CLAMPING OR GRIPPING DEVICE AND METHOD FOR GRIPPING OR CLAMPING A WORKPIECE

Description

[0001] The present invention relates to a clamping or gripping device with at least one clamping or gripping element operated by means of an electric power clamp, wherein the power clamp comprises an electric motor with a drive shaft, power transmission means for connecting the drive shaft to the at least one clamping or gripping element, and a power storage device for pre-tensioning the at least one clamping or gripping element, wherein the drive shaft has a bearing sleeve between the electric motor and the power transmission means, relative to which the electric motor is axially displaceable against a restoring force of the power storage device by means of a threaded spindle guided in a threaded sleeve, and wherein the restoring force of the power storage device is greater than a propulsive force required for driving the clamping or gripping element.as well as a corresponding method for gripping or clamping a workpiece using an electric power clamp.

[0002] Such a clamping or gripping device is already known from EP 2 548 681 A1, which discloses a device according to the preamble of claim 1. Reference is also made to US 2016 / 158848 A1, US 2012 / 119451 A1 and EP 3 175 942 A1.

[0003] A chuck with electric motors is already known from EP 3 059 036 A1. This patent describes such a chuck as comprising multiple jaws that hold a tool on several sides and support it during machining, for example, by a machining robot. It also provides that each jaw can be assigned a force storage device which, in the event of a jaw loosening due to vibrations during machining, applies force to the jaw and provides an additional clamping force.

[0004] However, such energy storage devices can only react to loosening that may occur after the clamping or gripping device has been tightened. Subsequent retightening is no longer possible.

[0005] While hydraulic clamping devices use a hydraulic accumulator to provide the necessary force for retightening, when using an electric motor, it is necessary to switch it off after clamping. Only when a so-called "safe torque off" signal is present can further machining of the workpiece begin. Consequently, unlike with a hydraulic clamping device where hydraulic pressure is still present, the motor's power is no longer available for retightening, and the purely mechanical elasticity of the workpiece is also insufficient for this purpose.

[0006] The present invention is therefore based on the objective of creating an electrically operated clamping or gripping device which can apply force to re-tighten the workpiece between the clamping or gripping means even after a Safe-Torque-Off signal has been applied.

[0007] This is achieved by a clamping or gripping device according to the features of independent device claim 1, and by a method for gripping or clamping a workpiece according to the features of dependent method claim 12. Useful embodiments of such a device or method can be found in the respective subsequent dependent claims.

[0008] The invention provides a clamping or gripping device with at least one clamping or gripping element operated by means of an electric power clamp, wherein the power clamp comprises an electric motor with a drive shaft, power transmission means for connecting the drive shaft to the at least one clamping or gripping element, and an energy storage device for pre-tensioning the at least one clamping or gripping element. According to the invention, this device is characterized in that the drive shaft has a bearing sleeve between the electric motor and the power transmission means, relative to which the electric motor is axially displaceable against a restoring force of the energy storage device by means of a threaded spindle guided in a threaded sleeve, wherein the restoring force of the energy storage device is greater than a propulsive force required for driving the clamping or gripping element.

[0009] In operation, this arrangement allows the electric motor to drive its drive shaft, which in turn transmits a driving force to the clamping or gripping devices via the power transmission means. In the case of a clamping chuck, clamping devices can be actuated in this way, while in other applications, such as gripper arms, robots, and the like, virtually any configuration can be used, in which at least one clamping or gripping device is clamped against a second clamping or gripping device, or a single clamping or gripping device is clamped against a fixed bearing. It is also possible to arrange such clamping devices in a chuck, whereby, in the case of a paired arrangement of opposing clamping devices, these can also be used in larger numbers, i.e., two, four, or six clamping devices.If the clamping device is operated only on one side, i.e., no opposing clamping device is used but rather a chuck with an odd number of clamping devices is implemented, then a power clamp will only operate one clamping device, whereas a power clamp can operate two clamping devices when there are opposing clamping devices, as in a clamping stock.

