Clamp and machine tool

Abstract

The utility model discloses a clamp and a machine tool, and relates to the technical field of clamps. The clamp comprises a chuck, clamping jaws and a first positioning block, the multiple clamping jaws are connected to the chuck and arranged around the central axis of the chuck, limiting parts are arranged on the clamping jaws and can penetrate through the central hole and abut against the hole wall of the central hole, and the first positioning block is arranged on the outer end face of the chuck. When the workpiece needs to be fixed, the workpiece is arranged on the limiting part in a sleeving mode through the center hole, meanwhile, one through hole of the workpiece is matched with the first positioning block in a positioning mode, and therefore the relative position of the workpiece and the clamp is determined. When the clamping jaws move in the direction close to the hole wall of the center hole, the limiting parts abut against the first hole section of the center hole, and the multiple limiting parts are matched with the position of a fixed workpiece. Due to the fact that the first hole section is the hole section, corresponding to the center hole, of the through hole in the radial direction of the workpiece, pressure generated by the clamp and transmitted to the outer wall of the workpiece can be reduced, the protruding amplitude of the outer wall of the workpiece is reduced, and the machining precision of the workpiece can be improved.

Description

[0001] This application is a divisional application with an application date of "2024.10.30", application number "202422646482X", and application title "Clamps and Machine Tools". Technical Field

[0002] This utility model relates to the field of fixture technology, and in particular to a fixture and machine tool. Background Technology

[0003] Before machining, the workpiece needs to be positioned using a fixture. For example, when hobbing or grinding the cycloidal gear of an RV reducer, a fixture is needed to fix the cycloidal gear in place. The cycloidal gear has a center hole. After the cycloidal gear is fitted onto the tensioning part of the fixture through the center hole, the outer diameter of the tensioning part can be increased, thus restricting the position of the cycloidal gear. Because the cycloidal gear also has multiple through holes, such as irregular holes and crankshaft holes, the tensioning part will generate a large pressure when it expands. This pressure is easily transmitted to the outer wall of the cycloidal gear through the structure between the irregular holes and the crankshaft hole, causing the corresponding part of the outer wall of the cycloidal gear to bulge. After the external teeth of the cycloidal gear are machined and the fixture is released, the bulging outer wall of the cycloidal gear will retract, resulting in worse radial runout of the external teeth and increased tooth pitch error. Utility Model Content

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a fixture that can reduce the extent of the protrusion on the outer wall of the workpiece, thereby improving machining accuracy.

[0005] This utility model also proposes a machine tool having the above-mentioned fixture.

[0006] According to a first aspect of the present invention, a clamp is used to clamp a workpiece having a central hole and a plurality of through holes arranged around the central hole, the clamp comprising: a chuck;

[0007] Multiple jaws are connected to the chuck and arranged around the central axis of the chuck. Each jaw includes a limiting part, and the multiple limiting parts can pass through the central hole and abut against the wall of the central hole.

[0008] A first positioning block is disposed on the outer end face of the chuck, and the first positioning block is used to position and cooperate with one of the through holes.

[0009] The multiple jaws can drive the limiting part to move along the hole wall near the center hole. When the multiple jaws clamp the workpiece, the limiting part abuts against the first hole segment of the center hole. The first hole segment is the hole segment of the through hole that corresponds to the center hole along the radial direction of the workpiece.

[0010] The clamp according to the embodiments of the present utility model has at least the following beneficial effects:

[0011] The fixture consists of multiple jaws connected to a chuck and arranged around its central axis. Each jaw has a limiting part that passes through a central hole and abuts against the hole wall. A first positioning block is located on the outer end face of the chuck. When a workpiece needs to be fixed, it is fitted onto the limiting part through the central hole. Simultaneously, a through hole in the workpiece engages with the first positioning block, thus determining the relative position of the workpiece and the fixture. As the jaws move along the hole wall near the central hole, the limiting part abuts against the first segment of the central hole, and the multiple limiting parts work together to fix the workpiece's position. Because the first segment is a through hole corresponding to the central hole radially along the workpiece, the pressure generated by the fixture is reduced from being transmitted to the outer wall of the workpiece, thus reducing the extent of the workpiece's outer wall protrusion and improving the workpiece's machining accuracy.

[0012] According to some embodiments of the present invention, the segment between two adjacent through holes that corresponds to the central hole along the radial direction of the workpiece is the second segment of the central hole. The limiting part is provided with a recess on the side facing the central hole. The recess is configured to be spaced apart from the second segment when the plurality of jaws clamp the workpiece.

