TENSION APPARATUS"

Description

The invention relates to an axial tension apparatus for generating an axial force for actuating a clamping device by means of a tension rod, and also to a machine tool having a rotating spindle and a clamping device that rotates with the rotating spindle and also having an axial tension apparatus, having a tension rod, for actuating the clamping device.

Such axial tension apparatuses are known in principle from the prior art. Thus, axial tension apparatuses having usually hollow tension rods are known in particular on machine tools which have a clamping device, for example a chuck or the like, that rotates together with a rotating spindle of the machine tool, wherein the clamping device, i.e. for example the chuck, is connected for actuation to the tension rod.

The tension rod is in turn actuated by the generally hydraulically or electrically operated axial tension apparatus, with the problem arising here in particular in the case of electrically actuated axial tension apparatuses that, in order to actuate the clamping jaws of the chuck, a motor having a comparatively high torque has to be used in order to be able to transmit a high linear force to the clamping jaws of the chuck, after conversion of the rotary movement into a linear movement, i.e. a movement acting in the axial direction, by means of the hollow tension rod. In order to obtain sufficiently high torques, it is known on the one hand to use relatively large, heavy, bulky and expensive electric motors in order to generate the necessary relatively high torque. On the other hand, it is likewise known to provide relatively small electric motors in order to be able to generate the necessary high torque or the necessary high linear force with interposition of a torque- or linear-force-amplifying gear mechanism at the expense of a higher necessary angle of rotation and thus also at the expense of the lifting time necessary for clamping or releasing the clamping jaws. Accordingly, the present invention is based on the problem of developing such a generic axial tension apparatus such that the necessary lifting times are reduced when the axial force is generated by means of a relatively small electric motor.

According to the invention, the problem is solved by an axial tension apparatus according to independent claim 1.

Specifically, the problem is solved in particular in that an axial tension apparatus for generating an axial force for actuating a clamping device, for example a chuck, preferably a clamping device that rotates with a rotating spindle of a machine tool, by means of a tension rod, has an electrically operated clamping motor having a stator that does not corotate when the spindle rotates and a rotor that corotates when the spindle rotates, a motor shaft connected to the rotor for transmitting the rotary movement of the clamping motor, a bearing housing, within which there is arranged a spindle nut that is axially displaceable to a limited degree by means of a spring store, and a coupling for the selective coupled transmission of a rotary movement between the motor shaft and the bearing housing. In this case, the coupling has a restoring device which is designed to bring the coupling into a closed position in an intrinsically safe manner. The motor shaft is connected to the tension rod in a rotatable manner. The tension rod has an external thread which is engaged with the spindle nut such that the tension rod and the spindle nut form a screw drive.

The solution according to the invention produces a number of advantages. Because no intermediate gear mechanism is provided, but rather the tension rod, together with the spindle nut which is axially displaceable to a limited degree within the bearing housing, allows the torque of the electric motor to be transmitted directly to the tension rod following conversion into an axial movement, the clamping device, i.e. for example the clamping jaws of a chuck, can be actuated very quickly and directly, as a result of which the (unproductive) lifting times can be minimized .

Furthermore, the configuration of the spindle nut as axially displaceable to a limited degree, with storage of the forces produced during the axial displacement of the spindle nut in a spring store which consists for example of disc springs, produces the particular advantage that the clamping force applied to the clamping device is kept largely constant even when the clamping device rotating together with the rotating spindle of the machine tool has to compensate relatively large centrifugal forces on account for example of a high rotational speed.

The fact that the coupling is brought intrinsically safely into a closed position, i.e. into a coupled state between the motor shaft and the bearing housing, by means of the restoring device, which is formed for example by a spring, also ensures that a torque, by way of which the tension rod is actuated counter to the clamping direction of the clamping device, with the rotating spindle of the machine tool still rotating, and the tool possibly clamped into the clamping device is released in an undesired manner, is not unintentionally transmitted to the spindle nut, for example as a result of a power outage or the like. Advantageous developments of the solution according to the invention are specified in the dependent claims. According to one aspect of the invention, it is provided that the tension rod and the spindle nut form a roller screw drive with roller recirculation. On account of the large number of contact surfaces, such a roller screw drive with roller recirculation provides very good load distribution and thus ensures a long service life. This significantly increases the number of clamping operations, i.e. the number of lifting operations. Furthermore, high positioning accuracy is ensured by such a roller screw drive with roller recirculation, i.e. the clamping force on the clamping device, thus for example the clamping force of the clamping jaws of a chuck, can be set very precisely and maintained.

According to one aspect of the invention, it is provided that the coupling is in the form of a toothed claw coupling. This ensures that the coupling in the form of a toothed claw coupling engages reliably when the drive of the rotating spindle of the machine tool is disconnected or in the event of a power outage and also does not release the coupling of the workpiece unintentionally, i.e. prematurely with the rotating spindle still rotating, in the event of increased wear.

According to one aspect of the invention, it is provided that the axial tension apparatus also has a housing. This housing is designed to absorb torques, in particular torques brought about during operation of the axial tension apparatus. Such torques brought about during operation occur primarily when the clamping device is adjusted by means of the tension rod, i.e. when the coupling has been brought into an open position which allows positioning actuation of the axial tension apparatus. This produces the particular advantage that no further supporting devices or the like are required for torque transmission.

