Abstract:
A chuck unit for automatic machine tools perform both power tasks and high speed finishing of pieces with lubricant/coolant fluid flowing through a chuck shaft. The chuck unit includes a support on which a first chuck for a tool is mounted and driven by a motor. A second chuck is mounted inside the first chuck and is driven by the same or a second independent motor. A set of springs acts against a shaft with an attached gripper, to close the gripper in order to clamp the tool. The unit can therefore receive different types of tools and perform different tasks, eliminating the need to use different machines for different tasks. The pull of the power tool on upstream mechanical parts is discharged against the support structure of the first chuck.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/823,156 filed Mar. 30, 2001 now abandoned, the entirety of which is hereby incorporated herein. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     This invention relates to a chuck unit for automatic machine tools, designed to perform both power tasks and high-speed finishing of pieces, with lubricant/coolant fluid flowing through the chuck shaft. For this purpose, the unit in accordance with the invention comprises two coaxial chucks fitted one inside the other, driven by separate motors or by the same motor. 
     In particular, the unit in accordance with the invention is designed in such a way that when tasks are performed with the power tool, the pull exerted by that tool on the upstream mechanical parts is only discharged onto the supporting structure of the power chuck, and no stresses are transmitted to the bearings of the second (speed) chuck. 
     The result is a unit which can receive different types of tool and perform different types of task, for which it has so far been most advantageous to use two separate machines. 
     Modern automatic machine tools designed to perform milling and contouring tasks, etc., comprise a structure to which an operating head with a number of degrees of freedom is fitted; this head comprises an end effector generally constituted by a chuck or an electric chuck, to which the tool required for each job is fitted. 
     The characteristics of these operating heads vary considerably, especially in chip-forming tasks, depending on whether the tasks performed are power tasks carried out with a roughing tool which rotates at a relatively low speed (approx. 2000-3000 rpm) to remove large amounts of material, and is therefore subjected to considerable stress, or finishing tasks in which the tool rotates at a much higher speed (15-20,000 rpm) to perform a finishing task, and therefore removes small amounts of material. The stresses to which the tool is subjected and the reactions it discharges onto the upstream devices require the use of chucks of different characteristics and dimensions, which necessitates the construction of different operating heads. 
     For this reason, when two different types of task need to be performed, separate machines are often used, partly because of the time taken to replace these heads and reset the machine. However, the need is felt for a machine which can perform both types of task, ie. power and speed tasks, with no need to replace the operating head or the end effectors. 
     This solution would bring considerable savings, enabling even small companies to equip themselves suitably with automatic machines of this kind. 
     SUMMARY OF THE INVENTION 
     This problem is now solved by the present invention, which relates to a chuck unit for automatic machine tools designed to perform both power and finishing tasks. The said unit comprises (i) two chucks mounted coaxially, one inside the other, (ii) means which allow a tool for roughing work and a tool for finishing work to be fitted to the said chucks, and (iii) means designed to discharge onto the structure of the assembly the pull exerted on the cone of the tool when the tool is fitted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will now be described in detail, by way of example but not of limitation, by reference to the enclosed figures in which: 
     FIG. 1 shows a cross-section of a chuck unit in accordance with the invention, with two motors; 
     FIG. 2 shows a cross-section of the chuck in the rest position; 
     FIG. 3 shows a cross-section of the chuck unit in the tool-receiving position; 
     FIG. 4 shows a cross-section of the chuck unit in accordance with the invention, with the power tool fitted; 
     FIG. 5 shows a cross-section of the chuck unit in accordance with the invention, with the finishing tool fitted; 
     FIGS. 6 &amp; 7 show the chuck unit in accordance with a further preferred embodiment of the invention, with the power and finishing tools fitted; 
     FIGS. 8 &amp; 9 show a cross-section of the chuck unit in accordance with the invention, with a single motor; and 
     FIG. 10 shows a cross-section of a further preferred embodiment of the chuck unit in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     By reference to FIG. 1, the chuck unit in accordance with the invention comprises a support structure indicated as  1 , to which are fitted an electric motor  2  and the actual chuck unit, indicated as  3  and housed in a sleeve  33  which is integral with structure  1 . 
     The chuck assembly comprises a power chuck  4 , inside which a speed chuck  5  is fitted coaxially with the said power chuck. 
