of the part obtained. GB 1438935 discloses a truck device for ultrasonic thickness measuring, in which a coupling liquid is flowing from a bottle onto the surface to be measured. A worker drives the movement of the probe by hand against opposed action of a return spring. US 6341525 discloses an apparatus for ultrasonic testing having a probe to be pushed against a cylindrical surface to be tested with interposition of a coupling liquid. The apparatus is guided by groups of rollers for sticking to the cylindrical surface.
EP0523865 discloses a ultrasonic animal inspection device, in which a rubber boot surrounds the probe, sticking to the body surface and it is filled of coupling liquid. JP021100309 discloses a device in which a probe is pushed by spring against a surface to be measured, while a external nozzle sprays a cooling liquid on the measuring area.
DE4019865 discloses an arrangement for measuring the wall thickness or non- uniformity of rotating tubes, in which the ultrasonic probes are mounted into a support which is slidable in a radial chamber between an initial and a measurement position. Coupling liquid is supplied between the probes and the tube. The probe movement toward the operative position is caused, against a spring action, by the hydraulic pressure of the coupling liquid before it arrives in the space between the probe and the tube. Also such device is not satisfactory in the automatic control of the support of the probe against the surface and the thickness of the liquid cushion. A first object of the invention is therefore to automate completely - i.e. without the need for action by an operator - the process for measuring the thicknesses of a structure during machining thereof, in particular a wing profile. A second equally important object of the invention is to reduce the time required for verifying and measuring the thicknesses of a surface, achieving at the same time a reduction in the overall product manufacturing time.
These and other objects are achieved with the device and the method for verifying and measuring the thickness of a surface according to the present invention as defined in the claims.
The advantages which can be achieved with the present invention will emerge more clearly from the description which follows of a preferred embodiment, provided with reference to the drawings in which: Fig. 1 shows the semi-finished part fixed on the jig during a second stage in which the cross-section of the part to be obtained after machining is already shown; Fig. 2 shows the same part after completion of machining;
Fig. 3 shows an axially sectioned view of the verification and measurement device according to the present invention in a first operating condition;
Figs. 4 and 5 are views, similar to that of Fig. 3, showing the device according to the invention in two further operating conditions; and
Fig. 6 is a view, similar to that of Figures 3-5, of the device equipped with a different coupling member suitable for a manipulator unit or a robot. Fig. 1 shows an end cross-section 10 of the semi-finished article consisting of a wing half-profile, held in position on a jig 12 by means of a vacuum applied, in a manner not shown, to the surface 11 of the semi-finished article. In Figure 2 the reference number 13 indicates the inner surface of the semi-finished article, i.e. the surface which undergoes machining and on which measurement is performed.
If we now consider Fig. 3 the verification and measurement device according to the invention comprises a support 16, provided at its top end with a coupling member which, in the specific case for the sake of clarity of the illustration and for constructional reasons, has been shown as a truncated cone, denoted generically and overall by the reference number 18.
In this case the device according to the present invention may be gripped directly by the chuck of a machine tool, in particular of the machine intended for machining the semi-finished article. The support 16 has a tubular end-piece 17 forming a cylindrical inner chamber 20 which slidably houses a sleeve 22 (sliding travel of a few tens of millimetres), the outer surface of which sleeve has an inset part so as to define an annular cavity 28 between the outer wall 24 of the sleeve and the inner wall 26 of the tubular end- piece 17 of the support 16. A seal or sealing ring 30 which has a lip 32 for the purpose clarified subsequently is fixed to the free bottom end, protruding from the support, of the sleeve 22.
The cylindrical cavity of the sleeve 22 slidably houses a bush 36 which has, fixed thereto, an ultrasound probe (thickness gauge), denoted generally and in its entirety by the reference number 34, said probe being connected by means of a cable 38 to an ultrasound generating unit, not shown but also integrally mounted, together with a transceiver unit (also not shown), on the support 16.
