DRIVE FOR MACHINE AGGREGATES, LIKE CARRIAGES, GRAB EQUIPMENTS AND SUCH A THING

1. Field of the Invention

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.

2. Description of the Related Art

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.

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.

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.

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.

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).

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.

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.

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.

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.

FIG. 1shows a drive which is embodied as a feed drive with which, for example, carriages on machine tools can be moved.FIG. 1shows such a machine with a machine frame1on which a threaded spindle2is rotatably supported. The spindle2, which can be, for example, a ball screw spindle, is guided in a nut7which is connected fixedly in the axial and radial directions in the pillow block10. This pillow block10is fastened on the machine frame1. At a spacing from the nut7, a further nut8is positioned on the spindle2which is secured in a carriage9so as to be immobile axially and radially. The threaded spindle2has two spindle sections3and4which have opposite axial pitch. The spindle section3can be, for example, a right-hand pitch and the spindle section4at the other end can be a left-hand pitch. The pitch directions of the nuts7and8are configured accordingly. For driving the spindle2, a motor16is provided whose motor shaft17is aligned with the spindle2and is connected to the end5of the spindle2by the clutch18for rotating the spindle2. The motor16is axially movable and is secured against rotation about the entire length of its travel stroke. For guiding the motor16, a guide20is provided which is fastened on a console23which is fastened on a sidewall of the machine frame1. The guide20has at least one guide path21provided on the console23, and at least one guide shoe22is moveable on the guide path21. The guide shoe22is provided on the underside of an angle member19which supports the motor16.

The end6of the spindle2facing away from the motor16is connected by means of at least one bearing14, preferably a rolling bearing, with an axle13. The bearing14is axially secured by a nut15which is screwed onto the free spindle end6. The bearing14rests under the force of the nut15on a shoulder26of the spindle2.

The axle13is guided in a pillow block11with at least one longitudinal bearing12which can be a sliding bearing or a rolling bearing. Since the spindle2is supported in the area of both ends in the described way by means of two pillow blocks10,11, the rotational speed limit of the spindle2is increased so that high moving speeds are possible.

The carriage9is provided at the underside facing the machine frame1with a cutout27in which the pillow block11, the spindle end6, and the bearing14are positioned.

The carriage9is slidably supported by means of at least one guide shoe28in a guide29which is provided at a spacing above the guide20for the motor16. In this way, the carriage9is not only guided by the nut8on the spindle2, but also by the guide shoe28on the guide29.

It is possible to configure the guide paths21,29as a unitary part, as will be explained with the aid of the embodiment ofFIG. 4infra. In this case, the motor16and the carriage9are supported and guided on the same guide path.

The spindle2and the motor16form a drive train with the spindle2being rotated by the motor16. The motor16and the parts which are axially fixedly connected with the motor shaft17move in the axial direction. As a result of the pitch direction of the nut8and the spindle section4, which is opposite to the pitch direction of the nut7and the spindle section3, the nut8moves axially relative to the spindle2when the spindle2rotates. The axial movement direction of the nut8is identical to the axial movement direction of the spindle2, but the axial movement is performed at a higher speed.

Depending on the rotational direction of the motor shaft17, the carriage9is moved in the corresponding direction on the machine frame1. The movement transmitted onto the carriage9is a combination of the axial movement of the spindle2and the axial relative movement between the nut8and the spindle2. The additive superposition of the movements results in higher travel speeds and accelerations.

The solid lines inFIG. 1illustrate one of the end positions of the carriage9. The dash-dotted line illustrates the other end position of the carriage9at maximum travel stroke.

FIG. 2shows an embodiment in which the motor16is positioned radially displaced to the spindle2on the support19. In this case, the motor shaft17is not connected directly with the spindle2but by means of a gear or a transmission, for example, a belt drive30. A pulley31is seated on the motor shaft17and is connected drivingly by means of a belt32with the pulley33which is seated fixedly on the spindle end5. The support19is supported by the guide shoe22on the guide path21on the console23. The spindle end5is rotatably supported by at least one bearing34, preferably a rolling bearing, in the support19. The bearing34is axially secured by a nut35which is screwed onto the free end of the spindle end5.

In other respects, this embodiment is identical to the embodiment of FIG.1. Since the motor16is not positioned axially behind the spindle2but in the area above the spindle2, this configuration is shorter than that of the embodiment of FIG.1.

FIG. 3shows a drive system in which the spindle2is supported on one end only. On the spindle end6no 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 toFIG. 3is identical to the one of FIG.1. However, it is also possible to provide this one-sided support of the spindle2in connection with an embodiment according to FIG.2. The drive system according toFIG. 3is suitable advantageously for relatively short travel strokes. As in the preceding embodiments, high-speeds and accelerations can be achieved.

FIG. 4shows a drive system in which a second motor16is provided on the spindle end6. In this way, the spindle2is driven at both ends5,6by a motor16, respectively. Each motor16is aligned with the spindle2. The two motor shafts17are fixedly connected by a clutch18with the respective spindle end5,6for rotating the spindle2.

The two motors16are mounted on angle supports19which, in contrast to the embodiment ofFIG. 1, is movable on the guide path29with the guide shoe22. The carriage9is supported with its guide shoe27on the same guide path29. The motors16are fastened on the downwardly extending legs of the angle support19and have a minimal spacing from the machine frame1.

In accordance with the preceding embodiments, the spindle2has spindle sections3,4with opposite axial pitch and nuts7and8correlated therewith, respectively. The two supports19are positioned mirror-symmetrically to one another wherein the motors16are covered relative to the spindle2by the downwardly extending legs of the support19. Since the spindle2is driven in rotation at both ends, it is possible to move even heavy loads on the carriage9at high speed and high acceleration. InFIG. 4, the solid lines show again one end position and the dash-dotted lines shows the other end position of the carriage9. Since the connection of the motors16at both spindle ends5,6is realized by identical parts, a very simple configuration is provided.

FIG. 5shows a drive system in which the motor16is mounted axially immobile on the console23by means of a console36. The motor shaft17according to the embodiment ofFIG. 2is in driving connection with the spindle end5via the belt drive30. In contrast to the embodiment ofFIG. 2, the pulley33is axially fixedly seated on the spindle end5and is provided on a sleeve37which is fixedly seated on the end5of the spindle2embodied as a spline shaft. The sleeve37is rotatably supported by at least one bearing38, preferably a rolling bearing, in the console36.

When the spindle2is rotated by the motor16by means of the belt drive30, the spindle end5moves in the axial direction relative to the axially stationary pulley33. Since the motor16, in contrast the preceding embodiments, is not axially moved by the belt drive30, the moved masses are minimal. This enables high speeds and accelerations. For reasons of precision, the spindle end5, formed as a spline shaft, engages the pulley33via a bearing38which is embodied as a prestressed linear rolling guide.

The spindle2is supported otherwise in the nuts7,8which have correlated therewith the spindle sections3,4provided with opposite axial pitch. The carriage9is supported by means of the guide shoe28on the linear guide29. The carriage9is moved by rotation of the spindle2in the same way as in the preceding embodiments. InFIG. 5, the two end positions of the carriage9are illustrated by solid and dash-dotted lines, respectively.

In all embodiments, the spindle sections3,4can 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 motor16in the different embodiments is smaller than the travel stroke of the carriage9; preferably, it is only approximately half the travel stroke of the carriage9.

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.