DESCRIPTION

«SYSTEM AND METHOD FOR DIMENSIONAL AND FORM DEVIATION CHECKING»

Technical Field

The present invention relates to a system for dimensional and form deviation checking of a mechanical piece that defines a rotation surface and a symmetry axis, including a support structure with a support and reference system for the mechanical piece, the support and reference system defining a longitudinal reference axis and being adapted to support the piece, the symmetry axis being substantially coincident with the longitudinal reference axis; a measuring group with a mechanical reference having two stationary bearings adapted to touch the rotation surface of the piece to be checked; a first translation system adapted for allowing mutual transversal translation displacements between the measuring group and the support and reference system on a transversal plane, and a second translation system adapted for causing mutual axial translation movements between the piece and the measuring group along a direction parallel to the reference axis. The present invention also relates to a method for dimensional and form deviation checking of a mechanical piece that defines a rotation surface and a symmetry axis, with a checking system including a support and reference system for the mechanical piece, the support and reference system defining a longitudinal reference axis, a measuring group having a mechanical reference with two stationary bearings adapted to touch the rotation surface of the mechanical piece, and a sensor adapted for cooperating with the rotation surface and for providing signals indicative of diametral dimensions of the mechanical piece.

Background Art

In the prior art, there are known systems for dimensional and form deviation checking of mechanical pieces including external or internal cylindrical surfaces.

Such cylindrical surfaces can be affected by errors, for example out-of-roundness (deviation of the considered transversal section of the piece with respect to a circle) , out-of-cylindricity (deviation of surface points of the piece with respect to a cylindrical surface) and out-of- concentricity (deviation of the centre of the transversal sections of the piece with respect to the symmetry axis) . There are known checking systems with measuring apparatus where the cylindrically shaped piece rotates about a rotation axis substantially coaxial to the longitudinal axis of the piece, and the displacements of one or more feelers with respect to one or more V-shaped reference elements, i.e. with two stationary bearings adapted for touching the cylindrical surface to be checked at two different points, are detected. For example, the U.S. patent US-A-3274693 discloses two V-shaped reference elements connected to spacer elements and laid on two separate transversal sections of the mechanical piece. Each V-shaped reference element is connected to a movable feeler coupled to an associated transducer that detects diametral variation of the piece at the considered section. As a consequence, rotating the piece about the rotation axis, it is possible to obtain two separated signals, the combination thereof can provide information about possible radial deviations of the piece with respect to its nominal dimensions. The checking performed by an apparatus of this type is limited to a certain number of sections which is determined by the number of utilized V-shaped reference elements; thus the achieved results may not be sufficiently representative of the actual dimensions and shape of the piece .

Disclosure of the invention

Object of the present invention is to provide a system and a method for dimensional and form deviation checking of mechanical pieces that enable to overcome the disadvantages of the known systems and methods.

This and other objects are achieved by a checking system and a checking method according to claim 1 and claim 10, respectively. A checking system according to the present invention provides not only improved standards of metrological performances and remarkable features of flexibility and versatility of employment, but also low costs of implementation and operation. A checking system for dimensional and form deviation checking of a mechanical piece defining a rotation surface and a symmetry axis, includes a support structure with a support and reference system for the mechanical piece which defines a longitudinal reference axis, adapted to support the mechanical piece having the symmetry axis substantially coincident with said longitudinal reference axis; a measuring group with a mechanical reference having two stationary bearings adapted to touch the rotation surface of the piece to be checked; a first translation system adapted for allowing mutual transversal translation displacements between the measuring group and said support and reference system on a transversal plane; a second translation system adapted to cause mutual axial translation movements between the piece and the measuring group along a direction parallel to the reference axis. The first translation system includes thrust devices adapted to keep contact between said mechanical reference of the measuring group and the rotation surface of the piece to be checked in the course of such mutual axial translation displacements. The checking system can advantageously include at least one measuring device for checking the mutual transversal translation displacements.

