Patent Description:
Machine tools with automatic transfer of the workpiece, also called "transfer machines", are known in the state of the art. Such transfer machines are configured to combine, in a single production unit, the functions of a series of separate machine tools. In detail, transfer machines comprise a series of workstations in which a workpiece is sequentially transferred to carry out a specific production cycle.

The known transfer machines allow obtaining high production rates and are configured to produce a single product, or at most a family of products. Consequently, the purchase of transfer machines is only justified by high production volumes.

The importance of maximizing the production capacity of transfer machines is therefore evident, for example by reducing the passive steps as much as possible, i.e., those in which the machining does not occur.

<CIT> describes a transfer machine comprising a plurality of machining stations, a rotating table configured to bring a plurality of workpieces in succession to the machining stations, and actuator members configured to rotate the workpieces about a rotation axis thereof.

In detail, a plurality of gripping members are arranged on the table comprising gripping jaws configured to lock a workpiece in a position facing a machining station.

The actuator members, arranged in the machining stations, are movable from and toward the table to connect with the gripping members and control the rotation of the jaws.

It should be noted that, before being able to perform rotating machining on a workpiece to be machined, it is necessary to wait for the actuator members to approach the table, engage the jaws, and accelerate the latter up to the angular speed of the regime envisaged for the machining.

Similarly, at the end of the machining, before taking the workpieces to be machined to the subsequent machining stations, it is necessary to wait for the angular speed of the jaws to be zero and for the actuator members to move away from the table so as to be disengaged from the jaws.

It should be noted that the production capacity of the machine tool is significantly reduced by the passive processing steps in which the actuator members are moved from and toward the table. In particular, it should be noted that the movement of the actuator members from and toward the table causes an increase in the duration of the passive steps both before and after the machining.

<CIT> discloses a machine tool according to the preamble of claim <NUM>.

In this context, the technical task underlying the present invention is to propose a machine tool for machining which overcomes the drawbacks of the prior art mentioned above.

In particular, it is an object of the present invention to provide a machine tool capable of maximising the production capacity, reducing the duration of the passive machining steps.

In other words, the object of the present invention is to provide a machine tool capable of making the cycle time tend to the actual time required to perform machining operations, i.e. to make the cycle time tend to the duration of the active step.

The present invention relates to a machine tool comprising a plurality of machining stations configured to simultaneously perform a plurality of machining on a plurality of workpieces. Examples of machining are for example chip removal operations performed by cutting tools such as cutters, drill bits, boring tools and the like.

The machine tool of the present invention further comprises a workpiece-supporting unit configured to position the workpieces sequentially at the machining stations. Such a workpiece-supporting unit has a plurality of gripping regions which can be sequentially associated with the machining stations. In detail, when operated, the workpiece-supporting unit is configured to sequentially associate the plurality of gripping regions to the machining stations.

Each gripping region has a workpiece gripping member arranged, comprising jaws rotatably operable about a rotation axis thereof. Furthermore, each gripping member comprises first rotatable engaging members which are kinematically connected in rotation to the plurality of jaws to control the rotation of the respective jaws about the rotation axis thereof.

The machine tool further comprises a plurality of actuator members adapted to actuate the rotation of the jaws about the respective rotation axes by acting on the first engaging members. In detail, each actuator member comprises second engaging members which are rotatable and movable from\toward the respective first engaging members to act on the latter.

Furthermore, the machine tool comprises a guide for the first engaging members extending between the machining stations. It should be specified that the first engaging members are configured to slide on the operating guide of the workpiece-supporting unit.

In detail, the guide has a plurality of gaps adapted to be positioned at the gripping regions of the support unit.

Each second engaging member is arranged, at least partially, in a gap of the guide so as to be engaged with a respective first engaging member when the gripping regions are positioned at the machining stations.

It should be noted that, following the operation of the support unit, the first engaging members are brought at the machining stations and engage with the respective second engaging members of the actuator means. Therefore, the machine object of the present invention, by means of the guide and the second engaging members arranged partially in the gaps of the guide, allows to rotatably couple the jaws and the actuator members as soon as the gripping regions are at the machining stations.