     Power chuck  4  is fitted to structure  1  via sets of bearings  6 , and a pulley or cogwheel  7 , to which motion is transmitted by motor  2  via a belt  8 , is fixed to the said power chuck. 
     Chuck  4  presents a conical opening  9  for a power tool, means for driving the tool being fitted in the said opening. 
     The tool is gripped by a gripper  10  shown in FIGS. 2 to  5 ; the said gripper is fitted to the end of a shaft  11  mounted inside speed chuck  5 . The axes of shaft  11 , chuck  5  and power chuck  4  coincide. 
     A set of springs  12  acts against one end of chuck  5  and against a shoulder of shaft  11 , pressing shaft  11  inwards, to the position in which the said shaft tends to close the gripper in order to clamp the tool applied to the chuck. 
     Speed chuck  5 , like power chuck  4 , has a conical opening at the end shown as  13 , in which means designed to drive the tool are fitted, and into which the cone of a finishing tool is inserted. 
     In accordance with the invention, the speed tools have a cone which is inserted into the seating of chuck  5 , without coming into contact with the walls of conical opening  9  of the power tool, while the cone of the power tools is dimensioned so that it can be inserted into the corresponding seating of chuck  4  without coming into contact with chuck  5 . 
     Chuck  5  is fitted inside chuck  4  via a set of bearings  15 . 
     A plate or discoidal element  16  is fitted at the inner end of power chuck  4 . A sliding grooved bushing  17  is fitted to chuck  5 , and motor  18 , which causes finishing chuck  5  to rotate, is mounted on the said bushing  17 . Bushing  17  widens at the front to define a ring-shaped wall  19  designed to rest against plate  16 . 
     A set of springs  20 , located inside ring-shaped wall  19 , act on one side against bushing  17  and on the other against plate  16 , tending to distance bushing  17  from chuck  4 . 
     Chuck  5  is fitted to structure  1 , near the rear end, via bearings  21 . 
     A cylinder  22  in which a piston  23  moves is fitted to the rear of sleeve  33 . Piston  23  is hollow, and a second piston  24  moves inside it. 
     Two chambers  31  and  32  are defined on opposite sides of piston  24 , and two more chambers  35  and  36  are defined on opposite sides of piston  23 . A bushing  25  is fitted to the rear end of speed chuck  5 . A body  26 , which slides inside the said bushing  25 , is pushed towards the exterior by a spring  27  which acts between the end wall of bushing  25  and body  26 . 
     Body  26  is hollow; end  34  of shaft  11  penetrates into it on one side, and a second shaft  28 , which is fitted with a gripper, illustrated in FIGS. 2 to  5  and indicated as  30 , penetrates into it on the other. 
     Bushing  25  comes to rest against bushing  17 , which is caused to rotate together with bushing  25  by chuck  5 . 
     Bushing  25  in turn causes body  26  to rotate; the said body  26  can rotate freely in relation to pistons  23  and  24 . 
     A spring  29  acts on shaft  28 , tending to distance it from shaft  11 . 
     The operation of the unit in accordance with the invention will now be explained, by reference to FIGS. 2 to  5 . 
     FIG. 2 shows the assembly in the rest position. 
     Spring  12  pushes shaft  11  back, with gripper  10  inside chuck  5 . 
     Springs  20  push bushing  17  back to that a gap of (for example) 1 or 2 millimeters remains between ring-shaped wall  19  and plate  16 . 
     To fit a roughing tool, the assembly is positioned as shown in FIG.  3 . 
     For this purpose, starting from the position shown in FIG. 2, a pressurized fluid is introduced into chamber  32  so that piston  24  advances and acts on gripper  30  via shaft  28  to bring the gripper into the opening position. 
     At the same time, a pressurized fluid is introduced into chamber  35  so as to advance piston  23 , which pushes forward body  26  and shaft  11 , to open gripper  10 . 
     The advance of body  26  compresses springs  27 , which in turn push forward bushing  25  and bushing  17 , overcoming the force of spring  20 , and bring ring-shaped wall  19  into contact with the corresponding seatings in plate  16 , thus closing the play between the two parts. 
     The power tool is then inserted into conical seating  9  in chuck  4  and locked with gripper  10 . 
