Patent Publication Number: US-2022234119-A1

Title: Locking device for workpieces that are adapted to be machined on machine tools

Description:
The present invention relates to a locking device for workpieces that are adapted to be machined on machine tools. 
     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. 
     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  1 , 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: 
         FIG. 1  is a perspective view of the locking device according to the invention; 
         FIG. 2  is an exploded perspective view of the locking device of  FIG. 1 ; 
         FIG. 3  is a perspective view of a first component of the locking device of  FIG. 1 ; 
         FIG. 4  is a side view of the component of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of  FIG. 4  taken along the axis V-V; 
         FIG. 6  is a cross-sectional view of  FIG. 4  taken along the line VI-VI; 
         FIG. 7  is a side view of a second component of the locking device according to the invention; 
         FIG. 8  is a cross-sectional view of  FIG. 7  taken along the line VIII-VIII; 
         FIG. 9  is a perspective view of the component of  FIG. 7  seen from a first angle; 
         FIG. 10  is a perspective view of the component of  FIG. 7  seen from a second angle; 
         FIG. 11  is a partially cross-sectional side view of the locking device according to the invention; 
         FIG. 12  is a cross-sectional view of  FIG. 11  taken along the line XII-XII; 
         FIG. 13  is an axial cross-sectional view of the device according to the invention in the operating configuration. 
     
    
    