It is therefore evident that the machine tool object of the present invention allows the jaws to be operated as soon as the gripping regions are located at the machining stations, thus reducing the duration of the passive steps before and after the machining to the time necessary to accelerate and brake the jaws.

Further features and advantages of the present invention will become more apparent from the description of an exemplary, but not exclusive, and therefore nonlimiting preferred embodiment of a machine tool for machining, as illustrated in the appended figures, in which:.

With reference to the appended figures, the present invention relates to a machine tool <NUM> adapted to perform machining, in particular for chip removal. In alternative embodiments, it is not excluded that the machine object of the present invention can also be used to perform other mechanical operations, such as assembly operations of one or more components.

The machine tool <NUM> comprises a plurality of machining stations <NUM> in which several machining operations are performed simultaneously on different workpieces. In detail, a workpiece is sequentially transferred to the machining stations and is subjected to a specific production cycle which transforms it into a given finished or semi-finished piece.

Each machining station <NUM> comprises special machining devices configured to interact with the workpiece to perform one or more mechanical processes. It should be specified that machining device means any tool adapted to perform mechanical operations for chip removal. Typically, but not necessarily, such machining devices comprise an insert with a cutting portion which, acting on the surface of the workpiece, removes material therefrom. By way of example, the machining devices can be cutters, boring tools, drill bits, or turning tools.

As shown in <FIG> and <FIG>, the machine tool <NUM> comprises a workpiece-supporting unit <NUM> adapted to arrange workpieces in the machining stations <NUM> where they are subjected to predetermined machining. It should be noted that the machining performed in each machining station <NUM> has comparable durations, so that they can be synchronized.

The workpiece-supporting unit <NUM> has a plurality of workpiece gripping regions <NUM> which can be sequentially associated with the machining stations <NUM>. In detail, when actuated, the workpiece-supporting unit <NUM> is configured to sequentially associate the plurality of gripping regions <NUM> to the machining stations <NUM>.

In the embodiments shown in the appended figures, preferably, the workpiece-supporting unit <NUM> is configured to rotate about a main rotation axis R-R. Furthermore, preferably, the gripping regions <NUM> are arranged so as to be spaced apart from the main rotation axis R-R of the workpiece-supporting unit <NUM>. In use, the gripping regions <NUM> are sequentially associable to the machining stations <NUM> upon rotation of the workpiece-supporting unit <NUM> about the main rotation axis R-R. In other words, the workpiece-supporting unit <NUM>, when operated in rotation, is configured to sequentially bring the gripping regions <NUM> to the machining stations.

With reference to <FIG>, preferably, the gripping regions <NUM> are spaced apart along a circumferential direction C-C from the main rotation axis R-R. Still more preferably, the gripping regions <NUM> are equidistant from each other along the circumferential direction C-C and are located at an equal distance from the main rotation axis R-R along a radial direction.

Furthermore, as shown in <FIG>, preferably also the machining stations <NUM> are arranged along the circumferential direction C-C, so that the gripping regions <NUM> are all available simultaneously in respective machining stations <NUM>.

In alternative embodiments not shown in the appended figures, the machine tool <NUM> could have a linear configuration. In such a case, the machining stations are arranged in succession along a movement direction and the workpiece-supporting unit is configured to move the workpiece gripping regions along such a movement direction.

The machine tool <NUM> further comprises gripping members <NUM> arranged in the gripping regions <NUM>. In detail, each gripping member <NUM> is arranged in a respective gripping region <NUM>.

Each gripping member <NUM> comprises gripping jaws <NUM>, which are rotatably operable about a jaw rotation axis P-P, preferably oriented parallel to the main rotation axis R-R. The gripping jaws <NUM> are configured to grip a respective workpiece and rotate it about the gripping rotation axis P-P. Within the scope of the present invention, gripping jaws <NUM> are intended as mechanical members capable of switching between a closed configuration adapted to clamp a workpiece, and an open configuration in which the workpiece is insertable/disengageable. Preferably, the plurality of gripping jaws <NUM> are of the self-centering type.