     For this purpose, piston  24  is released; the said piston  24  moves backwards and closes gripper  30 , which locks shaft  11  in the position which closes gripper  10 . 
     Piston  23  is then released, and is pushed backwards to release body  26 . Body  26  is pushed by springs  27 . 
     The force exerted by springs  27  acts on shaft  11  on one side, via body  26  and gripper  30 , to lock the tool, while on the other side, via bushing  27  and bushing  17 , it keeps ring-shaped wall  19  pressed against plate  16 . It is then possible to start up motor  2 , which transmits motion via belt  8  to pulley  7 , and from there to chuck  4 . 
     Chuck  4  performs the power task, and the thrust which counterbalances the traction force exerted on the tool by shaft  11  to maintain it in position is discharged onto bushing  17  and from there to plate  16  and chuck  4 , without subjecting bearings  15  and  21  of the finishing chuck to any particular stress. 
     When the finishing tool needs to be fitted to chuck  5 , the unit is returned to the position shown in FIG. 3, and the cone of the new tool is inserted into seating  13  of chuck  5 . 
     Piston  23  is then released, moves backwards and releases piston  24 , thus releasing gripper  30  which disengages from shaft  11 . 
     The two pistons  23  and  24  move backwards and springs  27  are released. The force of springs  20  then prevails over bushings  17  and  25 ; the said springs  20  push back bushing  17  and ring-shaped wall  19 , thus restoring the play with plate  16 . 
     At this point motor  18  of the electric chuck can be switched on. The said motor  18  causes bushing  17  to rotate and finishing chuck  5  rotates with it. Finishing chuck  5  can rotate freely on bearings  15  and  21 . 
     FIGS. 6 and 7 show a further preferred embodiment of the chuck unit according to the invention, which has more compact dimensions than the one described above and eliminates the need to fit flanges for conveyance of coolant, because the coolant can flow directly through shaft  11 . 
     In this configuration, two coaxial cylindrical bodies  41  and  42  are fitted to rear plate  40  of sleeve  33 , cylinder  41  having a lightly smaller inner diameter than cylinder  42 . 
     Internally, cylinders  41  and  42  are shaped to define a pair of ring-shaped chambers  43  and  44  in which two ring-shaped pistons shown as  45  and  46  slide. 
     Inside cylindrical bodies  41  and  42  there is a bushing  47 , fitted to slide on shaft  11 . 
     The diameter of bushing  47  is larger than the inner diameter of pistons  45  and  46 , and the said bushing  47  acts as a stop for them. 
     A flange  48  is also fitted to slide on shaft  11 ; the outer diameter of the said flange  48  is substantially equal to the inner diameter of bushing  47 . 
     A set of springs  60 , which tend to distance bushing  47  from flange  48 , are housed in bushing  47 . 
     A cylindrical body  61  which supports cylindrical body  49  is fitted to cylindrical body  41 . Piston  24  slides in cylindrical body  49 , defining two opposite ring-shaped chambers  31  and  32  inside it. 
     Shaft  11  projects from bushing  48  and is elongated at the rear so that it penetrates into a seating in piston  24 . 
     The unit operates as follows. 
     To fit the power tool, start with the configuration shown in FIG. 6, with pressurized fluid in chambers  43  and  44 . This pressure pushes pistons  45  and  46  towards one another; piston  46  strikes wall  65  of cylindrical body  41 , of smaller diameter, while piston  45  strikes the edge of bushing  47 , freeing a space which allows shaft  11  to slide. 
     Pressurized fluid is then conveyed into chamber  32 , thus causing the movement of piston  24 , which pushes forward shaft  11  (to the right in the figure), opening gripper  10  which is inserted into the cone of the power tool shown as P. 
     At this point, the pressure is released from chambers  32 ,  43  and  44 , causing pressurization of chamber  31 . 
     Springs  60  then push flange  48  towards the rear of the chuck unit, and shaft  11  moves with it. This movement of shaft  11  causes the gripper to lock power tool P in its seating. 
     Flanges  62  and  63 , via springs  64 , ensure that pistons  45  and  46  return to their end-of-stroke positions against flanges  61  and  42 . 
