A centering fixture

Abstract

The utility model discloses a centering fixture, include: power unit, locking unit, including fixture base and at least two clamping blocks, the clamping block can be movably installed in fixture base, the fixture base is equipped with the positioning portion for positioning workpiece, pull core, with power unit drive connection, wherein, pull core is equipped with the first guide surface, and the clamping block is equipped with the second guide surface with the first guide surface cooperation, power unit drive pull core linear motion along the axial, through the cooperation of first guide surface and second guide surface, the axial movement of pull core is converted for the radial movement of clamping block, to centering clamps or loosens workpiece.

Description

Technical Field

[0001] This utility model relates to the field of precision machining fixture technology, and in particular to a centering fixture. Background Technology

[0002] In the field of ophthalmic medical device manufacturing, the intraocular lens is a precision optical component used to replace the natural lens of the human eye. Its manufacturing process has extremely stringent requirements for precision and surface quality, especially in the machining of the blank stage. Any tiny scratch, nick, or shape deviation may lead to a decrease in the optical performance of the final product, or even cause the blank to be scrapped.

[0003] In existing technologies, pneumatic clamps used in the fabrication of ophthalmic medical devices generally rely on a single inner or outer conical hole structure for centering. To achieve effective positioning and transmission, such structures often require a large axial or radial space, resulting in a bulky overall clamp structure. This directly contradicts the compactness and high space utilization requirements of ophthalmic medical device fabrication, severely limiting the application of this technology in precision and miniaturized manufacturing scenarios. 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 centering fixture that can achieve high-precision automatic centering, with a compact structure and high space utilization.

[0005] A centering clamp according to a first aspect of the present invention includes: Power unit; The locking unit includes a clamping base and at least two clamping blocks, the clamping blocks being movably mounted on the clamping base, the clamping base being provided with a positioning part for positioning the workpiece; The core is pulled and connected to the power unit for driving; The core is provided with a first guide surface, and the clamping block is provided with a second guide surface that cooperates with the first guide surface. The power unit drives the core to move linearly along the axial direction. Through the cooperation of the first guide surface and the second guide surface, the axial movement of the core is converted into the radial movement of the clamping block to center and clamp or release the workpiece.

[0006] A centering fixture according to an embodiment of this utility model has at least the following beneficial effects: Through the axial linear motion of the pull core, and utilizing the cooperation of its first guide surface with the second guide surface on the clamping blocks, the axial driving force is precisely and synchronously converted into the radial motion of multiple clamping blocks, ensuring that the workpiece center always coincides with the fixture design center, resulting in high centering accuracy and effectively guaranteeing the workpiece machining quality; the linear output of the power unit is directly converted into the radial clamping motion of the clamping blocks through the internal pull core and guide surfaces, with the entire transmission chain integrated inside the fixture, eliminating the need for additional swing space, greatly optimizing the overall structure of the fixture, making it compact, and particularly suitable for use in space-constrained precision machining environments; the power unit provides a stable and precisely controllable driving force. This force is directly transmitted to the clamping blocks through the pull core and guide surfaces, making the clamping force acting on the workpiece uniform, stable, and reliable, avoiding loosening due to insufficient clamping force and preventing workpiece damage due to overload clamping.

[0007] According to some embodiments of the present invention, the first guide surface is a tapered convex surface disposed at the end of the core; the second guide surface is a tapered concave surface formed on the clamping block, wherein the tapered convex surface and the tapered concave surface cooperate with each other.

[0008] According to some embodiments of the present invention, a guide portion is provided on one side of the conical concave surface, and the guide portion is used to guide the conical convex surface into the conical concave surface.

[0009] According to some embodiments of the present invention, the clamping block is mounted on the clamping base by a hinge and has a clamping position and a releasing position; when the pull core moves away from the clamping block, it drives the clamping block to swing to the clamping position; when the pull core moves toward the clamping block, the clamping block swings to the releasing position.