It should be specified that the jaws <NUM> are configured to arrange the workpieces cantilevered from the workpiece-supporting unit <NUM>, so that they can be reached and machined by the machining devices.

As shown in <FIG> and <FIG>, each gripping member <NUM> comprises first engaging members <NUM> kinematically connected in rotation to respective jaws <NUM>. The first engaging members <NUM> are rotatable about a rotation axis P'-P', preferably distinct from the jaw rotation axis P-P with which they are associated. Even more preferably, the rotation axis P'-P' of the first engaging members <NUM> is oriented parallel to the jaw rotation axis P-P with which they are associated. In the embodiments of <FIG> and <FIG>, the rotation of the jaws <NUM> is constrained to that of the first engaging members <NUM> by means of a belt 4a which is tensionable by means of a special preloading element 4b (belt tensioner). However, other transmission members known in the state of the art such as, for example, an array of gears can be employed to transmit the rotary motion between the jaws <NUM> and the respective engaging members <NUM>.

More details on the first engaging members <NUM>, in particular on their geometric conformation, will be provided in the following disclosure.

With reference to <FIG>, the machine tool <NUM> further comprises actuator members <NUM> adapted to operate the rotation of the jaws <NUM> about the respective jaw rotation axes P-P by acting on the first engaging members <NUM>. Each actuator member <NUM> comprises second engaging members <NUM> rotatable and engageable in rotation with the first engaging members <NUM>. Preferably, the second engaging members <NUM> are configured to be rotated about the same rotation axis P'-P' as the respective first engaging members <NUM>.

Preferably, the actuator members <NUM> comprise an electric motor 5a configured to operate the rotation of the second engaging members <NUM>.

The second engaging members <NUM> are movable from\toward the respective first engaging members <NUM> of the gripping members <NUM> to act on such first engaging members <NUM>. With reference to <FIG>, preferably, each actuator member <NUM> comprises sliding means <NUM> configured to move the second engaging members <NUM> from\toward the first engaging members <NUM>. Preferably, the sliding members <NUM> are hydraulically, pneumatically or electronically operated.

In detail, the second engaging members <NUM> moving from and toward the respective first engaging members <NUM> switch between a pre-engaging and a locking configuration, respectively shown in <FIG>. In detail, the second engaging members <NUM> are movable from and toward the respective first engaging members <NUM> along an approaching/distancing direction M-M shown in <FIG>.

In the pre-engaging configuration the first and the second gripping members <NUM>, <NUM> are connected in rotation with clearance, while in the locking configuration the first and the second gripping members <NUM>, <NUM> are connected in rotation without clearance. Therefore, in the pre-engaging configuration the first and the second gripping members <NUM>, <NUM>, although coupled, can make minimum relative angular movements, otherwise in the locking configuration the first and the second gripping members <NUM>, <NUM> are firmly constrained in rotation to each other. Further details on forming the coupling between the first and the second gripping members <NUM>, <NUM> will be given in the following description.

The machine tool <NUM> object of the present invention further comprises a guide <NUM> for the first engaging members <NUM>. In detail, such a guide <NUM> extends between the machining stations <NUM>.

In the embodiments shown in the appended figures, preferably, such a guide <NUM> extends about the main rotation axis R-R between the machining stations <NUM>. In other words, preferably, the guide <NUM> extends along the circumferential direction C-C between the machining stations <NUM>.

In the aforementioned alternative embodiments in which the machine tool <NUM> has a linear shape, the guide extends along the movement direction between the machining stations. It should be specified that the movement direction can be both linear and serpentine.

In the following, reference will be made exclusively to the embodiments shown in the appended figures. However, what will be said in relation to the embodiments shown in the appended figures also applies to machine tools with linear conformation simply considering the movement direction as circumferential.

With reference to <FIG>, the first engaging members <NUM> are configured to slide on the guide <NUM> upon the operation of the workpiece-supporting unit <NUM>. Therefore, the guide <NUM> is shaped to lead the first engaging members <NUM> in the movement of the gripping regions <NUM> of the workpiece-supporting unit <NUM> between the machining stations <NUM>.

