EP0268176B1 - Electromotive clamping device for work pieces - Google Patents

Abstract

The work-piece clamping device is provided with a clamping lever (14) which is pivotally mounted in a holder and is connected, in articulated manner, via an intermediate member (13) to an actuating member (7) which is secured against rotation and can be moved axially by a drive. The rotary drive consists, in this case, of a threaded spindle (3), rotatably mounted on the holder and driveable by a reversing motor (1), with a self-locking thread pitch which is in engagement with the moveable actuating member (7) provided with an internal thread, and of an axial spring (19) which becomes active in between actuating member and spindle when the clamping end position is reached and prevents wedging of the thread. The reversing motor (1) is connected to the threaded spindle (3) with interposition of an axial coupling (2). The threaded spindle (3) is mounted, on the coupling side, so as to be axially displaceable in a limited manner in a bearing (20) arranged axially displaceably in the holder (H) and provided with the axial spring (19). The coupling-side end of the threaded spindle (3) is arranged so as to be fixed in terms of rotation but axially displaceable in the axial coupling (2). Lastly, the axial spring (19) is arranged between the bearing (20) and a coupling-side support (20') on the holder (H). As a result of this design according to the invention, self-wedging of the thread is prevented, independently of the position in which the lever (14) assumes the actual clamping end position. <IMAGE>

Description

The invention relates to a workpiece clamping device that can be driven by an electric motor according to the preamble of claim 1.

Such a tensioning device is known from FR-A-2 036 980. Clamping devices also provided with an electric rotary drive are known according to K. Schreyer, workpiece clamps (devices, 3rd edition, Springer-Verlag, Berlin, Heidelberg, New York 1969, pp. 80, 81; Fig. 246) and in particular for use on lathes for Actuation of mandrels, pliers and chucks determined, these devices can also be equipped with a spring to allow elastic clamping. Such an electromotive driven clamping device is not readily suitable for clamping devices of the type of interest here, since elastic clamping is not an option for workpiece clamping devices and such a known clamping device led to wedging of the threaded spindle with the actuator without a spring.

Clamping devices of the type that are actually of interest here are known, for example, from DE-A-30 22 376, but also from the following publications; DE-A-19 50 721, 12 68 074, DE-A-22 22 686, FR-A-12 55 515 and finally according to US-A-31 16 058. All of these known clamping devices are pneumatic or hydraulic Drives provided, the translatory stroke movement of the actuating elements articulated in the device into the pivoting movement of the clamping lever is implemented. With regard to this type of drive for such tensioning devices, there has been no shortage of attempts to provide such tensioning devices with rotary drives, in particular with electric drives, the rotary movement of which, however, cannot readily be converted into a translatory and subsequent pivoting movement of the actuators, since this is in the area of the holder for the clamping lever and its adjustment mechanism leads to a larger space requirement and thus the corresponding size of such devices, which is not acceptable in most applications, because several such clamping devices usually have to be attached as closely as possible to the workpiece in question (e.g. car bodywork).

According to US-A-41 37 784 a further electromotive rotary drive with a reversing motor is known. Apart from the fact that in this electromechanical rotary drive the drive motor is arranged axially parallel to the spindle drive of the actuator to take up space, this rotary drive provided for hooks, brackets or the like. Load carrier is also not readily suitable for tensioning devices of the type of interest here, since the elastic buffer, which is intended to prevent wedging of the threads involved is located at the free end of the threaded spindle and can only take effect if the non-adjustable stop inside the actuator sits on this buffer. The same applies to the fully extended position of the actuator. So if - provided that this rotary drive were coupled with a clamping device - the clamping lever was firmly clamped to a workpiece surface to be clamped and the buffer of the spindle had not yet come into contact with the inner drive-side stop of the actuator, the threads would wedge, ie the previously known rotary drive would have to be structurally exactly adjusted to each clamping position. A change and thus adjustability of the stop conditions would only be possible in the interior of the actuator designed as a sleeve and thus complicated.

The invention has for its object to improve a device of the type mentioned in such a way that a wedging in each clamping end position, i.e. should be preventable in the bottom, dead center and also over dead center clamping position, even in the case of unfavorable, additional circumstances.

This object is achieved with a workpiece clamping device of the type mentioned according to the invention by the features stated in the characterizing part of patent claim 1. Advantageous further developments and practical embodiments result from the subclaims.

