Omnidirectional locking device for clamping and / or supporting a workpiece to be machined

Abstract

An omnidirectional locking device (1) for clamping and / or supporting a workpiece (P) to be machined, susceptible to deformation and / or positioning errors and / or flatness errors on a machine tool. The device comprises a first end member (2) provided with a connection member (4) for clamping a workpiece (P) to be machined, a second lower end member (15) provided with a screw (6) for clamping to a base plate (B) of a machine tool, a third central member (20) defining a longitudinal axis (L), configured to mutually connect and lock the first and the second end member. The first end member (2) and the second end member (15) have respective opposite heads (10, 17) at least partially spherical-shaped. The third central member (20) is configured to enclose and retain the opposite heads (10, 17), allowing the omnidirectional angular movement thereof and the mutual translation thereof with respect to said longitudinal axis (L). The third central member (20) has clamping means (26, 27, 28) to lock said opposite heads (10, 17) in a desired angular and axial position and elastic means (35) interposed between the opposite heads (10, 17) and acting in an axial direction to keep them at a predetermined maximum distance in inoperative conditions.

Description

OMNIDIRECTIONAL LOCKING DEVICE FOR CLAMPING AND / OR SUPPORTING A WORKPIECE TO BE MACHINEDDESCRIPTIONField of the invention

[0001] The present invention is generally applicable to the technical field of devices for locking workpieces to be machined and it particularly relates to an omnidirectional locking device for clamping and / or supporting a workpiece to be machined on a base plate of a machine tool.Background art

[0002] The use of locking modules for clamping and / or supporting mechanical workpieces designed to be machined by a machine tool has been long known in the field of devices for locking mechanical workpieces.

[0003] Likewise known is the need of positioning and repositioning in an extremely accurate manner the workpiece to be machined on a base plate anchored to the machine tool.

[0004] Generally, the locking devices comprise at least one end member which is anchorable to a pin or other connection item fixed on the workpiece to be machined and another end member which is anchorable to the base plate by means of respective special or standard screws.

[0005] The device further comprises means for clamping the two end members by acting on the screws or tensioners. The actuation of these clamping means can be rather complex and laborious, with resulting increase in labour time for equipping the workpiece to be machined.

[0006] Furthermore, the positioning of the workpiece to be machined requires the need of making use of skilled labour capable of carrying out the sensitive and demanding preliminary positioning and centring operations.

[0007] A drawback of these locking modules lies in that the workpiece to be machined is subjected to subsequent processing operations, which frequently result in deformations or changes of planarity either caused by the release of internal tensions or by thermal treatments, for example reliefs, which displacethe spatial position and the inclination of the clamping means with respect to the initial positions.

[0008] Thus, it is usually difficult, if not impossible, to reposition the modules in the same positions and there arises the need to create new anchoring points for repositioning the clamping means.

[0009] In order to at least partially overcome such drawbacks, modules have been developed which provide for limited degrees of freedom, especially for counteracting the loss of planarity and small expansion.

[0010] WO2017 / 178522, in the name of the same Applicant, discloses a mounting device which comprises a first end member anchored to the base plate and a second end member fixed to the workpiece to be machined, both members being coupled by a rotary joint formed by two parts which are mutually rotatable around a relative transverse axis in such a manner to change the relative inclination thereof and which are lockable by reversible clamping means.

[0011] A drawback of this prior known clamping device lies in that the inclination can only be adjusted around a transverse axis. In addition, the length of the rotary joint cannot be significantly changed, limiting the possibility of changing the clamping position on the workpiece to be machined.

[0012] EP3175125 discloses a device for clamping a workpiece to be machined to a modular support, the device comprising a cylindrical symmetrical body and a clamping member provided with a head and with a threaded stem which can be screwed into a blind hole of a workpiece to be machined. The body has a through axial hole with an open end with a resting seat for locating the head. The head of the clamping member has a resting surface with a substantially spherical geometry which rests on a ring having a contact surface shaped to place the support surface of the clamping member and facilitate the rotary movement of the substantially spherical resting surface thereof in the seat. The arrangement is such that the threaded member is free to translate radially with respect to the axis of the body and it is free to rotatearound the centre of the substantially spherical surface with the head and the ring housed in the seat.

