WO2014067975A1

WO2014067975A1 - Checking device for checking the position of the central axis of a mechanical part and/or of a hole with rotational symmetry with respect to a reference system

Info

Publication number: WO2014067975A1
Application number: PCT/EP2013/072656
Authority: WO
Inventors: Antonio Ghielmi
Original assignee: Marposs Societa' Per Azioni
Priority date: 2012-10-31
Filing date: 2013-10-29
Publication date: 2014-05-08
Also published as: ITBO20120596A1

Abstract

A checking device (9) for checking the position of a central axis (A) of a mechanical part with rotational symmetry includes a transducer (15) defining a motion transmission direction and a couple of arms (18,19) connected to the transducer and carrying feelers (12,13) movable along a checking section. The arms are connected to a support frame (10) by means of fulcra (16,17) defining two transverse rotation axes, only one of said rotation axis being arranged between the motion transmission direction and the checking section. The device can be applied to a system with a gauge to perform a method for checking the alignment between the axes of a cylindrical portion (3') and a frustoconical seat (5) of a hole (3). The method includes the steps of inserting the gauge into the hole and centering it in the frustoconical seat to define a reference system, tilting the gauge to locate it with respect to a section of the cylindrical portion of the hole, defining a longitudinal reference plane (P) and determining, at a different section of the cylindrical portion of the hole, the position of the central axis of the hole with respect to the longitudinal reference plane by means of the checking device.

Description

DESCRIPTION

CHECKING DEVICE FOR CHECKING THE POSITION OF THE CENTRAL AXIS OF A MECHANICAL PART AND/OR OF A HOLE WITH ROTATIONAL

SYMMETRY WITH RESPECT TO A REFERENCE SYSTEM

Technical field

The present invention relates to a checking device for checking the position of the central axis of a mechanical part with rotational symmetry, to a method for checking the position of a central axis of a hole of a mechanical piece with respect to a reference system and to a related checking system including said device .

Devices and systems of this kind are used in metrological controls in different fields of application, among which production and assembly of components of the automotive, aeronautical and solar panel industry and any other field that requires high accuracy metrological controls.

In particular, a system, a method and a device of this kind can be used to check the concentricity of openings with rotational symmetry, such as adjoining holes adapted to house countersunk fasteners like rivets or bolts.

Background art

It is known to check the position of the axis of parts with rotational symmetry with respect to a stationary reference system by means of apparatuses, typically laboratory apparatuses but not just that, which comprise sensors cooperating, with or without contact, with the surface of the parts to be checked. A scan of the surface is performed, while the apparatus and/or the part to be checked rotate (-s) .

There are also known devices adapted to give a direct reading of the concentricity of mechanical parts, for example in workshops, without the need to perform complete scans of the parts to be checked .

Such devices typically include at least two sensors cooperating, for example with contact, with diametrically opposite areas of the surface of one of the parts to be checked and comprise respective transducers generating separated signals. The comparison of said signals gives indications on variations in the position of the axis of such surface with respect to a reference position.

To check parts of small dimensions, typically small holes the alignment of which must be checked in a simple and quick way, the known solutions which performs scans and/or comprise more transducers and require subsequent processing operations cannot be used because of excessive overall dimensions and unacceptable time of checking.

A solution enabling a direct reading of the eccentricity of two holes is shown in the patent No. US 3882608 describing a checking device which includes a support frame with two opposite feelers and a transducer consisting of a dial indicator. Axially movable mechanical transmission parts are connected between the feelers and the dial indicator. Displacements of the feelers, which are caused for example by an axial rotation, manually performed by an operator, of the device that is centered in one of the holes, cause axial movements of the respective movable parts and enable to directly detect displacements of the axis of the other hole by means of the dial indicator.