The subject of FR-A-2 036 980 mentioned at the outset, which is the starting point here, is apparently, without taking into account any risk of wedging at all, solely about the motor being brought to the device when the load increases or when the vehicle approaches an obstacle belonging elements, which are integrated in the device (spindle collar, brake or insulating disks and contacts), can be easily switched off. In order to keep the motor running at all, it is necessary with this known device that the motor circuit remains closed via contacts, for which it is in turn necessary for the collar to be kept exactly balanced by the springs directly attached to it between the disks, ie , the slightest imbalance between the two springs already leads to a switching operation, quite apart from the fact that such imbalances are open because the springs, which are in direct contact with the collar, are subject to either permanent wear and / or the collar, which is a constant opening and closing processes exposed clamping device, which is at issue here, would be absolutely unacceptable and, in addition, the problem of wedging would not be solved in the long run. The device known according to FR-A would therefore be conditionally suitable for adjustment processes subject to any loads, but not for tensioning devices of the type present here, for which, on the one hand, there has always been a desire to be able to drive them electrically as well as the known hydraulic or pneumatic drives , on the other hand, this is always divorced from the wedging of the threads involved.

In contrast, for the design of the device according to the invention it is essential that the threaded spindle can move to a limited extent due to the "floating" bearing. Since this floating bearing with its axial suspension is arranged on the coupling or drive side according to the invention, the axial suspension preventing thread wedging can come into effect in any clamping position. The axial suspension must of course be designed so that a driving force of the motor is required for a predetermined compression, in which the power consumption of the motor is switched off, in which the maximum clamping force is also generated via the clamping device and in which no self-wedging of the thread has yet taken place . Under this condition, the following occurs on the clamping device according to the invention:
The clamping lever is first brought into contact with the workpiece without axially retracting the axial suspension. Since the motor then still has power reserves, it rotates the spindle further, but with increasing clamping force it dodges axially towards the drive side and compresses the axial suspension until the maximum clamping force is reached, that is, the tensioning force now corresponds to the tensioning force of the compressed suspension and without the threading becoming wedged, which would occur if the spindle could not deflect axially in the opposite direction. Since the motor is designed for a certain current consumption or can be switched off, it is essential for the return of the spindle and the release of the clamping device from its clamping position that the threads have not wedged, which required a correspondingly greater restoring force for the release of the wedging. which the engine is unable to perform.

Unless the rotary drive is switched off when the opening position of the tensioning device is reached (rotary drive and actuator are moved together), the same principle of axial cushioning can advantageously also be used for this position, so that the tensioning device is also in this position to prevent wedging of the threads. Such an axial suspension can either be arranged between the free end of the spindle and inside the actuator, but preferably and advantageously between the coupling-side end of the actuator and a corresponding support in the device holder, because an arrangement on the free spindle end would require readjustment if the actuator would change in length.

In view of the slimest possible design of the entire device, the motor is preferably and advantageously arranged coaxially to the threaded spindle on the holder.

The workpiece clamping device according to the invention is explained in more detail below with reference to the drawing of an exemplary embodiment.

Fig. 1

die Spannvorrichtung teilweise in Schnitt und Ansich in geöffneter Stellung;

Fig. 2

die gleiche Spannvorrichtung in geschlossener Stellung;

Fig. 3

einen vergrößerten Schnitt durch die schwimmende Lagerung und

Fig. 4

die Schaltung des Umkehr-Motors in besonderer Ausführungsform.

It shows schematically

Fig. 1

the clamping device partly in section and in the open position;

Fig. 2

the same clamping device in the closed position;

Fig. 3

an enlarged section through the floating storage and

Fig. 4

the circuit of the reversing motor in a special embodiment.

As can be seen from FIGS. 1, 2, the tensioning device consists of a tensioning lever 14 which is pivotally mounted in a holder H and which is connected in an articulated manner via an intermediate member 13 to an actuator 7 axially guided in the holder H and axially movable by a drive. This known construction principle of such devices is thus retained in the present device, but the previously conventional pneumatic or hydraulic lifting drive is replaced by a reversible rotary drive in the direction of rotation, namely in the form of a reversing motor 1 arranged coaxially with the spindle 3 with an upstream planetary gear 1ʹ and an axial coupling 2, which, as can be seen from Fig. 2, allows a slight axial displacement of the trapezoidal screw 3, with which the axial coupling 2 is rotatably connected. The threaded spindle 3 is provided with a trapezoidal thread 3ʹ with a small pitch in order to ensure self-locking between the spindle 3 and the actuator 7 provided with a corresponding internal thread 3ʺ. In the illustrated embodiment, the actuator is formed from two parts, namely from the actuator head piece 7ʹ and a correspondingly internally threaded spindle sleeve 7ʺ, onto which the actuator head piece 7ʹ is screwed and fixed in the desired position by means of a lock nut 8. At the actuator head 7ʹ, the intermediate member 13 is articulated, which in turn with an articular process 14ʹ of the clamping lever 14 is articulated in connection, which is in Fig. 1 in the open position and in Fig. 2 in the closed and clamping position. As can be seen, the holder H of the device, in which the entire adjustment mechanism is mounted, consists of several parts, all of which are designated by 5. On the side facing away from the tensioning lever, the actuator head piece 7ʹ in the exemplary embodiment shown is provided with a thickening 15, specifically for receiving the one joint of the intermediate member 13 and for receiving small guide rollers 16 which are supported on a flat guide 17 of the holder H. This type of design of the actuator head piece is also known. However, other types of guidance of the actuator head piece 7ʹ can also be used. In view of an over-center locking of the tensioning lever, however, the illustrated embodiment of the actuator 7ʹ is advantageously used.

