Abstract:
A workpiece-gripping device for tool machines having a motorized chuck mounted on an operating head comprises a housing, a driving shaft journaled in the housing and provided with a shank engageable in the chuck, a locking member configured to engage a reaction member integral with the operating head when the shank engages the chuck, whereby the rotation of the device is prevented when the chuck is driven, and at least a pincer having jaws, of which at least one is movable and operatively connected via transmission means to said driving shaft for opening and closing.

Description:
BACKGROUND OF THE INVENTION 
   This invention is concerned with a workpiece-gripping device for tool machines. As well known, mechanical parts are generally manufactured starting from a steel or aluminum blank on which a tool machine having an operating head movable along one or more directions performs a number of machining operations such as boring, facing, drilling, tapping, and the like. Highly automated tool machines can automatically pick up a required tool from a tool magazine located beside the operating head of the machine. Loading and unloading of the workpiece to and from the worktable can be performed manually or, for a a higher productivity, by automated loading/unloading devices, such as disclosed in U.S. Pat. No. 4,716,647. There, the operating head picks the workpiece by means of a gripping device that is automatically mounted on the chuck, similarly to a regular tool. The head places the workpiece on the worktable, and the gripping device is then returned to the tool magazine, while a tool is mounted on the chuck. After the machining schedule is completed, the tool is returned to the tool magazine and the gripping device is again picked up, so that the operating head can remove the newly machined workpiece from the worktable and pick up a fresh one. 
   Known gripping devices such as disclosed in the above prior document are provided with pincers controlled by hydraulic cylinders driven by an external hydraulic circuit. However, there are drawbacks in hydraulically controlled pincers, notably that a supply circuit for high-pressure fluid has to be provided, with attendant increase of the costs of manufacturing, operating and maintaining the tool machine. Moreover, the very existence of the hydraulic circuit involves unavoidable long-term leakages due to wear of the controlling members, as well as leakages in the fluid-supply line. This circumstance leads to pollution of the working area and to possible malfunction. 
   Further, due to the intrinsic nature of hydraulic control systems, the delay from the control command and the completion of the actual mechanical event is never known accurately. Such a delay may vary considerably among different actions, and may change in the course of time due to line leakages, cylinder wear, and the like. Consequently, before displacing the head it is necessary to allow a certain time delay that is longer than the average foreseeable reaction time, with attendant lengthening of the work schedule. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is the main object of the invention to provide a workpiece-gripping device for tool machines which can overcome the drawbacks of known hydraulically controlled devices as mentioned above. More particularly, the gripping device of the invention should be suitable for use on conventional tool machines having a motorized chuck without requiring additional power sources, and should guarantee accurate and repeatable reaction times, thereby allowing the working schedule to be optimized. 
   The above and other objects and advantages, such as will better appear below, are attained by a gripping device having the features recited in claim  1 , while the dependent claims define other adavantageous though accessory features of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below with reference to a few preferred but non-esclusive embodiments, shown by way of non-limiting examples in the attached drawings, wherein: 
       FIG. 1  is a view in side elevation of a workpiece-gripping device according to the invention, 
       FIG. 2  is a plan view of the device of  FIG. 1 , 
       FIG. 3  is a cross-sectional view taken along line III-III of the device of  FIG. 2 , in association with an operating head of a conventional tool machine, 
       FIG. 4  is a view in cross-sectrion made along line IV-IV of the device of  FIG. 2 , 
       FIG. 5  is a view in cross-sectrion made along line V-V of the device of  FIG. 4 , 
       FIG. 6  is a schematic plan view of the operating mechanism of the device of  FIG. 1 , 
       FIG. 7  is a view in side elevation of a workpiece-gripping device according to an alternative embodiment of the invention, 
       FIG. 8  is a cross-sectional view taken along line VIII-VIII of the device of  FIG. 7 , in association with an operating head of a conventional tool machine, 
       FIG. 9  is a a cross-sectional view taken along line IX-IX of the device of  FIG. 8 , 
       FIG. 10  is a schematic plan view of the operating mechanism of the device of  FIG. 7 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1 to 6 , a workpiece-gripping device  10  is to be used in association with a conventional tool machine (not shown) having an operating head movable along one or more directions and capable of performing different machining operations on workpieces, such as boring, facing, drilling, tapping, and the like, while picking up machining tools as required from a tool magazine located beside the machine&#39;s operating head. 