[0013] Although this device allows to adapt to small deformations of the workpieces to be machined, it has limited mobility both in the radial and in the angular direction and has no degree of freedom in the axial direction. Thus, it is not suitable for anchoring large workpieces to be machined which are subject to significant thermal deformations and significant deviations from a flat surface to a base plate.

[0014] WO2023 / 155955 discloses a spherical device for clamping workpieces, which includes a shaft with a longitudinal axis equipped at one end with spherical means for clamping to the workpiece and at the other end with a spherical clamp consisting of a section of the shaft having a spherical element on the outer surface. There is a locking mechanism with a spherical base that rests on the surface of the spherical element. The shaft can be moved and rotated axially with respect to the spherical base only when the spherical base is unlocked by means of pneumatic or hydraulic actuation acting on a radial spring to cause it to swell and exert a radial force on the base.

[0015] A disadvantage of this known solution is the considerable complexity of the spherical clamp at the base of the shaft and the need for pneumatic or hydraulic operation, acting on a spring that acts radially with respect to the base and the shaft.Technical problem

[0016] In the light of the prior art, the technical problem addressed by the present invention is to simplify and facilitate the omnidirectional fixation of the workpiece being machined subject to deformations and non-planarity.Summary of the invention

[0017] The object of the present invention is to solve the aforementioned problem by providing a modular locking device for clamping and / or supporting a workpiece to be machined on a base plate of a machine tool which is highly efficient and cost-effective.

[0018] A particular object of the present invention is to provide a modular locking device for clamping and / or supporting a workpiece to be machined of the type indicated above which allows to adapt to even consistent displacements of the fixation points of the workpiece.

[0019] A further object of the present invention is to provide a locking device for clamping and / or supporting a non-planar deformed workpiece that ensures even significantly high locking forces.

[0020] Another object of the present invention is to provide a locking device that requires no particular expertise by an operator when performing the locking / unlocking operations.

[0021] The objects mentioned above and others which will be more apparent hereinafter, are achieved by a modular locking device for clamping and / or supporting a workpiece to be machined on a base plate of a machine tool, according to claim 1 .

[0022] The device comprises a first end member having an end provided with a pin for clamping to a workpiece to be machined, a second end member provided with a screw for clamping to a base plate of a machine tool, a third central member defining a longitudinal axis, configured to mutually connect and lock the first end member and the second end member, in which the first end member and the second end member have respective at least partially spherical-shaped opposite heads, in which the third central member is configured to surround and retain the opposite heads allowing the omnidirectional angular movement thereof and the mutual translation thereof with respect to the longitudinal axis, in which the third central member has clamping means for locking the opposite end heads in a desired angular and axial position and elastic means interposed between the opposite heads and acting in the axial direction to keep them at a maximum distance in inoperative conditions.

[0023] This configuration allows to clamp deformed and non-planar workpieces relatively easily, reducing the set-up times and ensuring asignificant stability of the workpiece to be machined, regardless of its change in shape.

[0024] In one embodiment, the third central member has a substantially annular body coaxial with the longitudinal axis, with a longitudinal cut to make the body open and elastically radially deformable.

[0025] The substantially annular body has a radial protrusion directed outwards and centred on the longitudinal cut; the radial protrusion is provided with a plurality of through holes for tightening screws that are substantially transverse with respect to the longitudinal axis.

[0026] In one embodiment, the clamping means comprise a pair of spherical half-shells arranged in the third central member adapted to enclose the opposite heads to stably retain and lock them in place.