According to one aspect of the invention, it is provided that the coupling is formed to be automatically actuable, and is preferably formed to be electrically actuable. As a result, fully automatic actuation of the clamping device by means of the axial tension apparatus is possible, in that, in order to start a clamping or releasing operation, first of all the coupling and the rotary connection between the motor shaft and the bearing housing are released in an automatic, preferably electrical manner. Subsequently, the clamping motor is then actuated in the desired direction, as a result of which the tension rod connected to the rotor of the clamping motor via the motor shaft is set into rotary movement. As a result, depending on the direction of rotation, the spindle nut is pressed against the spring store of the now corotating bearing housing and in this way brings about axial displacement of the tension rod, as a result of which the clamping device is actuated.

According to a further aspect of the invention, a machine tool having a rotating spindle and a clamping device that rotates with the rotating spindle is provided, wherein the machine tool has an axial tension apparatus according to the invention in order to actuate the clamping device.

An embodiment of the solution according to the invention is explained in more detail in the following text with reference to a drawing, in which:

Figure 1 (the single figure) shows a functional sectional view of an axial tension apparatus according to the invention.

Figure 1 shows an axial tension apparatus 100 for generating an axial force for actuating a clamping device (not illustrated in more detail in figure 1), for example a chuck. The axial tension apparatus 100 according to the embodiment in figure 1 has a hollow tension rod 32, wherein the tension rod 32 can be connected in the region illustrated on the right-hand side in figure 1 to a clamping device (not illustrated) that can be actuated by linear displacement. Such a clamping device may be for example a chuck having clamping claws, as is used in a lathe or the like.

The machine tool on which an axial tension apparatus 100 according to figure 1 can be used usually drives a rotating spindle, and both the tension rod and the (not illustrated) clamping device also rotate during operation of the machine tool.

The axial tension apparatus 100 illustrated in figure 1 has an electrically operated clamping motor composed of a stator 11 and a rotor 12. The stator 11 is designed to be stationary while the spindle rotates; by contrast, the rotor 12 also corotates when the spindle rotates.

In order to transmit the rotary movement of the clamping motor, there is provided a motor shaft 13. A bearing housing 18 which likewise corotates when the spindle rotates can be connected selectively to the motor shaft 13 by means of a coupling 21 which is in the form of a claw coupling in the exemplary embodiment according to figure 1. The coupling 21 is in this case formed such that it is pressed into a closed position in an intrinsically safe manner by means of (not illustrated) spring elements. Accordingly, when the coupling 21 is actuated, the selective connection between the motor shaft 13 and the bearing housing 18 is disconnected.

Arranged within the bearing housing is a spindle nut 28 which is arranged so as to be axially displaceable to a limited degree within the boundaries of the bearing housing. The boundaries of the possible axial displacement are defined by a spring store 17, in the exemplary embodiment according to figure 1 in the form of a disc spring store 17 formed in each case on the left-hand and right-hand sides. The disc spring store 17 is configured such that, even in normal operation, described further below, of the machine tool, i.e. with the rotating spindle rotating and the clamping device corotating in a corresponding manner, the spindle nut 28 bearing against the disc springs of the spring store 17 is not disconnected as a result of high centrifugal forces or the like, and does not bring about an axial displacement of the tension rod 32 in the unclamping direction, resulting in undesired opening of the clamping device.

The motor shaft 13 is rotationally connected to the tension rod 32. The tension rod 32 has an external thread 34 which is engaged with the spindle nut 28. As a result, the tension rod 32 and the spindle nut 28 arranged within the bearing housing 18 form a screw drive. In the exemplary embodiment according to figure 1, this screw drive is in the form of a roller screw drive with roller recirculation. A rear housing part 33 and a front housing part 18 connected thereto by means of screw connections form a housing of the axial tension apparatus, said housing being configured to absorb torques brought about during operation of the axial tension apparatus. Both the rear housing part 33 and the front housing part 18 and also the stator 11 are at a standstill during normal operation of the machine tool, i.e. they are not designed to corotate.

During such normal operation of the machine tool, i.e. during rotary operation of a rotating spindle, the rotor 12, the motor shaft 13, the bearing housing 18, the spring store 17 arranged within the bearing housing, the spindle nut 28 and the tension rod 32 thus belong to a rotating mass. This rotating mass is rotationally uncoupled from the housing parts 33, 18 by means of ball bearings 10, 14, 25.

The claw coupling 21 ensures that, even when the machine tool is transferred from normal rotary operation to a standstill, this rotating mass is always connected together, as long as the claw coupling 21 is not actuated into an active state. This ensures that the spindle nut 28 does not move on account of a relative rotational speed that may possibly occur during the deceleration of the machine tool, such that an axial movement transmitted to the tension rod 32 brings about accidental disconnection, i.e. releasing of the workpiece from the clamping device. A clamping and unclamping operation with deliberate actuation of the coupling 21 is described in the following text. As a result of an actuation of the coupling 21, a coupling part 22 on the clamping-motor side is detached from a coupling part 24 on the screw-drive side, such that a rotational movement generated by the clamping motor is now transmitted only to the tension rod 32. Accordingly, the bearing housing 18 does not corotate in this case. Depending on the direction of rotation of the rotor 12 and thus of the tension rod 32, the rotational movement of the spindle nut 28 is then converted into a linear movement of the tension rod 32, as a result of which, with the coupling 21 open, targeted clamping or unclamping of the clamping device takes place. It is noted at this point that all of the parts described above are claimed as essential to the invention in themselves alone and in any combination, in particular the details that are illustrated in the drawings. Modifications thereof are familiar to a person skilled in the art. List of reference signs

10, 14, 25 Ball bearings

11 Stator

12 Rotor

13 Motor shaft

16 Front housing part

17 Spring store, disc spring

18 Bearing housing

21 Coupling, claw coupling

22 Coupling part on the clamping-motor side

24 Coupling part on the screw-drive side

28 Spindle nut

32 Tension rod

33 Rear housing part

34 External thread

100 Axial tension apparatus