[0013] According to some embodiments of the present invention, the maximum depth of the recess along the radial direction of the clamp is H, which satisfies: 5μm≤H≤1000μm.

[0014] According to some embodiments of the present invention, the chuck further includes a support portion, which is connected to the side of the limiting portion away from the central axis of the chuck, and the support portion is used to abut against the end face of the workpiece.

[0015] According to some embodiments of the present invention, the fixture further includes a positioning part, which is connected to the outer end face of the chuck and is used to abut against the end face of the workpiece.

[0016] According to some embodiments of this utility model, the positioning part is annular and surrounds the plurality of limiting parts; or...

[0017] The positioning part is provided in multiple and spaced apart on the outer end face of the chuck, and the multiple positioning parts are arranged around the multiple limiting parts.

[0018] According to some embodiments of the present invention, the positioning part and the chuck are detachably connected.

[0019] According to some embodiments of the present invention, the fixture further includes a second positioning block, which is connected to the outer end face of the chuck. The second positioning block and the first positioning block are spaced apart, and the second positioning block is used to position and cooperate with another through hole of the workpiece.

[0020] According to some embodiments of the present invention, the first positioning block and the chuck are detachably connected, and the outer end face of the chuck is provided with a plurality of mounting positions at intervals, and the first positioning block is connected to one of the mounting positions.

[0021] According to some embodiments of the present invention, the outer end face of the chuck is provided with a plurality of guide grooves, the same number as the number of jaws, the plurality of guide grooves are radially distributed, the plurality of jaws are correspondingly provided in the plurality of guide grooves, and can slide along the extension direction of the guide grooves.

[0022] The machine tool according to a second aspect of the present invention includes the fixture described in the above embodiments.

[0023] The machine tool according to the embodiments of this utility model has at least the following beneficial effects:

[0024] The fixture, as described in the first aspect embodiment, is connected to a chuck by multiple jaws arranged around the central axis of the chuck. Each jaw has a limiting portion that passes through a central hole and abuts against the hole wall. A first positioning block is disposed on the outer end face of the chuck. When a workpiece needs to be fixed, it is fitted onto the limiting portion through the central hole. Simultaneously, a through hole in the workpiece engages with the first positioning block, thereby determining the relative position of the workpiece and the fixture. As the jaws move along the hole wall near the central hole, the limiting portion abuts against a first segment of the central hole, and the multiple limiting portions cooperate to fix the position of the workpiece. Since the first segment is a through hole corresponding to the central hole radially along the workpiece, the pressure generated by the fixture is reduced from being transmitted to the outer wall of the workpiece, thus reducing the extent of the workpiece's outer wall protrusion and improving the workpiece's machining accuracy.

[0025] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0027] Figure 1 This is a simplified schematic diagram of the clamp structure according to the first embodiment of this utility model;

[0028] Figure 2 This is a schematic diagram of the fixture according to the second embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the clamp holding the cycloidal wheel according to the second embodiment of the present invention;

[0030] Figure 4This is a simplified top view of the clamp holding the cycloidal wheel according to the second embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the fixture according to the third embodiment of the present invention;

[0032] Figure 6 This is a simplified top view of the clamp according to the third embodiment of the present invention.

[0033] Figure label:

[0034] Fixture 1000;

[0035] First positioning block 210; Second positioning block 220;

[0036] Cycloidal wheel 500; center hole 510; first hole section 511; second hole section 512; irregular hole 520; crankshaft hole 530;

[0037] Chuck 800; outer end face 801; jaw 810; limiting part 820; recess 120; support part 830; positioning part 840; mounting position 850; guide groove 860. Detailed Implementation

[0038] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0039] In the description of this utility model, it should be understood that the directional descriptions, such as up, down, front, back, left, right, etc., indicate the directional or positional relationship based on the directional or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0040] In the description of this utility model, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. If "first" or "second" is used in the description, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0041] In the description of this utility model, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this utility model in conjunction with the specific content of the technical solution.

