Abstract:
A machine tool comprises a tool spindle which can be positioned in 3 axes and a pivot bridge pivotable about an A axis with a round table for mounting a workpiece pallet supporting a workpiece. Furthermore, in front of the pivot bridge, a mount is provided for a processed workpiece or workpiece to be processed located on a workpiece pallet. Between the mount and the pivot bridge a pallet changer is provided which can only perform a vertical displacement movement and a pivot movement about a vertical axis. Workpiece pallets are picked up and put down only during the vertical displacement movement of the pallet changer, or possibly by pivoting the pivot bridge about the A axis.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2013 208 440.4, filed May 8, 2013, and German Patent Application, Serial No. 10 2013 216 752.0, filed Aug. 23, 2013, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     FIELD 
     The invention relates to a machine tool for 5-axis processing of workpieces comprising 
     a machine frame having a horizontal machine bed and a vertical stand, processing chamber formed on the machine frame, at least one rotary-driven tool spindle which is mounted in the stand and movable in the processing chamber in axes that are perpendicular to one another, namely an X axis and a Y axis, a pivot bridge mounted in the processing chamber which pivot bridge is drivable pivotably about an A axis parallel to the X axis, at least one round table arranged on the pivot bridge for releasably mounting a workpiece pallet, which round table is pivotable about a B axis perpendicular to the A axis, a loading and unloading chamber formed in front of the processing chamber, at least one pallet changer arranged in the loading and unloading chamber, wherein the pallet changer is displaceable only in vertical direction and is drivable pivotably about a vertical axis, wherein the pallet changer comprises first and second holding means for releasably mounting at least two workpiece pallets, wherein the pallet changer is movable from a lower loading and unloading position with a second workpiece pallet mounted in a second holding means in vertical direction via at least one middle position forming a connection between a first holding means and a first workpiece pallet located on a round table of the pivot bridge, wherein the pallet changer is movable from the middle position into an upper position, in which the first workpiece pallet connected to the first holding means is lifted upwards from the round table of the pivot bridge, wherein the pallet changer is rotatable in the upper position about the vertical axis by pivoting out the first workpiece pallet lifted from the pivot bridge into the loading and unloading chamber and by pivoting in the second workpiece pallet from the loading and unloading chamber into the processing chamber, and wherein the pallet changer is lowerable via the middle position back into the lower position. 
     BACKGROUND 
     The aforementioned machine tool for five-axis processing workpieces is known from U.S. Pat. No. 8,640,313 B2. In this workpiece, a Z axis is formed by the pivot bridge being formed on a tool carriage which is movable in the Z direction. The pallet changer comprises two pairs of arms serving for receiving the tool pallets. During the processing of the workpiece the pallet changer is moved in a lower position in which the arms facing the workpiece slide are received underneath the pivot bridge, so that the workpiece slide is freely movable in the Z direction. Due to this embodiment it is true that the loading and unloading position of the pallet changer is underneath the pivot bridge but above the lower area of the workpiece slide. During the loading and unloading process numerous movements in particular of the workpiece slide are required. Furthermore, there is considerable required space. 
     In a machine tool known from EP 2 623 256 A2 the removal of the processed workpieces and the insertion of workpieces to be processed into the loading and unloading chamber is performed during the processing of workpieces in the processing chamber. This is referred to in the field as concurrent loading. 
     In generic machine tools pallet changers are provided which have two linear directions of displacement and are pivotable about a vertical axis in order to avoid collisions between the pallet changer and the pivot bridge. 
     SUMMARY OF THE INVENTION 
     An underlying objective of the invention is to design a pallet changer that is simple, takes up a small amount of space and has a shortened changing process. 