The arrangement of the "floating" bearing (Fig. 3) between the spindle 3 and coupling 2 ensures that the threads can not wedge easily in the tensioned position. If any end stops 4 are provided to prevent the spindle 3 from being completely unscrewed from the actuator 7, the axial suspension 19 also functions in this regard, and the threads cannot self-wedge.

As can be seen in particular from FIGS. 2, 3, the trapezoidal threaded spindle 3 is mounted in the small coupling 2 with its drive-side end 3 ″ ″ in a torsion-proof but axially displaceable manner. Immediately before this coupling 2, the trapezoidal screw 3 is provided with two radial ball bearings 10, which are fixed on the spindle 3 with two lock nuts 12.

The two radial ball bearings 10 are in turn mounted in an axial sliding bush 11, which is slightly in one corresponding slide bearing guide 11ʹ of the holder H can move and is secured against rotation with a suitable element 18. The reversing motor 1 (electric gear motor) is designed for a specific current consumption and switches off in the event of an overload, which occurs when the axial suspension 19 is compressed to a predetermined load value.

If the tensioning lever 14 is to be released from its tensioning position, which can also be an over-dead center tensioning position, the motor 1, correspondingly switched over, rotates to the other side, with the existing self-locking of the threads being overcome without problems since there is no wedging between the threads . In order to prevent such wedging, the floating bearing is provided on the dome side with the axial suspension 19 in the form of a plate spring which is braced against the stop 20ʹ in the holder H. This stop can optionally also be made adjustable. The axial suspension 19 is, as mentioned, designed so that in the fully or partially compressed state of the maximum tension force that can be applied to the tensioning lever 14, which ensures that no further forces are introduced into the device when the tensioning position is reached, which would otherwise lead to wedging the thread would lead.

In order to ensure that when the tensioning lever 14 or the entire tensioning device is reset to the open position according to FIG. 1 that wedging of the threads does not occur as well, a limit switch 21 could of course be provided at a suitable point, which switches the reversing motor 1 in good time switches off. It is also advantageous, however, as can be seen from FIG. 3, to arrange a corresponding axial suspension 19ʹ on the tension side in front of the floating bearing, which makes such a limit switch unnecessary. This axial suspension 19ʹ is therefore in a suitable manner between the first radial ball bearing 10 and the stop 4ʹ Holder H arranged, whereby the axial suspension 19ʹ arranged there, like the axial suspension 19, comes into effect completely independently of the length of the actuator 7 that is actually set. The axial suspension 19ʹ could indeed be applied directly to the stop 4ʹ, but advantageously the stop can also be made axially adjustable in a suitable manner for its adjustability, which is not particularly shown.

The actuator head piece 7ʹ or the part of the actuator 7ʺ forming the spindle sleeve 7ʺ is provided with an end stop 6 in the form of an annular collar which interacts with the abovementioned stop 4. In the exemplary embodiment shown, the stop 4 forms a part with an exchangeable guide bush 9 which comprises the spindle 13 and the actuator 7 and which, as illustrated for example, is suitably integrated in the holder H.

This stop 4 now serves to prevent the spindle 3 from being completely unscrewed from the actuator 7 if the clamping lever 14 does not come to the clamping system for some reason on a workpiece, because then the motor 1 would not be loaded, simply continue to rotate and depending on Unscrew the spindle 3 from the actuator 7 according to the structural dimensions. Even if the end stop 6 of the spindle sleeve 7 'comes to rest against the stop 4, there is no thread wedging, since the "floating" bearing 20 then comes into operation again.

