Clamp system for machine tool

Abstract

To provide a clamp system capable of obtaining optimal sensor signal quality and easy handling.SOLUTION: There is provided a clamp system for clamping workpiece machined by a machine tool. The clamp system 1 includes: a pallet 10; a chuck 20 having a recess 21 provided on its upper face; a sensor unit 30 embedded in the recess of a chuck; a preload mechanism 31 which is configured to apply force to the sensor unit, so that mechanical contact between the sensor unit and a pallet contact surface is established, the pallet is clamped by a chuck; and a communication unit 40 that is configured to transmit sensor data generated by the sensor unit to a control unit arranged outside the clamp system, especially, in which the communication unit includes a radio communication interface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a clamping system for clamping a workpiece being machined by a machine tool.

Background Art

[0002] Machining process monitoring is an important means to ensure the quality of machined parts and avoid damage to machine tools. Therefore, an increasing number of monitoring units are being applied to monitor the machining process. It is well known that various sensors are incorporated into machine tools and sensor data is analyzed to determine the machining state, the quality of the machined parts, and the state of the machine tool.

[0003] European Patent Application Publication No. 3970913 is directed to a method for machining a structure on a workpiece by removing material from the workpiece. The sound generated from the structure during the machining process is detected by a sound sensor. The output signal of the sound sensor is used to control the feed of the tool on the workpiece. The sound sensor is disposed on the machining tool.

[0004] U.S. Patent Application Publication No. 2023050576 discloses an AE signal detection device for a grinding wheel. The AE sensor receives elastic waves generated in an annular grinding wheel and outputs an AE signal. The sensor is sandwiched between a fixed flange fixed to a rotating shaft and a movable flange configured to move toward and away from the fixed flange.

[0005] However, disposing a sensor on the side of a machining tool has drawbacks regarding sensor signal quality. When the sensor is disposed near the machining tool, the rotation of the spindle may cause distortion. The detection quality may be adversely affected. Therefore, disposing a sensor on the side of the workpiece can overcome this drawback. For example, the sensor can be disposed on the machine table.

[0006] However, depending on the application, the sensor should not be placed too far from the workpiece in order to obtain optimal signal quality. For example, if the mechanical interaction between the machining tool and the workpiece has to be monitored, it is important to place the sensor as close as possible to the area where the interaction takes place. Since the workpiece is generally mounted on a clamping system attached to the machine table, integrating the sensor into the clamping system makes it possible to place the sensor close to the interaction area between the machining tool and the workpiece. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0007] An object of the present invention is to provide a clamping system that enables optimization of machining process monitoring. In particular, an object of the present invention is to provide a clamping system that enables obtaining optimal sensor signal quality and easy handling. MEANS FOR SOLVING THE PROBLEM

[0008] According to the present invention, these objects are achieved by the features of the independent claims. In addition, further advantageous embodiments can be obtained from the dependent claims and the description.

[0009] The present invention relates to a clamping system for clamping a workpiece being machined by a machine tool. The clamping system comprises a pallet for holding the workpiece on an upper surface of the pallet and a chuck mounted on a machine table of the machine tool. The pallet includes a locking mechanism and a pallet contact surface. In particular, the pallet contact surface is a bottom surface of the pallet. The chuck includes a chuck contact surface and a chuck clamping mechanism. In particular, the chuck contact surface is an upper surface of the chuck. In a clamped state, the pallet locking mechanism engages with the chuck locking mechanism, and the pallet contact surface at least partially contacts the chuck contact surface. In particular, the pallet contact surface is maintained in contact with the chuck contact surface by a clamping force generated by the engagement of the pallet locking mechanism and the chuck locking mechanism. A recess opened on the chuck contact surface is provided in the chuck. The clamping system further comprises a sensor unit, a preloading mechanism, and a communication unit. The sensor unit is embedded in the recess of the chuck. The preloading mechanism is configured to apply a force to the sensor unit so that mechanical contact between the sensor unit and the pallet contact surface is established when the pallet is clamped by the chuck. The communication unit is configured to transmit sensor data generated by the sensor unit to a control unit arranged outside the clamping system. In particular, the communication unit includes a wireless communication interface.