     Said objective is achieved according to the invention by in which at least one workholder is provided, which workholder is arranged in the loading and unloading chamber underneath the pivot bridge for releasably mounting a workpiece pallet, in which the tool spindle mounted in the stand is movable in a Z axis which is perpendicular to the X axis and the Y axis, and in which the pivot bridge is supported on the machine bed. It is essential that the pallet changer can only perform a linear movement and a rotational movement and only needs to perform the latter movements. The supply of the workpieces to be processed clamped onto the workpiece pallets is performed linearly from the below and with a rotation of 180° about a vertical axis, wherein at the said time as the linear vertical upwards movement the processed workpieces along with the pallets supporting them can be lifted off the pivot bridge. After the pivot movement of the pallet changer about 180° and during the subsequent upwards movement the workpiece pallets with the workpieces to be processed are placed down on the pivot bridge and the workpiece pallets with the processed workpieces are placed down on the work holder in the loading and unloading chamber. As only a linear displacement is possible in vertical direction and a rotational movement about a vertical axis, the whole structure is very simple and thus inexpensive. Since the pallet changer is arranged very closely in front of and below the pivot bridge a very compact structure is obtained. As only two movements are necessary the changing process is shortened. One or more tables can be provided on the pivot bridge and accordingly the same number of work holders in the loading and unloading chamber. Furthermore, the same number of tool spindles can also be provided; however, it is also possible for the number of tool spindles to be lower, especially during the sequential processing of workpieces. 
     If the pallet changer with workpieces to be processed approaches the pivot bridge from below, this area may become contaminated with shavings. Therefore it is advantageous that between the processing chamber and the loading and unloading chamber a dividing wall is arranged which is openable. 
     Depending on the structure of the pivot bridge and possibly the mounting tables it is possible that during a linear vertical insertion of the holding means of the pallet changer below the workpiece pallets there may be a collision between the pivot bridge and the holding means of the pallet changer. In such cases it is particularly advantageous if the pivot bridge is pivotable into the vertical displacement path and out of the vertical displacement path of the pallet changer with workpiece pallet. In this case the generic pivotability of the pivot bridge about the A axis is used to replace the horizontal movement of the pallet changer, which is unnecessary according to the invention but is necessary in the prior art. 
     The measures according to the invention are particularly advantageous in an embodiment, in which space is saved in particular as only one pallet changer is provided in a machine tool with two tool spindles. 
     Further advantages and details of the invention are given in the following description of an embodiment with reference to the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a perspective view of a machine tool according to the invention, 
         FIG. 2  is a perspective part view of the machine tool enlarged relative to  FIG. 1 , in which workpiece pallets with clamped on workpieces have been omitted, 
         FIG. 3  is a vertical longitudinal cross section of the machine tool in a very schematic view, in which the pallet changer is located in a lower position prior to beginning a pallet change, 
         FIG. 4  is a view according to  FIG. 3 , in which the pallet changer is located in an already vertically raised first middle position, 
         FIG. 5  is a view corresponding essentially to  FIGS. 3 and 4 , in which the pallet changer is located in a position that is raised slightly further than  FIG. 4 , 
         FIG. 6  is a view corresponding to  FIGS. 3 to 5 , in which the pallet changer is located in a second middle position that is slightly raised relative to  FIG. 5 , and 
         FIG. 7  is a representation corresponding to  FIGS. 3 to 6 , in which the pallet changer is located in its upper position, in which workpiece pallets with processed workpieces are lifted from the pivot bridge. 
     
    
    
     DESCRIPTION 
     As shown in particular in  FIGS. 1 and 2  a machine tool according to the invention has an approximately angled machine frame  1  which is formed essentially by a horizontal machine bed  2  and a vertical stand  3 . In the frame-like stand  3  a drive unit  4  is arranged which has an X slide  6  which can be moved in horizontal X direction by means of an X drive  5 . On the X slide  6  a Y slide  7  is mounted which can be moved by means of a not shown Y drive in vertical Y direction. On the Y slide  7  a Z slide  9  is mounted which can be moved by means of a Z drive  8  in horizontal Z direction, in which by means of a not shown spindle drive rotary driven tool spindles  10  or  10 ′ are attached. The tool spindles  10 ,  10 ′ are used for mounting a processing tool  11 ,  11 ′ respectively. 
     On the machine bed  2  a pivot bridge  12  is supported which at its ends is mounted pivotably in pivot bearings  13 ,  13 ′ about an A axis parallel to the X direction and can be driven pivotably by means of a pivot drive  14 . 