     With reference to the figures, the reference numeral  10  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. 13 , a series of locking devices  10 , 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  10  is adapted to receive and retain a pin  12  fixed to the workpiece W. In a manner that is conventional per se, the pin  12  can be hollow and fixed to the workpiece W by way of a first screw S 1  inserted in the pin  12  and screwed into a threaded hole H that has been previously made in the workpiece W. 
     The locking device  10  comprises a support  14  extending about an axis A ( FIGS. 5, 11 and 13 ), which has an axial cavity  16  for receiving the pin  12 . The support  14  has a substantially cylindrical profile and is conventionally provided with retention means for retaining the pin  12  axially, by engaging a circumferential groove  18  thereof. 
     With particular reference to  FIG. 13 , in a manner that is conventional per se, the support  14  is adapted to be fixed at right angles to the platform P. In this embodiment, the support  14  is fixed to the platform P with a second screw S 2  which is inserted in a respective axial seat  19  of the support  14  and screwed into one of the threaded openings O of the platform P. 
     With particular reference to  FIGS. 2, 12 and 13 , the retention means according to the invention comprise two claws  20 ,  22  with curved profiles with opposing concavities, which are inserted so that they can slide in two respective mutually opposite slots  24 ,  26  of the support  14  in order to translate between an open position, in which they do not interfere with the insertion/extraction of the pin  12 , and a closed position, in which they engage the groove  18  of the pin  12  that has been inserted into the support  14 , in opposing positions, and they are functionally interconnected in an opening/closing relationship by an actuation screw  28  which is positioned so as not to interfere with the pin  12  and has at least one threaded end  28 L which engages a corresponding threaded hole  20 L provided in one of the claws  20 . 
     In the embodiment described herein, the actuation screw  28  passes through a passage  29  provided in the support  14  at right angles to the axis A, in such a position as to not interfere with the axial cavity  16 . 
     Preferably, the other end  28 R of the actuation screw  28  is also threaded but in the direction opposite to the first end, and engages a corresponding threaded hole  22 R of the other claw  22 . In this manner, the rotation of the actuation screw  28  in one direction or in the other simultaneously produces the approach/distancing of both claws  20 ,  22 , so as to halve the locking/release times. 
     As illustrated in detail in  FIGS. 7-10 and 13 , the two claws  20 ,  22  engage the groove  18  of the pin  12  with respective frustum-shaped internal edges  20 C,  22 C, in the manner that will be described in more detail below. 
     As illustrated in detail in  FIG. 13 , the pin  12  has a base  12 ′ designed to abut against the workpiece W. A cylindrical raised portion  12 S rises centrally from the base  12 ′ and engages a corresponding cylindrical seat WS in the workpiece W at the mouth of the threaded hole H. 
     The pin  12  has a frustum-shaped portion  12 C adjacent to the base  12 ′, which is adapted to engage a corresponding frustum-shaped inlet  16 C of the axial cavity  16  for centering purposes. 
     The groove  18  is delimited in a lower region, that is to say, on the side of the free end of the pin  12  opposite from the base  12 ′, by a frustum-shaped annular wall  18 C which, when the workpiece W is locked in place, is engaged by the frustum-shaped internal edges  20 C,  22 C of the claws  20 ,  22 . 
     With particular reference to  FIG. 8 , the frustum-shaped internal edges  20 C,  22 C have an angular extension, at the smallest diameter, which is preferably comprised between 60° and 120°, more preferably approximately 90°, so that the two claws  20 ,  22  together engage the frustum-shaped annular wall  18 C on a minimum arc of 180°. The actuation screw  28  engages respective extensions of the claws  20 ,  22  which extend beyond the frustum-shaped internal edges  20 C,  22 C, therefore outside the region of interference with the pin  12 . 
     With particular reference now to  FIGS. 2, 6, 8, 9 and 11 , the travel of the two claws  20 ,  22  is delimited in both directions by two respective grub screws  30 ,  32 , which are screwed into respective threaded passages  34 ,  36  of the support  14  at right angles to the axis of the actuation screw  28 , and which engage two respective elongated slits  38 ,  40  which are provided in the claws  20 ,  22 . The grub screws  30 ,  32 , by abutting against the opposing ends of the elongated slits  38 ,  40 , delimit the opening/closing travel of the claws  20 ,  22 . The threaded passages  34 ,  36  are advantageously closed by respective plugs such as  44  ( FIG. 11 ). 
     The claws  20 ,  22  are also provided with respective service holes  46 ,  48  in order to facilitate their extraction from the respective slots  24 ,  26  during maintenance, assembly, and the like. 
     In operation, in a manner that is conventional per se, once the number of locking devices  10  necessary has been established together with their positions, for each one a threaded hole H is created in the workpiece W and a pin  12  is fixed thereto by way of the first screw S 1 . Also in a conventional manner, the support  14  is fixed to one of the threaded openings O of the platform P with the second screw S 2 . 
     At this point, with the claws  20 ,  22  in the open configuration, in which they leave the axial cavity substantially free, the workpiece W is placed on the supports  14  fixed to the platform P, inserting the pins  12  into the axial cavities  16 . 
     After this, the locking devices  10  are tightened by rotating the actuation screw  28  in the direction to close the claws  20 ,  22  on the pin  12 . The frustum-shaped internal edges  20 C,  22 C of the claws  20 ,  22  engage the frustum-shaped annular wall  18 C of the groove  18  so as to axially bias the pin  12  toward the inside of the cylindrical support  14 , with the frustum-shaped portion  12 C engaging the frustum-shaped inlet  16 C and thus ensuring perfect centering ( FIG. 13 ). 
     As illustrated in  FIG. 13 , the inner faces of the claws  20 ,  22  do not come into contact with the groove  18 . In this manner, the closing clamping action carried out by the claws  20 ,  22  does not interfere with the centering action which, as mentioned above, is determined by the coupling between the frustum-shaped portion  12 C of the pin  12  and the frustum-shaped inlet  16 C of the cavity  16 . 
     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  28  directly engaging the two claws  20 ,  22 , in addition to being strong and resistant to wear, influences neither the diameter of the support  14  nor the diameter of the axial cavity, therefore making it possible to maximize the diameter of the pin  12  without needing to excessively dimension the outside diameter of the support. 
     The two claws  20 ,  22  with curved profiles, by engaging an ample frustum-shaped surface of the groove  18  of the pin  12  with their frustum-shaped internal edges  20 C,  22 C, is capable of exerting a very high retaining force without risk of yielding. 
     The double threading on the actuation screw  28  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. 
     Also, as the skilled person will easily grasp, by conveniently shaping the claws, the actuation screw, instead of passing through the support, could interconnect the claws externally to the support. 
     The disclosures in Italian Patent Application No. 102021000001679 from which this application claims priority are incorporated herein by reference.