A containing and measuring chamber 64 is created into the sleeve 22, between the probe and the surface to be measured. Since the wing profiles may also reach a length of several tens of metres and the cable for connecting together the probe and the probe management unit must be as short as possible and is not suitable for a mobile arrangement prone to repeated and frequent flexing (as in the case of the cables which travel inside the cable-housing guides of a machine tool) and since this cable must be continuous between probe and management unit, this latter unit must be positioned on the measuring device itself and it must be possible to transmit easily the data from this device to the numerical control system of the machine.
The reference number 40 is intended to indicate a management unit integral with the support 16 and comprising both the ultrasound generating unit and a receiver/transmitter unit, being able to dialogue with the numerical control system of the machine tool. The transceiver unit may be powered by means of a battery or by a direct power supply via the independent connection 41 situated alongside the gripping device. Sliding of the bush 36 together with the ultrasound probe 34 relative to the sleeve 22 is subject to the action of first and second elastic compensation means, which are indicated respectively by the reference numbers 42 and 44. Such elastic means are preferably formed by two compression spring means.
The spring 42 is a compression spring acting between the top end of the bush 36 and the top inner wall 46 of the chamber 20, so that it biases the bush 36 and, with it, the ultrasound probe towards the bottom end of the device.
The spring 44, which is also a compression spring, acts between the bottom end of the bush 36 and a contact surface 48 formed at the bottom end of the inner cavity of the sleeve 22 by a second bush 50 fixed to the bottom end of the sleeve 22 and provided with a lip seal 30. The rigidity of the springs 42 and 44 is designed so that, during the initial approach phase, the rigidity of the spring 44 is greater than that of the spring 44, so that the spring 44 is compressed by the spring 44 until the probe 34 is brought into contact with the surface 13 of the finished part 10, whereas, the instant the probe enters into contact with the surface 13, the rigidity of the spring 42 becomes greater than that of the spring 42 which, compressed by the spring 42, allows further forward movement of the body 16 keeping practically constant the force with which the probe 34 acts on the surface 13 of the part 10. Preferably the support 16 has a tubular projection 43 which is coaxial with the tubular end-piece 17 and the outer surface 45 of which acts as a guide for the top end spirals of the spring 42, so that the downwards translatory movement of the support 16 results in guided and controlled compression of the spring 42. Moreover, the axial hole 47 of the tubular projection 43 has the function of receiving and guiding the connection cable 38 and, preferably, the hole 47 is connected to a radial passage 39 for guiding the cable towards the ultrasound generation unit.
A plurality of ducts described in greater detail below have the function of connecting, respectively, a coupling fluid source and a washing liquid source to ducts 60 with a radial-like progression situated in the said second bush 50 and designed to supply the desired fluid below the bottom end of the ultrasound probe 34.
In connection with the present invention the term "coupling fluid" is understood as meaning a liquid or a fluid with gelatinous (gel-like) consistency which is preferably the machining fluid and which may be water, water emulsified with mineral, vegetable or animal oils (commonly used for machining fluids), cutting oils, or a non-water based fluid, if necessary with a controlled viscosity (ranging for example between 5,000 and 8,000 cSt). Since, in addition to the use of the coupling fluid according to the present invention, it is also envisaged washing the surface of the part whose thickness is to be measured, said washing being preferably carried out on a restricted area which surrounds the specific position where the thickness is measured, "washing liquid" is understood as indicating the liquid used during this step, which is preferably the machining fluid (especially in the case of a machine tool, the chuck of which is used as an operating unit for the measuring device), but may also be water or a water-based fluid (emulsion or solution as already previously specified). More specifically, the support 16 is provided with internal ducts 52, 54 and 56 which establish the connection between the annular cavity 28, formed between sleeve 22 and support 16, and the aforementioned fluid source.
In particular, depending on the type of fluid used or the particular mounting solution chosen (namely mounting of the device on the chuck of a machine tool or mounting via different gripping jaws, such as those of a robotized unit, on a different operating unit), the fluid supply duct may be inside the gripping cone of the device or on the outside of the latter, or also both solutions are possible.
Below the expression "operating unit" is also understood as meaning the chuck of the machine tool.
The chamber 28 also communicates via the ducts 58 with the aforementioned radial-like ducts 60, which are preferably formed with an inclination such as to direct the jets of coupling fluid and washing liquid into the zone of the machined part situated immediately below the ultrasound probe 34.