Even though this device gives a direct reading of the variation in the position of the axes by means of the dial indicator, its mechanical structure is complex and bulky. Indeed, the mechanical transmission parts consist of a plurality of reciprocally connected elements that create a jointed kinematic motion requiring close tolerances. Moreover, in the described device, the proportionality between displacements of the feelers and movements of the respective movable parts, which is essential to get a reliable checking, is ensured by a precise slope of the contact surfaces between the feelers and the movable parts. The contact between surfaces of the feelers and surfaces of the movable parts causes frictions that can alter the measurement. Furthermore, the sloping surfaces are subjected to unavoidable wear which unpredictably alters the surfaces and the relative slope. Variations in the slope of one or both the sloping surfaces change the proportionality ratio between the displacements of the feeler and the movements of the movable parts and consequently the reading of the position of the central axis provided by the dial indicator.

Disclosure of the invention

Object of the present invention is to provide a checking device for checking the position of the central axis of a mechanical part with rotational symmetry, and a checking system for checking the position of a central axis of a hole of a mechanical piece with respect to a reference system, which overcome the above-mentioned inconveniences, have a simpler structure and, in particular, can be actuated in a simpler way, are easy to use and are portable.

A further object of the present invention is to provide a method for checking the position of a central axis of a hole of a mechanical piece with respect to a reference system which enables to perform checking operations in a simple and quick way .

This and other objects are achieved by a checking device for checking the position of the central axis of a mechanical part with rotational symmetry, and a system and a method for checking the position of a central axis of a hole of a mechanical piece with respect to a reference system as defined in the enclosed claims .

Brief description of the drawings

A checking device for checking the position of the central axis of a mechanical part with rotational symmetry, and a method and a relative system for checking the position of a central axis of a hole of a mechanical piece with respect to a reference system according to the invention are hereinafter described with reference to the attached sheets of drawings given by way of non-limiting examples, wherein:

figure 1 is a simplified, longitudinal section, with some parts shown in front view, of a checking system for checking the position of a central axis of a hole with respect to a reference system in a checking phase;

figure 2 is a longitudinal section, with some parts in front view and others omitted, of the checking system taken along the line II-II of figure 1 ;

figure 3 is a cross section of the checking system taken along the line III-III of figure 2 ;

figure 4 is a simplified, longitudinal section of the checking system corresponding to the section of figure 1 which shows a checking method for checking the position of a central axis of a hole with respect to a reference system according to the invention;

figure 5 is a cross section of the checking system taken along the line V-V of figure 4;

figure 6 is a cross section of the checking system taken along the line VI-VI of figure 4;

figure 7 is a simplified representation of a checking device for checking the position of the central axis according to the invention;

figure 8 is a diagram of the checking device of figure 7 in a first example of checking;

figure 9 is a diagram of the checking device of figure 7 in a second example of checking;

figure 10 is a simplified representation of an alternative embodiment of the checking device of figure 7; and

figure 11 is a simplified representation of a checking device for checking the position of the central axis according to a different embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows a checking system 1 for checking the position of a central axis of a hole with respect to a reference system in a mechanical piece 2, in particular a central axis A of a cylindrical portion 3' of a hole 3 with respect to a frustoconical seat 5 located in the upper part of the hole 3. The mechanical piece 2 can be formed in one piece or consisting, for example, of two or more layers which can be quickly assembled by means of fasteners, such as countersunk rivets, inserted in the hole 3.

The system 1 includes a support frame 10 to which a gauge 6 is fixed. The gauge 6 defines a longitudinal axis E and includes an elongate body 7 which comprises reference portions 11 and is inserted in the hole 3, and a portion with at least partially spherical surface 8 which is housed in the frustoconical seat 5 of the mechanical piece 2. The reference portions 11 define the parts of the elongate body 7 which touch the surface of the cylindrical portion 3' of the hole 3. In other words, the elongate body 7 leans against the surface of the hole 3 at said reference portions 11. In the embodiment shown in the figure the elongate body 7 is prismatic-shaped with rounded edges and the reference portions 11 are defined by a couple of adjacent edges. The elongate body 7 can also have sharp edges or be cylindrical- shaped with reference portions defined by balls protruding from the surface of the body. Moreover, the gauge 6 includes a checking device 9 featuring a reference device axis B for checking the position of the central axis of a mechanical part. In the specific case of the hole 3 of the mechanical piece 2, the checking device 9 includes a first arm 18 and a second arm 19 carrying a first feeler 12 and a second feeler 13, respectively. Such checking device 9 will be described in detail later .

