SPANN-ODER GREIFVORRICHTUNG UND VERFAHREN ZUM GREIFEN ODER VERSPANNEN EINES WERKST?CKS

Abstract

With electrically operated clamping or gripping devices such as vices, it is necessary to switch them off after clamping the workpiece in order to prevent overheating. Machining by means of a machining robot, for example, is able to commence only once a safe torque off signal is present. However, the workpiece can become loose due to vibrations during such machining, since the de-energized electric motor can no longer perform retightening. This can lead to damage to the workpiece and, in the worst case, injuries to operating personnel. It is therefore the object of the invention to propose a solution for enabling retightening to be performed from an energy accumulator.

This is achieved in that the drive shaft of the motor can be extended via a threaded spindle, thereby preloading the energy accumulator. This makes effective retightening of the clamping or gripping device possible, particularly when using a steep-threaded spindle.

Claims

1. A clamping or gripping device comprising: at least one clamping or gripping means operated by means of an electric power clamp, wherein the power clamp comprises an electric motor comprising a drive shaft; force transmission means for connecting the drive shaft to the at least one clamping or gripping means; and an energy accumulator for preloading the at least one clamping or gripping means; wherein the drive shaft comprises a bearing sleeve between the electric motor and the force transmission means relative to which the electric motor is mounted so as to be displaceable in the axial direction against a restoring force of the energy accumulator by means of a threaded spindle that is guided in a threaded sleeve; wherein the restoring force of the energy accumulator is greater than the propulsive force that is required to advance the clamping or gripping means; and wherein the threaded spindle is embodied as a steep-threaded spindle that is guided in a steep-threaded sleeve.

2. The clamping or gripping device according to claim 1, wherein the steep-threaded spindle comprises a thread with a pitch of from 10 mm to 80 mm, preferably 30 mm to 40 mm, most preferably 35 mm.

3. The clamping or gripping device according to claim 1, wherein the threaded spindle is operatively connected to the electric motor, and the threaded sleeve is accommodated in a rotationally fixed manner in the bearing sleeve.

4. The clamping or gripping device according to claim 1, wherein the electric motor is braked in its end position.

5. The clamping or gripping device according to claim 1, wherein the force transmission means comprise a gear mechanism.

6. The clamping or gripping device according to claim 1, wherein at least one spring assembly consisting of at least one, preferably several, compression springs, preferably coil springs or gas springs, is provided as an energy accumulator.

7. The clamping or gripping device according to claim 1, wherein the electric motor has a motor housing which is connected in a rotationally fixed manner to a motor plate, wherein the energy accumulator is supported on the motor plate on the one hand and on the fixed motor bearing on the other hand.

8. The clamping or gripping device according to claim 1, wherein the at least one clamping or gripping means is driven using a self-locking trapezoidal thread spindle or a ball screw.

9. The clamping or gripping device according to claim 1, wherein the at least one first clamping or gripping means can be clamped against a fixed bearing.

10. The clamping or gripping device according to claim 1, wherein the at least one first clamping or gripping means can be clamped against a second adjustable clamping or gripping means.

11. A clamping or gripping device with a chuck body with multiple pairs of adjustable clamping or gripping means which are each arranged opposite one another in pairs and are each actuated in pairs by a power clamp.

12. A method for gripping or clamping a workpiece using an electric power clamp which actuates at least one clamping means by means of an electric motor comprising a drive shaft, force transmission means for connecting the drive shaft to the at least one clamping or gripping means, and an energy accumulator for preloading the at least one clamping or gripping means, wherein: the drive shaft comprises a bearing sleeve between the electric motor and the force transmission means, and the electric motor, which continues to rotate after reaching a stop on the workpiece, is displaced in the axial direction, and wherein the motor counteracts a restoring force by means of a threaded spindle that is provided within the bearing sleeve and guided in a threaded sleeve of the energy accumulator, which restoring force is greater than a propulsion force that is required for the propulsion of the clamping or gripping means; wherein the threaded spindle is a steep-threaded spindle, with long spring travel being generated by a small actuation.

13. The method according to claim 12, characterized in that the electric motor is de-energized after reaching an end position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the drawings,

[0021] FIG. 1 shows a perspective view of a vise with a first and a second clamping means which is operated with an electric motor via a power clamp according to the invention;

[0022] FIG. 2 shows the vice according to FIG. 1 in a side sectional view;

[0023] FIG. 3 shows the power clamp from the vice according to FIG. 2 in the untightened state in a perspective view;

[0024] FIG. 4 shows the power clamp according to FIG. 3 in the untightened state in a side sectional view;

[0025] FIG. 5 shows the power clamp according to FIG. 3 in a tightened state in a side sectional view; and

