Clamp device

Abstract

To provide a clamp device for holding a workpiece and capable of reliable and verifiable monitoring of an interval between a workpiece and a placing surface and / or a clamp jaw before a whole processing process and during a process.SOLUTION: A free space 11 is processed in a housing 4, and a symmetry axis of the free space extends perpendicularly to a placing surface 6'. The free space faces a workpiece 3 pinched by an open end surface side, and / or at least one free space is processed in one clamp jaw of clamp jaws 7, 8, 9, and a proximity sensor 12 is inserted in each free spaces. A monitoring area is formed between the placing surface and the workpiece by the proximity sensor, and the monitoring area is monitored by an evaluation unit 14 for the presence of the workpiece.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a clamping device for holding a workpiece to be machined by a machine tool, which is described in the preamble of claim 1, and particularly to a clamping device used as a chuck, a vice or a zero-point clamping system.

[0002] Such clamping devices are already known from German Patent Application Publication No. 102007048121. Furthermore, reference is also made to US Patent No. 6257077, German Patent Application Publication No. 102008052809, European Patent Application Publication No. 3391991, European Patent Application Publication No. 3578294, European Patent Application Publication No. 3266546, German Patent Application Publication No. 102017213400 and German Utility Model No. 202010001139.

[0003] Such a clamping device may be formed as a vice having one clamping jaw or two clamping jaws that can be moved towards each other and are movably supported to hold the workpiece in a fixed position during the machining process. However, such a clamping device may also be formed as a chuck having at least three clamping jaws that can be fed in the radial direction in order to attach and hold the workpiece in a defined position during the machining process of the machine tool.

[0004] Such a clamping device is arranged in a so-called machining center and is often used in a pallet or tool table together with a zero-point clamping system. The zero-point clamping system achieves that the clamping device can be accurately assembled at a preset same position together with the workpiece when the clamping device is replaced. This means that no re-calibration is required when the clamping device holding the workpiece is replaced.

[0005] The pallet or tool table is rotated during the machining process. Therefore, significant centrifugal forces act on the rotating workpiece and clamping device during the machining process.

[0006] Therefore, it is necessary to monitor the precise position of the workpiece relative to the clamping device not only when assembling the workpiece into the clamping device, but also throughout the entire machining process.

[0007] For several years, it has been known that such monitoring processes are carried out using a medium, particularly air or gas. In this case, the medium needs to be guided from a stationary state into the rotating clamping device. Therefore, a coupling unit or adapter must be provided in the transition area between the stationary medium storage device and the rotating clamping device to compensate for the rotational motion of the clamping device. Furthermore, the medium must be introduced at a constant pressure into each hole machined in the housing of the clamping device, because compressed air needs to flow out at the mounting surface, that is, between the upper surface of the housing of the clamping device and the workpieces being clamped.

[0008] Therefore, the gap between the mounting surface of the clamping device and the lower surface of the workpiece facing the housing of the clamping device serves as a measure of the pressure present there. In other words, when the gap between the mounting surface and the workpiece is within tolerance, for example 0.02 mm, a known pressure state is present, allowing us to know that the gap between the workpiece and the housing is correct or within tolerance. If the workpiece changes position before or during the machining process due to foreign particles, such as chips or other impurities, or due to a decrease in the required clamping force of the clamp jaws, an increased gap is created between the workpiece and the mounting surface of the clamping device, through which the medium flows out. This results in a pressure drop in the transition area between the mounting surface and the workpiece. This pressure drop is measurable and therefore suggests that the workpiece is no longer in the correct position.

[0009] This known monitoring device for clamping equipment has been found to have a disadvantage in that considerable structural effort is required to transport the medium from a constant environment to the rotating environment of the clamping equipment, particularly to the transition area between the mounting surface and the workpiece. In this case, it is technically crucial that the medium is supplied uniformly throughout the entire processing process and discharged at the desired outlet point, i.e., between the mounting surface and the workpiece under constant pressure, where it discharges at a preset pressure. Such technically constrained settings inevitably lead to considerable structural effort and increased costs.