The checking system 1 is also shown in figure 2, where the elongate body 7 and the portion with at least partially spherical surface 8 are shown in front view and only one, 13, of the two feelers is visible and is shown frontally. In this figure, the gauge 6 is tilted so that a section of the elongate body 7 touches the internal surface of the hole 3.

The checking device 9 for checking the position of the central axis is shown simplified in figure 7 with the first feeler 12 and the second feeler 13 arranged in opposite positions and contacting the internal surface of the cylindrical portion 3' of the hole 3 and with a transducer 15. The contact between the feelers 12, 13 and the internal surface of the cylindrical portion 3' of the hole 3 defines a checking section, schematically represented by a dashed line, at which the feelers 12, 13 are movable along a contact direction. The contact direction corresponds to the direction along which the feelers displace and contact the internal surface of the hole.

The feelers 12, 13 are connected to the transducer 15 by means of a first movable transmission element 20 and a second movable transmission element 21 which include the first movable arm 18 and the second movable arm 19, respectively, and are connected to the support frame 10 by means of a first fulcrum 16 and a second fulcrum 17 which are fixed to the support frame 10 and define two rotation axes, transverse to the reference device axis B, around which the arms 18, 19 rotate. The arms 18, 19 are connected to the transducer 15 by means of a first mechanical transmission portion 30 and a second mechanical transmission portion 31, that are schematically indicated by two segments in figure 7 and that can be embodied by means of different mechanical items, per se known, or can even simply consist of areas of the arms 18, 19 directly connected to the transducer 15. The first mechanical transmission portion 30 and the second mechanical transmission portion 31 define a motion transmission direction, represented by a dashed line as well, which is substantially parallel to the checking section and corresponds to the direction along which the displacements carried out by the feelers 12, 13 are transmitted to the transducer. More particularly, the mechanical transmission portions 30, 31 connect the arms 18, 19, respectively, to a first movable part and a second movable part of the transducer 15, for example the windings and the core of an inductive transducer of the LVDT type, which are adapted to perform mutual translation movements along a transducing direction that, in the embodiment of figure 7, corresponds to the motion transmission direction. The connection between the mechanical transmission portions 30, 31 and the transducer 15 can be made in different ways depending on the type and arrangement of the transducer used. When an inductive transducer arranged as shown in figure 7 is used, the mechanical transmission portions can be integrally connected to the transducer, as schematically shown in figure 7. When a different type of transducer is used, for example a mechanical transducer, and/or the transducer is differently arranged so that the transducing direction does not correspond to the motion transmission direction (as in the example of figure 9 that will be described hereinbelow) , there can be additional transmission elements that connect the mechanical transmission portions to the transducer.

As visible in the figures, just one of the two rotation axes is arranged between the checking section and the motion transmission direction. More specifically, the first fulcrum 16 defining the rotation axis of the first arm 18 is arranged between the checking section defined by the feelers 12, 13 and the motion transmission direction, while the second fulcrum 17 defining the rotation axis of the second arm 19, is arranged at the end of the arm 19 opposite to the end carrying the feeler 13 so that the motion transmission direction is between the checking section and the fulcrum 17.

The dimensions of the arms 18, 19, the arrangement of the fulcra 16, 17 and the connection to the movable parts of the transducer and to the feeler are such as to define the same arm ratio Rb, that is the ratio between the extent of the displacements of each feeler 12, 13 and the displacements of the corresponding part of the transducer 15 is the same for both the arms 18, 19. In the embodiment of figure 7, the distances between the fulcra 16 and 17 and the respective parts of the transducer are marked with hi and HI, and the distances between the fulcra 16 and 17 and the respective feelers 12 and 13 are marked with h2 and H2. The dimensions of these distances are such that the ratios hl/h2 and H1/H2 that define the arm ratio are the same (Rb=hl/h2=Hl/H2) . In other words, the ratio in the first arm (18) between the distances of the first fulcrum (16) from the first movable part of the transducer (15) and from the first feeler (12) is the same as the ratio in the second arm (19) between the distances of the second fulcrum (17) from the second movable part of the transducer (15) and from the second feeler (13) .