With reference to <FIG>, <FIG> and <FIG>, the guide <NUM> has a plurality of gaps <NUM> adapted to be positioned at the gripping regions <NUM>, when the latter are associated with the machining stations <NUM>. It should be specified that the gaps <NUM> are arranged at the machining stations <NUM>.

Preferably, gaps <NUM> is intended as discontinuities along the circumferential extension direction C-C of the guide <NUM>.

Preferably, in the embodiments shown in <FIG>, <FIG> and <FIG>, the guide <NUM> comprises a plurality of guide portions <NUM>, each extending along the circumferential direction between two adjacent machining stations <NUM>. Adjacent stations are to be understood as adjacent machining stations along the circumferential direction C-C which the workpiece crosses in sequence. In other words, preferably, the guide portions <NUM> extend in succession along the circumferential direction C-C and are interspersed with the gaps <NUM>.

In detail, preferably, each guide portion <NUM> has a pair of opposite ends <NUM>, and each gap <NUM> is delimited along the circumferential direction by ends <NUM> of adjacent guide portions <NUM>. Therefore, the gaps <NUM> are similar to circumferential openings in the guide <NUM> which divide it into a plurality of guide portions <NUM>.

As shown in <FIG>, each second engaging member <NUM> is arranged, at least partially, in a respective gap <NUM> of the guide <NUM>. It is therefore evident that the gaps are specially dimensioned to accommodate therein at least part of respective second engaging members <NUM> in both the pre-engaging and in the locking configuration. Preferably, the second engaging members <NUM> being configured to complete the guide <NUM> at the gaps <NUM> so as to describe a closed path on which the first engaging members <NUM> can slide.

Each second engaging member <NUM> is engaged with the respective first engaging member <NUM> when the gripping regions <NUM> are associated with the machining stations <NUM>. In other words, when the workpiece-supporting unit <NUM>, following a rotation, arranges the gripping regions <NUM> in subsequent machining stations <NUM>, the first and the second engaging means <NUM>, <NUM> are engaged. More precisely, they are located in the aforementioned pre-engaging configuration.

Therefore, as soon as the first engaging means <NUM> arrive at a machining station <NUM>, they are already engaged with the second engaging means <NUM> and it is therefore immediately possible to operate them to rotate the jaws <NUM>.

It is therefore evident that, advantageously, it is possible to bring the jaws <NUM> to the regime rotation speed while the second engaging means <NUM> approach the first engaging means <NUM>. Similarly, it is possible to brake the rotation of the jaws <NUM>, following machining, while the second engaging means <NUM> move away from the first engaging means <NUM>. This makes it possible to significantly reduce the passive times before and after machining, stretching the cycle time as much as possible to the actual machining time.

It should be clarified that finishing machining can also be performed in the pre-engaging configuration, even though this is not specifically intended for machining. In fact, in such a configuration the first and the second engaging means <NUM>, <NUM> are connected with clearance and this would create rotational vibrations which would significantly compromise the quality of the machining. Otherwise, the finishing machining can be performed in the locking configuration, where the first and the second engaging means <NUM>, <NUM> are firmly constrained in rotation (no clearance). However, it should be noted that, in order to reduce cycle times, it is possible to perform/start certain machining, such as roughing, already in the pre-engaging configuration.

It should also be specified that the guide <NUM> is configured to change the orientation of the first engaging members <NUM> which slide thereon, so as to orient them correctly to allow the coupling with the respective second engaging members <NUM> at the machining stations <NUM>. Orientation is intended as the angular position of the first engaging members <NUM> about the respective rotation axis P'-P'.

As shown in <FIG>, preferably, each second engaging member <NUM> is configured to continuously connect two distinct guide portions <NUM> along the circumferential direction C-C. By doing so, following the rotation of the workpiece-supporting unit <NUM>, the first engaging members <NUM> oriented by the guide <NUM> are arranged in the gaps <NUM>, coupling with the respective second engaging members <NUM>.

