Patent Description:
As is known, workpieces intended to be machined on machine tools can be fixed on a platform - which in turn is installed in the work area of the machine tool - by way of a series of locking devices.

In particular, each one of the locking devices can comprise a hollow cylindrical support which is fixed at right angles to the platform and is provided with retention means for receiving and axially retaining a pin which is fixed to the workpiece.

In some known systems, the retention means can comprise a triad of inserts which, on command by an irreversible clamping mechanism, can slide radially in the hollow cylindrical support between an open position, in which they free up the cavity of the hollow cylindrical support, allowing the insertion and extraction of the pin, and a closed position, in which with their inner ends they engage a circumferential groove of the pin that has been inserted in the hollow cylindrical support, so as to axially retain it.

The clamping mechanism can comprise an annular element which, by rotating about its own axis on command from a screw, interacts with the inserts with a cam action, causing their radial translation.

The conventional devices described above have a number of limitations and drawbacks, which are explained below.

The reduced contact surface between the ends of the inserts and the pin inevitably limits the maximum retaining force that can be exerted by the device.

In addition, the clamping mechanism is made up of many mechanical parts, some of which interact by slipping against each other, which entails high manufacturing costs and limitations in terms of reliability and lifetime, owing to the wear to which the mechanical parts are subjected.

Last but not least, the dimensions of the clamping mechanism on the one hand make it necessary to increase the diameter of the hollow cylindrical support, with drawbacks in terms of manufacturing costs, weight and encumbrance, while on the other hand they reduce the useful diameter for the seat of the pin and, as a consequence, the diameter of the pin and therefore its strength. This aspect is especially unwelcome because, usually, the pin is made hollow so as to coaxially accommodate the screw for fixing to the workpiece. For reasons of strength, it would therefore be desirable for the pin to have an outside diameter as wide as possible.

<CIT> discloses a modular structure for supporting blanks, which comprises a locking device (referred to as "fixing element") according to the preamble of claim <NUM>. In <CIT>, the claws (referred to as "jaws") have cylindrical profiles with toothed grip surfaces at their ends, which are adapted to restrainedly engage corresponding toothed portions of the pin. In addition, the jaws can be opened/closed by means of a screw, which is inserted in a through hole formed in one of the jaws and engages a threaded hole formed in the other jaw. The pin is provided with a passage for the screw, since the latter interferes with the cavity of the fixing element in which the pin is received.

The aim of the present invention is to provide a locking device for workpieces that are adapted to be machined on machine tools which, with respect to conventional systems, is capable of exerting a greater retaining force, is stronger, less subject to wear and cheaper to make, and which is capable of accommodating pins of relatively wide diameter without needing to excessively dimension the diameter of the cylindrical support.

Within this aim, an object of the present invention is to provide a device that makes it possible to manually lock/unlock the workpiece in relatively rapid times.

This aim and this and other objects, which will become clearer from the description that follows, are achieved by a locking device having the characteristics recited in the appended claim <NUM>, while the appended dependent claims define other characteristics of the invention which are advantageous, although secondary.

Now the invention will be described in greater detail, with reference to a preferred but not exclusive embodiment thereof, which is illustrated for the purposes of non-limiting example in the accompanying drawings, wherein:.

With reference to the figures, the reference numeral <NUM> generally designates a locking device for obtained workpieces that are adapted to be machined on machine tools and machining centers.

In particular, with initial reference to <FIG>, a series of locking devices <NUM>, e.g., four locking devices, can be used for positioning and locking in place a generic workpiece W on a platform P installed in the working area of the machine tool (not shown) and conventionally provided with a grid of threaded openings O.

Each one of the locking devices <NUM> is adapted to receive and retain a pin <NUM> fixed to the workpiece W. In a manner that is conventional per se, the pin <NUM> can be hollow and fixed to the workpiece W by way of a first screw S1 inserted in the pin <NUM> and screwed into a threaded hole H that has been previously made in the workpiece W.

The locking device <NUM> comprises a support <NUM> extending about an axis A (<FIG>, <FIG> and <FIG>), which has an axial cavity <NUM> for receiving the pin <NUM>. The support <NUM> has a substantially cylindrical profile and is conventionally provided with retention means for retaining the pin <NUM> axially, by engaging a circumferential groove <NUM> thereof.