The through-holes 37 formed in the bush 36 allow evacuation, outside the body 16, of the excess coupling fluid during measurement, via the outlet hole 62 formed in the body 16.
Since, during programming of the machining cycle, periods are envisaged where the machining operation is interrupted and measurement of the thicknesses is performed, during these periods, in a preferred embodiment, the operating unit deposits the machining tool in the tool crib of the machine and engages with the measurement and verification device which will be calibrated beforehand to the sound propagation velocity in the material being machined.
The operating principle of the device is as follows: the operating unit, in accordance with a suitable program for measuring the part, positions the measurement and verification device in the vicinity (preferably at a distance varying between 10 mm and 40 mm depending on the type of surface, the material, etc.) of the point to be measured; the flow of high-pressure washing liquid (usually cooling emulsion used for machining the part at a pressure varying between 10 bar and 20 bar) is activated, said liquid passing through the ducts 56, 54, 52, the chamber 28 and the ducts 58 and 60 and flowing to the bottom end of the device, in order to perform cleaning of the machined surface; at the same time, the measurement and verification device, moved by the operating unit, continues its approach movement towards the surface at a low speed and with a slow rotational movement (1-10 rpm) so as to perform cleaning of the surface in the region of the measuring zone (see Fig. 3). the flow of high-pressure washing liquid is interrupted automatically when the measurement device is situated at a short distance - which may vary from 3 to 6 mm - from the surface of the part; at this point, rotation is interrupted and the flow of low-pressure coupling fluid, variable from 1 to 3 bar, is activated, and the measuring device resumes its approach movement in a direction perpendicular to the surface to be measured; the device moves towards the surface 13 of the part 10 until the lip 32 of the sealing ring 30 comes into contact with the surface of the part (see Fig. 4), said seal being designed to adapt to the geometrical form of the surface and forming with the enclosed surface a chamber for containing the coupling liquid, which is filled by the said liquid which continues to flow out of the holes 60 before the probe 34 comes into contact with the surface 13 of the part 10, so as to ensure an optimum continuous coupled condition of the probe and part during measurement; the measurement device continues its approach movement towards the part, compressing the seal 30 against the surface 13 of the part 10 by means of the lip 32 and, once the seal 30 has been compressed, the sleeve 22, in contact with the surface 13 of the part via the lip 32 of the seal 30, retracts a few millimetres inside the chamber 20, compressing the two springs 44 and 42, while the probe 34, pushed by the support 16 via the spring 42 which in turn compresses the spring 44, continues its downwards movement until it comes into contact with the surface 13 of the part 10 to be measured (see Fig. 5); the low-pressure coupling liquid, which, from the initial condition shown in Fig. 4, i.e. once the sleeve 22 has come into contact with the surface 13 via the lip 32 of the seal 30, remains enclosed inside the measuring chamber 64, forms, between the surface 13 of the part and the bottom end of the probe 34, a fluid cushion which forms the auxiliary coupling substance able to ensure uninterrupted contact between probe and surface to be measured; - both during the approach movement of the probe 34 towards the surface 13 of the part 10 and during the measuring operation, the coupling liquid continues to be supplied so as to ensure that the aforementioned fluid cushion between probe and surface is always present. The through-holes 37 inside the bush 36 surrounding the probe 34, which holes connect the measuring chamber 64 with the internal chamber 20 of the body 16 and from here with the exterior via the outlet hole 62 formed in the support 16, ensure drainage of the coupling liquid which exceeds the volume of the measuring chamber during the measurement operation itself, thus preventing the occurrence of overpressures which may impair correct measurement.
If a continuous and not an instantaneous measurement must be performed, as an alternative the cleaning operation could be extended to the entire surface to be measured instead of being limited to a restricted area around the measuring zone. It should be noted that cleaning of the surface to be measured could also be performed using the same machining chuck or other device different from that of the invention, before passing to the thickness verification cycle using the measurement and verification device. It is also possible to envisage, with a different management of the measurement cycle, interrupting the supply of the coupling liquid once filling of the cavity between probe and surface has been performed, by means of the numerical control system of the machine, and therefore dispensing with breather holes. From the above description it is clear that the approach movement of the probe 34 towards the part 10 is determined, over an initial section, by lowering of the support 16 controlled by the operating unit via the cone piece 18.
