Actuator for self-centering workpiece-holding chucks

Abstract

A housing (12) accommodates actuation means (14) which are adapted to be connected to the control member (D) of a workpiece-holding chuck in order to actuate it along a chuck axis (X) and determine the opening / closure of workpiece-clamping means (1). The actuation means (14) comprise a screw-and-nut transmission (16) which is provided with a first threaded transmission member (16a) which extends along an actuator axis (X') and is adapted to be coaxially connected to the control member (D), and with a second threaded transmission member (16b) in irreversible rotary-translational engagement with the first threaded transmission member (16a). Torque multiplier means (18) are provided with a rotary input member (18a) and with a rotary output member (18b) which is integral in rotation with the second threaded member (16b) and is operatively connected to the rotary input member (18a) in a torque multiplication ratio.

Description

[0001] ACTUATOR FOR SELF-CENTERING WORKPIECE-HOLDING

[0002] CHUCKS

[0003] The present invention relates to an actuator for self-centering workpiece-holding chucks.

[0004] As known, in modern numerical controlled machine tools, the workpiece can be mounted on a pallet arranged in the work area of the machine tool using a self-centering workpiece-holding chuck.

[0005] A self-centering workpiece-holding chuck typically comprises a body which supports two or more jaws that can translate radially with respect to a chuck axis, so as to be opened and closed in relation to the workpiece. The translation of the jaws is controlled by an axially actuated control member.

[0006] In the known systems used conventionally, the control member is actuated by a hydraulic cylinder, which is capable of providing the necessary closing force while occupying relatively little space.

[0007] However, as known, the use of hydraulic cylinders entails a number of drawbacks.

[0008] First of all, as known, the use of oil generates problems of environmental pollution and the associated need for planned and controlled disposal.

[0009] Furthermore, the installation and maintenance times and costs of the hydraulic system and of the mechanical apparatuses necessary to power the hydraulic cylinder are relatively high.

[0010] The hydraulic cylinder itself requires regular maintenance, particularly with regard to the sealing elements.

[0011] Moreover, the pumps that feed the hydraulic actuators must remain active for the full processing cycle, with consequently high energy consumption.

[0012] In light of the foregoing, the aim of the present invention is to provide an actuator for self-centering workpiece-holding chucks that is capable of ensuring the same clamping force and the same reliability as the hydraulic cylinders used conventionally, with comparable or even less space occupation, and without being affected by the above-mentioned drawbacks of hydraulic systems.

[0013] Another object of the invention is to provide an actuator for selfcentering workpiece-holding chucks that requires extremely low maintenance.

[0014] The above aims and other advantages, which will become clearer from the description that follows, are achieved by an actuator for selfcentering workpiece-holding chucks having the characteristics recited in the appended claim 1, while the appended dependent claims define other characteristics of the invention which are advantageous, although secondary.

[0015] Now the invention will be described in more detail, with reference to some preferred, but not exclusive, embodiments thereof, which are illustrated for the purposes of non-limiting example in the accompanying drawings, wherein:

[0016] Figure 1 is a perspective view of an actuator according to the invention, associated with a self-centering workpiece-holding chuck of conventional type;

[0017] Figure 2 is a partially cross-sectional side view of the actuator associated with the self-centering workpiece-holding chuck of Figure 1;

[0018] Figure 2a is an enlarged- scale view of a portion of Figure 2;

[0019] Figure 3 is a plan view of the actuator of Figure 1;

[0020] Figure 4 is a cross-sectional view of Figure 3 taken along the line IV- IV;

[0021] Figure 5 is a side view of the actuator of Figure 3;

[0022] Figure 6 is a view similar to Figure 4, showing the actuator according to another embodiment of the invention.

[0023] With reference to Figures 1 and 2, a generic self-centering workpieceholding chuck, which for the sake of brevity is henceforth referred to as a “chuck” C, is adapted to be mounted on a pallet P (Figure 2) arranged in the work area of a generic machine tool (not shown) and has a supporting surface P'.