[0027] Each of the spherical half-shells has a substantially cylindrical outer surface adapted to slide within the third central member and a substantially hemispherical inner surface complementary to the hemispherical outer surface of each of the opposite heads.

[0028] In one embodiment, each of the spherical half-shells is formed by two mirror-image parts facing each other and divided by a diametrical plane passing through the longitudinal axis, such parts being able to be brought together by tightening the clamping screws to exert a clamping force in a radial direction on the opposing heads.

[0029] The spherical half-shells have pairs of elongated slots of predetermined length in diametrically opposite positions, running parallel to the longitudinal axis, designed as longitudinal end stop means fixed on the central third member.

[0030] The longitudinal limit switches are preferably made of screws inserted in diametrically opposed holes of the third central member, directed radially inwards and aligned with the slotted holes on the semi-spherical half-shells to limit the maximum longitudinal travel of the upper and lower member.

[0031] In one embodiment, the spherical half-shells are axially spaced apart from each other by a distance greater than twice the length of the slotted holes to form a substantially discoidal hollow space within the central third member.

[0032] Preferably, the elastic means comprise a compression spring arranged in the discoidal cavity to act against the opposite heads and hold them normally spaced apart.

[0033] Suitably, the first end member comprises an expanded cylindrical portion joined to the respective at least partially spherical head, in which the expanded cylindrical portion and the head are crossed by an axial cylindrical cavity, the upper end of this axial cylindrical cavity being flared and provided with a claw mechanism for coupling to the pin connection element for fixing to a workpiece.

[0034] The second end member comprises an enlarged base joined to the respective at least partially spherical head and defining a surface at the bottom that rests on a perforated plate of a machine tool.

[0035] In one embodiment, the base plate is of the type having a plurality of threaded through holes in which there may be screwed the threaded end of a clamping screw which protrudes from the rest surface of the second end member for anchoring the latter.

[0036] In this case, between the second end member and the hole of the base plate there is interposed a centring bush, which is insertable into respective annular counterbores formed in the rest surface of the second end member and in the plate.

[0037] Alternatively, the base plate is not of the type with threaded through holes but it has several T-shaped longitudinal cavities into which there may be inserted a bushing with an enlarged edge adapted to abut against the edges of the cavity, avoiding the use of the centring bush.

[0038] In a second aspect of the invention, there is provided a method for clamping on a base plate a workpiece or of a semi-finished product to be subjected to subsequent machining and having deformations, using a locking device of the type described above.Brief description of the drawings

[0039] Further features and advantages of the invention will be more apparent in the light of the detailed description of a preferred but not exclusive embodiment of an omnidirectional locking device for clamping and / or supporting a workpiece to be machined on a base plate of a machine tool, shown by way of non-limiting example with reference to the drawings below, wherein:FIG. 1 is a general perspective view of a modular clamping device according to the invention fixed surmounted by a pin for clamping to a workpiece to be machined;FIG. 2 is a lateral view of the device of FIG. 1 ;FIG. 3 is a front view of the device of FIG. 1 ;FIG. 4 is a top view of the device of FIG. 1 ;FIG. 5 is a view of the device of FIG. 2 sectioned according to the plane of line V-V;FIG. 6 is a view of the device of FIG. 2 sectioned according to the plane of line VI-VI;FIG. 7 is a perspective view of a detail of the device of FIG.1 ;FIG. 8 is a perspective view of another detail of the device of FIG. 1 ;FIG. 9 provides lateral views of the device of FIG. 1 in four different operative positions;FIG. 10 is a cross-sectional view of the device of FIG. 1 in a first mode of anchoring to the base plate;FIG. 11 is a cross-sectional view of the device of FIG. 1 in a second mode of anchoring to the base plate.Detailed description of a preferred embodiment

[0040] With particular reference to the figures, an omnidirectional locking device is illustrated, indicated globally with the reference numeral 1 , for the clamping and / or support of a workpiece P on a base plate B of a machine tool not illustrated in the figures.