It should be specified that continuously connecting means that the second engaging members <NUM>, in particular during the transfer of the workpieces from one machining station to the next, extend within the gaps <NUM> along the circumferential direction C-C, connecting two adjacent guide portions <NUM>. More in detail, the second engaging members <NUM> are configured to continuously connect the ends <NUM> of adjacent guide portions <NUM> along the circumferential direction C-C.

In the embodiments of <FIG> and <FIG>, preferably, each second engaging member <NUM> comprises an engaging portion <NUM> projecting into a respective gap <NUM> and adapted to continuously connect two guide portions <NUM> along the circumferential direction C-C according to the above. Furthermore, the engaging portion <NUM> is rotatably couplable with clearance with the first engaging member <NUM>. In detail, the engaging portion <NUM> is configured to form a coupling with clearance between the first and the second engaging member <NUM>, <NUM>, when the second engaging member <NUM> is located in the pre-engaging configuration.

As indicated in <FIG> and <FIG>, preferably, each guide portion <NUM> extends along the circumferential direction C-C with a first radius of curvature R1, and the engaging portions <NUM> extend along the circumferential direction C-C with a second radius of curvature R2. Preferably, the first and the second radius of curvature R1, R2 are the same, so that when arranged with the same center they describe a closed circumferential path. It should be noted that in alternative embodiments, the first and the second radius of curvature R1, R2 can be different. Furthermore, in alternative embodiments, the radius of curvature of the guide portions <NUM> and the engaging portions <NUM> may not be constant in their extension along the circumferential direction C-C. By doing so, the guide portions <NUM> and the engaging portions <NUM> can be arranged to describe a closed path, for example, in the shape of an oval or the like.

Preferably, the guide <NUM>, and therefore each portion <NUM> thereof, is fixed and the workpiece-supporting unit <NUM> is configured to rotate with respect thereto around the main rotation axis R-R. In detail, the workpiece-supporting unit <NUM> rotating about the main rotation axis R-R slides the first engaging members on the guide <NUM> to position the gripping members <NUM> sequentially at the machining stations <NUM>.

In the following description we will focus on the conformation of the first and the second engaging members to better explain their couplings.

With reference to <FIG>, <FIG>, <FIG>, preferably, each first and second engaging member <NUM>, <NUM> comprises pre-engaging means 7a, 7b and locking means 8a, 8b.

The pre-engaging means 7a, 7b of the first and the second engaging members <NUM>, <NUM> are mutually engageable to form a coupling with clearance. In detail, the pre-engaging means 7a of each first engaging member <NUM> are couplable in rotation with clearance with the respective pre-engaging means 7b of the second engaging members. It should be specified that in the aforementioned pre-engaging configuration, the pre-engaging means 7a, 7b of the first and the second engaging members <NUM>, <NUM> are mutually engaged.

Preferably, the pre-engaging means 7a, 7b of the first and the second engaging members <NUM>, <NUM> are embodied in a female element and a male element which are mutually insertable into each other with clearance. It should be specified that the male and female element can be made independently of the first or the second engaging members <NUM>, <NUM>. In the embodiment shown in <FIG>, <FIG>, <FIG> the first engaging members <NUM> are shaped to make the female element, while the second engaging members <NUM> make the male element.

The locking means 8a, 8b of the first and the second engaging members <NUM>, <NUM> are mutually engageable to form a coupling without clearance. In detail, the pre-engaging means 7a of each first engaging member <NUM> are couplable in rotation without clearance with the respective pre-engaging means 7b of the second engaging members. It should be specified that in the aforementioned locking configuration, the pre-engaging means 7a, 7b of the first and the second engaging members <NUM>, <NUM> are mutually engaged. It should be specified that in the context of the present invention, coupling without clearance means that the first and the second engaging members <NUM>, <NUM> are firmly rotatably constrainable so that they cannot make relative rotations.