   Device  10  comprises, according to the invention, a box-like housing  12 , whose bottom is closed by a cover  14 . A driving shaft  16  is journaled within housing  12  and is terminated, outside the housing, in a shank  18  that is axially engageable in a motorized chuck  20  carried on operating head  21  of the tool machine. 
   Driving shaft  16  is journaled on rolling bearings  22 ,  24  which are respectively housed in a cylindrical socket  26  of housing  12  and in a bore  28  in cover  14 , the bore being sealed by a sealing cap  30 . A sealing ring  32  is carried on the inner edge of cylindrical seat  26  and seals the outer surface of shaft  16 . The shaft has an eccentric portion  34  in the stretch between bearings  22  and  24 . 
   A pair of driven shafts  36 ,  38 , parallel to driving shaft  16 , are journaled within housing  12 , in front of driving shaft  16 , and have respective terminations  36   a ,  38   a  projecting outside cover  14  and carrying respective L-shaped, integral jaws  40 ,  42 , which cooperate with each other to act as pincers. 
   Each of the driven shafts  36 ,  38  is journaled in a pair of bearings  44 ,  46  and  48 ,  50 , respectively, of which one bearing  44 ,  48  is housed in a socket in housing  12 , while the other bearing  46 ,  50  is housed in a respective cylindrical opening in cover  14 . Sealing rings  56 ,  58  are received in the openings and seal the external surface of the respective driven shaft  36 ,  38 . 
   Both driven shafts  36 ,  38  carry respective, mutually engaging gear sections  36   b ,  38   b . Driven shaft  36  has an arm  60  radially extending beneath its own gear section  36   b  and arranged for camming cooperation with the eccentric portion  34  of driving shaft  16 , as well as an elongated projection  62 , radially extending on the opposite side. An elastic member, shown as a helical spring  64  on  FIG. 5 , is compressed between projection  62  and the internal wall of housing  12 , so that it will contrast the rotation of driven shaft  36 , caused by the rotation of driving shaft  16  due to the camming cooperation between the eccentric portion  34  and radial arm  60 . 
   A pillar  66  rising from housing  12  supports a peg  68  parallel to driving shaft  16  and axially insertable into a corresponding fixed socket  70  that is integral with the machine&#39;s operating head  21 . Peg  68  and socket  70  comprise respective complementary frustoconical portions  68   a ,  70   a , designed to help self-centering of peg  68  during insertion. 
   The operation of gripping device  10  when mounted on a conventional tool machine is described below. 
   When at rest, gripping device  10  is received in the tool magazine together with the machining tools. When a workpiece is to be loaded, operating head  21  of the machine picks up the gripping device from the tool magazine, the shank  18  of the gripping device being automatically axially inserted into chuck  20 , similarly to what would happen with a machining tool. At the same time, peg  68  becomes axially inserted into fixed socket  70 . The operating head  21  is then moved to a position above the workpiece to be loaded and the jaws  40 ,  42  are opened, by rotating the chuck (clockwise in  FIGS. 5 ,  6 ) against the elastic force of spring  64 , due to a camming cooperation between eccentric portion  34  and radial arm  60 , as well as to the meshing engagement between gear sections  36   b ,  38   b  of driven shafts  36 ,  38 . 
   A relative rotation between gripping device  10  and operating head  21  during rotation of the chuck is prevented by the engagement of peg  68  in socket  70 . Subsequently, operating head  21  moves jaws  40 ,  42  to a position around the waiting workpiece, and the chuck is then rotated back to its initial condition, so that the jaws are drawn back to their closed configuration, thereby gripping the workpiece. Operating head  21  now moves the workpiece to the worktable and releases it by causing the pincers to open following the same steps as above described. The operating head then returns the gripping device to the tool magazine and picks up the machining tool. At the end of the machining, the operating head returns the tool to the tool magazine and again picks ip the gripping device, in order to remove from the worktable the newly machined workpiece and pick up a fresh one. 
   As a person skilled in the art will appreciate, by mechanically operating the pincers as proposed by the invention several advantages are obtained. In particular, it is not necessary to implement an external operating system, because the rotation of the chuck is exploited directly, thereby reducing costs and substantially avoiding any operating delays, due to the mechanical connection from the chuck to the driven shafts carrying the jaws. Having now reference to  FIGS. 7 to 10 , a gripping device  110  according to an alternative embodiment of the invention comprises an elongated box-like housing  112  that is closed by a cover  114  at its bottom. 