[0010] According to some embodiments of this utility model, the clamping block forms a power arm and a resistance arm with its hinge point as the boundary. The power arm is the distance from the end that cooperates with the pull core to the hinge point, and the resistance arm is the distance from the end used to clamp the workpiece to the hinge point. The length ratio of the power arm to the resistance arm is greater than or equal to 1.3.

[0011] According to some embodiments of this utility model, the power unit is a cylinder, and the output shaft of the cylinder is threadedly connected to the core puller.

[0012] According to some embodiments of the present invention, the outer circumferential side of the clamp base is provided with a mounting hole; the clamping block is installed on the clamp base by a bolt passing through the mounting hole.

[0013] According to some embodiments of the present invention, the upper end of the clamp base is provided with a mounting groove that matches the shape and number of the clamping blocks; when the clamping blocks are in a clamping state, the outer contour of the clamping blocks is flush with the corresponding contour of the upper end of the clamp base.

[0014] According to some embodiments of the present invention, the number of clamping blocks is three, and they are evenly distributed in the circumferential direction of the positioning part at intervals of 120°.

[0015] According to some embodiments of the present invention, the end face of the clamping block that contacts the workpiece is an arc-shaped clamping surface, and the contour of the arc-shaped clamping surface is adapted to the outer circumferential contour of the workpiece.

[0016] 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

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of a centering clamp according to an embodiment of the present utility model; Figure 2 This is a schematic diagram of the locking unit and the pull core according to an embodiment of the present utility model; Figure 3 This is a schematic diagram of the clamp base according to an embodiment of the present utility model; Figure 4 This is a schematic diagram of the clamping block according to an embodiment of the present utility model.

[0018] Reference numerals: Power unit 100; Locking unit 110; Clamping block 120; Pulling core 130; Hinge point 140; Arc-shaped clamping surface 150; Mounting groove 160; Mounting hole 170; Positioning part 180; Conical concave surface 190; Guide part 200; Conical convex surface 210; Fixture base 220. Detailed Implementation

[0019] 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.

[0020] 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.

[0021] 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.

[0022] In the description of this utility model, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly. Those skilled in the art can reasonably determine the specific meaning of these terms in this utility model based on the specific content of the technical solution. In the description of this utility model, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. In the description of this specification, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0023] Reference Figures 1 to 4 A centering clamp, comprising: Power unit 100; The locking unit 110 includes a clamping base 220 and at least two clamping blocks 120. The clamping blocks 120 are movably mounted on the clamping base 220. The clamping base 220 is provided with a positioning part 180 for positioning the workpiece. Core pulling 130 is driven and connected to power unit 100; The core 130 is provided with a first guide surface, and the clamping block 120 is provided with a second guide surface that cooperates with the first guide surface. The power unit 100 drives the core 130 to move linearly along the axial direction. Through the cooperation of the first guide surface and the second guide surface, the axial movement of the core 130 is converted into the radial movement of the clamping block 120 to center and clamp or release the workpiece.

[0024] During clamping, the power unit 100 is activated, driving the pull core 130 to move linearly along the axial direction. The first guide surface on the pull core 130 moves relative to the second guide surface on the clamping block 120. Through the action of the conical surfaces, the axial movement of the pull core 130 is forcibly converted into the synchronous radial movement of multiple clamping blocks 120 toward the center, thereby uniformly clamping the workpiece from all sides and achieving high-precision centering clamping.

[0025] When released, the power unit 100 reverses the drive, causing the pull core 130 to reset in the opposite direction. The conical surface of the pull core 130 disengages from or acts in the opposite direction with the clamping block 120, releasing the radial constraint on the clamping block 120. At this time, the clamping block 120 may open outward radially under the action of the elastic reset element, gravity, or the workpiece itself, thereby releasing the workpiece and completing one work cycle.

