Abstract:
A drive for machine components has at least one threaded spindle having spindle sections with oppositely oriented axial pitch. Nuts are seated on the at least one threaded spindle and engage the spindle sections, respectively. At least one motor is connected to the at least one threaded spindle for driving the at least one threaded spindle. A first one of the nuts is connected to a machine component. A second one of the nuts is spatially stationary. The at least one threaded spindle provides a drive moment for driving the machine component.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a drive for machine components such as carriages, gripping devices or the like, comprising at least one threaded spindle which can be driven by at least one motor and on which nuts are positioned, wherein at least one of the nuts is connected with the machine component and wherein the nuts are in engagement with spindle sections having oppositely oriented axial pitch.  
           [0003]    2. Description of the Related Art  
           [0004]    Because of the required precision, the axle movements of machine tools as well as simple and combined linear and rotational movements of workpieces and tools must follow very exactly, essentially without delay, and with a high degree of repeating accuracy the preset values of the numerical control, and this is to be achieved independent of the acting counter forces such as feed force, friction, or acceleration forces of the linearly or rotationally driven masses. The moving speed and the acceleration must be as high as possible in order to take up as little time as possible for a precise positioning.  
           [0005]    In known drive systems a rotary current synchronous motor mounted on the machine frame drives a ball screw spindle rotatably supported on the machine frame. The spindle engages a nut which is fixedly connected in a carriage or a stand. The carriage or the stand are longitudinally movable on guides relative to the machine frame. As a function of the stroke length or the required rapid traverse of the carriage, the spindle and the nut have different limits of rotational speed. Above certain slenderness ratios, or for other constructive reasons, the ball screw spindle can also be positioned so as to be fixed in regard to rotation and the nut can be driven in rotation instead.  
           [0006]    Moreover, drives are known from European patent application 1 013 373 A1 which provide a second drive motor for driving the threaded spindle or the nut for the purpose of increasing the moving speeds and accelerations.  
           [0007]    Furthermore, spindle drive devices are known from German patent application 39 38 353 which, by means of two spindle drive heads and one spindle with right-hand and left-hand thread on the same threaded spindle section, perform translatory as well as rotary movements.  
           [0008]    Also, threaded spindles are known which have left-hand and right-hand threads on two adjacent spindle sections and are used for a central clamping of workpieces (Heinrich Matuszewski, Handbuch Vorrichtungen: Konstruktion und Einsatz, Verlag Vieweg, 1986, page 123).  
           [0009]    The technical limits of these known drive systems lie in the rotational speed rating of the ball screw spindles and in the rotational speed rating of commercial servo motors. The doubling of the moving speed requires for the same axial spindle pitch a doubling of the motor speed. When the motor speed increases past the speed of maximum torque, the motor torque decreases as a matter of the functional limitations of the motor, and this causes the acceleration to decrease. Also, when doubling the motor speed, the run-up time of the motor increases. An increase of the axial pitch is possible; however; this requires that the spindle diameter must be increased which would result in higher mass moments of inertia.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to configure the drive of the aforementioned kind such that for high positioning speeds in the case of handling devices and high-speed cutting with machine tools the acceleration as well as the rapid traverse speeds and feed speeds are high.  
           [0011]    In accordance with the present invention, this is achieved in that one of the two nuts is spatially fixed and that the drive moment is introduced via the threaded spindle.  