[0010] Furthermore, such mechanically operated monitoring means have the disadvantage of requiring the measurement values ​​to be transmitted to an external evaluation device. While pressure drops certainly occur directly in the transition area between the workpiece and the mounting surface of the clamping device, the measurement value must first be detected as a pressure state and only then can it be converted into a digital switching signal by a corresponding electrical component. Therefore, if the change in the gap between the workpiece and the mounting surface is considerably undesirable, the deviation from the acceptable range cannot be immediately transmitted to another electrical device, for example, to immediately turn off the machine tool.

[0011] Therefore, the object of the present invention is to improve the clamping device of the form described at the beginning so that reliable and inspectable monitoring of the distance between the workpiece and the mounting surface and / or clamping jaws of the clamping device can be performed before and during the entire machining process without requiring large structural means for this purpose. At the same time, it is required that the measurement results obtained regarding the distance between the workpiece and the mounting surface of the clamping device be digitally generated, and therefore immediately evaluateable, and thus usable as a switching signal.

[0012] At least one free space is machined into the housing, the axis of symmetry of the free space extends perpendicular to the mounting surface, the free space faces the clamped workpiece with its open end face side, and / or at least one free space is machined into one of the clamping jaws, the free space opening to each clamping face of the clamping jaw, a proximity sensor is inserted into each free space, the proximity sensor forms a monitoring area between the mounting surface and the workpiece, the monitoring area is monitored by an evaluation unit for the presence of the workpiece, the position of the workpiece is monitored during mounting, clamping operation and throughout the entire machining process of the machine tool, and if the distance of the workpiece from the mounting surface as a reference plane changes outside a preset tolerance range, the evaluation unit immediately detects this and generates an electrical or digital switching signal, which can stop the machine tool without any time delay.

[0013] Furthermore, and particularly advantageously, the medium does not need to be transported within the rotating housing of the clamping device. Therefore, all connecting adapters between the stationary pressure-forming means and the rotating housing of the clamping device are eliminated. This, on the one hand, provides free space for the machine tool, and on the other hand, completely eliminates the need for such a medium. This significantly reduces manufacturing costs.

[0014] The energy required to operate an inductive proximity sensor can be supplied via an electrical line. Simultaneously, this electrical line can transmit data or signals to an evaluation unit, from which they can be transmitted to a machine tool or other electrical control device.

[0015] It is possible to easily replace electrical lines with inductive interfaces, which allows the evaluation unit to be placed both inside and outside the clamp device housing.

[0016] The drawings show three clamping devices used for various applications in clamping technology, and these three clamping devices are described in detail below. [Brief explanation of the drawing]

[0017] [Figure 1] This is a perspective view of a clamping device as a chuck, comprising a housing into which a mounting element for holding a workpiece is assembled, and three clamping jaws supported axially by the housing and capable of gripping the workpiece. [Figure 2] This is a cross-sectional view of the clamping device shown in Figure 1, where the workpiece is optimally held. [Figure 3] This figure shows the clamping device shown in Figure 1 with the workpiece incorrectly mounted. [Figure 4a] This is a perspective view of a clamping device as a zero-point clamping system, comprising a housing with an annular mounting surface for holding a workpiece, and three clamping jaws supported axially by the housing, which can grip and center the workpiece. [Figure 4b] This is a perspective view of a clamping device as a zero-point clamping system, comprising a housing with an annular mounting surface for holding a workpiece, and three clamping jaws supported axially by the housing, which can grip and center the workpiece. [Figure 5] This figure shows a clamping device as a vise, with two clamping jaws positioned opposite each other and axially movable to hold a workpiece, and a housing between them that holds the workpiece to be machined.

[0018] Figures 1, 2, and 3 show a clamping device 1 positioned within the area of ​​the machine tool 2. This clamping device 1 holds the workpiece 3 to be machined by the machine tool 2 in a defined position, thereby enabling the machine tool 2 to perform the appropriate machining operations. Since each machining step of the machine tool 2 is required to be performed with as little error as possible, the position of the workpiece 3 to be clamped must be monitored both when it is mounted to the clamping device 1 and throughout the entire machining process of the machine tool 2.

[0019] The clamping device 1 consists of a housing 4 that is normally rotated during the machining process of the machine tool 2. Three guide grooves 5 are machined into this housing 4. These three guide grooves 5 extend radially, that is, they are directed toward the center point 21 of the housing 4.