[0026] The axial linear motion of the pull core 130, combined with the engagement of its first guide surface and the second guide surface on the clamping block 120, precisely and synchronously converts the axial driving force into the radial motion of multiple clamping blocks 120. This ensures that the workpiece center always coincides with the fixture design center, resulting in high centering accuracy and effectively guaranteeing the workpiece's machining quality. The linear output of the power unit 100 is directly converted into the radial clamping motion of the clamping blocks 120 through the internal pull core 130 and guide surfaces. The entire transmission chain is integrated within the fixture, eliminating the need for additional oscillation space and greatly optimizing the overall structure of the fixture. This results in a compact size, making it particularly suitable for use in space-constrained precision machining environments. The power unit 100 provides a stable and precisely controllable driving force. This force is directly transmitted to the clamping blocks 120 through the pull core 130 and guide surfaces, ensuring that the clamping force acting on the workpiece is uniform, stable, and reliable. This avoids loosening due to insufficient clamping force and also prevents workpiece damage caused by overload clamping.

[0027] The first guide surface is a tapered convex surface 210 located at the end of the core 130; the second guide surface is a tapered concave surface 190 formed on the clamping block 120, with the tapered convex surface 210 and the tapered concave surface 190 cooperating.

[0028] When the pull core 130 is driven to produce axial linear motion, the tapered convex surface 210 at its end and the tapered concave surface 190 on the clamping block 120 undergo relative displacement. Due to the inclined plane effect of the tapered surface, the axial displacement of the pull core 130 is converted into the radial displacement of the clamping block 120. When the pull core 130 moves downward, the tapered convex surface 210 presses against the tapered concave surface 190, forcing the clamping block 120 to slide along the inclined plane direction (i.e., radially inward), achieving clamping. When the pull core 130 moves upward, the constraint between the tapered convex surface 210 and the tapered concave surface 190 is released or reversed, allowing the clamping block 120 to open radially outward under the action of the restoring force or external force, thus releasing the workpiece.

[0029] The conical surface mating mechanism possesses inherent self-centering characteristics. During mating, the conical convex surface 210 automatically guides and corrects the position of the conical concave surface 190, ensuring that multiple clamping blocks 120 move synchronously and equidistantly towards the center. This achieves high-precision automatic centering of the workpiece, guaranteeing the accuracy of repeated clamping from a structural principle perspective. The conical structure decomposes the axial driving force along the inclined plane, with the effective radial component used to drive the clamping blocks 120. This inclined plane mechanism itself is a force amplification mechanism, capable of obtaining a larger radial output clamping force with a smaller axial input force, resulting in efficient and smooth transmission.

[0030] A guide portion 200 is provided on one side of the conical concave surface 190, which guides the conical convex surface 210 into the conical concave surface 190. Before the conical convex surface 210 of the pull core 130 begins to contact and enter the conical concave surface 190 of the clamping block 120, the guide portion 200 first contacts the end or side of the conical convex surface 210. Due to its design as a transition structure such as a slope, chamfer, or arc, it provides a tolerant contact range in the presence of minor alignment errors, avoiding rigid collisions between the conical convex surface 210 and the edge of the concave surface 190. By replacing direct edge collisions with gentle guidance, the impact of conical surface mating is effectively eliminated, ensuring smooth completion of each clamping action and improving the working stability and service life of the fixture.

[0031] The clamping block 120 is mounted on the clamp base 220 by a hinge and has a clamping position and a loosening position. When the core puller 130 moves away from the clamping block 120, it drives the clamping block 120 to swing to the clamping position. When the core puller 130 moves toward the clamping block 120, the clamping block 120 swings to the loosening position.

[0032] As the core 130 moves in a direction away from the clamping block 120 (usually downward), it contacts the clamping block 120 through the tapered surface or other transmission surface at its end and applies a force to the clamping block 120. Since the clamping block 120 is constrained to the fixture base 220 by the hinge axis, this force will drive the clamping block 120 to swing like a lever toward the workpiece about its hinge axis until it reaches and stabilizes in the clamping position.

[0033] When it is necessary to release the workpiece, the pull core 130 moves in the direction toward the clamping block 120 (usually upward). At this time, the driving force of the pull core 130 on the clamping block 120 is released or reversed. Under the action of its own weight, elastic reset element or external auxiliary force, the clamping block 120 swings away from the workpiece around the same hinge axis until it returns to and stabilizes in the released position.