           [0012]    With the drive according to the invention, the drive moment is introduced by means of the threaded spindle. By using a threaded spindle with two spindle sections having oppositely oriented pitch and a nut which is spatially fixed, an increase of the acceleration and of the moving speeds of the machine component is achieved for the same motor speed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]    In the drawing:  
         [0014]    [0014]FIG. 1 is a sectional view of a first drive according to the invention for a machine component;  
         [0015]    [0015]FIG. 2 is a sectional view of a second drive according to the invention for a machine component;  
         [0016]    [0016]FIG. 3 is a sectional view of a third drive according to the invention for a machine component;  
         [0017]    [0017]FIG. 4 is a sectional view of a fourth drive according to the invention for a machine component; and  
         [0018]    [0018]FIG. 5 is a sectional view of the fifth drive according to the invention for a machine component. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    [0019]FIG. 1 shows a drive which is embodied as a feed drive with which, for example, carriages on machine tools can be moved. FIG. 1 shows such a machine with a machine frame  1  on which a threaded spindle  2  is rotatably supported. The spindle  2 , which can be, for example, a ball screw spindle, is guided in a nut  7  which is connected fixedly in the axial and radial directions in the pillow block  10 . This pillow block  10  is fastened on the machine frame  1 . At a spacing from the nut  7 , a further nut  8  is positioned on the spindle  2  which is secured in a carriage  9  so as to be immobile axially and radially. The threaded spindle  2  has two spindle sections  3  and  4  which have opposite axial pitch. The spindle section  3  can be, for example, a right-hand pitch and the spindle section  4  at the other end can be a left-hand pitch. The pitch directions of the nuts  7  and  8  are configured accordingly. For driving the spindle  2 , a motor  16  is provided whose motor shaft  17  is aligned with the spindle  2  and is connected to the end  5  of the spindle  2  by the clutch  18  for rotating the spindle  2 . The motor  16  is axially movable and is secured against rotation about the entire length of its travel stroke. For guiding the motor  16 , a guide  20  is provided which is fastened on a console  23  which is fastened on a sidewall of the machine frame  1 . The guide  20  has at least one guide path  21  provided on the console  23 , and at least one guide shoe  22  is moveable on the guide path  21 . The guide shoe  22  is provided on the underside of an angle member  19  which supports the motor  16 .  
         [0020]    The end  6  of the spindle  2  facing away from the motor  16  is connected by means of at least one bearing  14 , preferably a rolling bearing, with an axle  13 . The bearing  14  is axially secured by a nut  15  which is screwed onto the free spindle end  6 . The bearing  14  rests under the force of the nut  15  on a shoulder  26  of the spindle  2 .  
         [0021]    The axle  13  is guided in a pillow block  11  with at least one longitudinal bearing  12  which can be a sliding bearing or a rolling bearing. Since the spindle  2  is supported in the area of both ends in the described way by means of two pillow blocks  10 ,  11 , the rotational speed limit of the spindle  2  is increased so that high moving speeds are possible.  
         [0022]    The carriage  9  is provided at the underside facing the machine frame  1  with a cutout  27  in which the pillow block  11 , the spindle end  6 , and the bearing  14  are positioned.  
         [0023]    The carriage  9  is slidably supported by means of at least one guide shoe  28  in a guide  29  which is provided at a spacing above the guide  20  for the motor  16 . In this way, the carriage  9  is not only guided by the nut  8  on the spindle  2 , but also by the guide shoe  28  on the guide  29 .  
         [0024]    It is possible to configure the guide paths  21 ,  29  as a unitary part, as will be explained with the aid of the embodiment of FIG. 4 infra. In this case, the motor  16  and the carriage  9  are supported and guided on the same guide path.  
         [0025]    The spindle  2  and the motor  16  form a drive train with the spindle  2  being rotated by the motor  16 . The motor  16  and the parts which are axially fixedly connected with the motor shaft  17  move in the axial direction. As a result of the pitch direction of the nut  8  and the spindle section  4 , which is opposite to the pitch direction of the nut  7  and the spindle section  3 , the nut  8  moves axially relative to the spindle  2  when the spindle  2  rotates. The axial movement direction of the nut  8  is identical to the axial movement direction of the spindle  2 , but the axial movement is performed at a higher speed.  
         [0026]    Depending on the rotational direction of the motor shaft  17 , the carriage  9  is moved in the corresponding direction on the machine frame  1 . The movement transmitted onto the carriage  9  is a combination of the axial movement of the spindle  2  and the axial relative movement between the nut  8  and the spindle  2 . The additive superposition of the movements results in higher travel speeds and accelerations.  
         [0027]    The solid lines in FIG. 1 illustrate one of the end positions of the carriage  9 . The dash-dotted line illustrates the other end position of the carriage  9  at maximum travel stroke.  
         [0028]    [0028]FIG. 2 shows an embodiment in which the motor  16  is positioned radially displaced to the spindle  2  on the support  19 . In this case, the motor shaft  17  is not connected directly with the spindle  2  but by means of a gear or a transmission, for example, a belt drive  30 . A pulley  31  is seated on the motor shaft  17  and is connected drivingly by means of a belt  32  with the pulley  33  which is seated fixedly on the spindle end  5 . The support  19  is supported by the guide shoe  22  on the guide path  21  on the console  23 . The spindle end  5  is rotatably supported by at least one bearing  34 , preferably a rolling bearing, in the support  19 . The bearing  34  is axially secured by a nut  35  which is screwed onto the free end of the spindle end  5 .  