   A driving shaft  116  is journaled within housing  112  and is terminated, outside housing  112 , in a shank  118  that is axially engageable in a motorized chuck  20  carried on operating head  21  of the tool machine. Driving shaft  116  is journaled on rolling bearings  122 ,  124  which are respectively housed in a cylindrical socket  126  of housing  112  and in a bore  128  in cover  114 , the bore being sealed by a sealing cap  130 . A sealing ring  132  is carried on the inner edge of cylindrical seat  126  and seals the outer surface of shaft  116 . The shaft has an eccentric portion  134  in the portion between bearings  122  and  124 . 
   Two pairs of driven shafts  136 ,  138  and  136 ′,  138 ′, aligned with each other and parallel to driving shaft  116 , are journaled within housing  112 , in mirror positions with respect to cross-plane A ( FIG. 9 ) through the axis of driving shaft  116 . The driven shafts have respective terminations  136   a ,  138   a  and  136 ′ a ,  138 ′ a , projecting outside cover  114  and carrying respective L-shaped, integral jaws  140 ,  142  and  140 ′,  142 ′, which cooperate with each other in pairs to act as a pair of pincers. 
   Each of the driven shafts  136 ,  138  and  136 ′,  138 ′ is journaled in a pair of bearings such as  144 ,  146  and  148 ,  150 , respectively, of which one is housed in a socket in housing  112 , while the other is housed in a respective cylindrical opening in cover  114 . Sealing rings such as  156 ,  158  are received in the openings and seal the external surface of the respective driven shaft. 
   The driven shafts in each pair are mutually coupled by respective, gear sections  136   b ,  138   b  and  136 ′ b ,  138 ′ b , integral therewith. Driven shafts  136  and  136 ′ nearer to driving shaft  116  have respective arms  160 ,  160 ′, arranged for camming cooperation with respective adjacent spans of eccentric portion  134  of driving shaft  116 , with interposed anti-friction bearings  135  and  135 ′. 
   Driven shafts  138  and  138 ′ farther from driving shaft  116  have respective elongated projections  162 ,  162 ′, radially extending from the opposite side of driving shaft  116 . Elastic members  164  and  164 ′, shown as helical springs on  FIG. 9 , are compressed between elongated projections  162 ,  162 ′ and the internal wall of housing  112 , so that they will contrast the rotation of driven shafts  136 ,  136 ′, caused by the rotation of driving shaft  116 , due to the camming cooperation between the eccentric portion  134  and radial arms  160 ,  160 ′. 
   A pillar  166  rising from housing  112  supports a peg  168  parallel to driving shaft  116  and axially insertable into a corresponding fixed socket  70  which is integral with operating head  21  of the machine. Peg  168  and socket  70  comprise respective complementary frustoconical portions  168   a ,  70   a , designed to help self-centering of peg  168  during insertion. 
   The operation of gripping device  110  according to the above described alternative embodiment is similar to the operation of the first embodiment, except that the device of the second embodiment can pick up two side-by-side workpieces at the same time. 
   More particularly, after the operating head  21  has moved to a position above the desired workpieces, a rotation of the chuck (clockwise in  FIG. 10 ) against the elastic force of springs  164  will cause the jaws  140 ,  142  and  140 ′,  142 ′ to open due to camming cooperation between eccentric portion  134  and arms  160  and  160 ′, and to meshing engagement between gear sections  136   b ,  138   b  and  136 ′ b ,  138 ′ b  of driven shafts  136 ,  138  and  136 ′,  138 ′. 
   A few preferred embodiments of the invention have been described, but a person skilled in the art will be able to make changes to them within the same inventive concept. In particular, other kinds of mechanical operation of the pincers may be provided, by using different camming members or by using linkages which can take different configurations, provided they are driven by the rotation of the chuck. Gear transmissions may also be used, e.g. by providing the driving shaft with a toothed wheel meshing with transverse racks or with respective driven wheels operatively connected with the jaws of the pincers. Further, other kinds of interconnecting members may be provided between the the jaws of the pincers instead of gear sections, such as leverages or linkages of different types. Moreover, such alternative systems may effect either a rotating opening movement of the jaws, as in the above described examples, or a linear movement. Further, the reaction member contrasting the rotation of the device with respect to the operating head, which in the example disclosed consists of a peg axially insertable into a fixed socket in the operating head, might be differently designed, provided that it is capable of engaging with the operating head when the device shank is engaged by the chuck. It should also be understood that it also falls within the scope of the invention that only one jaw of the pincer is movable, the other being fixed. 
   The disclosures in European Patent Application No. 05425503.9 from which this application claims priority are incorporated herein by reference.