[0010] The bearing sleeve located in the drive shaft rotates with the electric motor during the positioning of the clamping or gripping devices, as the energy storage device initially ensures a frictional connection between the threaded spindle and the threaded sleeve. Only when the clamping or gripping device comes into contact with a workpiece does the required additional positioning force become greater than the static frictional force between the threaded spindle and the threaded sleeve, and the threaded spindle unscrews itself from the threaded sleeve. In this process, the force applied by the motor, which must continue to rotate after reaching the stop, is transferred to the energy storage device, thus tensioning it.

[0011] If the workpiece is then machined and a loosening occurs in the clamping or gripping device, which would cause the threaded spindle to rotate backwards, the restoring force of the energy storage device ensures that the spindle cannot rotate backwards, thus ultimately re-tensioning the clamping or gripping device.

[0012] According to the invention, the threaded spindle is designed as a high-pitch threaded spindle, which is guided in a high-pitch threaded sleeve. In contrast to conventional threaded spindles, such a high-pitch threaded spindle has a particularly large pitch. The pitch here refers to the distance the spindle travels in the longitudinal direction while rotating once around its axis, i.e., the distance between two thread crests. In a specific embodiment, the thread of the high-pitch threaded spindle can have a pitch of 10 mm to 80 mm, preferably 30 mm to 40 mm, and most preferably 35 mm. Such a large thread pitch means that even a slight rotation of the spindle results in a strong load on the energy storage device, enabling the energy storage device to exert a large force on the power transmission means.

[0013] It can further be provided that the threaded spindle is operatively connected to the electric motor and the threaded sleeve is rotationally fixed within the bearing sleeve. In principle, the reverse is also possible, but this is the preferred configuration. In this configuration, the threaded spindle extends the drive axis, and the bearing sleeve can be displaced longitudinally relative to the threaded spindle. The threaded sleeve can be held in a clamping fit within the bearing sleeve by friction, but it is advantageous to additionally secure the threaded sleeve to the bearing sleeve, for example, by means of set screws, in order to be able to withstand greater force.

[0014] A particularly advantageous feature is that the electric motor can also be braked in its end position. This prevents the electric motor from rotating backwards due to the spring force of the energy storage device. Furthermore, the power transmission system can advantageously include a gearbox, which allows the design to be adapted to a preferred motor speed.

[0015] In a specific embodiment, at least one spring assembly consisting of at least one, preferably several, compression springs, preferably coil springs or gas springs, can be provided as the energy storage device. These can preferably be arranged around the electric motor and mounted on spring pins to prevent lateral deflection under compressive load. The electric motor can have a motor housing which is rotationally fixed to a motor plate, with the energy storage device being supported on the motor plate on one side and on the motor's fixed bearing on the other. This creates a cage for the springs of the energy storage device, so that when the motor housing is moved away from the bearing sleeve, the motor plate is moved onto the motor's fixed bearing, and the springs have no opportunity to deflect.The spring pins can be attached to the motor plate, but then only strike the motor's fixed bearing on one side, so that they can evade the coupled force through the motor's fixed bearing.

[0016] Furthermore, at least one clamping or gripping device can be driven by a self-locking trapezoidal lead screw or a ball screw. A self-locking screw requires overcoming a higher static friction force to be set in motion. Loosening clamping or gripping devices driven by such a screw is therefore even more difficult.

[0017] A further method is provided for gripping or clamping a workpiece using an electric power clamp, which actuates at least one clamping device by means of an electric motor with a drive shaft, power transmission means for connecting the drive shaft to the at least one clamping or gripping device, and a power storage device for pre-tensioning the at least one clamping or gripping device. According to the invention, this method is characterized in that the drive shaft has a bearing sleeve between the electric motor and the power transmission means, and the electric motor continues to rotate after reaching a stop on the workpiece, whereby the motor is displaced axially against a restoring force of the power storage device, which is greater than a propulsive force required for advancing the clamping or gripping device, by means of a threaded spindle provided within the bearing sleeve and guided in a threaded sleeve.

[0018] The invention described above will be explained in more detail below using an exemplary embodiment.