[0042] In related technologies, RV reducers include a planetary carrier, a crankshaft, and a cycloidal wheel. The cycloidal wheel has a central hole at its center, surrounded by multiple crankshaft holes and multiple irregularly shaped holes. The irregularly shaped holes are for the planetary carrier's support column to pass through; because the support column requires a large moving area, the opening area of ​​these irregularly shaped holes is also relatively large. The crankshaft needs to pass through the crankshaft holes; because the crankshaft requires a smaller moving area, the opening area of ​​the crankshaft holes is usually smaller than the opening area of ​​the irregularly shaped holes. When machining the external teeth of the cycloidal wheel, a fixture is used to fix the cycloidal wheel. The expansion sleeve of the fixture is fixed by abutting against the hole wall of the cycloidal wheel by increasing its outer diameter.

[0043] During the tensioning process, the pressure generated by the tensioning part is easily transmitted to the outer wall of the cycloidal wheel, causing the outer wall of the cycloidal wheel to bulge. Because the structural connection between the outer wall of the cycloidal wheel corresponding to the irregular hole and the area near the central hole is weak, the pressure generated by the tensioning part is difficult to transmit to the outer wall of the cycloidal wheel corresponding to the irregular hole; that is, the outer wall of the cycloidal wheel corresponding to the irregular hole rarely deforms due to the tensioning part. However, the outer walls of the cycloidal wheels corresponding to adjacent irregular holes are prone to bulging. After the external teeth of the cycloidal wheel are machined and the clamp is released, the bulging outer wall of the cycloidal wheel will retract, resulting in worse radial runout of the external teeth and increased tooth pitch error.

[0044] Reference Figure 1 As shown, the clamp 1000 of one embodiment of the present invention can be used to clamp workpieces, such as cycloidal wheels 500, gears, bushings, rigid wheels, etc. For ease of explanation, the following description will take clamping cycloidal wheels 500 as an example. Cycloidal wheels 500 are provided with a central hole 510 and a plurality of through holes arranged around the central hole 510. A portion of the plurality of through holes is an irregular hole 520, and another portion is a crankshaft hole 530.

[0045] Reference Figure 1 and Figure 2As shown, the fixture 1000 of this embodiment includes a chuck 800, jaws 810, and a first positioning block 210. Multiple jaws 810 are provided and connected to the chuck 800, and are arranged around the central axis of the chuck 800. Each jaw 810 includes a limiting portion 820, which can pass through the central hole 510 of the cycloidal wheel 500 and abut against the wall of the central hole 510. The first positioning block 210 is located on the outer end face 801 of the chuck 800. Since one end of the chuck 800 needs to be fixedly connected to the machine tool, while the other end of the chuck 800 protrudes from the outside of the machine tool, the end of the chuck 800 exposed on the machine tool is referred to as the outer end face 801. The first positioning block 210 is used for positioning and engaging with one of the through holes of the cycloidal wheel 500, for example, with the crankshaft hole 530 or the irregular hole 520. Among them, multiple jaws 810 can drive the limiting part 820 to move along the direction close to the hole wall of the center hole 510. When multiple jaws 810 clamp the workpiece, the limiting part 820 abuts against the first hole section 511 of the center hole 510. The first hole section 511 is a through hole that corresponds to the hole section of the center hole 510 along the radial direction of the workpiece. The through hole can be a special-shaped hole 520 or a crankshaft hole 530.

[0046] Reference Figure 4 As shown, it should be noted that, taking the through hole as an irregular hole 520 as an example, the first hole segment 511 of the irregular hole 520 corresponding to the center hole 510 along the radial direction of the workpiece refers to: the central angle corresponding to the maximum arc length of the irregular hole 520 in the circumferential direction of the cycloidal wheel 500 is α, and the hole segment of the center hole 510 within the range of the central angle α is the first hole segment 511 corresponding to the irregular hole 520. The limiting part 820 abuts against at least a portion of the first hole segment 511.

[0047] Understandably, when the above scheme requires fixing the cycloidal wheel 500, the cycloidal wheel 500 is fitted onto the limiting part 820 through the central hole 510. Simultaneously, a through hole in the cycloidal wheel 500 engages with the first positioning block 210, thereby determining the relative position of the cycloidal wheel 500 and the fixture 1000. When the chuck 810 moves along the wall near the central hole 510, the limiting part 820 abuts against the first hole segment 511 of the central hole 510. Since the first hole segment 511 is a through hole corresponding to the hole segment of the central hole 510 along the radial direction of the cycloidal wheel 500, the pressure generated by the fixture 1000 is reduced from being transmitted to the outer wall of the cycloidal wheel 500, thus reducing the bulge of the outer wall of the cycloidal wheel 500 and improving the machining accuracy of the cycloidal wheel 500.