[0041] The workpiece can be a metal block of any shape or a semi-finished product that is initially bracketed to the base plate B and must be machined so as to have at least one substantially flat face suitable for receiving one or more pins or connecting members.

[0042] The locking device 1 comprises a first member 2 configured to be fixed with the upper end 3 thereof to the workpiece P by means of a connection member 4 of the type know per se.

[0043] Preferably, the connecting element 4 includes a sleeve 5 of substantially conical shape having an annular groove 6 and a central through hole in within there is housed a screw 7 designed to be screwed into a threaded blind hole formed in the workpiece P.

[0044] In one embodiment, the first member 2 comprises a substantially cylindrical upper portion 8 joined with a lower portion 9 also substantially cylindrical from which an at least partially spherical-shaped head 10 protrudes.

[0045] The first member 2 is crossed throughout its entire length by an axial cavity 11 with a conical upper end 12 adapted to accommodate the bush 5 of the connection member 4.

[0046] In the lower portion 9 of the first member 2 there is a transverse screw 13 which is used to actuate a radial claw mechanism 14 for stably locking the bush 5 of the connection member 4.

[0047] The locking device 1 further comprises a second end member 15 configured for clamping thereof to the base plate B of the machine tool.

[0048] The second end member 15 comprises an enlarged base 16 defining a surface for resting against the base plate B, from which an at least partially spherical-shaped head 17 extends. The second end member 15 has an axial through cavity 18 in which there is accommodated a screw 19 for anchoring to the base plate B.

[0049] The first end member 2 and the second end member 15 can be mutually coupled by a central member 20 defining a longitudinal axis L.

[0050] As clearly shown in FIGS. 5 and 6, the third central member 20 is configured to enclose and hold the opposite spherical heads 10, 17 so as toform an omnidirectional articulated joint which allows the angular movement of the two end members 2, 15 with respect to the longitudinal axis L but also a translation movement along the longitudinal axis L, as better clarified hereinafter.

[0051] In one embodiment, the third central element 20 has a substantially annular steel body 21 coaxial to the longitudinal axis L, with a substantially cylindrical central cavity 22 and a longitudinal cut 23 that extends for the entire length of the central cavity 22 to make the annular body 21 open and elastically radially deformable.

[0052] Preferably, the annular body 21 has a protrusion 24 that is radially directed outwards and centred on the longitudinal cut 23, so as to form two jaws of a vice, separated by a metal plate.

[0053] In order to allow the locking of the two end members 2, 15 there are provided suitable clamping means which will be actuated after having correctly positioned the device with respect to the base plate B and to the workpiece P.

[0054] In one embodiment, the radial protrusion 24 is provided with a plurality of recesses with transversal through holes 25 with respect to the longitudinal axis L for respective tightening screws 26.

[0055] In the embodiment illustrated in the figures, there are four holes 25 and clamping screws 26, in order to increase the total clamping force exerted by the annular body 21. Indeed, the number of clamping screws may also be different, for example fewer, without significantly changing the resulting clamping effect, with the only difference being that a greater tightening torque of screws 26 is required.

[0056] In one embodiment, see specifically FIG. 7, the clamping means further comprise two spherical half-shells 27, 28, preferably made of steel, arranged peripherally with respect to the heads 10, 17 in the third central member 20. The spherical half-shells 27, 28 are longitudinally staggered by a predetermined maximum distance D adapted to obtain a discoidal cavity 29.

[0057] Suitably, each of the spherical half-shells 27, 28 has a substantially cylindrical outer surface with diameter slightly smaller than that of thecylindrical cavity 22 of the third member 20 so as to allow the longitudinal sliding of the half-shells in the inner cylindrical cavity 22 of the annular body 21, and a substantially hemispherical inner surface that is complementary to the spherical outer surface of each of the opposite heads 10, 17.