When lowering of the support 16 brings the lip 32 of the seal 30 into contact with the surface 13 of the part 10 (condition shown in Fig. 4) further lowering of the support 16 results in compression of the spring 42 which, overcoming the opposing force of the less rigid spring 44 - which is in fact compressed - causes displacement of the bush 36 and the probe 34 integral therewith towards the surface 13.
When the final position shown in Fig. 5 is reached, namely the position where measurement is performed by activating the ultrasound probe, the downwards pressure exerted by the spring 42 is offset by the opposing force exerted by the spring 44 in the compressed condition which, as a result of this compression, is more rigid than the spring 42.
For this reason, the bottom opposition spring 44 and top opposition spring 42 which support the probe 34 inside the sliding sleeve 22 and which ensure that the main movement of the body 16 is independent from that of the probe 34, allow contact between the probe 34 and the surface 13 of the part 10 to be achieved with the desired contact force and without damaging either the probe or the part, so as to ensure efficient contact during measurement and programming of the final point of the measuring movement with ample tolerance. In this connection an important advantage achieved with the present invention and in particular with the set of two springs 42 and 44 should be mentioned. The measurement of the thickness refers to a theoretical or nominal value which the part being machined must assume at each point. Therefore, for each measurement, the operating unit, based on this theoretical value, tends to move the end of the ultrasound probe as far as this theoretical value, ensuring correct contact pressure between probe and surface of the part being machined. Since the thickness of the semi-finished part is in nearly all cases greater the nominal thickness, by an amount normally of not more than one millimetre, and since the surface 13 of the semi-finished part may be to a large extent in a position which does not correspond perfectly to the theoretical position owing to deformation of the material which has occurred during machining, lowering of the ultrasound probe causes the probe itself to strike with force against the surface of the part being machined with the obvious possibility of damage. Owing to the structure of the present invention, lowering of the probe is performed by the operating unit via the top spring 42 which presses against the bush 36 and causes further lowering of the bottom end of the probe owing to compression of the bottom spring 44.
When, however, the end of the probe comes into contact with the surface of the semi-finished part whose thickness is to be measured (in which position, if the springs were not present, the probe would tend to continue its downwards displacement until it reaches the programmed position), the spring 44 is substantially compressed and generates a reactive force greater than the thrusting force exerted by the top spring 42 such as to keep the probe 34 in a stable position, while the body 16 continues its movement towards the programmed point. Obviously this involves suitable calibration of the resilient force produced by each of the two springs 42 and 44 as well as suitable definition of their dimensions. Once the measurement value is reached, the advancing movement of the reading unit is stopped, the ultrasound probe is activated and the management unit acquires the recorded data which is then sent by means of the transceiver unit to the CNC system of the machine.
The supply of the coupling liquid is interrupted and the verification and measurement device is raised from the part and positioned at another predefined point for performing a new measurement, repeating the operations described above. Once the measurement operation has been terminated at all the predetermined points, the data acquired, as mentioned above, is processed by dedicated software resident inside the CNC system of the machine and any machining corrective factors are determined and then the new travel paths of the tool for machining the part within the required tolerances are defined.
The chuck repositions the verification and measurement device in its storage crib and picks up a tool in order to resume final machining of the part. It should be noted how the cooling liquid used for machining the part (obviously suitably filtered so that it does not contain metal particles with a diameter greater than 0.005 mm which could generate measurement errors) and conveyed through the washing duct of the chuck to the bottom end of the measurement and verification device may be used both for cleaning the surface of the part and as an auxiliary substance or coupling fluid for achieving continuous contact between probe and part. As already mentioned, the coupling fluid which in this case was regarded as being the same machining cooling liquid, could also be of a different nature, such as a viscous or gelatinous (high-density) fluid able to be conveyed through the machine ducts. It is in fact feasible to consider using, depending on the material whose thickness is to be measured and the machining roughness, more or less viscous vegetable or mineral oils and fluid substances in the form of gel which nevertheless ensure a good spreading capacity on the surface to be measured and optimum continuity of contact. It is evident that, if a fluid different from that used for machining is used as coupling fluid, it will be required to provide the machine with storage tanks, pumps and ducts suitable for the fluid to be supplied.