[0048] Reference Figure 1As shown, in the first embodiment of this utility model, the outer wall of the limiting part 820 can be a complete wall surface, and the outer wall of the limiting part 820 abuts against the first hole segment 511 of the central hole 510. By having multiple limiting parts 820 abut against the first hole segment 511, the position of the cycloidal wheel 500 is fixed, while also reducing the possibility of the limiting part 820 transmitting pressure to the outer wall of the cycloidal wheel 500.

[0049] Reference Figure 2 and Figure 4 As shown, in the second embodiment of this utility model, the limiting part 820 has a recess 120 on the side facing the central hole 510. The recess 120 is configured to be spaced apart from the second hole segment 512 of the central hole 510 when the multiple claws 810 clamp the cycloidal wheel 500. The second hole segment 512 is a hole segment between two adjacent through holes that corresponds to the central hole 510 along the radial direction of the cycloidal wheel 500. The two adjacent through holes refer to two adjacent irregular holes 520, or they can be adjacent irregular holes 520 and crankshaft holes 530, or two adjacent crankshaft holes 530. For ease of explanation, the second hole segment 512 between two adjacent irregular holes 520 that corresponds to the central hole 510 along the radial direction of the cycloidal wheel 500 will be used as an example.

[0050] Reference Figure 4 As shown, the second hole segment 512 between two adjacent irregular holes 520 along the radial direction of the cycloidal wheel 500, corresponding to the center hole 510, refers to the hole segment of the center hole 510 within the range of the maximum arc length of the two adjacent irregular holes 520 in the circumferential direction of the cycloidal wheel 500, which is the second hole segment 512 corresponding to the two adjacent irregular holes 520.

[0051] It is understandable that by adopting the above solution, since the recess 120 and the second hole segment 512 of the center hole 510 are spaced apart, the pressure transmitted by the limiting part 820 to the outer wall of the cycloidal wheel 500 through the structure between the adjacent irregular holes 520 can be effectively reduced, thereby reducing the amplitude of the outer wall protrusion of the cycloidal wheel 500, improving the machining accuracy of the cycloidal wheel 500, and reducing the radial runout and tooth pitch error of the cycloidal wheel 500.

[0052] Reference Figure 4As shown in the embodiment of this utility model, along the radial direction of the fixture 1000, the maximum depth of the recess 120 is H, satisfying: 5μm≤H≤1000μm. For example, the value of H can be 5μm, 20μm, 50μm, 100μm, 200μm, 400μm, 800μm, 1000μm, etc. When H is less than 5μm, the maximum depth of the recess 120 is too shallow, which easily leads to the sidewall of the recess 120 abutting against the wall of the central hole 510, resulting in the outer wall of the cycloidal wheel 500 protruding and reducing the machining accuracy. When H is greater than 1000μm, the maximum depth of the recess 120 is too large, which will reduce the strength of the limiting part 820 and make it prone to breakage. Therefore, by reasonably designing the size of H to be between 5μm and 1000μm, the abutment between the sidewall of the recess 120 and the hole wall can be effectively reduced, and the machining accuracy of the cycloidal wheel 500 can be improved.

[0053] Reference Figure 2 and Figure 3 As shown in the embodiment of this utility model, the end of the chuck 810 facing the central axis is provided with a limiting part 820. The chuck 810 also includes a support part 830 connected to the side of the limiting part 820 away from the central axis of the chuck. The upper end face of the limiting part 820 protrudes from the upper end face of the support part 830. The support part 830 is used for abutting and positioning with the end face of the cycloidal wheel 500, that is, the upper end face of the support part 830 abuts and positions with the end face of the cycloidal wheel 500. It is understood that during the clamping process of the cycloidal wheel 500, it is also necessary to keep the central axis of the cycloidal wheel 500 and the central axis of the chuck 800 flush to avoid tilting during clamping. Therefore, by providing a support portion 830 on the chuck 810 for positioning the end face of the cycloidal wheel 500, the position of the cycloidal wheel 500 can be restricted, so that the central axis of the cycloidal wheel 500 is aligned with the central axis of the fixture 1000, thereby improving the machining accuracy of the cycloidal wheel 500.