[0020] Within each guide groove 5, one of the three clamp jaws, 7;8;9, is inserted and supported to move in the axial direction. The clamp jaws 7,8,9 can be driven hydraulically, electrically, or mechanically by corresponding drive means (not shown) located inside the housing 4. Therefore, when removing a workpiece 3, the clamp jaws 7,8,9 are moved outward in synchronous motion. When a new workpiece 3 to be processed is mounted on the clamping device 1, the three clamp jaws 7,8,9 are moved synchronously toward the outer circumferential surface of the workpiece 3. Subsequently, the clamp jaws 7,8,9 make contact with the workpiece 3, applying a preset, appropriate holding force to the workpiece 3.

[0021] Furthermore, a mounting element 6 is fixed to the housing 4. The mounting element 6 has three arms protruding from the center point 21. These three arms form a mounting surface 6' on which each workpiece 3 is placed. Therefore, this mounting surface 6' supports the workpiece 3 in one direction. Three clamping jaws 7, 8, 9 center the workpiece 3 and clamp it parallel to the reference plane formed by the mounting surface 6'. Therefore, when the clamping jaws 7, 8, 9 are actuated, the workpiece 3 is centered and held in space.

[0022] In order to monitor the position of the workpiece 3 relative to the mounting surface 6', the housing 4 is first provided with three holes 11 arranged offset from each other. These three holes 11 extend perpendicular to the mounting surface 6' and are open in the direction of the workpiece 3 to be clamped.

[0023] In each hole 11, an inductive proximity sensor 12 is inserted, and the outer contour formed by this proximity sensor 12 extends slightly below the mounting surface 6'. Therefore, there is a gap of, for example, 0.02 mm between the workpiece 3 to be clamped and each proximity sensor 12. Even when the workpiece 3 is placed on the mounting surface 6' over its entire surface, the preset gap exists between the proximity sensor 12 and the workpiece 3.

[0024] Furthermore, as is apparent from FIG. 1, the three clamping jaws 7, 8, 9 are arranged at a pitch angle of 120°, and the three holes 11 extend between two adjacent clamping jaws 7; 8; 9. Therefore, the holes 11 are also arranged at a pitch angle of 120°, whereby the position of the workpiece 3 is monitored by the proximity sensors 12 inserted into the holes 11 during mounting and throughout the entire machining process.

[0025] As can be seen from FIG. 2, the workpiece 3 is placed on the placement surface 6' without error and evenly clamped by the clamp jaws 7, 8, 9. Therefore, the distance between the lower surface of the workpiece 3 and the upper surface of the placement surface 6' is equal across the entire plane of the placement surface 6'. Each proximity sensor 12 forms a monitoring area 13 schematically shown. This monitoring area 13 extends over a distance of 0.02 mm to 3 mm. Therefore, the distance of the monitoring area 13 is sufficient for the proximity sensor 12 to confirm the desired distance between the workpiece 3 and the placement surface 6'. In this case, the monitoring area 13 is formed by the schematically shown lines of force 13' that strike the lower surface of the workpiece 3. Therefore, each proximity sensor 12 can continuously monitor the distance between this proximity sensor 12 and the clamped workpiece 3.

[0026] In FIG. 3, there is a chip 30 that accidentally changes the position of the workpiece 3 between the placement surface 6' and the workpiece 3.

[0027] The hole 11 may be machined in the carriage or other components supported movably, whereby the position of the hole 11 relative to the center point 21 of the housing 4 can be changed. That is, since the diameter of the workpiece 3 to be machined is increased or decreased, the proximity sensor 12 and thus the hole 11 can be adapted to the diameter of the workpiece 3.

[0028] Each proximity sensor 12 is connected to an evaluation unit 14 by an electrical line 15. Therefore, the measurement data regarding the presence of the workpiece 3 obtained by each proximity sensor 12 is electrically transmitted to the evaluation unit 14 through the electrical line 15. This evaluation unit 14 is connected to the machine tool 2 or its control device via another electrical line 15. Therefore, any change in the distance between each proximity sensor 12 and the workpiece 3 can be immediately transmitted to the evaluation unit 14, and from the evaluation unit 14 to the machine tool 2, which can be stopped in an emergency. This situation is shown, for example, in Figure 3. This is because, in Figure 3, the workpiece 3 is mounted at an angle, and as a result, the gap or distance between the workpiece 3 and the illustrated proximity sensor 12 is greater than the amount allowed by the preset tolerance range. In other words, if the distance between the workpiece 3 and the mounting surface 6' is increased by more than 0.02 mm, the workpiece 3 is located outside the preset tolerance range. Furthermore, it can be seen that the rotational force generated by the change in spacing during the machining process displaces the workpiece 3 from its secure holding position between the clamp jaws 7, 8, and 9. However, such displacement of the workpiece 3 can lead to it being completely released from the clamping device 1. Therefore, for safety reasons, the machine tool 2 can be immediately turned off to terminate the machining operation.