[0058] In one preferred embodiment, adapted to facilitate the fitting of the device, each of the spherical half-shells 27, 28 is formed by two mirrored halves respectively indicated with 27’, 27” e 28’, 28”, mutually facing and divided by a plane passing diametrical through the longitudinal axis L.

[0059] The speculated halves 27’, 27” and 28’, 28” may be mutually approached due to the closing of the tightening screws 26 of the central member 20, so as to exert a friction and locking force in the radial direction on the opposite heads 10, 17.

[0060] In this manner, the half-shells 27, 28 define ball bearings adapted to guide the heads 10, 17 in their angular movements. Thanks to their mutual axial distance, the two half-shells 27, 28 will also allow the longitudinal movement of the two end members 2, 15 by a maximum width equal to the distance D.

[0061] In order to maintain the speculated halves 27’, 27” and 28’, 28” of the half-shells 27, 28 suitably spaced apart in the radial direction, two pairs of plates 30 and 31 are interposed between the same halves, bound with pins.

[0062] In order to limit the longitudinal stroke of the half-shells 27, 28, pairs of diametrically opposite holes are formed on the walls of the third central member 20 in which there are inserted screws 33 which pass through the slotted holes 34 formed on the speculated halves 27’, 27” and 28’, 28” with elongation along a direction parallel to the longitudinal axis L.

[0063] The length of these slotted holes 34 determines the maximum stroke of the half-shells and therefore the maximum distance between the first and the second end member 2, 15.

[0064] According to the invention, between the opposite heads 10, 17 elastic means are provided for acting in the axial direction to maintain the opposite heads at a predetermined maximum distance in inoperative conditions.

[0065] In one embodiment, the elastic means comprise a compression spring 35 arranged in the discoidal cavity 29 to act against the opposite heads and maintain them normally spaced apart.

[0066] Preferably, the compression spring is of the flat undulated spiral type, also called multiwave.

[0067] Thanks to these elastic means, the two end members, when they are not locked, are at the maximum distance and therefore the operator may check whether the selected device is sufficiently strong to optimally fix the workpiece P to be machined on the base plate. Otherwise, the operator may select another larger device to carry out the operation better.

[0068] FIG. 9 schematically shows some operative conditions of the locking device in the event of misalignment with respect to the initial clamping conditions caused by deformations or lack of planarity of the workpiece to be machined.

[0069] In particular, FIG. 9a shows the two end members 2, 15 which are locked at the maximum distance from each other while maintaining their axes aligned with the longitudinal axis.

[0070] FIG. 9b shows the two end members 2, 15 which are locked at the minimum distance from each other.

[0071] FIG. 9c shows the two end members 2, 15 which are staggered in the horizontal direction while maintaining the axes thereof parallel to the longitudinal axis of the third central member 20.

[0072] FIG. 9d shows the two end members 2, 15 which are locked with respect to the third central member 20 so as to stagger the axis of the first end member both angularly and in horizontal translation with respect to the longitudinal axis L.

[0073] The value of the maximum vertical stroke of the two end members may be comprised between 4 and 8 mm and it is preferably close to ±5mm. The value of the inclination angle of the axes of the two end members is smaller than 6° and it is preferably close to 4°.

[0074] For sake of completeness, FIGS. 10 and 11 show two operating modes of anchoring the device 1 to the base plate B.

[0075] In the first operating mode, shown in FIG. 10 and employed to meet highly accurate locking needs, the clamping screw 19 of the second end member 15 is screwed in a threaded hole of the base plate B by interposing a highly precise alignment bush 40 housed in respective counterbores both of the base of the second member 15 and in the base plate B.

[0076] In the second operating mode, shown in FIG. 11 and employed for less precise locking conditions, the clamping screw 19 is screwed into a bush 50 inserted into a tenon slot with an inverted T-section obtained in the base plate.

[0077] According to a further aspect of the invention, a method is provided for clamping a workpiece or semi-finished product P, which has deformations or has planarity errors, to a base plate B of a machine tool, to be subjected to subsequent machining.