     On the pivot bridge  12  two mounting tables designed in the form of round tables  15 ,  15 ′ are arranged, which are each assigned to a tool spindle  10 ,  10 ′. Said round tables  15 ,  15 ′ can be rotary driven respectively by means of a not shown rotary drive about a B axis perpendicular to the A axis. The round tables  15 ,  15 ′ are used for mounting workpiece pallets  17 ,  17 ′, on which a respective workpiece  18 ,  18 ′ or  18 ″,  18 ′″ to be processed is clamped. The chamber above the machine bed  2  and in front of the stand  3  is a processing chamber  19  of the machine tool. 
     In Z direction in front of and below the processing chamber  19  a loading and unloading chamber  20  is formed with a pallet changing unit  21 , in which two work holders  23 ,  23 ′ for two workpiece pallets  17 ″,  17 ′″ are arranged on a pallet changer frame  22 . Between said work holders  23 ,  23 ′ and the pivot bridge  12  the actual pallet changer  24  is arranged, which—as shown in  FIGS. 2 and 3 —is arranged on a vertically displaceable pallet changer slide  25 . The vertical drive of the pallet changer slide  25  is performed by means of a slide drive  26  via a pinion rack drive  27 . The pallet changer  24  designed essentially as a plate is pivotable by 180° by means of a pallet pivot drive  28  attached to the slide  25  about a vertical pallet changer pivot axis  29 . 
     As shown in particular in  FIGS. 1, 2 and 3 , but also the other Figures, the pallet changer  24  comprises guide openings  30 ,  30 ′, in which vertical guide rods  31 ,  31 ′ attached to the pallet changer frame  22  engage in lower positions of the pallet changer  24 , whereby the pallet changer  24  in its lower positions achieves a precisely aligned and stabilised position. 
     On two longitudinal edges of the pallet changer  24  holding means  32 ,  32 ′,  32 ″,  32 ′″ assigned respectively to the round tables  15 ,  15 ′ or the work holders  23 ,  23 ′ are formed, which have holding openings  33  that are open at the top, which are delimited at the bottom by supports  16 . On each workpiece pallet  17 ,  17 ′,  17 ″,  17 ′″ a counterpiece  34 ,  34 ′,  34 ″,  34 ′″ is attached which is adapted to the holding opening  33  in the respective holding means  32 ,  32 ′,  32 ″,  32 ′″ such that it is held in a form-fitting manner in the respective holding means  32 ,  32 ′,  32 ″,  32 ′″ on the associated support  16 , when the pallet changer  24  is started up and in this way the respective holding means  32 ,  32 ′,  32 ″,  32 ′″ mounts or holds a counterpiece  34 ,  34 ′,  34 ″,  34 ′″. 
     As can be taken in particular from  FIG. 2 , on the round tables  15 ,  15 ′ and on the work holders  23 ,  23 ′ of the pallet changing unit  21  known clamping elements  35  are formed, by means of which the tool pallets  17 ,  17 ′,  17 ″,  17 ′″ can be held in precise alignment. It is also shown in  FIG. 2  that on the work holders  23 ,  23 ′ media couplings  36 ,  36 ′ are provided, i.e. hydraulic connections, by means of which not shown, known, workpiece clamping devices formed on the workpiece pallets  17 ,  17 ′,  17 ″,  17 ′″ are opened or closed, by means of which workpieces  18 ,  18 ′ or  18 ″,  18 ′″ in the loading and unloading chamber  20  are clamped onto a workpiece pallet  17 ,  17 ′ or  17 ″,  17 ′″ or released from the latter. 
     As shown in  FIG. 1 , between the processing chamber  19  and the loading and unloading chamber  20  a dividing wall  37  is provided as a protective wall, by means of which during the processing in the processing chamber  19  it is possible to prevent the escape of shavings, oil and the like into the loading and unloading chamber  20 . It is only opened for pallet changing. On the side of the loading and unloading chamber  20  facing the operator  38  a protective door  39  can also be provided which is only opened for removing processed workpieces  18 ,  18 ′,  18 ″,  18 ′″ and for fitting with workpieces  18 ,  18 ′,  18 ″,  18 ′″ to be processed. 