         [0029]    In other respects, this embodiment is identical to the embodiment of FIG. 1. Since the motor  16  is not positioned axially behind the spindle  2  but in the area above the spindle  2 , this configuration is shorter than that of the embodiment of FIG. 1.  
         [0030]    [0030]FIG. 3 shows a drive system in which the spindle  2  is supported on one end only. On the spindle end  6  no support and bearing are provided so that the constructive configuration of this embodiment is simpler than that of the two previously described embodiments. In other respects, the drive system according to FIG. 3 is identical to the one of FIG. 1. However, it is also possible to provide this one-sided support of the spindle  2  in connection with an embodiment according to FIG. 2. The drive system according to FIG. 3 is suitable advantageously for relatively short travel strokes. As in the preceding embodiments, high-speeds and accelerations can be achieved.  
         [0031]    [0031]FIG. 4 shows a drive system in which a second motor  16  is provided on the spindle end  6 . In this way, the spindle  2  is driven at both ends  5 ,  6  by a motor  16 , respectively. Each motor  16  is aligned with the spindle  2 . The two motor shafts  17  are fixedly connected by a clutch  18  with the respective spindle end  5 ,  6  for rotating the spindle  2 .  
         [0032]    The two motors  16  are mounted on angle supports  19  which, in contrast to the embodiment of FIG. 1, is movable on the guide path  29  with the guide shoe  22 . The carriage  9  is supported with its guide shoe  27  on the same guide path  29 . The motors  16  are fastened on the downwardly extending legs of the angle support  19  and have a minimal spacing from the machine frame  1 .  
         [0033]    In accordance with the preceding embodiments, the spindle  2  has spindle sections  3 ,  4  with opposite axial pitch and nuts  7  and  8  correlated therewith, respectively. The two supports  19  are positioned mirror-symmetrically to one another wherein the motors  16  are covered relative to the spindle  2  by the downwardly extending legs of the support  19 . Since the spindle  2  is driven in rotation at both ends, it is possible to move even heavy loads on the carriage  9  at high speed and high acceleration. In FIG. 4, the solid lines show again one end position and the dash-dotted lines shows the other end position of the carriage  9 . Since the connection of the motors  16  at both spindle ends  5 ,  6  is realized by identical parts, a very simple configuration is provided.  
         [0034]    [0034]FIG. 5 shows a drive system in which the motor  16  is mounted axially immobile on the console  23  by means of a console  36 . The motor shaft  17  according to the embodiment of FIG. 2 is in driving connection with the spindle end  5  via the belt drive  30 . In contrast to the embodiment of FIG. 2, the pulley  33  is axially fixedly seated on the spindle end  5  and is provided on a sleeve  37  which is fixedly seated on the end  5  of the spindle  2  embodied as a spline shaft. The sleeve  37  is rotatably supported by at least one bearing  38 , preferably a rolling bearing, in the console  36 .  
         [0035]    When the spindle  2  is rotated by the motor  16  by means of the belt drive  30 , the spindle end  5  moves in the axial direction relative to the axially stationary pulley  33 . Since the motor  16 , in contrast the preceding embodiments, is not axially moved by the belt drive  30 , the moved masses are minimal. This enables high speeds and accelerations. For reasons of precision, the spindle end  5 , formed as a spline shaft, engages the pulley  33  via a bearing  38  which is embodied as a prestressed linear rolling guide.  
         [0036]    The spindle  2  is supported otherwise in the nuts  7 ,  8  which have correlated therewith the spindle sections  3 ,  4  provided with opposite axial pitch. The carriage  9  is supported by means of the guide shoe  28  on the linear guide  29 . The carriage  9  is moved by rotation of the spindle  2  in the same way as in the preceding embodiments. In FIG. 5, the two end positions of the carriage  9  are illustrated by solid and dash-dotted lines, respectively.  
         [0037]    In all embodiments, the spindle sections  3 ,  4  can have same or different pitch and/or the same or different diameter and/or the same or different length. With appropriate selection of these parameters, an optimal adjustment of the drive to the respective application is possible. As a result of the described embodiments, the travel stroke of the motor  16  in the different embodiments is smaller than the travel stroke of the carriage  9 ; preferably, it is only approximately half the travel stroke of the carriage  9 .  
         [0038]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.