[0034] The hinged design provides a clear pivot point for the movement of the clamping block 120, forcing it to swing along a preset arc trajectory. This ensures that the clamping block 120 moves precisely and repeatedly between the clamping and releasing positions, avoiding the uncertainty and wear caused by sliding friction, and greatly improving the reliability and consistency of the action.

[0035] The clamping block 120 forms a power arm and a resistance arm with its hinge point 140 as the boundary. The power arm is the distance from the end that cooperates with the core 130 to the hinge point 140, and the resistance arm is the distance from the end used to clamp the workpiece to the hinge point 140. The length ratio of the power arm to the resistance arm is greater than or equal to 1.3.

[0036] The clamping block 120 acts as a single lever, swinging around its hinge point 140. When the pull core 130 applies a downward driving force to the end of the power arm, the clamping force output at the end of the resistance arm is amplified according to the lever principle. This structure effectively amplifies the input force. This allows the clamp to achieve a reliable final clamping force with a smaller power source output, reducing the performance requirements of the power unit 100.

[0037] The power unit 100 is a cylinder, and its output shaft is threadedly connected to the core puller 130. It can be understood that the power unit 100 could also be an electric cylinder or a hydraulic cylinder. Cylinders, hydraulic cylinders, and electric cylinders are all standardized linear drive components, providing continuous, stable, and precisely controllable axial thrust, providing fundamental power for the clamping and releasing actions of the fixture, and ensuring the consistency of clamping force. Using a threaded connection or similar rigid connection method, the output shaft of the power unit 100 is directly fixed to the core puller 130, resulting in a compact structure, good connection rigidity, high transmission efficiency, and no backlash or lag caused by intermediate links, ensuring the immediacy and accuracy of power transmission.

[0038] The clamp base 220 has mounting holes 170 on its outer circumferential side. The clamping block 120 is mounted to the clamp base 220 by bolts passing through the mounting holes 170. The clamping block 120 is connected by lateral bolts, providing a precise and stable fulcrum for rotation. After the bolts pass through the mounting holes 170 on the side of the clamp base 220, they are fastened to the corresponding structures on the clamping block 120 (such as threaded holes or through holes with nuts). This connection method does not completely lock the clamping block 120, but rather constrains it to the base while allowing it to swing flexibly within a certain angle range around the bolt axis. The bolts constitute the fixed hinge point 140 for the clamping block 120 to achieve lever movement, converting the axial driving force transmitted by the pull core 130 into the radial clamping movement of the clamping block 120. Compared to a fully cantilever structure, the lateral bolt mounting directly transfers the force of the clamping block 120 to the robust clamping base 220 body, significantly improving the overall rigidity and deformation resistance of the clamping block 120 assembly under clamping conditions, and enabling it to stably withstand greater cutting forces.

[0039] The upper end of the fixture base 220 is circumferentially provided with mounting grooves 160 that match the shape and number of clamping blocks 120. When the clamping blocks 120 are in the clamped state, the outer contour of the clamping blocks 120 is flush with the corresponding contour of the upper end of the fixture base 220. When the clamping blocks 120 are in the clamped state, their outer contour is flush with the fixture base 220, forming a smooth and complete outer surface, completely eliminating protruding or loose parts. This effectively prevents the operator's gloves, clothing, etc. from being caught, and also avoids accidental interference and collision with other moving parts of the machine tool, significantly improving the safety of the equipment. The mounting grooves 160 provide all-round circumferential support for the clamping blocks 120, more effectively dispersing and transmitting the cutting force borne by the clamping blocks 120 to the robust fixture base 220 body, reducing the overhang and deformation of the clamping blocks 120 themselves, thereby greatly improving the rigidity and stability of the entire locking unit 110 under heavy-duty machining conditions.