There are also elastic means 24, for example springs, between the support frame 10 and the arms 18, 19. In the embodiment shown in the figure, such springs 24 are represented as return springs placed at each arm 18, 19 between the respective fulcrum 16, 17 and the motion transmission direction.

The operation of the checking device 9 for checking the position of the central axis and of the checking system 1 comprising such device is explained hereinafter. A checking method for checking the position of a central axis with respect to a reference system is also described.

According to such method, the gauge 6 in inserted, as shown in figure 1, into the hole 3 of the mechanical piece 2 to be checked in such a way that the elongate body 7 is arranged in the cylindrical portion 3' and the portion with at least partially spherical surface 8 leans on the surface of the frustoconical seat 5, centers itself, or more specifically mechanically self-centers, in the latter and defines a reference system with a center C lying on the longitudinal axis E.

The position of the central axis A of the cylindrical portion 3' of the hole 3 with respect to the reference system, that is the alignment or misalignment between the central axis A of the cylindrical portion 3' and a reference axis R of the seat 5 that is parallel to the central axis A and passes through the center C, is checked as follows.

As shown in figure 4, where a case of misalignment between the reference axis R and the central axis A is represented in a simplified and deliberately exaggerated manner, the gauge 6 is transversely, or more specifically perpendicularly, tilted with respect to the contact direction of the feelers, while the portion with at least partially spherical surface 8 leans on the frustoconical seat 5, until the elongate body 7, more specifically the couple of adjacent edges defining the reference portions 11, leans against the internal surface of the cylindrical portion 3' of the hole 3. A leaning section is thus defined in which a V-shaped mechanical reference 14 defined by the reference portions 11 cooperates with the surface of the hole 3. As shown in figures 3 and 5, in this position the gauge 6 is centered, in the leaning section, with respect to the diameter d of the cylindrical portion 3' of the hole 3 which is aligned along the bisector of the angle defined by the V-shaped reference mechanical reference 14.

The diameter d and the longitudinal axis E of the gauge 6 define a longitudinal reference plane.

In figures 5 and 6, besides the smaller diameter circumference corresponding to the cylindrical portion 3' of the hole 3, a larger diameter circumference with the center C is shown by dashed line. Such larger diameter circumference represents the contact line at which the portion with at least partially spherical surface 8 leans on the frustoconical seat 5 of the mechanical piece 2.

The longitudinal axis E of the gauge, to which the center C belongs, coincides with the reference device axis B of the checking device 9, which serves to determine the position of the central axis A of the cylindrical portion 3' of the hole 3 with respect to the reference system with the center C. More specifically, at one section of the elongate body 7, between the leaning section and the seat 5, a component of such position is determined with respect to the longitudinal reference plane. Such section corresponds to the checking section defined by the contact between the feeler 12, 13 and the internal surface of the hole 3.

More particularly, the feelers 12, 13 contact the internal surface of the hole 3 along the contact direction which is transverse, more specifically perpendicular, to the diameter d on which the gauge 6 is centered at the leaning section, and thus with respect to the longitudinal reference plane comprising such diameter d and the longitudinal axis E. The longitudinal reference plane is shown in figure 6 by the dashed line P.

The displacements performed by the feelers along the contact direction correspond to the distances 22, 23 (visible in figure 6) between the reference device axis B (coinciding with the longitudinal axis E) and the points of the surface of the hole 3 which the feelers 12, 13 contact. If the distances 22, 23 are equal, the transducer 15 emits no signal and no difference in the position of the axis A of the hole 3 with respect to the reference device axis B is detected. This means that the axis A of the cylindrical portion 3' of the hole 3 is aligned with the reference device axis B. On the contrary, if the distances 22, 23 are different, as shown in figure 6, the transducer 15 detects the misalignment between the axis A of the hole 3 and the reference device axis B and emits a signal indicative of the difference in the position of the axis A of the hole 3 with respect to the reference device axis B.