With reference to Figure 6, this shows the embodiment in which, instead of the cone piece for coupling with the chuck of a machine tool (indicated by the reference number 18 in Figures 3 to 5), a specific coupling member for engagement with a manipulator unit or robot is provided. In this case the manipulator coupling member is indicated by the reference number 19.
Moreover, for supplying of the cleaning liquid and/or the coupling fluid, a separate supply hole indicated by the number 51 is provided, this hole, as shown in Figures 3 to 5, being closed by a cap 53.
In the embodiment shown in Fig. 6 a union or connector 55 is provided, having, connected thereto, an external pipe fitted onto the section 57. In this case, preferably, both the fluid connector 55 and the electrical connector 41 are of the automatic type, so that engagement with the manipulation unit via the coupling member 19 performs automatically the electrical and hydraulic connection.
Moreover, this automatic connectivity may also be envisaged in the case of engagement with a chuck of a machine tool. The above description clearly highlights the main advantages achieved with the present invention. These advantages may be summarised as follows:
Firstly, the entire measuring cycle, including the preliminary operation of distributing the auxiliary coupling substance between probe and surface (and if necessary preferably also the operation of cleaning the surface to be measured), is completely automated and no longer requires any manual action, it thus being possible to perform machining also without monitoring of the cycle. Intervention by a specialized operator is no longer required.
In addition, both the duration of the individual measuring step and the overall duration of the entire measuring cycle are reduced, with a consequent reduction in the machining cycle/time and therefore an increase in the efficiency of the production system.
The possibility of errors, in general those resulting from any manual operation or from the action of operators and in particular those associated with the manual introduction of the data for correction of the machining programs, is reduced. Another not insignificant advantage is that of being able to operate directly the machine tool, using its chuck and the machine's features, in order to pick up and deposit tools from/into the associated crib, since the device according to the invention becomes one of the tools stored in the crib itself. Also the measurement procedure is organized more efficiently since it is possible to provide a grid-like arrangement of points where measurement can be performed, said grid arrangement being then stored by the CNC system of the machine and converted into subsequent coordinated measurement cycles.
Finally an equally advantageous feature is that of using, both for cleaning of the surface to be measured and for measurement, the same liquid or fluid used for machining the part, or alternatively using the ducts of the chuck to supply both the cleaning liquid and the auxiliary coupling liquid between probe and surface, should they be different from the machining liquid, by connecting the chuck to the suitable liquid or fluid sources in question. The invention has been described in connection with a preferred embodiment, but it is understood that conceptually and mechanically equivalent modifications and variations are possible and may be envisaged without departing from the scope of the invention. Firstly, as shown in Fig. 6, instead of associating the device according to the invention with a machine tool intended to perform other machining operations, it is possible to envisage a machine which is designed solely for verification of the thickness of the entire part, as a station separate from the other machining stations, in which case it is also possible to associate permanently the measurement device with the end of the tool coupling member. Secondly, different solutions are possible as regards association of the ultrasound probe with means, such as the two opposition springs, for adjustably keeping the end of the probe in contact with the surface whose thickness is to be measured, replacing the springs for example with cylinder and piston assemblies which can be supplied with compressed air or with fluids. Thirdly, also the specific mechanical design consisting in the assembly comprising the hollow-chamber support, the sleeve slidable inside the hollow chamber and projecting from one end and the probe housed slidably inside the sleeve, may be modified with alternative mechanically equivalent solutions where, for example, the probe could be fixed inside a deformable casing which functions in the manner of a variable-rigidity pneumatic spring where distribution of the fluid or liquid both for cleaning the surface and for distributing the layer of auxiliary coupling fluid is performed by means of external and separate supply lines.
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