[0024] In a per se known manner, the chuck C comprises a body B that extends along a chuck axis X and has a lower end face B' for fixing to the pallet P and an upper end face B". The body B supports workpiece-clamping means which are operatively controlled by a control member D which can be actuated in translation along the chuck axis X. The control member D is arranged so that it can slide in an axial cavity H of the hollow body B.

[0025] In this embodiment, the workpiece-clamping means comprise a plurality of jaws, e.g., six jaws J, which, at the command of the control member D, can perform a radial translational motion with respect to the chuck axis X on the upper end face B" of the body B, so as to open and close in relation to a generic workpiece (not shown).

[0026] To immobilize the workpiece, a conveniently contoured locking element L can be installed on each one of the jaws J.

[0027] For the purposes of example and in a per se known manner, the control member D and the jaws J can have mutually-engaged inclined surfaces (not shown) for the transmission of motion from the control member to the jaws.

[0028] The chuck C, taken on its own, can be of conventional type.

[0029] The control member D can be actuated by an actuator 10 which, in this embodiment, is adapted to be interposed between the pallet P and the chuck C as illustrated in Figure 2.

[0030] With reference now to Figures 3-5, the actuator 10 comprises a housing 12 which, in this embodiment, has a substantially axially symmetrical profile. The housing 12 has a lower fixing surface 12' provided on a base flange 12f, with which it rests on the supporting surface P' of the pallet P, and an upper fixing surface 12" with which it engages the lower end face B' of the chuck C.

[0031] The housing 12 contains actuation means, generally designated by the reference numeral 14 in Figure 2, which are connected to the control member D in order to actuate it along the chuck axis X and, as a consequence, command the opening and closing of the jaws J.

[0032] The actuation means 14 according to the invention comprise:

[0033] - a screw-and-nut transmission 16, provided with a first threaded transmission member 16a which extends along an actuator axis X' and is adapted to be coaxially connected to the control member D, and with a second threaded transmission member 16b in irreversible rotary- translational engagement with the first threaded transmission member 16a, and

[0034] - torque multiplier means, generally designated by the reference numeral 18 in Figure 2, which are provided with a rotary input member 18a and with a rotary output member 18b which rotates about the actuator axis X', is integral in rotation with the second threaded member 16b, and is operatively connected to the rotary input member 18a in a torque multiplication ratio.

[0035] In the embodiment described herein, the first threaded member 16a comprises a ring 20 which has an internal thread 20', advantageously a trapezoidal thread, while the second threaded member 16b comprises a screw 22 which has a corresponding external thread 22' in irreversible rotary-translational engagement with the internal thread 20' of the ring 20.

[0036] In this example, the ring 20 is externally threaded in order to be screwed into a threaded seat D' of the control member D.

[0037] Advantageously, elastic means 24 are operatively interposed between the rotary output member 18b of the torque multiplier means 18 and the control member D and are axially yielding along the actuator axis X' in at least one of the two directions of translation of the control member D, advantageously in both directions of translation.

[0038] In particular, in the embodiment described herein, the screw 22 is supported so that it can slide axially along the actuator axis X' with respect to the rotary output member 18b, with the elastic means 24 being operatively interposed between them.

[0039] Advantageously, the elastic means 24 comprise at least two coaxially mutually opposite Belleville springs, in this embodiment two pairs of coaxially mutually opposite Belleville springs 24a', 24b' and 24a", 24b". The Belleville springs 24a', 24b' and 24a", 24b" are advantageously accommodated in a shell 26 which is integral with the rotary output member 18b, and act with their inner edges on the opposite faces of an annular abutment 22a formed on a portion of the screw 22 that is inserted in the shell 26, and with their outer edges on two opposite inner faces 26', 26" of the shell 26.

[0040] Preferably, the rotary input member 18a of the torque multiplier means 18 can be actuated about an axis of rotation Y that is perpendicular to the actuator axis X'.

[0041] In this embodiment, the torque multiplier means 18 comprise a worm screw transmission.

[0042] In particular, the rotary input member 18a advantageously comprises a worm screw 28 which is rotatably supported in a lateral channel 30 of the housing 12, preferably by way of a pair of screw-guide bushings 31a, 31b, and the rotary output member 18b comprises a helical gear 32 in meshing engagement with the worm screw 28.