More particularly, with reference to figures 7-9, when the feelers 12, 13 contact the surface of the hole 3, the arms 18, 19 perform rotation movements about the rotation axes defined by the fulcra 16, 17 to transmit the displacements of the feelers 12, 13 to the transducer 15 by means of the mechanical transmission portions 30, 31.

The different arrangements of the two rotation axes, defined by the fulcra 16, 17 with respect to the motion transmission direction and to the checking section, have the result that the sense of the motion of only one mechanical transmission portion 30 (or 31) out of the two is inverted with respect to the sense of the motion of the corresponding feeler 12 (or 13) .

In the known systems for dimensional checking including two- parts transducers, the sense of the motion of both the movable parts of the transducer is the same as, or opposite to, the sense of the motion of the feelers they are coupled to.

In the device according to the invention, instead, the displacement of one of the feelers (the feeler 12 in the embodiment shown) causes, thanks to the position of the relative fulcrum (16), a displacement in the opposite sense of the respective mechanical transmission portion (30) and thus of the associated movable part of the transducer 15, while the displacement of the other feeler (the feeler 13) causes a displacement in the same sense of the respective mechanical transmission portion (31) and thus of the associated movable part of the transducer 15.

As stated above, the first fulcrum 16 is arranged between the checking section and the motion transmission direction, while the second fulcrum is arranged with respect to the fulcrum 16 on the opposite side of the motion transmission direction, at the end of the arm 19 opposite to the end carrying the feeler 13. With reference to the position of the first fulcrum 16 and of the second fulcrum 17, more specifically to the position of each fulcrum with respect to the corresponding arm, the arm 18 defines a first class lever while the arm 19 defines a second class lever. As the arm 18 defines a first class lever, the first mechanical transmission portion 30 and the associated movable part of the transducer 15, in this case the windings, move in an opposite sense with respect to the sense of the motion of the feeler 12. As the arm 19 defines instead a second class lever, the second mechanical transmission portion 31 and the other movable part of the transducer, that is the core, move in the same sense as the feeler 13.

Unlike the known devices for checking axial positions in which each arm is associated with a transducer detecting its displacement, this particular arrangement, with respect to the motion transmission direction and to the checking section, of the rotation axes defined by the fulcra around which the arms rotate, enables to detect the position of the axis by using only one transducer. This provides remarkable advantages in terms of overall dimension and portability.

The device according to the invention doesn't detect dimensional differences as such in the mechanical part but differences in the position of the central axis which can be associated with dimensional differences in the mechanical part or not. If the displacements of the feelers with respect to a position centered on the reference device axis B are symmetrical, that is they have equal extent and opposite sense with respect to each other (which means that the difference in the dimensions of the mechanical part is symmetrical with respect to the central axis of the mechanical part itself) , both the mechanical transmission portions and, in the embodiment of figures 7-9, the associated movable parts of the transducers, thanks to the arrangement of the fulcra and the arm ratio, carry out displacements of the same extent and in the same sense, and no difference in the position of the central axis A with respect to the reference device axis B is detected. A case of this type is shown simplified in figure 8 where arrows indicate the sense of the motion of the feelers 12, 13 and of the mechanical transmission portions 30, 31 carrying the movable parts of the transducer 15. On the contrary, if the displacements carried out by the feelers with respect to the position centered on the reference device axis B are not symmetrical, that is they have different extent and/or the same sense (as in the case shown in figure 9) , the mechanical transmission portions and, in the embodiment of figures 7-9, the associated movable parts of the transducer carry out displacements of different extent and an overall displacement value is detected and sent to an external processing unit of the known type, not shown in the figure. The displacement value As detected by the transducer 15 is proportional to the actual position variation Δχ of the axis A according to the formula As=2AxRb.