[0078] The method comprises the following steps: a) providing a locking device 1 with a first end member 2 and a second end member 15 having at least partially spherical opposite heads 10, 17 and a third central member 20 having clamping means and a longitudinal axis L; b) coupling the second end member 15 to the base plate B coupled to the machine tool by means of a clamping screw 19; c) clamping a connection member 4 on the workpiece P to be machined in a predetermined position; d) loosening the clamping means of the third central member 20 so as to allow the angular and vertical movement of the first and second end member 2, 15 with respect to the third central member 20; e) stably coupling the first end member 2 to the connection member 4 fixed on the workpiece P to be machined; f) actuating the clamping means 27, 28, 26 of the third central member 20 to lock the first end member 2 and the second end member 15 with respect to the third central member 20 with angular orient

[0079] In view of the foregoing, it appears clearly that the locking device achieves the pre-established objects and in particular it allows to adapt to even consistent displacements of the coupling points of the workpiece under machining.

[0080] Although the modular device has been described with particular reference to the attached figures, the reference numbers used in the description and in the claims are used to improve the intelligibility of the invention and do not constitute any limitation to the scope of protection claimed.

[0081] The reference throughout the description to ‘one embodiment’ or ‘the embodiment’ or ‘some embodiments’ indicates that a particular feature, structure or element described is included in at least one embodiment of the subject of this invention.

[0082] Furthermore, the particular features, structures or elements may be combined in any appropriate fashion in one or more embodiments.Industrial applicability

[0083] The present invention is industrially applicable in that the device for the omnidirectional clamping and / or support of a workpiece can be produced on an industrial scale by companies in the machine tool and workpiece clamping device field.

Claims

CLAIMS1. An omnidirectional locking device (1) for clamping and / or supporting a workpiece (P) to be machined, susceptible to deformation and / or positioning errors and / or flatness errors on a machine tool, comprising:- a first end member (2) provided with a connection member (4) for clamping to a workpiece (P) to be machined;- a second lower end member (15) provided with a screw (19) for clamping to a base plate (B) of a machine tool;- a third central member (20) defining a longitudinal axis (L), configured to mutually connect and lock said first (2) and said second end member (15); wherein said first end member (2) and said second end member (15) have respective opposite heads (10, 17) at least partially spherical-shaped; wherein said third central member (20) is configured to surround and retain said opposite heads (10, 17), allowing the omnidirectional angular movement thereof and the mutual translation thereof with respect to said longitudinal axis (L); wherein said third central member (20) has clamping means (27, 28; 26) to lock said opposite heads (10, 17) in a desired angular and axial position and elastic means (35) interposed between said opposite heads (10, 17) and acting in an axial direction to keep them at a predetermined maximum distance in inoperative conditions.

2. Locking device as claimed in claim 1 , characterised in that said third central member (20) has an annular body (21) coaxial to said longitudinal axis (L), with a substantially cylindrical axial cavity (22) and a longitudinal cut (23) to make said annular body (21) open and elastically radially deformable.

3. Locking device as claimed in claim 2, characterised in that said annular body (21) has a radial protrusion (24) directed outwards and centred on said longitudinal cut (23), said radial protrusion (24) being provided with at least one plurality of through holes (25) for tightening screws (26) that are substantially transverse with respect to said longitudinal axis (L).

4. Locking device as claimed in claim 1 , characterised in that said clamping means comprise a pair of spherical half-shells (27, 28) arranged inside said third central member (20) adapted to enclose said opposite heads (10, 17) of said first (2) and said second end member (15) to stably retain and lock them, said spherical half-shells (27, 28) being longitudinally staggered by a predetermined maximum distance adapted to obtain a discoidal cavity (29).