[0043] The worm screw 28 has an actuation end 28' which is contoured so that it can be operatively engaged by a manual tightening tool, such as a crank, or by an automatic tightening device, such as an electric screw gun. In this embodiment, the actuation end 28' has a polygonal profile, advantageously a hexagonal profile.

[0044] In this embodiment, the helical gear 32 has an axial opening 32a through which it is integrally fitted onto the shell 26.

[0045] To withstand the radial thrust forces, the shell 26 is rotatably supported by an upper bushing 34, which engages a corresponding seat 36 of the housing 12, and by a lower bushing 38, which is fitted over an axial centering projection 26c of the shell 26 and engages a corresponding centering hole P" of the pallet P. To withstand the axial thrust forces, the shell 26 is rotatably supported by an upper center bearing 40 interposed between a first annular surface 26a' of the shell 26 and an inner annular abutment 12a' of the housing 12, and by a lower center bearing 42 interposed between a second annular surface 26a" of the shell 26 and the supporting surface P' of the pallet P

[0046] The screw 22 is rendered integral in rotation with the shell 26 by the engagement of a polygonal end portion 22p of the screw 22 in a corresponding polygonal axial seat 26p of the shell 26 (Figure 2a).

[0047] In operation, the rotation of the worm screw 28 produces the translation of the control member D through the helical gear 32, the shell 26, the screw 22 and the ring 20, with consequent radial translation of the jaws J outward or inward according to the direction of rotation of the worm screw 28.

[0048] Since the combined rotational and translational motion between the ring 20 and the screw 22 is irreversible, once the workpiece has been immobilized between the jaws J and a corresponding one of the two pairs of Belleville springs 24a', 24b' and 24a", 24b" has been compressed, the jaws J will stably maintain their position and the opening / closing force will be ensured by the pair of Belleville springs that is in the compressed configuration.

[0049] For example, if the immobilization is obtained by pulling the control member D in Figure 2 downward, the pair of Belleville springs that will ensure the closing force will be the upper pair, i.e. the pair of Belleville springs 24a', 24b'.

[0050] If, instead, the immobilization is obtained by pushing the control member D in Figure 2 upward, then the pair of Belleville springs that will ensure the closing force will be the lower pair, i.e. the pair of Belleville springs 24a", 24b".

[0051] Figure 6 shows another embodiment of the invention, which differs from the previous embodiment solely in that the housing 112 incorporates an electric motor 150 which is operatively connected to a motorized end 128" of the worm screw 128. Preferably, in this embodiment too the worm screw 128 has an actuation end 128' opposite to the motorized end 128", which is contoured so that it can be operatively engaged by a manual tightening tool in order to be released in an emergency.

[0052] The electric motor 150, which can be of conventional type, comprises a stator 150a accommodated in a compartment 152 provided at one end of the channel 130 that contains the worm screw 128, and a rotor 150b which is fitted on a cylindrical support 154 which is screwed onto the motorized end 128" of the worm screw 128. The compartment is advantageously sealed closed by a cover 156.

[0053] This embodiment has the advantage of enabling greater automation of the workpiece immobilization / release operations.

[0054] Some preferred embodiments of the invention have been described herein, but obviously the person skilled in the art may make various modifications and variations within the scope of protection of the claims.

[0055] For example, in the embodiments described herein, the actuator is a self-contained device that is adapted to be installed on the supporting surface of the pallet. However, in order to further reduce the vertical space occupation of the system for supporting the workpiece, the actuator could be installed in a seat provided in the pallet, or it could even form an integral part of the latter, in the sense that the housing could form a single piece with the pallet.

[0056] Similarly, the actuator could also be integrated in the chuck.

[0057] Furthermore, although in the present description specific reference has been made to workpiece-holding chucks of the self-centering type, for which the invention is particularly advantageous, obviously the actuator according to the invention can be applied to any workpiece immobilizer that is controlled by an axially actuated control member.

[0058] Furthermore, the elastic means, if any, can be of a different type from the Belleville springs used in the embodiments described and explained herein, e.g., one could use conical springs, diaphragm springs, and the like.