The transducer 15 emits a signal that, once processed by the external processing unit, indicates the difference in the position of the central axis A of the cylindrical portion 3' of the hole 3 with respect to the reference device axis B, in particular with respect to the longitudinal reference plane P. As the reference device axis B coincides, as stated above, with the longitudinal axis E of the gauge 6 passing through the center C of the reference system, the position of the axis A of the hole 3 is determined with respect to the reference system itself, which is centered with respect to the frustoconical seat 5. In other words, as the longitudinal axis E of the gauge 6 has one end aligned with a central point, that is the center C, of the frustoconical seat 5 and the opposite end lying on a diameter d of the cylindrical portion 3' of the hole 3 (thanks to the centering performed by the V-shaped reference 14), misalignments that are detected by the transducer 15 at the checking section which is positioned halfway in the hole 3 (typically in an area of the cylindrical portion 3' near the frustoconical seat 5) are indicative of the misalignment of the axis A with respect to the center C, more specifically with respect to the reference axis R passing through the center C, along a direction transverse to the bisector of the V-shaped reference 14.

To determine the alignment or misalignment of the axis A with respect to the center C is necessary to perform at least two checking cycles like the one described above to get an indication of the position of the axis A along at least two directions of the checking section. As such position is determined with respect to the longitudinal plane P comprising the diameter d defined by the bisector of the V-shaped reference 14, it is necessary, once the first checking cycle is finished, to vary the angular position of the gauge in the hole (3) around the central axis A by rotating it, for example by 90°, and to repeat the checking cycle at a new contact direction, preferably transverse, more specifically perpendicular, to the contact direction of the previous checking cycle. In other words, the gauge 6 is tilted to define such new contact direction and a longitudinal reference plane differing from the one defined in the previous checking cycle is defined. The position of the central axis A of the hole is determined with respect to the different longitudinal reference plane.

More checking cycles performed in different directions of the hole, higher the accuracy with which the misalignment of the axis A with respect to the center C is determined.

The checking in different directions can be performed by taking the gauge 6 back to the central position at the end of each checking cycle, and then rotating and tilting it against the internal surface of the hole 3 in a different direction, or by keeping the gauge 6 tilted and rotating it continuously so that the couple of edges 11 touch different points of the internal surface. It is possible to keep the gauge 6 tilted manually or thanks to elastic means placed inside the hole 3 which apply a continuous radial thrust to the gauge 6.

The gauge 6 can be moved inside the hole 3 manually or by means of automatic motion systems of the known type.

The alignment between the axis A of the hole and the reference device axis B is checked at a section, that is the checking section, which is near the seat 5. Knowing the distances among the leaning section and the checking section of the gauge and the center C of the reference system, it is possible to determine easily the misalignment value of the axis A of the cylindrical portion 3' of the hole 3 at any other sections of the hole 3, for example at the frustoconical seat 5.

The control system 1 according to the invention ensures a high flexibility of use: as the leaning section, at which the couple of edges 11 lean against the internal surfaces of the hole 3, can correspond to any of the intermediate sections of the elongate body 7 of the gauge 6, the selfsame gauge can be used to check holes of different depth.

According to an alternative embodiment, the elongate body 7 of the gauge 6 includes, at an intermediate cross section, a couple of balls that are placed at two adjacent edges of the elongate body 7 and protrude from the latter. The couple of balls define the reference portions 11 and thus a precise leaning section of the gauge, and enable to identify more precisely the section of the elongate body 7 that contacts the internal surface of the hole 3.

The checking device 9 for checking the position of the central axis, shown in figure 7 and previously described, includes an electrical transducer, but it can include a mechanical or a different type of transducer even differently arranged, e.g. in a configuration like the one shown in figures 7-9 or in a different configuration. Figure 10 shows an alternative embodiment with mechanical transmission elements, which can include an electrical transducer like the one shown in the figures 7-9 (but with a different arrangement) or a different type of transducer, for example a mechanical transducer. The mechanical transducer comprises a transmission system 29, connected for example to a dial indicator, which includes a movable element 27 with sloping surfaces 28 adapted to contact mechanical transmission portions 25, 26 that can be integral with the first arm 18 and second arm 19 or fixed thereto, along the motion transmission direction.