[0029] The electrical lines 15 are bundled in the region of the housing 4 along a symmetric axis 21' that extends in alignment with the center point 21. The lines 15 may be replaced by an inductive interface 16, which inductively operates the communication between the proximity sensor 12 and the evaluation unit 14. The evaluation unit 14 may be placed inside or outside the housing 4, i.e., in an immutable environment.

[0030] In the embodiments described and illustrated, a chuck with three clamp jaws 7, 8, and 9 is selected as the clamping device 1 according to the present invention. Naturally, in such a clamping device 1, more clamp jaws 7, 8, and 9 may be used, and several holes 11 may be arranged to surround the illustrated circular orbit 20 over the mounting surface 6'. This circular orbit 20 has a predetermined radius, and the center point of the circular orbit 20 is the center point 21 of the housing 4. Naturally, any number of holes 11 may be provided at different intervals from the center point 21.

[0031] It is possible to retrofit the proximity sensor 12 according to the present invention to an existing clamping device 1 without difficulty. This is because the necessary holes 11 can be machined into the housing 4 later. In this case, the insertion of the proximity sensor 12 and the operation of the proximity sensor 12 and the evaluation unit 14 via the electrical line 15 can be retrofitted.

[0032] In Figures 4a and 4b, the clamping device 1 is formed and used as a so-called zero-point clamping system. Essentially, the zero-point clamping system 1 is superior in that it holds a clamping pin in space that either fixes the workpiece 3 or directly centers the workpiece 3. In other words, the known zero-point clamping system ensures that the workpiece 3 is repeatedly and precisely positioned on the pallet or tool table of the machine tool 2 during the machining process of identical workpieces 3. Thus, the zero-point clamping system 1 sets a precise reference point for the machining operations that the machine tool 2 should perform, because each workpiece 3 being replaced corresponds as accurately as possible to the preceding position of a workpiece 3 of the same structure.

[0033] Firstly, the clamp pin 23 supporting the workpiece or the workpiece 3 is pulled into the housing 4 by three clamp jaws 7, 8, 9 supported axially by the housing 4. Secondly, the three clamp jaws 7, 8, 9, which are synchronously and can approach each other, center and restrain the workpiece 3 so that its position corresponds with the preceding or succeeding position of a workpiece 3 of the same structure with the smallest possible error. Thus, the mounting surface 6' is formed as an annular surface extending in the circumferential direction and is inclined with respect to the symmetry axis 21' of the housing 4. Consequently, the necessary tensile force is generated by corresponding structural means between the clamp surfaces 7', 8', 9' of the clamp jaws 7, 8, 9 to pull the workpiece 3 into the housing 4, and the annular mounting surface 6' directly forms a stopper for the pin or workpiece 3 to which the workpiece 3 is attached, based on a preset inclination. The mounting surface 6' is a direct component of the housing 4.

[0034] The holes 11 are machined into the mounting surface 6' and / or the clamping surfaces 7', 8', and 9' of three clamping jaws 7, 8, and 9 called clamp sliders, and a proximity sensor 12 inserted into each hole 11 faces the respective workpiece 3. Therefore, the distance between the proximity sensor 12 and the workpiece 3 is monitored and measured by the proximity sensor 12 used, with respect to the placement of the holes 11 on the mounting surface 6' or the clamping jaws 7, 8, and 9.

[0035] The clamping device 1 shown in Figure 5 is formed as a vise with two clamping jaws 7 and 8 positioned opposite each other and ready for use. The clamping jaws 7 and 8 are supported by the housing 4 so as to be axially movable and may be selectively moved away from each other or towards each other to release or clamp a workpiece 3. Typically, both clamping jaws 7 and 8 are moved synchronously so that the workpiece 3 is aligned with and held relative to a preset centering axis of the housing 4. However, it is also possible that one of the clamping jaws 8 is formed as a corresponding stopper with an immovable position and is therefore fixed in position and provided on the housing 4. Thus, only the clamping jaw 7 positioned opposite the other clamping jaw 8 is moved, and the workpiece 3 to be clamped is held between the clamping jaw 7 and the corresponding stopper 8.