5. Locking device as claimed in claim 3, characterised in that each of said spherical half-shells (27, 28) has a substantially cylindrical outer surface adapted to slide inside the axial cavity (22) of said third central member (20) and a substantially semi-spherical inner surface complementary to the hemispherical outer surface of each of said opposite heads (10, 17).

6. Locking device as claimed in claim 5, characterised in that each of said spherical half-shells (27, 28) comprises two mirrored halves (27’, 27”; 28’, 28”) mutually facing and divided by a plane passing diametrically through said longitudinal axis, said mirrored halves (27’, 27”; 28’, 28”) being adapted to be mutually approached through the action of tightening of said screws (26) of said third central member (20) so as to exert on said opposite heads (10, 17) a locking force in the radial direction.

7. Locking device as claimed in claim 5, characterised in that said spherical half-shells (27, 28) have pairs of slotted holes (34) in diametrically opposite positions with elongation along a direction parallel to said longitudinal axis and with predetermined length (D) arranged as longitudinal end-stroke means fixed on said third central member.

8. Locking device as claimed in claim 7, characterised in that said longitudinal end-stroke means consist of screws (33) which are inserted into diametrically opposite holes of said third central member (20) and radially directed inwards and aligned with said slotted holes (34) present on said spherical half-shells (27, 28) to limit the maximum longitudinal translation stroke (D) of said first and second end member (2, 15).

9. Locking device as claimed in claim 1 , characterised in that said elastic means comprise a compression spring (35) arranged inside saiddiscoidal cavity (29) to act against said opposite heads (10, 17) and maintain them normally spaced apart.

10. Locking device as claimed in claim 1 , characterised in that said compression spring (35) is preferably an undulated flat spiral spring.11 . Locking device as claimed in claim 1 , characterised in that said first end member (2) comprises an expanded cylindrical portion (8) from which a respective substantially spherical head (10) extends, said first end member (2) being crossed along its entire length by an axial cylindrical cavity (11), the upper end (12) of said axial cylindrical cavity (11) being conical and provided with a claw mechanism (14) for the stable coupling to said connection member (4).

12. Locking device as claimed in claim 1 , characterised in that said second end member (15) comprises an enlarged base (16) joined to the respective head (17) and defining at the bottom a surface for resting on a base plate (B).

13. Locking device as claimed in claim 12, characterised in that said second end member (15) is passed through by an axial cylindrical cavity adapted to accommodate a clamping screw (19) for anchoring to a base plate (B).

14. Locking device as claimed in claim 13, characterised in that said clamping screw (19) is adapted to be screwed into a threaded hole of the base plate (B) for anchoring it to the latter by interposing a centring bush (40) which can be inserted into respective annular recesses of said enlarged base (16) and of said base plate (B).

15. Locking device as claimed in claim 13, characterised in that said clamping screw (19) is adapted to be screwed into a sealing bush (50) which can be inserted into a tenon slot with an inverted T-section obtained in the base plate (B).

16. A method for clamping to a base plate (B) of a machine tool a workpiece or semi-finished product (P) to be subjected to subsequentmachining operations and having deformations or non-planarity errors, which method comprising the following steps: a) providing a locking device (1 ) with a first end member (2) and a second end member (15) from which extend at least partially spherical heads (10, 17) and a third central element (20) having clamping means (26, 27, 28) and a longitudinal axis (L); b) coupling said second end member (15) to the base plate (B) secured to the machine tool by means of a clamping screw (19); c) clamping a connection member (4) on the workpiece (P) to be machined in a predetermined position; d) loosening the clamping means (26, 27, 28) of said third central member (20) so as to allow the angular and vertical movement of said first and said second end member (2, 15) with respect to said third central member (20); e) stably coupling said first end member (2) to said connection member (4) fixed on the workpiece (P) to be machined; f) actuating the clamping means (26, 27, 28) of the third central member (20) to lock said first end member (2) and said second end member (15) on said third central member (20) with angular orientation and vertical stroke to stabilize the workpiece in the optimal working position.

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