The movable element 27 performs displacement along a transducing direction perpendicular to the motion transmission direction as a function of the displacements performed by the feelers 12, 13 and transmitted by the arms 18, 19. Asymmetrical displacements, that is displacements of different extent and/or in the same sense with respect to each other, of the arms 18, 19 are transmitted to the movable element 27 thanks to clearance in the transmission system 29. Even the embodiment including the mechanical transducer provides remarkable advantages with respect to the solution according to the patent No. US 3882608 both in terms of simplicity and flexibility and of reduction in friction among the components.

The checking device can even include a transducer of a different, per se known, kind, for example a capacitive transducer, or an optical transducer with an emitter and a receiver, or a transceiver and a mirror. In a configuration like the one shown in figure 7, the emitter and the receiver (or the transceiver and the mirror) can be connected to the first mechanical transmission portion 30 and the second mechanical transmission portion 31, respectively.

A checking device 9' in which the second arm defines a third class lever, rather than a second class lever, and the first arm is suitably arranged falls within the scope of the present invention. More specifically, with reference to the configuration shown in figures 7 and 10, the portions of each arm which are connected to the feeler and to the transducer are inverted with respect to each other, as schematically shown in the sketch of figure 11.

The checking device for checking the position of the central axis and the method and the related checking system for checking the position of a central axis with respect to a reference system are described and shown in figures 7-10 with reference to the check of internal surfaces of a mechanical part. However, the same check can be applied to a different system to check external surfaces of a mechanical part by inverting the sense in which the feelers contact the surface of the mechanical part and the position of the springs fixed to the support frame and acting on the arms 18, 19.

Claims

1. Checking device (9) for checking the position of the central axis of a mechanical part with rotational symmetry with respect to a support frame (10), the checking device featuring a reference device axis (B) and including:

a transducer (15),

a first feeler (12) and a second feeler (13) arranged at opposite positions, mutually movable and adapted to contact surfaces of the mechanical part to be checked, the contact between the first feeler (12) and the second feeler (13) and the surfaces of the mechanical part defining a checking section, and a first movable transmission element (20) and a second movable transmission element (21) connected to the transducer (15) and to the first feeler (12) and to the second feeler (13) respectively, to transmit displacements of the first feeler (12) and the second feeler (13) to the transducer (15) ,

characterized in that

the first movable transmission element (20) and the second movable transmission element (21) include a first arm (18) and a second arm (19) connected to the first feeler (12) and the second feeler (13) respectively,

a first fulcrum (16) between the first arm (18) and the support frame (10), and a second fulcrum (17) between the second arm (19) and the support frame (10), the first and second fulcra defining two rotation axes transverse to the reference device axis (B) , and enabling the first arm (18) and the second arm (19) to rotate with respect to the support frame (10) about said two rotation axes, and

a first mechanical transmission portion (25,30) and a second mechanical transmission portion (26,31), connected to the first arm (18) and second arm (19) and to the transducer (15) and defining a motion transmission direction, along which displacements of said first feeler (12) and second feeler (13) are transmitted to the transducer (15) , the motion transmission direction being substantially parallel to the checking section and only one of said two rotation axes being arranged between the checking section and the motion transmission direction.

2. Checking device (9) according to claim 1, wherein said first fulcrum (16) and second fulcrum (17) are arranged in such a way that said first arm (18) define a first class lever and said second arm (19) defines a second class lever.

3. Checking device (9) according to claim 1, wherein said first fulcrum (16) and second fulcrum (17) are arranged in such a way that said first arm (18) defines a first class lever and said second arm (19) defines a third class lever.

4. Checking device (9) according to any one of claims 1 to 3, wherein the transducer 15 includes a first movable part and a second movable part connected to the first mechanical transmission portion (25) and to the second mechanical transmission portion (26) respectively, and adapted to perform mutual translation movements along the motion transmission direction .