[0010] Directly embedding the sensor unit at the interface between the pallet and the chuck ensures a short distance between the sensor unit and the area where machining is performed. In particular, when structural-borne sound or vibration generated by the interaction between the machining tool and the workpiece should be detected, it is important to place the sensor unit as close as possible to the interaction area.

[0011] Furthermore, by clamping the pallet with a chuck, the preloading mechanism automatically applies a force to the sensor unit and presses the sensor unit against the pallet contact surface. A very tight contact between the sensor unit and the pallet contact surface can be achieved. This tight contact is advantageous for optimally detecting vibrations generated during machining. Measurements can achieve high accuracy.

[0012] The adequacy of machining is also a factor related to production. Therefore, the clamping system should be suitable for use with an automation system, for example, for pallet exchange by an automatic pallet changer. Usually, the chuck is mounted on the machine table in the preparation stage, and during machining, only the pallet holding the workpiece or the machined part has to be automatically exchanged. Arranging a sensor unit and a preloading mechanism in the chuck enables automatic pallet handling.

[0013] In a preferred variant, the preloading mechanism is configured to bring the sensor unit into contact with the pallet by applying a preload.

[0014] In particular, the preloading mechanism is configured such that the sensor unit automatically comes into contact with the pallet by clamping the pallet with a chuck. That is, the sensor unit contacts the pallet contact surface while the pallet is being clamped by the chuck. In this way, clamping of the pallet and the chuck and bringing the sensor unit into contact with the pallet are performed almost simultaneously. Therefore, no additional idle time is required. The adequacy of machining is not affected. Furthermore, the sensor unit can be maintained in the contact position as long as the pallet and the chuck remain clamped.

[0015] In one modification, the preloading mechanism is a spring element, which is fixedly attached on the inner lower surface of the recess, and the sensor unit is seated on the spring element. For example, the recess has a U-shaped cross section. The preloading mechanism is attached on the bottom surface of the recess. When the pallet is not clamped by the chuck, the spring element is released. The spring element is selected such that the sensor unit protrudes from the chuck contact surface in the unclamped state. When the pallet is clamped by the chuck, the clamping force that locks the pallet to the chuck compresses the spring element downward. As a result, a reaction force is applied to the sensor unit to push the sensor unit upward in order to achieve close contact with the pallet. In particular, the mechanical contact between the sensor unit and the pallet contact surface is established simultaneously with the clamping.

[0016] To provide a simple design, the preloading mechanism includes only the spring element. The selection of the spring element depends on the type, size and weight of the sensor unit. The height of the spring element in the uncompressed state should be large enough so that the sensor unit seated thereon protrudes from the chuck contact surface when the pallet is not clamped by the chuck.

[0017] In some embodiments, two or more sensor units are provided. In one modification, all the sensor units are arranged on the same spring element. In another modification, each sensor unit is arranged on an individual spring element.

[0018] This arrangement of the sensor units can be easily realized in any clamping system. The handling is simple. This can also be used together with an automated system for automatically exchanging the pallet. The contact between the sensor unit and the pallet is reliable. Since the contact between the sensor unit and the pallet is established by clamping the pallet with the chuck, no additional time is required.

[0019] In a modification, the preloading mechanism is a preloading element made of an elastic material that is compressible, and in particular, the preloading element can be compressed vertically within a range of 0.1 mm to 4 mm, preferably within a range of 0.5 mm to 2 mm.

[0020] In particular, the preloading element is an elastomer.

[0021] Preferably, the preloading element is made of rubber, is disposed on the inner lower surface of the recess, and the sensor unit is seated on the preloading element.

[0022] In particular, the preloading element is a ring-shaped element, for example, an O-ring made of rubber. When the pallet is clamped by the chuck, the clamping force compresses the preloading element so that the sensor unit contacts the pallet. The ring shape has the advantage that a cable connected to the sensor unit can pass through the preloading element. Using an O-ring as the preloading element provides a simple but reliable solution.