     The force exerted by springs  60  overcomes that of springs  20 , with the result that on one side springs  60  push bushing  47  to press against bushing  17 , thus pushing ring-shaped wall  19  against plate  16 , while on the opposite side flange  48  engages the enlarged end of shaft  11 , shown as no. 50, exerting sufficient force on the shaft to counteract the thrust discharged by the tool. 
     To fit the finishing tool, start with the configuration shown in FIG. 6, with the pressurized fluid in chambers  43  and  44 . Bring gripper  10  forward again and insert the cone of the finishing tool, which penetrates into seating  13 , after which the pressurized fluid is only discharged into chamber  32 , thus pressurizing chamber  31 . 
     Springs  60  remain compressed as a result of the force exerted by pistons  45  and  46 . 
     In this position, the edge of flange  47  remains a few millimeters away from flange  17 , which can therefore be pushed backwards by springs  20 , thus interrupting contact between ring-shaped wall  19  and plate  16 . 
     In this position, shaft  11  is pushed backwards, but this time by springs  12 , which exert the necessary force to clamp the cone of the finishing tool. 
     FIG. 10 shows a further embodiment of the chuck unit in accordance with the invention, which is more compact and practical. 
     In this embodiment the power chuck  4  is actuated by a motor  80 , housed inside the sleeve  33 . 
     The support structure is no more necessary, and this enhances the interchangeability of the apparatus. 
     FIGS. 8 and 9 show a further embodiment of the chuck unit in accordance with the invention, which is much cheaper than the one described above because electric motor  2 , pulley or cogwheel  7  and belt  8  are not used; if motor  18  is sufficiently powerful, it can be used for power tasks as well as finishing tasks. 
     In this configuration, power chuck  4  has a male coupling  70  on the back. Flange  17  has a female coupling  71  on ring-shaped wall  19 . 
     The unit operates as follows: 
     To fit the power tool, always start with the configuration shown in FIG. 6, with the pressurized fluid in chambers  43  and  44 . 
     Pressurized fluid is then conveyed into chamber  32 , thus causing the movement of piston  24 , which pushes forward shaft  11  (to the right in the figure), opening gripper  10  which is inserted into the cone of the power tool shown as P. 
     At this point, the pressure is released from chambers  32 ,  43  and  44 , causing pressurization of chamber  31 . 
     Springs  60  then push flange  48  towards the rear of the chuck unit, and shaft  11  moves with it. This movement of shaft  11  causes the gripper to lock power tool P in its seating. 
     Flanges  62  and  63 , via springs  64 , ensure that pistons  45  and  46  return to their end-of-stroke positions against flanges  61  and  42 . 
     The force exerted by springs  60  overcomes that of springs  20 , with the result that on one side springs  60  push bushing  47  to press against bushing.  17 , thus causing ring-shaped wall  19  to engage with female connector  71  above male connector  70  of chuck  4 . 
     On the opposite side flange  48  engages the enlarged end of shaft  11 , shown as no.  50 , exerting sufficient force on the shaft to counteract the thrust discharged by the tool. 
     To fit the finishing tool, start with the configuration shown in FIG. 6, with the pressurized fluid in chambers  43  and  44 . Bring gripper  10  forward again and insert the cone of the finishing tool, which penetrates into seating  13 , after which the pressurized fluid is only discharged into chamber  32 , thus pressurizing chamber  31 . 
     Springs  60  remain compressed as a result of the force exerted by pistons  45  and  46 . 
     In this position, the edge of flange  47  remains a few millimeters away from flange  17 , which can therefore be pushed backwards by springs  20 , thus interrupting contact between ring-shaped wall  19  and female connector  71 , and between chuck  4  and male connector  70 . 
     In this position, shaft  11  is pushed backwards, but this time by springs  12 , which exert the force necessary to clamp the cone of the finishing tool. As will be clear from the description given, the chuck unit in accordance with the invention is very useful because it enables two different types of job to be performed with a single machine, and allows the operator to change from one to the other in a few seconds merely by replacing the tool, with no need to use a second machine or to replace the end effectors, which would involve resetting the zeros, repositioning the workpieces and so on, leading to considerable wastage of time and long machine stoppages. 
     An expert in the field could devise numerous modifications and variations, all of which should be deemed to fall within the scope of this invention.