With particular reference to <FIG>, in a manner that is conventional per se, the support <NUM> is adapted to be fixed at right angles to the platform P. In this embodiment, the support <NUM> is fixed to the platform P with a second screw S2 which is inserted in a respective axial seat <NUM> of the support <NUM> and screwed into one of the threaded openings O of the platform P.

With particular reference to <FIG>, <FIG> and <FIG>, the retention means according to the invention comprise two claws <NUM>, <NUM> with curved profiles with opposing concavities, which are inserted so that they can slide in two respective mutually opposite slots <NUM>, <NUM> of the support <NUM> in order to translate between an open position, in which they do not interfere with the insertion/extraction of the pin <NUM>, and a closed position, in which they engage the groove <NUM> of the pin <NUM> that has been inserted into the support <NUM>, in opposing positions, and they are functionally interconnected in an opening/closing relationship by an actuation screw <NUM> which is positioned so as not to interfere with the pin <NUM> and has at least one threaded end <NUM> which engages a corresponding threaded hole <NUM> provided in one of the claws <NUM>.

The actuation screw <NUM> passes through a passage <NUM> provided in the support <NUM> at right angles to the axis A, in such a position as to not interfere with the axial cavity <NUM>.

Preferably, the other end 28R of the actuation screw <NUM> is also threaded but in the direction opposite to the first end, and engages a corresponding threaded hole 22R of the other claw <NUM>. In this manner, the rotation of the actuation screw <NUM> in one direction or in the other simultaneously produces the approach/distancing of both claws <NUM>, <NUM>, so as to halve the locking/release times.

As illustrated in detail in <FIG> and <FIG>, the two claws <NUM>, <NUM> engage the groove <NUM> of the pin <NUM> with respective frustum-shaped internal edges 20C, 22C, in the manner that will be described in more detail below.

As illustrated in detail in <FIG>, the pin <NUM> has a base <NUM>' designed to abut against the workpiece W. A cylindrical raised portion <NUM> rises centrally from the base <NUM>' and engages a corresponding cylindrical seat WS in the workpiece W at the mouth of the threaded hole H.

The pin <NUM> has a frustum-shaped portion 12C adjacent to the base <NUM>', which is adapted to engage a corresponding frustum-shaped inlet 16C of the axial cavity <NUM> for centering purposes.

The groove <NUM> is delimited in a lower region, that is to say, on the side of the free end of the pin <NUM> opposite from the base <NUM>', by a frustum-shaped annular wall 18C which, when the workpiece W is locked in place, is engaged by the frustum-shaped internal edges 20C, 22C of the claws <NUM>, <NUM>.

With particular reference to <FIG>, the frustum-shaped internal edges 20C, 22C have an angular extension, at the smallest diameter, which is preferably comprised between <NUM>° and <NUM>°, more preferably approximately <NUM>°, so that the two claws <NUM>, <NUM> together engage the frustum-shaped annular wall 18C on a minimum arc of <NUM>°. The actuation screw <NUM> engages respective extensions of the claws <NUM>, <NUM> which extend beyond the frustum-shaped internal edges 20C, 22C, therefore outside the region of interference with the pin <NUM>.

With particular reference now to <FIG>, <FIG>, <FIG>, <FIG> and <FIG>, the travel of the two claws <NUM>, <NUM> is delimited in both directions by two respective grub screws <NUM>, <NUM>, which are screwed into respective threaded passages <NUM>, <NUM> of the support <NUM> at right angles to the axis of the actuation screw <NUM>, and which engage two respective elongated slits <NUM>, <NUM> which are provided in the claws <NUM>, <NUM>. The grub screws <NUM>, <NUM>, by abutting against the opposing ends of the elongated slits <NUM>, <NUM>, delimit the opening/closing travel of the claws <NUM>, <NUM>. The threaded passages <NUM>, <NUM> are advantageously closed by respective plugs such as <NUM> (<FIG>).

The claws <NUM>, <NUM> are also provided with respective service holes <NUM>, <NUM> in order to facilitate their extraction from the respective slots <NUM>, <NUM> during maintenance, assembly, and the like.