Preferably, the locking means 8a, 8b of the first and the second engaging members <NUM>, <NUM> are embodied in a female element and a male element mutually insertable into each other without play. The foregoing regarding the male and female element of the pre-engaging means applies mutatis mutandis also to the male and female element of the locking means, taking into account, however, that the latter must form a coupling without clearance.

With reference to <FIG>, when the second engaging member <NUM> is in the pre-engaging configuration, the pre-engaging means 7a, 7b of the first and second engaging members <NUM>, <NUM> are mutually engaged, while the locking means 8a, 8b are disengaged. Therefore, in the pre-engaging configuration the first and the second engaging members are kinematically connected in rotation about the axis P'-P', but can make small relative angular rotations.

With reference to <FIG>, when the second engaging member <NUM> is in the locking configuration, at least the locking means 8a, 8b of the first and the second engaging members <NUM>, <NUM> are mutually engaged. Therefore, in the locking configuration the first and the second engaging members are firmly constrained in rotation about the rotation axis P'-P'.

Preferably, the pre-engaging means 7a, 7b are arranged in a central portion of the first and the second engaging members <NUM>, <NUM> and the locking means 8a, 8b are arranged laterally with respect to the pre-engaging means 7a, 7b. Even more preferably, the locking means 8a, 8b are arranged laterally by both parts of the pre-engaging means 7a, 7b.

With reference to <FIG> and <FIG>, the pre-engaging means 7a of each first engaging member <NUM> preferably comprise two sliding surfaces <NUM> separated by an interspace <NUM>. In detail, the sliding surfaces <NUM> extend along a first main direction of extension D1-D1 and are spaced apart from the interspace <NUM> along a direction transverse to the first main direction of extension D1-D1.

The sliding surfaces <NUM> are configured to slide on the guide <NUM> upon rotation of the workpiece-supporting unit about the main axis R-R. Therefore, the guide <NUM>, in particular the guide portions <NUM>, is insertable into the interspace <NUM> and the sliding surfaces <NUM> guide the movement of the first engaging members along the circumferential direction C-C. Preferably, the sliding surfaces <NUM> are curved and have a radius of curvature equal to the first radius of curvature R1 of the guide <NUM>.

With reference to <FIG> and <FIG>, the pre-engaging means 7b of each second engaging member <NUM> comprise a pre-engaging wall <NUM> arranged in a relative gap <NUM> of the guide <NUM>. In detail, the pre-engaging wall <NUM> extends along a second main direction of extension D2-D2, and can be inserted with clearance in the interspace <NUM> between the pair of sliding surfaces <NUM>. Therefore, the pre-engaging wall <NUM> is configured to abuttingly receive the sliding surfaces <NUM> on opposite sides. The pre-engaging wall <NUM> is configured to be rotated about the rotation axis P'-P' of the second engaging member <NUM>. It should be noted that the rotation axis P'-P' of the second engaging member <NUM> passes through the central portion.

Preferably, the pre-engaging wall <NUM> comprises the above-described engaging member <NUM>.

In a first embodiment shown in <FIG>, <FIG>, the locking means 8a of each first engaging member <NUM> comprise a pair of locking surfaces <NUM> extending substantially along the first main direction of extension D1-D1 of the pair of sliding surfaces <NUM>. The locking surfaces <NUM> are spaced apart from the interspace <NUM>, i.e., they are arranged on opposite sides of the interspace <NUM>. It should be noted that each locking surface <NUM> is arranged laterally with respect to a sliding surface <NUM> associated therewith. It should be specified that laterally means that the locking surface <NUM> is spaced along a direction transverse to the first main direction of extension D1-D1. The locking surfaces <NUM> are thus spaced farther away from the interspace <NUM> with respect to the sliding surfaces <NUM>.

Preferably, the locking surfaces <NUM> are straight. Still more preferably, the locking surfaces <NUM> are oriented parallel to each other.

Still in the first embodiment, the locking means 8b of each second engaging member <NUM> comprise a locking wall <NUM> extending substantially along the main direction of extension of the respective pre-engaging wall <NUM>. In detail, the locking wall <NUM> is insertable without clearance in the interspace <NUM> between the pair of locking walls <NUM>. Therefore, the locking wall <NUM> is configured to abuttingly receive the locking surfaces <NUM> on opposite sides.