[0023] In another modification, the preloading mechanism includes a fluid channel communicably connected to the recess. The preloading mechanism is configured to supply pressurized fluid to the recess through the fluid channel in order to push the sensor unit pneumatically or hydraulically toward the pallet contact surface until the sensor unit contacts the pallet contact surface when the pallet is clamped by the chuck. In this modification, a hydraulic or pneumatic drive mechanism is applied to push the sensor unit toward the pallet. The fluid may be a liquid or air. Preferably, the recess has a hole on the bottom surface. The fluid channel is communicably connected to the recess through this hole to supply fluid to the recess and push the sensor unit upward toward the pallet.

[0024] In particular, a fluid inlet is disposed within the chuck and is connected to the fluid channel of the pallet to receive fluid from the outside of the chuck.

[0025] In an advantageous variant, the preloading mechanism is initially configured to move the sensor unit upward toward a position protruding from the chuck contact surface before the pallet is clamped to the chuck. Then, the pressure on the fluid or air is released so that the sensor unit can be pushed downward while the pallet is being clamped. This means that the pallet first contacts the sensor unit and further pushes the sensor unit slightly downward. When the pallet is clamped by the chuck, the pressure on the fluid or air is applied again to maintain a tight contact between the sensor unit and the pallet contact surface. In particular, a limiting element is provided to limit the downward movement of the sensor unit.

[0026] Preferably, a sealing ring is arranged on the inner side surface of the recess and surrounds the sensor unit.

[0027] In a further variant, the preloading mechanism comprises a magnetic element.

[0028] In particular, a permanent magnet is attached to the upper part of the sensor unit, a metal element is arranged on the pallet contact surface, and the permanent magnet is coupled to the metal element when the pallet is clamped by the chuck.

[0029] Alternatively, a permanent magnet is attached to the pallet contact surface, a metal element is attached to the upper part of the sensor unit, and the permanent magnet is coupled to the metal element when the pallet is clamped by the chuck.

[0030] The cross-section of the recess can have various shapes such as circular, square, etc.

[0031] In one variant, the sensor unit is an acoustic emission sensor. In particular, the clamping system is applied to a grinding process. In this application, the acoustic emission sensor can detect the noise generated by the grinding process and transmitted through the part clamping structure. The sensor data helps to monitor the process and identify problems early.

[0032] In another variant, the sensor unit is an acceleration sensor for detecting vibrations generated by the interaction between the machining tool and the workpiece.

[0033] In a preferred variant, the preloading mechanism is arranged symmetrically along the central axis of the chuck.

[0034] Alternatively, the preloading mechanism is arranged asymmetrically along the central axis of the chuck.

[0035] The communication unit is a wired or wireless communication interface. The type of communication interface depends on the structure of the machine table of the machine tool. In a 5-axis machine tool, a wireless communication interface is preferred. In a 3-axis machine tool, a wired communication interface is also applicable.

[0036] To improve the monitoring accuracy, two or more sensor units can be applied to detect signals at different positions. It is also possible to arrange different types of sensors at different positions to obtain different types of sensor data. For example, one acoustic emission sensor and one acceleration sensor are provided, several acoustic emission sensors and several acceleration sensors are provided, adjacent to each other, but dispersed at a specified distance. The distances between the sensor units may or may not be equal. Therefore, in a preferred variant, at least two preloading mechanisms are provided. They can be arranged away from each other or close to each other. One sensor unit is attached to each preloading mechanism. Alternatively, only one preloading mechanism is provided to hold at least two sensor units.

[0037] The plurality of preloading mechanisms can be arranged in a single recess or in several separate recesses depending on the type of the clamping system.

[0038] In some embodiments, holes are provided on one side wall or on the inner lower surface of the recess to pass the connection lines required for the sensor unit.

[0039] The present invention is directed to the use of the clamping system of the present invention. Sensor data is collected during machining and transmitted to a processing unit. The processing unit can be arranged outside or within the machine tool. The collected sensor data is analyzed by the processing unit to determine machining quality.

[0040] The following provides a more detailed description of the present invention. Embodiments are described and explained in detail with reference to the accompanying drawings.

Brief Description of the Drawings

[0041]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0042] Figures 1 and 2 show cross-sectional views of a first embodiment of the clamping system 1. The clamping system 1 includes a pallet 10 and a chuck 20. Figure 1 shows the clamped state, that is, the pallet is clamped by the chuck, while Figure 2 shows the unclamped chuck, that is, the pallet is not clamped by the chuck.