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A method for dimensional and form deviation checking of a mechanical piece defining a rotation surface and a symmetry axis, with a checking system comprising a support and reference system for the mechanical piece which defines a longitudinal reference axis, a measuring group with a mechanical reference having two stationary bearings adapted to touch the rotation surface of the mechanical piece, and a sensor adapted for cooperating with the rotation surface and to provide signals indicative of diametral dimensions of the piece, includes the step of causing mutual longitudinal translations between the piece and the measuring group along a direction parallel to the longitudinal reference axis; and the step of detecting, in the course of such longitudinal translations, diametral dimensions of the piece. The method can advantageously include the step of detecting, in the course of such longitudinal translations, the mutual position of said mechanical reference and said longitudinal reference axis on a plane perpendicular to the direction parallel to the reference axis.

The checking system and method according to the present invention enable to concurrently carry out dimensional checking and form deviation checking, more specifically cylindricity/concentricity checking of mechanical pieces, resulting in a considerable reduction of time with respect to the known systems and methods.

A first preferred embodiment of the system according to the present invention includes a measuring group with a snap gauge for checking external diameters of mechanical pieces. A second preferred embodiment of the system according to the present invention includes a measuring group with a plug gauge for checking internal diameters of mechanical pieces .

Brief Description of the Drawings

The invention is now described with reference to the

enclosed sheets of drawings, given by way of non limiting examples, wherein: figure 1 is a simplified side view of a first embodiment of an apparatus for checking external diameters according to the present invention; figure 2 is a simplified top view of a detail of the checking system shown in figure 1 ; figure 3 is a simplified side view of a detail of the checking system shown in figure 1 ; - figure 4 is a simplified side view of a system for checking internal diameters according to a second preferred embodiment of the present invention; and figure 5 is a simplified top view, partly cross- sectioned, of a checking system like the one shown in figure 4.

Best Mode for Carrying Out the Invention

Figures 1-3 show in a simplified way a system 1 for dimensional and form deviation checking of a mechanical piece 27 defining a longitudinal symmetry axis and a rotation surface, more specifically an external cylindrical surface. The checking system 1 includes a stationary support structure, or bench 3, that is coupled to a support arm 5. The support arm 5 is stationary with respect to the bench 3 and carries a first translation system 10 with a first floating slide 9 coupled to a measuring group with a snap gauge 7 for checking external diameters of the piece 27. The floating slide 9 can translate along a direction X and a direction Y that are mutually perpendicular and define a plane X-Y. Advantageously, the floating slide 9 can be pneumatically actuated for enabling to insert the piece in the measuring position in an easier way, as it will be hereinafter described in more detail. The bench 3 includes a second translation system with a guide 13 defining a direction Z perpendicular to the plane X-Y, on which a second slide 15 and a third slide 17 can

slide. The slides 15 and 17 are of the high precision type translating along the direction Z. The mechanical piece 27 is mounted and located on a support and reference system including a live center 21 and a dead center 23 that define a longitudinal reference axis parallel to the axis Z and are urged to contact the ends of the piece 27 by means of springs not shown in the figures. Under this condition, the symmetry axis of the piece 27 is substantially coincident with the longitudinal reference axis. A manual lever device, not shown in the figure, enables to mutually displace away and approach the live center 21 and the dead center 23 for inserting/removing and locking the piece 27. The slide 15 carries a rotation system with an electric motor 19 adapted to drive into rotation the live center 21 about a rotation axis parallel to the direction Z. The slide 17 carries an arm 25 that in turn carries the dead center 23 by means of an idle connection allowing to follow the piece 27 when the latter is driven into rotation by the electric motor 19 through the live center 21. An angular detection system with an angular transducer of a known type, for example an encoder 20, provides electrical signals representative of angular positions about the direction Z of the live center 21 and consequently of the piece 27. The second translation system includes actuation devices of a known type and thus not shown in the figures, for example one or more controlled electric motors, that are adapted to translate the slides 15 and 17 along the guide 13, in order to move the piece along the direction Z. A measuring device illustrated in a simplified way and designated with reference number 16, for example an optical linear scale, detects the position of the slides 15, 17 and thus of the piece 27, along the direction Z. The floating slide 9 connected to the support arm 5 is a high precision slide translating on the plane X-Y. The snap gauge 7, connected to the slide 9, can consequently translate with respect to the support arm 5 and to the

piece 27 on the plane X-Y. Thrust devices, for example a spring 29 which has one end connected to the support arm 5 urges the snap gauge 7 to contact the piece 27 and ensures, as it will be hereinafter clarified, contact between the piece 27 and the snap gauge 7 in the course of mutual rotations about the rotation axis and/or mutual displacements along the direction Z.