[0040] There are three clamping blocks 120, evenly distributed around the circumference of the positioning part 180 at 120° intervals. The three clamping blocks 120 surround the circumference of the workpiece positioning part 180 at 120° intervals. When the core 130 drives the three clamping blocks 120 to move synchronously towards the center, the clamping force applied by each clamping block 120 to the workpiece is 120° apart, and the three forces are evenly distributed circumferentially. Because the three clamping blocks 120 are completely symmetrical on the circumference, the clamping forces they apply to the workpiece are equal in magnitude and evenly distributed in direction. This avoids minor deformation or displacement of the workpiece caused by uneven clamping force, making it particularly suitable for clamping thin-walled or easily deformable precision parts. It is understood that, depending on different clamping accuracy and force distribution requirements, the number of clamping blocks 120 can be adaptively adjusted to four, five, or a different number.

[0041] The end face of the clamping block 120 that contacts the workpiece is an arc-shaped clamping surface 150, the contour of which is adapted to the outer circumferential contour of the workpiece. The end face of the clamping block 120 that contacts the workpiece is machined into an arc shape, and its radius of curvature is adapted to the outer circumferential contour radius of the workpiece to be processed. When the clamping block 120 retracts towards the center under drive, the arc-shaped clamping surface 150 can fit against the outer circumferential surface of the workpiece with maximum area, forming an enveloping contact. This contact transforms traditional point contact or small-area contact into stable line contact or surface contact, allowing the clamping force to be applied evenly and dispersedly along the tangential direction of the workpiece's outer circumference.

[0042] Due to the significantly increased contact area, the pressure per unit area acting on the workpiece surface is reduced under the same clamping force. This effectively avoids indentations, scratches, or clamping damage on the surface of precision workpieces (such as intraocular lens blanks), perfectly protecting the surface integrity of the workpiece. The enveloping contact method provides greater static friction, making the workpiece less prone to rotation or slight displacement during processing. Simultaneously, the curved surface fit provides auxiliary automatic fine-tuning and positioning for the workpiece, further improving centering accuracy and processing stability.

[0043] This embodiment provides a centering fixture for processing artificial lens blanks, which has a compact structure, high centering accuracy, and can effectively protect the surface of the blank.

[0044] See attached document Figure 1-4 The centering fixture mainly includes a power unit 100, a locking unit 110, and a pull core 130 connecting the two.

[0045] In this embodiment, the power unit 100 is preferably a cylinder. The cylinder is fixedly mounted on a cylinder base by four cylinder fixing bolts. U-shaped grooves are provided on both sides of the cylinder base, and the cylinder is securely mounted on the machine tool worktable by the base fixing bolts. The cylinder has two air pipe interfaces, used for connecting and discharging compressed air respectively, to drive its internal piston to reciprocate up and down. An internal thread is provided at the center of the piston.

[0046] The locking unit 110 mainly includes a clamping base 220 and three clamping blocks 120. The clamping base 220 is fixedly connected to the top of the cylinder by four clamping base 220 fixing bolts. A product mounting countersunk hole is opened at the center of the top of the clamping base 220, forming a positioning part 180 for positioning the workpiece. Three clamping block 120 mounting positions are equally divided along the circumference of the upper end of the clamping base 220, and bolt holes are correspondingly opened on the outer circumferential side of the blocks.

[0047] The core 130 is the core component for transmitting power. Its bottom end is provided with an external thread, which connects with the internal thread of the cylinder piston to realize threaded transmission. The top end of the core 130 is provided with an outwardly convex conical surface 210, which serves as the first guide surface.

[0048] Three clamping blocks 120 are respectively installed on three mounting positions of the fixture base 220 by three fixing bolts. Each clamping block 120 has a concave conical surface 190, which serves as a second guide surface to cooperate with the conical convex surface 210 of the core 130. The entrance edge of the conical concave surface 190 is machined with a guide slope or chamfer to form an inlet portion 200, which facilitates the smooth entry of the conical convex surface 210 of the core 130. The clamping block 120 forms a lever structure with its hinge point 140 as the boundary. The distance from the end that cooperates with the core 130 to the hinge point 140 is the power arm, and the distance from the end used to clamp the workpiece to the hinge point 140 is the resistance arm. In this embodiment, the length ratio of the power arm to the resistance arm is designed to be 1.3, forming an efficient and labor-saving lever. The end face of the clamping block 120 that contacts the workpiece is an arc-shaped clamping surface 150, the radius of curvature of which matches the outer circumferential contour of the workpiece.