5. Checking device (9) according to any one of claims 1 to 4, wherein the ratio in the first arm (18) between the distances of the first fulcrum (16) from the first movable part of the transducer (15) and from the first feeler (12) is equal to the ratio in the second arm (19) between the distances of the second fulcrum (17) from the second movable part of the transducer (15) and from the second feeler (13) .

6. Checking device (9) according to any one of the preceding claims, wherein the transducer (15) is an inductive transducer.

7. Checking device (9) according to any one of the preceding claims, including a transmission system (29) with a movable element (27) which has sloping surfaces (28) adapted to contact the first mechanical transmission portion (25,30) and the second mechanical transmission portion (26,31) along the motion transmission direction, the movable element (27) being adapted to perform displacements along a direction perpendicular to the motion transmission direction as a function of the displacements performed by the feelers (12,13) transmitted by the first arm (18) and the second arm (19) .

8. Checking system (1) for checking the position of a central axis (A) of a hole (3) of a mechanical piece (2) with respect to a reference system including:

a gauge (6) with

an elongate body (7) with reference portions (11) which is adapted to be inserted into the hole (3) and to lean against the surface of the hole (3) at the reference portions (11) in order to define a leaning section; and

a portion with at least partially spherical surface (8) adapted to cooperate with the mechanical piece (2) and to define the reference system;

a checking device (9) for checking the position of the central axis (A) according to any one of the claims 1 to 7 to determine the position of the central axis (A) of the hole (3) with respect to the reference system; and

a processing unit connected to the checking device (9) for processing signals in output from the checking device (9) .

9. System according to claim 8, wherein the elongate body (7) is prismatic-shaped and the reference portions (11) are defined by a couple of adjacent edges.

10. System according to claim 8, wherein the elongate body (7) includes, at a cross section, a couple of balls that protrude from the elongate body (7) and define the reference portions (11) ·

11. Method for checking the position of a central axis (A) of a hole (3) of a mechanical piece (2) with respect to a reference system, the hole (3) comprising a cylindrical portion (3') and a frustoconical seat (5) , by means of a checking system including a gauge (6) defining a longitudinal axis (E) with an elongate body (7) which has reference portions (11), a portion with at least partially spherical surface (8) and a checking device (9) with a transducer and a first arm (18) and a second arm (19) carrying a first feeler (12) and a second feeler (13), respectively, the first and second feelers being movable along a contact direction, the method including the steps of:

inserting the gauge (6) into the hole (3), the portion with at least partially spherical surface (8) leaning on and self-centering in the frustoconical seat (5) and defining the reference system with a center (C) lying on said longitudinal axis (E) ,

tilting the gauge (6), in a direction transverse to the contact direction, so that the elongate body (7) leans against the surface of said cylindrical portion (3') at the reference portions (11) to define a leaning section and a V-shaped mechanical reference (14) between the reference portions (11) and the surface of the cylindrical portion (3') of the hole (3), the gauge (6) being centered at said leaning section with respect to the diameter (d) of the cylindrical portion (3') of the hole (3) aligned along the bisector of the angle defined by the V-shaped mechanical reference (14),

defining a longitudinal reference plane (P) including the longitudinal axis (E) of the gauge (6) and the diameter (d) , and

determining the position of the central axis (A) of the hole (3) with respect to the longitudinal reference plane

(P) by means of the checking device (9) at a checking section defined by the contact between the first feeler

(12) and the second feeler (13) of the checking device (9) and the surface of the hole (3) .

12. Method according to claim 11, including the further steps of varying the angular position of the gauge (6) in the hole (3) about the central axis and repeating said steps of tilting the gauge (6), defining a different longitudinal reference plane and determining the position of the central axis (A) of the hole (3) with respect to said different longitudinal reference plane.

13. Method according to claim 11 or 12, wherein the distances among the leaning section and the checking section of the gauge (6) and the center (C) of the reference system are known and the position of the central axis (A) of the hole (3) with respect to the reference system is determined at any other section of said hole (3) .

14. Method according to any one of claims 11 to 13, wherein the checking system includes a checking device (9) according to any one of claims 1 to 7.