Figure 2 shows in a more detailed but still simplified way, the measuring group with the snap gauge 7 according to a section plane which corresponds to the transversal section of the piece 27 to be checked. The snap gauge 7 includes a main body 11 carrying a V-shaped mechanical reference with two stationary bearings 31, 33 and a fourth slide 35 of the high precision, axial movement type. The main body 11 includes a side opening 12 for inserting the piece in such a way that this latter contacts the stationary bearings 31, 33. Through the same side opening 12, the piece 27 is removed when the checking of such piece is finished. The slide 35 carries a measuring device 37 with a sensor, for example a movable feeler 39 adapted to contact the piece 27. The slide 35 enables the measuring device 37 to translate along the direction X lying on the plane X-Y, and can be advantageously actuated by means of electrical or pneumatic actuation devices, that are known and thus not shown in the figures, for approaching/displacing the measuring device 37 to/away from the piece 27. The measuring device 37 is of a known type and can be for example a pneumatically or mechanically actuated measuring cell having an inductive position transducer - not shown in the figures - adapted to detect displacements of the feeler 39 along the measuring axis, and to provide electrical signals representative of such displacements. A reference element 41, stationary with respect to the main body 11, acts as abutment for the slide 35, and defines an operative position for the slide 35 and consequently for the measuring device 37. A measuring device 43, stationary with respect to the main body 11, checks the position of

the slide 35 along the measuring direction in order to allow for possible repeatability errors that the reference element 41 may introduce into the operative position of the slide 35. Even the measuring device 43 is of a known type, for example a measuring cell with a feeler 44 adapted to contact the slide 35 and an inductive position transducer

(not illustrated) adapted to provide electrical signals representative of the position of the feeler 44.

According to an alternative embodiment of the present invention, the slide 35 can be dispensed with and the measuring device 37 is stationary with respect to the main body 11. According to such alternative embodiment, neither the reference element 41 nor the measuring device 43 are needed. The measuring group can be advantageously protected by a protection element 40, visible in figure 3, which is stationary with respect to the support arm 5 and has an opening 42 for enabling to insert the piece 27 to be checked. The position of the snap gauge 7, that as previously mentioned is integral with the slide 9 and thus movable with respect to the support arm 5 on the plane X-Y, is checked with respect to the support arm 5 by means of two known measuring devices 45, 47 connected to the main body 11. Advantageously, the measuring devices 45, 47, illustrated in a simplified way in figure 2 too, can be measuring cells including feelers 46, 48 adapted to contact the support arm 5 and inductive transducers adapted to provide electrical signals representative of the position of the feelers 46, 48. The feelers 46, 48 can move on the plane X-Y, advantageously along measuring directions that substantially pass through the stationary bearing 31 and the rotation axis, and through the stationary bearing 33 and the axis of rotation, respectively. The support arm 5 is advantageously shaped in such a way as to provide contact surfaces 49, 50 for the feelers 46, 48 that are perpendicular to the associated measuring directions.

The several measuring devices send electrical signals to a known processing and checking unit, not illustrated in the figures .

Under operative conditions, the position of the main body 11 is defined by the cooperation between the rotation surface of the piece 27 and the stationary bearings 31, 33, that keep contact with the piece 27 by virtue of the thrust applied along the direction X by the spring 29 on the main body 11. As the snap gauge 7 is movable on the plane X-Y, the contact between the piece 27 and the stationary bearings 31, 33 is ensured. The measuring devices 45, 47 provide the position of the main body 11 on the plane X-Y with respect to the support arm 5, while the measuring device 16 provides the position of the checked transversal section of the piece 27 along the direction Z.