Preferably the locking wall <NUM> is straight so that it can be interposed between straight locking surfaces <NUM>.

Preferably, according to what is shown in <FIG>, the pre-engaging wall <NUM> and the locking wall <NUM> are integrally formed with each other and arranged in series along the approaching/distancing direction M-M of the second engaging members <NUM> to/from the first engaging members <NUM>. It should be specified that the pre-engaging wall <NUM> is closer to the first engaging members <NUM> with respect to the locking wall <NUM>. Furthermore, the locking wall <NUM> is laterally projecting from opposite sides of the engaging wall <NUM>.

In a second embodiment shown in <FIG> and <FIG>, the locking means 8a of each first engaging member <NUM> comprise a pair of locking surfaces <NUM> extending along a direction transverse to the first main direction of extension D1-D1 of the sliding surfaces <NUM>. Therefore, the locking surfaces <NUM> extend away from the sliding surfaces <NUM>. Preferably, the locking surfaces <NUM> extend from both parts of the sliding surfaces <NUM>. Even more preferably, the locking surfaces <NUM> substantially define a cross with the sliding surfaces <NUM>.

Still in the second embodiment, the locking means 8b of each second engaging member <NUM> comprise a locking wall <NUM> extending along the second main direction of extension of the respective pre-engaging wall <NUM>. The locking wall <NUM> is insertable without clearance between the pair of locking surfaces <NUM>. Preferably, in accordance with what is shown in <FIG>, the second engaging members comprise at least one tooth arranged laterally with respect to the pre-engaging wall <NUM> and forming the locking wall <NUM>. Still more preferably, there are two teeth arranged on opposite sides of the pre-engaging wall <NUM>.

With reference to <FIG>, <FIG>, the locking means 8a, 8b comprise centering means adapted to recover the angular clearance during the switching of the second engaging members <NUM> from the pre-engaging to the locking configuration.

In the embodiment of <FIG>, the centering means are made by means of an elastically deformable element. Preferably, the locking wall <NUM> comprises the elastically deformable element. Still more preferably, the elastically deformable element is made by a notch in the locking wall <NUM>.

Claim 1:
A machine tool (<NUM>) for machining, comprising:
- a plurality of machining stations (<NUM>) configured to machine a plurality of workpieces;
- a workpiece-supporting unit (<NUM>) having a plurality of gripping regions (<NUM>) adapted to be sequentially associated to the machining stations (<NUM>);
- a plurality of gripping members (<NUM>), each gripping member (<NUM>) being placed in a respective gripping region (<NUM>) of the workpiece-support unit (<NUM>) and comprising:
- a plurality of jaws (<NUM>) adapted to be rotated about a jaw rotation axis (P-P) and configured to grip a workpiece;
- first engaging members (<NUM>) rotating and kinematically rotatably connected to the plurality of jaws (<NUM>);
- a plurality of actuator members (<NUM>) for actuating the rotation of the jaws (<NUM>) about respective jaws rotation axes (P-P) by acting on the first engaging members (<NUM>), each actuator member (<NUM>) comprising second engaging members (<NUM>), rotatable and movable from\toward their respective first engaging members (<NUM>) of the gripping members (<NUM>) to act on said first engaging members (<NUM>);
characterised in that:
- the machine tool comprises a guide (<NUM>) for the first engaging members (<NUM>), extending between the machining stations (<NUM>), the first engaging members (<NUM>) being configured to slide on the guide (<NUM>) upon actuation of the workpiece-supporting unit (<NUM>), the guide (<NUM>) having a plurality of gaps (<NUM>) adapted to be positioned at the gripping regions (<NUM>);
- each second engaging member (<NUM>) is at least partially arranged in a respective gap (<NUM>) of the guide (<NUM>), the second engaging member (<NUM>) being engaged with its respective first engaging member (<NUM>) when the gripping regions (<NUM>) are associated with the machining stations (<NUM>).