In operation, in a manner that is conventional per se, once the number of locking devices <NUM> necessary has been established together with their positions, for each one a threaded hole H is created in the workpiece W and a pin <NUM> is fixed thereto by way of the first screw S1. Also in a conventional manner, the support <NUM> is fixed to one of the threaded openings O of the platform P with the second screw S2.

At this point, with the claws <NUM>, <NUM> in the open configuration, in which they leave the axial cavity substantially free, the workpiece W is placed on the supports <NUM> fixed to the platform P, inserting the pins <NUM> into the axial cavities <NUM>.

After this, the locking devices <NUM> are tightened by rotating the actuation screw <NUM> in the direction to close the claws <NUM>, <NUM> on the pin <NUM>. The frustum-shaped internal edges 20C, 22C of the claws <NUM>, <NUM> engage the frustum-shaped annular wall 18C of the groove <NUM> so as to axially bias the pin <NUM> toward the inside of the cylindrical support <NUM>, with the frustum-shaped portion 12C engaging the frustum-shaped inlet 16C and thus ensuring perfect centering (<FIG>).

As illustrated in <FIG>, the inner faces of the claws <NUM>, <NUM> do not come into contact with the groove <NUM>. In this manner, the closing clamping action carried out by the claws <NUM>, <NUM> does not interfere with the centering action which, as mentioned above, is determined by the coupling between the frustum-shaped portion 12C of the pin <NUM> and the frustum-shaped inlet 16C of the cavity <NUM>.

In practice it has also been found that the invention fully achieves the set aims.

In particular, since the locking device is composed of a small number of parts that have a relatively solid structure, it is extremely strong and reliable, as well as being relatively cheap to make.

The clamping mechanism constituted by the actuation screw <NUM> directly engaging the two claws <NUM>, <NUM>, in addition to being strong and resistant to wear, influences neither the diameter of the support <NUM> nor the diameter of the axial cavity, therefore making it possible to maximize the diameter of the pin <NUM> without needing to excessively dimension the outside diameter of the support.

The two claws <NUM>, <NUM> with curved profiles, by engaging an ample frustum-shaped surface of the groove <NUM> of the pin <NUM> with their frustum-shaped internal edges 20C, 22C, is capable of exerting a very high retaining force without risk of yielding.

The double threading on the actuation screw <NUM> makes it possible to manually lock/release the workpiece W extremely rapidly, to the advantage of productivity.

A preferred embodiment of the invention has been described, but obviously the person skilled in the art may perform various modifications and variations within the scope of protection of the claims.

For example, although the double threading on the actuation screw makes it possible to accelerate the locking/release of the device, if timing is not a critical factor then the actuation screw could be provided with a single threading which acts on one of the claws, and simply be pivoted to the other claw in a relationship of thrust/traction.

Claim 1:
A locking device for workpieces (W) that are adapted to be machined on machine tools, which comprises a support (<NUM>) extending about an axis (A), which has an axial cavity (<NUM>), adapted to receive a pin (<NUM>) fixed to the workpiece (W), and has retention means for retaining said pin (<NUM>) axially, said retention means comprising two claws (<NUM>, <NUM>) which are inserted so that they can slide in two respective mutually opposite slots (<NUM>, <NUM>) of the support (<NUM>) in order to translate between an open position, in which they do not interfere with the insertion/extraction of the pin (<NUM>), and a closed position, in which they are adapted to engage a circumferential groove (<NUM>) of the pin (<NUM>) that has been inserted into the support (<NUM>), in opposing positions, and they are functionally interconnected in an opening/closing relationship by an actuation screw (<NUM>) which is positioned so as not to interfere with the pin (<NUM>) and has at least one first threaded end (<NUM>) which engages a corresponding threaded hole (<NUM>) provided in one of the claws (<NUM>), characterized in that said two claws (<NUM>, <NUM>) have curved profiles with opposite concavities, and in that said actuation screw (<NUM>) passes through a passage (<NUM>) provided in said support (<NUM>) at right angles to the axis (A), in such a position as not to interfere with the axial cavity (<NUM>).