[0054] As an alternative embodiment, refer to Figure 5 As shown, in the third embodiment of this utility model, the fixture 1000 further includes a positioning part 840. The positioning part 840 is connected to the outer end face 801 of the chuck 800. The positioning part 840 is used to abut and position the cycloidal wheel 500 against the end face. The positioning part 840 can be a flat sheet or a block, etc. It can be understood that by providing the positioning part 840 on the outer end face 801 of the chuck 800, the cycloidal wheel 500 can be positioned, making the central axis of the cycloidal wheel 500 flush with the central axis of the fixture 1000, thereby improving the machining accuracy of the cycloidal wheel 500.

[0055] Reference Figure 5As shown, in this embodiment of the present invention, the positioning part 840 is annular and surrounds multiple limiting parts 820. By making the positioning part 840 annular, the flatness of the side of the positioning part 840 that abuts against the cycloidal wheel 500 can be ensured, effectively reducing unevenness in the positioning part 840. As an alternative embodiment, see... Figure 6 As shown, multiple positioning parts 840 can be provided, with multiple positioning parts 840 spaced apart on the outer end face 801 of the chuck 800, and multiple positioning parts 840 surrounding multiple limiting parts 820. By providing multiple positioning parts 840, compared with the solution of providing annular positioning parts 840, the amount of material used for positioning parts 840 can be reduced, thereby reducing production costs.

[0056] It should be noted that due to frictional wear between the positioning part 840 and the cycloidal wheel 500, prolonged use may lead to damage or deformation of the positioning part 840. Therefore, in this embodiment of the invention, the positioning part 840 and the chuck 800 are detachably connected. When the positioning part 840 is damaged or deformed, it can be disassembled and replaced with a new one to extend the service life of the clamp 1000. The detachable connection can be achieved through fasteners, snap-fit ​​connections, or similar methods, such as fixing the positioning part 840 to the outer end face 801 of the chuck 800 using screws or bolts. When screws are used, a countersunk groove is provided on the positioning part 840 so that the screw head can fit within the groove, preventing the screw head from protruding beyond the outer end of the positioning part 840.

[0057] Reference Figure 2 and Figure 4 As shown in the embodiment of this utility model, the clamp 1000 further includes a second positioning block 220, which is connected to the outer end face 801 of the chuck 800. The second positioning block 220 and the first positioning block 210 are spaced apart. The second positioning block 220 is used to position and cooperate with another through hole of the cycloidal wheel 500, such as the irregular hole 520 or the crankshaft hole 530 of the cycloidal wheel 500. It can be understood that by setting the first positioning block 210 and the second positioning block 220, the purpose is to make the limiting part 820 and the recess 120 correspond to the first hole segment 511 and the second hole segment 512 of the cycloidal wheel 500. For example, the first positioning block 210 is positioned and cooperated with the crankshaft hole 530, and the second positioning block 220 is positioned and cooperated with the irregular hole 520. Since the cross-sectional area of ​​the irregular hole 520 is larger than that of the crankshaft hole 530, positioning the irregular hole 520 is relatively simpler, which is beneficial for the rapid alignment of the cycloidal wheel 500 and the limiting part 820. The first positioning block 210 can be used for fine positioning, and the second positioning block 220 can be used for coarse positioning to improve positioning efficiency.

[0058] To improve the versatility of fixture 1000, refer to Figure 2 As shown in the embodiment of this utility model, the first positioning block 210 and the chuck 800 are detachably connected. This detachable connection can be achieved through fasteners such as screws or bolts, or through a snap-fit ​​connection. The outer end face 801 of the chuck 800 is provided with multiple mounting positions 850 at intervals, and the first positioning block 210 is connected to one of these mounting positions 850. It is understood that by cooperating the first positioning block 210 with different mounting positions 850, the first positioning block 210 can be positioned and engaged with the through holes of different models of cycloidal wheels 500, thereby improving the versatility of the fixture 1000 and reducing production costs.

[0059] Reference Figure 2 As shown in the embodiment of this utility model, the outer end face 801 of the chuck 800 is provided with a plurality of guide grooves 860, the number of guide grooves 860 being the same as the number of jaws 810. The plurality of guide grooves 860 are radially distributed, and the plurality of jaws 810 are correspondingly disposed in the plurality of guide grooves 860 and are capable of sliding along the extending direction of the guide grooves 860. Therefore, by pushing the jaws 810 to move along the guide grooves 860, the limiting part 820 can be moved closer to or away from the central axis of the clamp 1000, so as to release or clamp the cycloidal wheel 500.