[0026] FIG. 6 shows the power clamp according to FIG. 3 in a tightened state in a perspective view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] FIG. 1 shows a clamping device 1 in the form of a vice with a first clamping means 2 and a second clamping means 3 which are accommodated on a housing 20. The two clamping means 2 and 3 are guided in a longitudinally displaceable manner on the housing 20 and are operated in mirror symmetry to one another using a trapezoidal thread spindle 19, which is shown in the sectional view according to FIG. 2. FIG. 2 shows a lateral section through the clamping device 1, in the housing 20 of which the first clamping means 2 is connected to the second clamping means 3 via the trapezoidal thread spindle 19. The trapezoidal thread spindle 19 has threads extending in mirror symmetry from the center, so that, depending on the direction of rotation of the trapezoidal thread spindle 19, the clamping means 2 and 3 either move toward or away from one another. The trapezoidal thread spindle 19 also has a threaded section near its center which meshes with force transmission means 17 of the power clamp which is arranged beneath the clamping means 2 and 3. The force of an electric motor 5 of the power clamp 4 is ultimately transmitted to the trapezoidal thread spindle 19 and thus to the clamping means 2 and 3 via a thread 18.

[0028] FIG. 3 only illustrates the power clamp 4, which is shown from its underside. The electric motor 5 initially extends through a fixed motor bearing 7 and is displaceably mounted in this fixed motor bearing 7. A rotationally fixed and frictional connection is implemented in the electric motor 5 on the motor plate 6, which is situated opposite the fixed motor bearing 7. A spring assembly 9 is arranged as an energy accumulator between the motor plate 6 and the motor fixed bearing 7, which spring assembly 9 is formed in the present case from six spiral compression springs that are fixed with spring pins. The spring pins are attached to the motor plate 6 and, like the electric motor 5 itself, slidably mounted on the motor fixed bearing 7, the spring pins forming a stop which limits the greatest possible distance between the motor plate 6 and the motor fixed bearing 7.

[0029] Gear wheels are arranged as force transmission means 17 between two gear blocks 14, which gear wheels are operatively connected to the drive shaft 16 (not shown here) of the electric motor 5 via a gear mechanism 18 that is flanked by a bearing block 15 and a motor counter-bearing 8. A bearing sleeve 11, which is part of the drive shaft 16 of the electric motor 5, is guided through the gear blocks 14.

[0030] The bearing sleeve 11 represents a central functional element that is explained in greater detail in FIG. 4. In this sectional view, it can be seen that the electric motor 5 is connected beyond the motor plate 6 to a threaded spindle 13, which is accommodated in a corresponding threaded sleeve 12. Specifically, the threaded spindle 13 is a steep-threaded spindle with a pitch of 35 mm; the threaded sleeve 12 has a corresponding mating thread, enabling the threaded spindle 13 to be unscrewed from the threaded sleeve 12 by rotating relative thereto.

[0031] Such a relative movement between the threaded spindle 13 and the threaded sleeve 12 is initially prevented by friction. This is created by the preload of the spring assembly 9, which presses the electric motor 5 in the direction of its drive shaft 16. As long as the rotation of the electric motor 5 is able to effect a movement in the gear mechanism 18, a rotation of the force transmission means 17 and, ultimately, a movement of the clamping means 2 and 3, and the force for this is less than the frictional engagement between the threaded spindle 13 and the threaded sleeve 12 caused by the spring assembly 9, there is no relative movement between the threaded spindle 13 and the threaded sleeve 12. Only when the clamping means 2 and 3 come to a stop, for example when they grip a workpiece, does the force required for the actuation become greater than the frictional engagement, and the threaded spindle 13 begins to rotate in the threaded sleeve 12.

[0032] This situation is shown in FIG. 5. There, the threaded spindle 13 has already been unscrewed from the threaded sleeve 12 by a certain distance, whereby the motor plate 6 has been pressed in the direction of the motor fixed bearing 7. This displacement requires pressure to be exerted on the spring assembly 9, causing the force required for this to be stored in the spring assembly. In this situation, which is also shown in perspective in FIG. 6, if the workpiece comes loose between the clamping means 2 and 3, the spring assembly 9 pushes forward and ensures that the threaded spindle 13 can only be turned back against the force of the spring assembly 9 and that any movements will be balanced out again as a result. It is especially advantageous if the thread of the threaded spindle 13 is embodied as a steep thread, so that even a slight rotation results in a strong spring force or, conversely, so that the spring can act on the threaded spindle 13 with a powerful force.

[0033] What is described above is an electrically operated clamping or grip ping device that can apply force to retighten the workpiece between the clamping or gripping means even after a safe torque off signal has been generated.

LIST OF REFERENCE SYMBOLS

[0034] 1 clamping device [0035] 2 first clamping means [0036] 3 second clamping means [0037] 4 power clamp [0038] 5 electric motor [0039] 6 motor plate [0040] 7 motor fixed bearing [0041] 8 motor counter-bearing [0042] 9 spring assembly [0043] 10 motor housing [0044] 11 bearing sleeve [0045] 12 threaded sleeve [0046] 13 threaded spindle [0047] 14 gear blocks [0048] 15 bearing block [0049] 16 drive shaft [0050] 17 force transmission means [0051] 18 gear mechanism [0052] 19 trapezoidal thread spindle [0053] 20 housing