[0019] They show Figure 1 shows a clamping stock with a first and a second clamping device, which is operated by an electric motor via a power clamp according to the invention, in perspective view; Figure 2 shows the clamping stock according to Figure 1 in a lateral sectional view, Figure 3, the power clamp from the clamping stock according to Figure 2 in an untensioned state in perspective view, Figure 4 the power clamp according to Figure 3 in an untensioned state in a lateral sectional view, Figure 5, the power clamp according to Figure 3 in tensioned state in lateral sectional view, as well as Figure 6 the force clamp according to Figure 3 in a tense state, shown in perspective.

[0020] Figure 1Figure 1 shows a clamping device 1 in the form of a clamping stock with a first clamping element 2 and a second clamping element 3, which are mounted on a housing 20. The two clamping elements 2 and 3 are guided longitudinally displaceably on the housing 20 and are actuated by means of a trapezoidal threaded spindle 19, which is shown in the sectional view according to Figure 2. Figure 2 The two are shown as mirror images of each other. Figure 2The figure shows a lateral section through the clamping device 1, in whose housing 20 the first clamping device 2 is connected to the second clamping device 3 via the trapezoidal threaded spindle 19. The trapezoidal threaded spindle 19 has threads that run symmetrically from the center, so that, depending on the direction of rotation of the trapezoidal threaded spindle 19, the clamping devices 2 and 3 move either towards each other or away from each other. The trapezoidal threaded spindle 19 also has a threaded section in the region of its center that meshes with power transmission means 17 of the power clamp located below the clamping devices 2 and 3. The force of an electric motor 5 of the power clamp 4 is ultimately transmitted via a thread 18 to the trapezoidal threaded spindle 19 and thus to the clamping devices 2 and 3.

[0021] Figure 3The figure shows only the power clamp 4, which is depicted from its underside. The electric motor 5 initially passes through a fixed motor bearing 7, in which it is slidably mounted. A rotationally fixed and frictional connection is realized between the electric motor 5 and the motor plate 6, which is opposite the fixed motor bearing 7. A spring assembly 9, acting as a force storage device, is arranged between the motor plate 6 and the fixed motor bearing 7. This assembly consists of six coiled compression springs, which are fixed with spring pins. The spring pins are attached to the motor plate 6, and the electric motor 5 itself is slidably mounted on the fixed motor bearing 7. The spring pins form a stop that limits the maximum possible distance between the motor plate 6 and the fixed motor bearing 7.

[0022] Between two gear webs 14, 17 gears are arranged as power transmission means, which are operatively connected to the drive shaft 16 of the electric motor 5 (not shown) via a gearbox 18 flanked by a bearing web 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 webs 14.

[0023] The bearing sleeve 11 represents a central functional element, which is located in Figure 4This is explained in more detail below. 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 received in a corresponding threaded sleeve 12. Specifically, the threaded spindle 13 is a high-pitch threaded spindle with a pitch of 35 mm, and the threaded sleeve 12 has a corresponding mating thread, so that the threaded spindle 13 can unscrew itself from the threaded sleeve 12 by a relative rotation.

[0024] Such relative movement between the threaded spindle 13 and the threaded sleeve 12 is initially prevented by friction. This friction is generated by the preload of the spring assembly 9, which pushes the electric motor 5 towards its drive shaft 16. As long as the rotation of the electric motor 5 can cause movement in the gearbox 18, rotation of the power transmission means 17, and ultimately movement of the clamping devices 2 and 3, and the force required for this is less than the frictional engagement between the threaded spindle 13 and the threaded sleeve 12 caused by the spring assembly 9, relative movement between the threaded spindle 13 and the threaded sleeve 12 will not occur. Only when the clamping devices 2 and 3 reach a stop, for example, when they grip a workpiece, does the force required for the feed become greater than the frictional engagement, and the threaded spindle 13 begins to rotate in the threaded sleeve 12.

[0025] This situation is in Figure 5shown. There, the threaded spindle 13 has already unscrewed itself from the threaded sleeve 12 by a certain distance, thereby pushing the motor plate 6 towards the motor fixed bearing 7. This displacement requires pressure on the spring assembly 9, and the force required for this is stored in the spring assembly. In this situation, which is also shown in perspective in Figure 6 As shown, when the workpiece is clamped between the clamping devices 2 and 3, the spring assembly 9 pushes forward, ensuring that the threaded spindle 13 can only be turned backward against the force of the spring assembly 9 and that any movements are thereby compensated for. It is particularly advantageous if the thread of the threaded spindle 13 is designed 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 large force.