[0060] One embodiment of the machine tool of this utility model includes the fixture 1000 described in the above embodiments. The machine tool can be a gear grinding machine, a gear hobbing machine, a composite machine tool with gear grinding or hobbing functions, a grinding machine, a milling machine, a lathe, etc. The machine tool of this utility model embodiment uses the fixture 1000 described in the above embodiments. Multiple jaws 810 of the fixture 1000 are connected to a chuck 800 and arranged around the central axis of the chuck 800. Each jaw 810 has a limiting part 820 that can pass through a central hole 510 and abut against the wall of the central hole 510. A first positioning block 210 is disposed on the outer end face 801 of the chuck 800. When a workpiece needs to be fixed, the workpiece is fitted onto the limiting part 820 through the central hole 510, and simultaneously, a through hole of the workpiece engages with the first positioning block 210, thereby determining the relative position of the workpiece and the fixture 1000. When the chuck 810 moves along the wall of the hole near the center hole 510, the limiting part 820 abuts against the first hole section 511 of the center hole 510. Since the first hole section 511 is a through hole that corresponds to the hole section of the center hole 510 along the radial direction of the workpiece, the pressure generated by the fixture 1000 can be reduced from being transmitted to the outer wall of the workpiece, thereby reducing the extent of the bulge on the outer wall of the workpiece and improving the machining accuracy of the workpiece.

[0061] Since the machine tool adopts all the technical solutions of the fixture 1000 in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments, which will not be repeated here.

[0062] The embodiments of the present utility model have been described in detail above with reference to the accompanying drawings. However, the present utility model is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present utility model.

Claims

1. A clamp for clamping a workpiece having a central hole and a plurality of through holes arranged around the central hole, characterized in that, The clamp includes: Chuck; Multiple jaws are connected to the chuck and arranged around the central axis of the chuck. Each jaw includes a limiting part, and the multiple limiting parts can pass through the central hole and abut against the hole wall of the central hole. A first positioning block is disposed on the outer end face of the chuck, and the first positioning block is used to position and cooperate with one of the through holes. The multiple jaws can drive the limiting part to move along the hole wall near the center hole. When the multiple jaws clamp the workpiece, the limiting part abuts against the first hole segment of the center hole. The first hole segment is the hole segment of the through hole that corresponds to the center hole along the radial direction of the workpiece.

2. The clamp according to claim 1, characterized in that: The section of the workpiece between two adjacent through holes, corresponding to the central hole in the radial direction, is the second section of the central hole. The limiting part has a recess on the side facing the central hole. The recess is configured to be spaced apart from the second section when the multiple jaws clamp the workpiece.

3. The clamp according to claim 2, characterized in that: Along the radial direction of the clamp, the maximum depth of the recess is H, which satisfies: 5μm≤H≤1000μm.

4. The clamp according to claim 1, characterized in that: The chuck also includes a support portion connected to the side of the limiting portion away from the central axis of the chuck, and the support portion is used to abut against the end face of the workpiece.

5. The clamp according to claim 1, characterized in that: The fixture also includes a positioning part, which is connected to the outer end face of the chuck and is used to abut against the end face of the workpiece.

6. The clamp according to claim 5, characterized in that: The positioning part is annular and surrounds the plurality of limiting parts; or... The positioning part is provided in multiple and spaced apart on the outer end face of the chuck, and the multiple positioning parts are arranged around the multiple limiting parts.

7. The clamp according to claim 5, characterized in that: The positioning part and the chuck are detachably connected.

8. The clamp according to claim 1, characterized in that: The fixture further includes a second positioning block, which is connected to the outer end face of the chuck. The second positioning block and the first positioning block are spaced apart. The second positioning block is used to position and cooperate with another through hole of the workpiece.

9. The clamp according to claim 1, characterized in that: The first positioning block and the chuck are detachably connected. The outer end face of the chuck is provided with multiple mounting positions at intervals, and the first positioning block is connected to one of the mounting positions.

10. The clamp according to claim 1, characterized in that: The outer end face of the chuck is provided with a plurality of guide grooves, the same number as the number of jaws. The plurality of guide grooves are radially distributed, and the plurality of jaws are correspondingly provided in the plurality of guide grooves and can slide along the extension direction of the guide grooves.

11. A machine tool, characterized in that: Includes the clamp as described in any one of claims 1 to 10.

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