[0049] The upper end of the clamp base 220 is provided with mounting grooves 160 that are adapted to the shape of the three clamping blocks 120. When the three clamping blocks 120 are in the clamping state, their outer contours are flush with the corresponding contours at the upper end of the clamp base 220, forming a complete, smooth circular outer contour without any protrusions.

[0050] Compressed air enters the cylinder through the air pipe interface, driving the piston to move downwards. The piston drives the threaded core 130 to move downwards. Because the tapered convex surface 210 at the top of the core 130 engages with the tapered concave surface 190 of the clamping block 120, the downward axial movement of the core 130 is converted into synchronous, radially oscillating movement of the three clamping blocks 120 towards the center through the tapered surface engagement. The clamping blocks 120 rotate around their fixing bolts, and their arc-shaped clamping surfaces 150 evenly grip the workpiece from all sides, achieving high-precision centering clamping. Thanks to the leverage ratio of 1.3, the driving force of the cylinder is amplified, thus obtaining a reliable clamping force with a smaller input.

[0051] Compressed air enters from another air pipe interface, driving the piston to move upward and causing the core 130 to return to its original position. The conical convex surface 210 of the core 130 disengages from the conical concave surface 190 of the clamping block 120, and the clamping block 120 swings outward radially under its own weight or elastic restoring force, releasing the workpiece.

[0052] 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 centering fixture, characterized in that, include: Power unit; The locking unit includes a clamping base and at least two clamping blocks, the clamping blocks being movably mounted on the clamping base, the clamping base being provided with a positioning part for positioning the workpiece; The core is pulled and connected to the power unit for driving; The core is provided with a first guide surface, and the clamping block is provided with a second guide surface that cooperates with the first guide surface. The power unit drives the core to move linearly along the axial direction. Through the cooperation of the first guide surface and the second guide surface, the axial movement of the core is converted into the radial movement of the clamping block to center and clamp or release the workpiece.

2. A centering fixture according to claim 1, characterized in that, The first guide surface is a tapered convex surface disposed at the end of the core; the second guide surface is a tapered concave surface formed on the clamping block, wherein the tapered convex surface and the tapered concave surface cooperate with each other.

3. A centering fixture according to claim 2, characterized in that, A guide portion is provided on one side of the conical concave surface, which is used to guide the conical convex surface into the conical concave surface.

4. A centering fixture according to claim 1, characterized in that, The clamping block is mounted on the fixture base by a hinge and has a clamping position and a releasing position; when the pull core moves away from the clamping block, it drives the clamping block to swing to the clamping position; when the pull core moves toward the clamping block, the clamping block swings to the releasing position.

5. A centering fixture according to claim 4, characterized in that, The clamping block forms a power arm and a resistance arm with its hinge point as the boundary. The power arm is the distance from the end that cooperates with the pull core to the hinge point, and the resistance arm is the distance from the end used to clamp the workpiece to the hinge point. The length ratio of the power arm to the resistance arm is greater than or equal to 1.

3.

6. A centering fixture according to claim 1, characterized in that, The power unit is a cylinder, and the output shaft of the cylinder is threadedly connected to the core puller.

7. A centering fixture according to claim 1, characterized in that, The outer circumferential side of the clamp base is provided with mounting holes; the clamping block is installed on the clamp base by bolts passing through the mounting holes.

8. A centering fixture according to claim 1, characterized in that, The upper end of the clamp base is provided with a mounting groove that matches the shape and number of the clamping blocks; when the clamping blocks are in the clamping state, the outer contour of the clamping blocks is flush with the corresponding contour of the upper end of the clamp base.

9. A centering fixture according to claim 1, characterized in that, The number of clamping blocks is three, and they are evenly distributed on the circumference of the positioning part at a 120° interval.

10. A centering fixture according to claim 1, characterized in that, The end face of the clamping block that contacts the workpiece is an arc-shaped clamping surface, and the contour of the arc-shaped clamping surface is adapted to the outer circumferential contour of the workpiece.

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