Figure 4 shows in a simplified way a system 51 for dimensional and form deviation checking of internal diameters of a cylindrical hole 55 of a mechanical piece 53 defining a rotation surface and a symmetry axis. The checking system 51 includes a stationary support structure, or bench 57 carrying a support and reference system with a high accuracy rotary table 59 of a known type that rotates about a longitudinal reference axis. Rotation devices including for example an electric motor 63 and an angular transducer, or encoder 65, are adapted to drive into rotation the rotary table 59 and to provide a signal representative of angular positions taken by the rotary table 59. The checking system 51 includes a support and reference system 67 comprising a nosepiece 61 integrally fixed to the rotary table 59 which carries the piece 53, a support plate 69 contacting the piece 53, and an elastic element, for example a spring 71. Advantageously, the spring 71 acts along the direction of the longitudinal reference axis and its first end is connected to the nosepiece 61, while its second end is connected to a substantially cylindrical element 73 which is rigidly coupled to the support plate 69. The cylindrical element 73

is coupled to an hole 75 of the nosepiece 61, the axis thereof is parallel to the reference axis. The cylindrical element 73 and the hole 75 define a guide system 77 for the support plate 69 that consequently urges and locks the piece 53 along the direction of the reference axis against the nosepiece 61, by means of the spring 71. A transversal reference system, which is of a known type and thus not illustrated, including for example resilient laminae, prevents the piece 53 from moving with respect to the nosepiece 61 along directions transversal to the reference axis. There can be utilized other known support and reference systems, including for example elastic elements integral with the support plate. The checking system 51 further includes a support arm 58 that carries a first translation system with a floating slide 79 of the high precision type translating along two directions X and Y perpendicular to the reference axis, which carries, in turn, a measuring group with a plug gauge 81 for checking internal diametral dimensions. The bench 57 carries a second translation system with a guide 60, whereon a high precision slide 62 translating along the direction Z parallel to the reference axis slides, actuated by actuation devices - not illustrated - for example one or more controlled electric motors. The support arm 58 is connected to the slide 62, and can consequently translate along the direction Z with respect to the bench 57. A not illustrated checking device, for example an optical linear scale, detects the position of the slide 62 and thus the position of the plug gauge 81, along the direction Z. The plug gauge 81 is of a known type and includes a mechanical reference with two stationary bearings, or stationary feelers 74, 76, and a sensor, or movable measuring feeler 78 with an inductive position transducer which provides signals representative of mutual displacements of the stationary feelers 74, 76 and of the movable feeler 78. As shown in figure 5, which is partly cross-sectioned along a plane including the section to be checked of the piece 53,

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the stationary feelers 74, 76 of the plug gauge 81 achieve a V-shaped mechanical reference for the piece 53. The plug gauge 81 is pneumatically retracted, thus providing the advantage of enabling the feelers 74, 76, 78 to mutually approach and facilitating the positioning of the plug gauge 81 into the hole 55 in an easier way. The plug gauge 81 is integrally connected to a mechanical element 83 which includes an abutment surface 85. Thrust devices, in particular a spring 89, which cooperates at one end with the arm device 58 and at the other end with the abutment surface 85 of the mechanical element 83, urges the latter along the direction X and ensures contact between the stationary feelers 74, 76 of the plug gauge 81 and the wall of the hole 55 in the course of the rotations of the piece 53 and of the translations of the plug gauge 81 along the direction Z. The mechanical element 83 also carries known measuring devices, for example one or more measuring cells 68, shown in simplified form in figure 5, having a feeler 70 for checking the position on the plane X-Y of the mechanical element 83 and thus of the plug gauge 81 with respect to the bench 57. The several measuring devices send electrical signals to a known processing and control unit, not illustrated in the figures. Likewise the checking system shown in figures 1-3, as the plug gauge 81 is floating on the plane X-Y, such plug gauge 81 self-locates with respect to the piece 53 and can keep the contact even when there are dimensional or form deviation errors in the piece 53, and in the course of mutual rotations and/or translations. The checking systems that have been just described enable to perform different types of dimensional and/or form deviation checking of mechanical pieces, for example checking of external and internal diameters, checking of roundness, concentricity and/or cylindricity . Methods for dimensional and/or form deviation checking of mechanical pieces according to the present invention are hereinafter described with reference to the checking system

of the figures 1-3, namely with reference to systems for dimensional and form deviation checking of external diameters .