[0026] The above description thus describes an electrically operated clamping or gripping device which can apply force to re-tighten the workpiece between the clamping or gripping means even after a Safe-Torque-Off signal has been applied. REFERENCE MARK LIST

[0027] 1Clamping device 2First clamping device 3Second clamping device 4Power clamp 5Electric motor 6Motor plate 7Motor fixed bearing 8Motor counter bearing 9Spring package 10Motor housing 11Bearing sleeve 12Threaded sleeve 13Threaded spindle 14Gear cheeks 15Bearing cheek 16Drive shaft 17Power transmission means 18Gear 19Trapezoidal thread spindle 20Housing

Claims

1. Clamping or gripping device (1) with at least one clamping or gripping means (2, 3) operated by means of an electric power clamp (4), wherein the power clamp comprises an electric motor (5) with a drive shaft (16), power transmission means (17) for connecting the drive shaft to the at least one clamping or gripping means, and a power accumulator (9) for preloading the at least one clamping or gripping means, characterised in that the drive shaft has a bearing sleeve (11) 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 force accumulator by means of a threaded spindle (13) guided in a threaded sleeve (12), and wherein the restoring force of the energy storage device is greater than a propulsive force required for the propulsion of the clamping or gripping means, wherein the threaded spindle (13) is designed as a steep-thread spindle which is guided in a steep-thread sleeve.

2. Clamping or gripping device according to claim 1, characterised in that the steep-thread spindle has a thread with a pitch of 10 mm to 80 mm, preferably 30 mm to 40 mm, most preferably 35 mm.

3. Clamping or gripping device according to one of the preceding claims, characterised in that the threaded spindle is operatively connected to the electric motor and the threaded sleeve is rotatably mounted in the bearing sleeve.

4. Clamping or gripping device according to one of the preceding claims, characterised in that the electric motor is braked in its end position.

5. Clamping or gripping device according to one of the preceding claims, characterised in that the power transmission means comprise a gearbox (18).

6. Clamping or gripping device according to one of the preceding claims, characterised in that at least one spring assembly (9) comprising at least one, preferably several, compression springs, preferably coil springs or gas pressure springs, is provided as the force accumulator.

7. Clamping or gripping device according to one of the preceding claims, characterised in that the electric motor has a motor housing which is connected in a rotationally fixed manner to a motor plate (6), wherein the force accumulator is supported on the one hand on the motor plate and on the other hand on the motor fixed bearing (7).

8. Clamping or gripping device according to one of the preceding claims, characterised in that the at least one clamping or gripping means is driven by means of a self-locking trapezoidal threaded spindle or a recirculating ball screw.

9. Clamping or gripping device according to one of the preceding claims, characterised in that the at least one first clamping or gripping means can be clamped against a fixed bearing.

10. Clamping or gripping device according to one of claims 1 to 8, characterised in that the at least one first clamping or gripping means can be clamped against a second adjustable clamping or gripping means.

11. Clamping or gripping device with a chuck body with several pairs of adjustable clamping or gripping means, which are each arranged in pairs opposite each other and are each actuated in pairs by a power clamp.

12. 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 with a drive shaft, power transmission means for connecting the drive shaft to the at least one clamping or gripping means, and a power accumulator for preloading the at least one clamping or gripping means, characterised in that the drive shaft has a bearing sleeve between the electric motor and the power transmission means, and the electric motor continues to rotate after reaching a stop on the workpiece, and wherein the motor is displaced in the axial direction by means of a threaded spindle provided inside the bearing sleeve and guided in a threaded sleeve against a restoring force of the energy storage device, which is greater than a propulsive force required for the propulsion of the clamping or gripping means, wherein the threaded spindle is a steep-thread spindle, whereby a large spring travel is generated by a small feed.

13. Method according to claim 13, characterised in that the electric motor is de-energised after reaching an end position.