[0059] Also, in the embodiments described herein, the elastic means act bidirectionally. However, depending on the circumstances, it may be sufficient to have elastic means that are adapted to generate the closing force in only one direction.

[0060] The worm screw mechanism could be substituted by torque multiplier means of different type, e.g., an epicyclic reduction gear unit or a reduction gear unit of conventional type based on strain wave gearing or harmonic gearing. In this case, there could be a conical torque in input to the torque multiplier means, so that the actuator can still be actuated by acting on an axis that is perpendicular to the axis of translation of the control member of the chuck.

[0061] The disclosures in Italian Patent Application No. 102024000001257 from which this application claims priority are incorporated herein by reference.

[0062] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

CLAIMS1. An actuator for a workpiece-holding chuck of the type provided with a body (C) which supports workpiece-clamping means (J) which are operatively controlled by a control member (D) which can be actuated to translate along a chuck axis (X), said actuator (10) comprising a housing (12) which accommodates actuation means (14) which are adapted to be connected to said control member (D) in order to actuate it along said chuck axis (X), characterized in that said actuation means (14) comprise:- a screw-and-nut transmission (16), provided with a first threaded transmission member (16a) which extends along an actuator axis (X') and is adapted to be coaxially connected to said control member (D), and with a second threaded transmission member (16b) in irreversible rotary- translational engagement with said first threaded transmission member (16a), and- torque multiplier means (18), provided with a rotary input member (18a) and with a rotary output member (18b) which is integral in rotation with said second threaded member (16b) and is operatively connected to said rotary input member (18a) in a torque multiplication ratio.

2. The actuator according to claim 1, characterized in that said first threaded member (16a) comprises a ring (20) which has an internal thread (20') and said second threaded member (16b) comprises a screw (22) which has a corresponding external thread (22') in irreversible rotary-translational engagement with said internal thread (20') of the ring (20).

3. The actuator according to claim 1, characterized in that it comprises elastic means (24) which are operatively interposed between said rotary output member (18b) and said control member (D) and are axially yielding along said actuator axis (X') in at least one of the two directions of translation of the control member (D).

4. The actuator according to claim 2, characterized in that said screw (22) is supported so that it can slide axially along said actuator axis (X')with respect to said rotary output member (18b) and said elastic means (24) are operatively interposed between said screw (22) and said rotary output member (18b).

5. The actuator according to claim 3, characterized in that said elastic means (24) are axially yielding along said actuator axis (X') in both directions of translation.

6. The actuator according to claim 3, characterized in that said elastic means (24) comprise at least two coaxially mutually opposite Belleville springs.

7. The actuator according to claim 6, characterized in that said Belleville springs (24a', 24b' and 24a", 24b") are accommodated in a shell (26) which is integral with said rotary output member (18b) and act with their inner edges on an annular abutment (22a) formed on a portion of said screw (22) that is inserted in said shell (26), and with their outer edges on two opposite inner faces (26', 26") of said shell (26).

8. The actuator according to one claim 1, characterized in that said rotary input member (18a) can be actuated about an axis of rotation (Y) which is perpendicular to said actuator axis (X').

9. The actuator according to claim 1, characterized in that said torque multiplier means (18) comprise a worm screw transmission.

10. The actuator according to claim 1, characterized in that said rotary input member (18a) comprises a worm screw (28; 128) which is rotatably supported in a lateral channel (30) of said housing (12), and said rotary output member (18b) comprises a helical gear (32) in meshing engagement with said worm screw (28).

11. The actuator according to claim 10, characterized in that said worm screw (28) has an actuation end (28') which is contoured so that it can be operatively engaged by a manual tightening tool or by an automatic tightening device.

12. The actuator according to claim 10, characterized in that saidworm screw (128) has a motorized end (128') which is operatively connected to an electric motor (150) incorporated in said housing (112).

13. The actuator according to one or more of the preceding claims, characterized in that it is incorporated in a workpiece-holding chuck of the type provided with a body (C) which supports workpiece-clamping means (J) which are operatively controlled by a control member (D) which can be actuated to translate along a chuck axis (X).

14. The actuator according to one or more of the preceding claims, characterized in that it is incorporated in a pallet for supporting workpieces within the working area of a machine tool.

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