According to a first method for dimensional and form deviation checking, the piece 27 is locked between the live center 21 and the dead center 23 and is referred with respect to the bench 3. Advantageously, in order to easily lock the piece 27 between the live center 21 and the dead center 23, both the feeler 39 and the associated measuring device 37 are pneumatically retracted, which means that they are displaced along the direction X away from the stationary bearings 31, 33. The main body 11 is also displaced by pneumatically actuating in a known way the floating slide 9 in such a way as to oppose the thrust of the spring 29. Moreover, by means of the manual lever device, the live center 15 and the dead center 17 are displaced away from each other and, once the piece 27 is inserted through the opening 12 of main body 11, they are subsequently approached for locking the piece 27. As a consequence, the piece 27 is referred with respect to the bench 3 having the symmetry axis substantially coincident with the reference axis defined by the live center and the dead center along a direction which does not change during the subsequent checking, in particular in the course of displacements along the direction Z caused by the slides 15, 17.

When the piece 27 has been locked, the floating slide 9 can freely move under the thrust applied by the spring 29, and the measuring device 37 is displaced to an operative condition by actuating the slide 35. As a consequence, the stationary bearings 31, 32 and the feeler 39 contact the piece 27 at a transversal section to be checked. The stationary bearings 31, 32 are advantageously arranged according to an angular arrangement which is asymmetric with respect to the feeler 39. As known, for example from international patent application WO-A-01/66306, such angular asymmetric arrangement increases the sensitivity of

the measuring device 37 to form deviation errors that frequently occur in the piece 27.

The piece 27 is consequently driven into rotation by means of the electric motor 19, and the measuring device 37, which has been previously calibrated on a master part, provides electrical signals indicative of the radial dimensions of the piece 27 at the considered transversal section for each rotation angle, which is detected by means of the encoder 20. By processing data corresponding to signals provided in a whole 360° rotation of the piece 27, it is possible to evaluate the circularity of the considered section. Moreover, at the considered section - the position thereof along the direction Z being known by virtue of the optical linear scale 16 - the measuring devices 45, 47 provide signals indicative of the position of the main body 11 on the plane X-Y. In such a way, displacements of the mechanical reference with the stationary bearings 31, 33 are checked, and the position of the centre of the considered section of the piece 27 can be determined.

By actuating the slides 15 and 17 that cause displacements of the piece 27 along the direction Z with respect to the snap gauge 7, it is possible to repeat the circularity checking at different transversal sections of the piece 27 and to concurrently obtain the corresponding position of the centre of the considered section both on the plane X-Y and along the direction Z. The spring 29 and the floating slide 9 ensure that the stationary bearings 31, 33 and the feeler 39 contact the piece 27 at all the considered transversal sections and in the course of associated displacements between the piece 27 and the snap gauge 7 along the direction Z. As in the course of the displacements along the direction Z the axis of the piece 27 does not undergo displacements on the plane X-Y, possible displacements of the snap gauge 7 that are detected by the measuring devices 45, 47 are only caused by dimensional and/or form deviation errors of the piece 27.

Once information about the roundness and about the position of the centre of different transversal sections are obtained, it is possible to determine the out-of-roundness and the out-of-concentricity of the piece 27, by means of per se known processing.

Alternatively, according to a second checking method is possible to determine form deviation errors of the piece 27

(concentricity and cylindricity) by detecting the arrangement of generating lines of the surface of the piece 27 at different rotation angles.

More specifically, once the measuring group is positioned in operative position, with the stationary bearings 31, 33 and the feeler 39 contacting the piece 27, a scan of the piece is performed by translating, without rotating, the piece 27 along the direction Z (by means of the slides 15, 17 and of the associated actuation means) . In the course of the scan, in addition to the signals of the snap gauge 7, also the signals of the measuring cells 45, 47 are acquired, thus obtaining data relevant to the arrangement of a first generating line of the surface of the piece 27 at a first angular position. Once the first scan is completed, the piece 27 is rotated through a pre-set angle, and a second scan is carried out for detecting data relevant to a second generating line of the surface of the piece 27 at a second angular position rotated with respect to the first one. Rotating the rotary table 59 again through pre-set angles that are equal to or different from the preceding angles, any number of generating lines of the hole 55 can be checked. Then, from such data relevant to generating lines it is possible to obtain form deviation errors of the piece 53, for example out-of-cylindricity and out-of-concentricity, by means of per se known processing. Similarly to what has been described with reference to the checking system of figures 1-3, it is possible to carry out dimensional and form deviation checking for internal diameters of the piece 53 by means of the checking system shown in figure 4.