[0036] Furthermore, the vise 1 is assigned a mounting surface 6' formed or provided by the housing 4, which allows the workpiece 3 to be clamped to be placed on the mounting surface 6'. The clamp jaws 7 and 8 are moved parallel to and spaced apart from the mounting surface 6' provided on the vise 1, thereby fixing the workpiece 3 in position on the mounting surface 6' and between the clamp jaws 7 and 8.

[0037] To check the proper distance between the workpiece 3 and each proximity sensor 12, the holes 11 are machined into the mounting surface 6' and / or clamping surfaces 7', 8' or the corresponding stoppers 8, each directed toward the workpiece 3 to be held.

Claims

1. A clamping device (1) for holding a workpiece (3) to be machined by a machine tool (2), said device being used as a chuck, vice or zero-point clamping system, A housing (4); a rest element (6) which is a constituent part of the housing (4) or which is fixed to the housing (4) and which forms a rest surface (6') on which each of the workpieces (3) rests during the machining process; at least one clamping jaw (7) supported axially movably on the housing (4) and at least one corresponding stopper or at least one axially movable clamping jaw (8) formed by the housing (4) for clamping the workpiece (3) in the region of the placement surface (6'), or at least three clamping jaws (7, 8, 9) supported axially movably on the housing (4) for clamping the workpiece (3) in the region of the placement surface (6'); It consists of: at least one free space (11) is machined in the housing (4), the axis of symmetry of which runs perpendicular to the placement surface (6') and which faces the clamped workpiece (3) with its open end side, and / or at least one free space (11) is machined in one of the clamping jaws (7, 8, 9), which free space (11) opens into the respective clamping surface (7', 8', 9') of the clamping jaws (7, 8, 9), A proximity sensor (12) is inserted into each of said free spaces (11), a monitoring area (13) is formed between the placement surface (6') and the workpiece (3) by the proximity sensor (12), the monitoring area (13) being monitored by an evaluation unit (14) for the presence of the workpiece (3); In the clamping device (1), A clamping device (1), characterized in that the distance of the free space (11) to the center point (21) of the housing (4) is variably adjustable depending on the diameter of the workpiece (3) to be machined.

2. 2. The clamping device according to claim 1, characterized in that three free spaces (11) are arranged in the rest surface (6') at a pitch angle of 120° to one another.

3. 3. The clamping device according to claim 1 or 2, characterized in that the free space (11) is arranged on a circular orbit (20) extending around a center point (21) of the housing (4) on the support surface (6').

4. 3. The clamping device according to claim 1 or 2, characterized in that one of the clamping jaws (7; 8; 9) is arranged between two adjacent free spaces (11) on the rest surface (6').

5. 3. The clamping device according to claim 1 or 2, characterized in that the energy required for operation and / or the electrical signals required for communication are transmitted between each of the proximity sensors (12) and the evaluation unit (14) by means of an inductively operated interface (16) arranged in the housing (4) or outside the housing (4).

6. 3. The clamping device according to claim 1 or 2, characterized in that each of the proximity sensors (12) inserted in the free space (11) is connected to the evaluation unit (14) by an electrical line (15) or an inductive interface (16).

7. 7. The clamping device according to claim 6, characterized in that the evaluation unit (14) is arranged on the axis of symmetry (21') of the free space (11) and the electrical lines (15) of each of the proximity sensors (12) are led in a bundle to the evaluation unit (14) and led outwardly in a bundle from the evaluation unit (14).

8. The clamping device according to claim 1 or 2, characterized in that each of the proximity sensors (12) forms a monitoring area (13) of 0.02 mm to 3 mm, the monitoring area (13) is formed as a range protruding vertically from the placement surface (6'), and the workpiece (3) to be clamped is mounted within this range.

9. 3. A clamping device according to claim 1 or 2, characterized in that each proximity sensor (12) is inductively operated, capacitively operated or emits light waves, respectively, for the distance determination.

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