[0043] Figure 1 further shows the situation where the clamping system is mounted on the machine table 2. Generally, before machining, the chuck is first mounted on the machine table. During the machining preparation stage, a pallet with a workpiece attached is prepared. When the workpiece has to be machined by a machine tool, the prepared pallet with the workpiece on it is automatically picked up by an automation device and clamped by the chuck. The machine table 2 shown in Figures 1 and 4 is a machine table of a 5-axis machine tool. However, the clamping system can also be applied to other machine tools having different machine tables.

[0044] The pallet has a pallet clamping mechanism and a reference element not shown in the figure. The chuck has a chuck clamping mechanism and a reference element also not shown in the figure.

[0045] The pallet has an upper surface 11 and a bottom surface 12. The workpiece is attached to the upper surface, and the contact surface is the bottom surface. The chuck also has an upper surface and a bottom surface. The upper surface of the chuck is the chuck contact surface, and the bottom surface of the chuck is in contact with the machine table.

[0046] The recess 21 is formed in the upper portion of the chuck. The opening side of the recess is on the chuck contact surface. FIG. 3 shows an enlarged view of the recess and the arrangement of the sensor unit 30 therein. A spring element 31 is fixedly attached to the inner lower surface 22 of the recess. The sensor unit is seated on the spring element. As shown in FIG. 2, in the clamp release state, the spring element is released, so that the sensor unit protrudes from the opening side of the recess onto the chuck contact surface 26. When the pallet is clamped by the chuck, the sensor unit and the spring element are pushed downward by the pallet, so that the spring element is compressed. As a reaction force, the spring element applies an upward force to the sensor unit to bring the sensor unit into contact with the pallet contact surface. This ensures a close contact between the sensor unit and the pallet, which is essential for obtaining optimal measurement conditions. The communication unit 40 is arranged outside the chuck. A hole 25 is formed in the inner lower surface of the recess. Further, a guide channel 27 is formed in the chuck. The hole is connected to the guide channel for passing a connection line connected to the sensor unit. The positions of the hole and the guide channel can be formed at other positions. For example, the hole can also be formed on the side wall of the recess, and a guide channel with one open end on the bottom surface of the pallet and the other open end connected to the hole can be formed.

[0047] FIGS. 1 and 2 show an embodiment in which the recesses are symmetrically provided in the chuck. The center line of the recess in the axial direction coincides with the center line of the chuck in the axial direction.

[0048] FIGS. 4 and 5 show another embodiment in which the recesses are asymmetrically provided in the chuck. The center line of the recess in the axial direction shown as B is separated from the center line of the chuck in the axial direction shown as C by a specified distance. FIG. 5 shows a clamping system attached to the machine table 3 of a three-axis machining center. The figure shown as D in FIG. 5 shows a partial view of the sensor unit and the spring element. In particular, since the pallet is not clamped by the chuck, the spring element is in a released state.

[0049] Figures 6, 7, and 8 respectively show the third, fourth, and fifth embodiments of the clamping system.

[0050] The third embodiment shown in Figure 6 is based on the principle of pneumatic or hydraulic pressure. In addition to the recess 21, a fluid channel 53 and a fluid chamber 54 are embedded in the chuck. When the fluid in the fluid chamber is pushed into the recess, the sensor unit is pushed upward from below by the fluid and contacts the pallet contact surface. Further, a first seal 51 is disposed in the recess around the sensor unit, and a second seal 52 is disposed in the guide channel 27. The first seal and the second seal can also be attached onto the sensor unit. In particular, a limiting element 28 is provided under the chuck to limit the downward movement of the sensor unit.

[0051] The fourth embodiment shown in Figure 7 includes an O-ring 55 as an elastic element. The material of the O-ring is selected such that the O-ring can be slightly compressed when the pallet is clamped by the chuck and released when the pallet is unclamped from the chuck.