According to a first preferred method, the piece 53 is referred and locked with respect to the nosepiece 61 by means of the reference and locking system 67. The plug gauge 81, previously calibrated on a master part, is then inserted inside the hole 55 of the piece 53 and is positioned at a transversal section to be checked. Subsequently, the rotary table 59 is driven into rotation by the electric motor 63, and signals representative of the internal diameter of the considered section of the piece 53, for each rotation angle, are detected by the plug gauge 81. The measuring cells 68 provide signals representative of the position on the plane X-Y of the plug gauge 81, whereby the centre of the considered section can be determined through per se known processing. When a 360° rotation is completed, the rotary table 59 is stopped and the plug gauge 81 is displaced along the direction Z at a different transversal section of the piece 53 to be checked, by means of actuation devices connected to the slide 62, for performing a new checking. Afterwards, the rotary table 59 is driven into rotation again and electrical signals representative of radial dimensions at the considered section and of the axial position of such section are detected as described above by means of the plug gauge 81 and of the measuring cells 68, respectively. Once the positions of the section centre and of the out-of- roundness are acquired for a suitable number of sections, possible out-of-cylindricity and/or out-of-concentricity of the piece 53 can be detected through per se known processing. Alternatively, according to a second checking method according to the present invention, form deviation errors of the piece 53 (concentricity and cylindricity) can be obtained by detecting the arrangement of generating lines of the surface of the hole 55 at different angles of rotation. In practice, once the plug gauge 81 is inserted inside the hole 55, a scan of the piece 53 is carried out by displacing the plug gauge 81 along the direction Z (by

means of the slide 62) keeping the rotary table stationary. During the scan, in addition to the signals of the plug gauge 81, the signals of the measuring cells 68 are acquired, too, thus obtaining data relevant to the arrangement of a first generating line of the hole 55 at a first angular position of the piece 53. Once the first scan is completed, the rotary table 59 is rotated through a preset angle and a second scan is carried out in order to obtain data relevant to the arrangement of a second generating line of the hole 55 at a second angular position of the piece 53, such second angular position being rotated with respect to the first position through the pre-set angle. Rotating the rotary table 59 again through pre-set angles, equal to or different from the preceding ones, it is possible to obtain information about the arrangement of any number of generating lines of the hole 55, whereby form deviation errors of the piece 53, for example out-of- cylindricity or out-of-concentricity, can be detected in a known way. In practice, the systems and methods according to the present invention enable to obtain at the same time and in a very rapid way information for obtaining dimensional

(diameter) and form deviation (cylindricity/concentricity) errors of the mechanical piece (53;27). Advantageously, the mechanical piece can be a component of injectors and injection pumps, or a component of hydraulic valves, steering systems, bearings, and compressors. The checking systems and methods hereinbefore described can be modified without departing from the scope of the present invention.

For example, even thought the measuring groups hereinbefore described feature electric gauges, known pneumo-electronic gauges can be utilized. Moreover, the same results can be achieved by driving into rotation the measuring group with respect to the piece, or arranging the piece, instead of the measuring group, on sliding means for allowing it to translate on the plane X-Y

with respect to the measuring group and thus checking the position of the piece on the plane X-Y with respect to the bench. In the event it is the piece that can translate on the plane X-Y, the thrust device, for example a preload spring, acts on such piece or on a piece support. Furthermore, as illustrated in the embodiments of figures 1-3 and 4, is also possible to enable the piece and the measuring group to mutually translate along the direction Z by translating either the piece (figures 1-3) or the measuring group (figure 4) .

In addition, the position and the orientation of the illustrated measuring devices can be modified. It is also possible to take into account and compensate possible limited displacements of the rotation axis of the piece to be checked on the plane X-Y during translations along the direction Z, by means of known measuring devices that check the position on the plane X-Y of the reference systems of the piece, for example live center and dead center with respect to the bench or with respect to the support arm.