     The working process of the pallet changer  24  is as follows: 
     In the processing chamber  19  there are two workpieces  18 ,  18 ′ clamped onto workpiece pallets  17 ,  17 ′ on the round tables  15 ,  15 ′. They are subjected to a 5-axis processing by the tools  11 ,  11 ′, wherein the tool spindles  10 ,  10 ′ supporting the tools  11 ,  11 ′ are supplied in X, Y and Z direction. The workpieces  18 ,  18 ′ are moved by pivoting about the A axis of the pivot bridge  12  and by rotating about the B axis of the round tables  15 ,  15 ′. Simultaneously, with an open door  39  in the loading and unloading chamber  20  already processed workpieces are removed and workpieces  18 ″,  18 ′″ to be processed are clamped onto workpiece pallets  17 ″,  17 ′″ located on the work holders  23 ,  23 ′ and held by the pallet changer  24 . 
     After completing the processing of the workpieces  18 ,  18 ′ the pallet changing begins, and for this the dividing wall  37  is moved into the opened position shown  FIG. 1 . The pallet changer  24  is located in the lower loading and unloading position  40  shown in  FIGS. 1 and 3 , in which the holding means  32 ″,  32 ′″ mount the counterpieces  34 ″,  34 ′″ of the two workpiece pallets  17 ″,  17 ′″ located on the work holders  23 ,  23 ′ in a form-fitting manner. 
     The pallet changer  24  is then displaced upwards by the slide drive  26  in vertical displacement direction  41  into a first middle position  42 . In said first middle position  42  the pivot bridge  12  is pivoted about its A axis such that the holding means  32 ,  32 ′ of the pallet changer  24  facing the pivot bridge  12  does not collide with the pivot bridge  12 . In this first middle position  42  the holding means  32 ,  32 ′ facing the pivot bridge  12  are still below the counterpieces  34 ,  34 ′ of the workpiece pallets  17 ,  17 ′ located on the round tables  15 ,  15 ′, as can be seen in  FIG. 4  and in enlarged form in  FIG. 5 . Then, as shown in  FIG. 6 , the pivot bridge  12  is pivoted about the A axis such that the respective B axis of the round tables  15 ,  15 ′ is vertical, i.e. parallel to the displacement direction  41  of the pallet changer  24 . The pallet changer  24  is located according to  FIG. 6  in a second middle position  43 , in which the holding means  32 ,  32 ′ are located immediately underneath the counterpieces  34 ,  34 ′ of the two workpiece pallets  17 ,  17 ′ located on the round tables  15 ,  15 ′. 
     The pallet changer  24  is displaced further without rotation about the axis  29  upwards into an upper position  44 , which is shown in  FIG. 7 . In this case, the holding means  32 ,  32 ′ of the pallet changer  24  have already mounted the counterpieces  34 ,  34 ′ of the workpiece pallets  17 ,  17 ′ located on the round tables  15 ,  15 ′ with finally processed workpieces  18 ,  18 ′ and the workpiece pallets  17 ,  17 ′ are lifted off the round tables  15 ,  15 ′. In this upper position  44  a 180° rotation of the pallet changer  24  is performed about the pallet changer pivot axis  29 , so that the processed workpieces  18 ,  18 ′ are pivoted into the loading and unloading chamber  20  and at the same time the unprocessed workpieces  18 ″,  18 ′″ are pivoted into the processing chamber  19 . The pallet changer  24  is lowered in a reverse sequence to the upwards movement. 
     If the pivot bridge  12  in a vertical position of the B axis is not in the collision zone of the pallet changer  24  during its upwards or downwards movement, the pallet changer  24  can then be moved directly out of the lower position  40  into the second middle position  43 . In principle, stopping the pallet changer  24  in the first middle position  42  and the second middle position  43  is not absolutely necessary, if the control allows this. 
     Said control of the numerous drives including the clamping elements  35  and the mentioned clamping devices is performed by means of a central programmable control which is not shown.