[0052] The fifth embodiment shown in Figure 8 is based on the magnetic principle. A magnetic element 56 is attached to the upper part of the sensor unit. As a corresponding part, a metal element 57 is attached onto the pallet contact surface. When the pallet contact surface approaches the chuck, the magnetic element is attracted by the metal element, which is caused by the magnetic force.

Explanation of Reference Numerals

[0053] 1 Clamping system 2 Machine table of a 5-axis machine tool 3 Machine table of a 3-axis machine tool 10 Pallet 11 Upper surface of the pallet 12 Bottom surface of the pallet 20 Chuck 21 Recess 22 Inner lower surface of the recess Side wall of the recess Opening side of the recess Hole in the recess Chuck contact surface Guide channel Limiting element Sensor unit Spring element Communication unit First seal Second seal Fluid channel Fluid chamber O-ring Magnet element Metal element

Claims

1. A clamping system (1) for clamping a workpiece being machined by a machine tool, comprising: a. a pallet (10) for holding the workpiece on an upper surface of the pallet including a pallet locking mechanism and a pallet contact surface, in particular the pallet contact surface being a bottom surface of the pallet; b) a chuck (20) mounted on a machine table of the machine tool, the chuck including a chuck contact surface and a chuck locking mechanism, the chuck (20) including a pallet contact surface and a chuck locking mechanism, the pallet contact surface engaging with the chuck locking mechanism in a clamped state, the chuck (20) including an open recess (21) on the chuck contact surface, the chuck (20) being an upper surface of the chuck; c. a sensor unit (30) embedded in the recess of the chuck; d. a preload mechanism (31) configured to apply a force to the sensor unit such that mechanical contact between the sensor unit and the pallet contact surface is established when the pallet is clamped by the chuck; e. a communication unit configured to transmit sensor data generated by the sensor unit to a control unit arranged outside the clamping system, in particular the communication unit including a wireless communication interface; A clamping system (1).

2. The system of claim 1 , wherein the preload mechanism is a spring element fixedly mounted on an inner lower surface of the recess, the sensor unit seated on the spring element.

3. The system of claim 1 , wherein the preload mechanism is a preload element made of a compressible elastic material, in particular, the preload element can be compressed vertically within a range of 0.5 mm to 2 mm.

4. 4. The clamping system according to claim 3, wherein the preload element is elastomer and is arranged on the inner lower surface of the recess, the sensor unit being seated on the preload element, in particular the preload element being an O-ring.

5. 2. The clamping system of claim 1, wherein the preload mechanism includes a fluid channel communicatively connected to the recess, the preload mechanism configured to supply pressurized fluid to the recess to pneumatically or hydraulically urge the sensor unit toward the pallet contact surface until the sensor unit contacts the pallet contact surface when the pallet is clamped to the chuck.

6. The clamping system of claim 5 , wherein a fluid inlet is disposed within the chuck and connected to the fluid channel of the pallet for receiving fluid from outside the chuck.

7. The clamping system of claim 6 , wherein a seal ring is disposed on an inner side of the recess and surrounds the sensor unit.

8. The clamping system of claim 1 , wherein the preload mechanism comprises a magnetic element.

9. 9. The clamping system of claim 8, wherein a permanent magnet is attached to an upper portion of the sensor unit and a metal element is disposed on the pallet contact surface, the permanent magnet being coupled with the metal element when the pallet is clamped with the chuck.

10. 9. The clamping system of claim 8, wherein a permanent magnet is mounted on the pallet contact surface and a metal element is mounted on top of the sensor unit, the permanent magnet being coupled with the metal element when the pallet is clamped with the chuck.

11. The system of claim 1 , wherein the preload mechanisms are symmetrically disposed along a central axis of the chuck.

12. The system of claim 1 , wherein the preload mechanism is asymmetrically positioned along a central axis of the chuck.

13. 13. A system according to any one of claims 1 to 12, wherein at least two preload mechanisms are provided, a sensor unit being mounted on each preload mechanism.

14. The system of claim 1 , wherein a plurality of recesses are formed in the chuck, and a preload mechanism and a sensor unit are provided in each recess.

15. Application of the clamping system according to any one of claims 1 to 14, wherein sensor data is collected during machining and transmitted to a processing unit, and the obtained sensor data is analysed by said processing unit to determine the machining quality.

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