This described embodiment ensures that the threaded spindle 3 cannot wedge with the actuator 7. If, however, there are unfavorable circumstances, e.g. expansion of the clamped workpiece due to the effects of heat or high stress on the clamping arm when swiveling back due to additional loads on the tension arm (e.g. shape-matched pressure pieces that have to be fastened to the tension arm), the case may occur that the nominal current consumption of the motor 1 is not sufficient to move the tension arm or its actuator 7 out of its more heavily loaded end position. For this reason, the device is designed such that the circuit of the reversing motor 1 contains two measuring circuits IC1 and IC2 which are relatively matched with respect to the current consumption of the motor in such a way that the reversing motor 1 receives a higher current supply when moving from the two end positions than the nominal current when entering the end positions. The two measuring circuits are preferably adjusted in a ratio of 1: 1.5. This circuit is illustrated in Fig.4.
By means of this circuit, such "overload cases" are taken into account in that the reversing motor 1 receives an extremely short supply of current above the nominal current for which it is designed, for the moment it "breaks away" from the end positions, which enables it to overcome the overload that entered the clamping device from the outside and to be able to "gently" move out of its end positions. In the circuit shown in Figure 4 are denoted by D 1 u. D 2 Zener diodes, R 1 - R22 resistors, R 4 uR 11 trimming potentiometers and with IC3 and IC4 logic elements. The Optok 1-4 are optically acting switches, and S1 and S2 are the buttons or switches for initiating the closing or opening process of the clamping device. This circuit assigned to the motor circuit works as follows:
The start signal that sets the 1st and 2nd input S in the IC3 is given via the button S 1. At the same time, the 4th input R in IC3 is reset. The free passage is switched in the "undister" of the IC4 and the motor 1 is switched to open via the optocouplers 3 and K1. At the same time the current is measured via the IC2. As soon as the drawn current exceeds the set value of R 11, the IC2 switches through and the 1st input R in the IC3 is reset, whereby the motor 1 is switched off. The same happens when the tensioner is closed using button S2 and IC1.

Claims (8)

1. A workpiece-clamping device capable of being driven by an electric motor, comprising a threaded spindle (3) capable of being driven by an electric reversing motor (1) and having a self-locking thread pitch, said threaded spindle engaging with a positioning member (7), which has an internal thread, is axially displaceable and is secured against rotation, and said spindle further being provided with a springing which is supported against the housing (H) of the device and comes into effect on the positioning member (7) when the clamping position is reached, the motor (1), when overloaded, being capable of switching off, and being connected via an axial coupling (2) to the threaded spindle (3) in an axially displaceable, but rotationally fixed manner, and a threaded spindle bearing (10) being arranged in the housing (H) of the device between the axial coupling (2) and the threaded spindle (3), characterised in that the positioning member (7) is connected, via an intermediate member (13) ensuring the non-rotation thereof, to a clamping lever (14) pivotally mounted at the end of the housing (H) of the device remote from the drive,
   in that the threaded spindle bearing (10) secured to the threaded spindle (3) is axially displaceably mounted in the housing (H) of the device and supported on the housing (H) of the device through the intermediary on both sides of axial springs (19, 19') forming the springing and
   in that the circuit of the reversing motor (1), capable of switching off as a function of the current consumption required for maximum clamping force, comprises two measuring circuits (IC1 and IC2) which are proportionally set up with respect to the current consumption of the motor (1), whereby the current consumed by the reversing motor (1), when starting-up from the two end positions, is greater than that corresponding to the rated current when moving into the end positions.
2. Device according to claim 1, characterised in that the threaded spindle bearing (10) is mounted in an axial sliding sleeve (11) movable in the housing (H) of the device.
3. Device according to claim 1 or 2 characterised in that the axial springs (19, 19') are in the form of plate springs.
4. Device according to any one of claims 1 to 3, characterised in that a safety limit switch (21) is arranged, on the coupling or drive side, in the positioning path of the threaded spindle bearing (10) or the axial sliding sleeve (11).
5. Device according to any one of claims 1 to 4, characterised in that the positioning member (7) comprises a headpiece (7') and a spindle sleeve (7'') and that the headpiece (7') is capable of being screwed onto the spindle sleeve (7'') and is securable by means of a lock-nut (8).
6. Device according to any one of claims 1 to 5, characterised in that at least one of the axial springs (19) is placed against an abutment (20') adjustable in the housing (H) of the device.
7. Device according to any one of claims 1 to 6, characterised in that a limit stop (4) is arranged, remote from the drive, in the housing (H) of the device, said stop being formed as a part of a bush (9) which is arranged in the housing (H) of the device and surrounds the threaded spindle (3) and the positioning member (7).
8. Device according to any one of claims 1 to 7, characterised in that the two measuring circuits (IC1 and IC2) are set up at a ratio of 1:1.5.

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