Tooling fixture for bearing cage

Abstract

The present invention relates to a fixture for a bearing cage, which includes a chuck, a base seat and a fastener. A plurality of clamping jaws are arranged on the chuck, and the base seat is clamped and fixed to the chuck by the plurality of clamping jaws. An annular positioning groove is arranged on the base seat, and the bearing cage is fixed in the annular positioning groove of the base seat through the fixing assembly. The fastener is located between the outer diameter side surface of the annular positioning groove and the outer peripheral surface of the bearing cage. During positioning, the fastener abuts against the outer diameter side surface of the annular positioning groove and the outer peripheral surface of the bearing cage respectively. It fixes the bearing cage in the annular positioning groove of the base seat through the fixing assembly, which can not only ensure that the bearing cage is evenly stressed radially to meet the requirements of high-precision roundness and flatness, but also improve the time for replacing and adjusting different bearing cages.

Description

Technical Field

[0001] The present invention relates to the technical field of machining, and particularly to a fixture for a bearing cage. Background Art

[0002] At present, the production of large thin-walled bearing cage products on lathes mainly uses traditional six-jaw fixtures. The clamping force is mainly achieved by radially clamping the jaws through threaded connections. It is impossible for manual operation to make the radial forces of the jaws in contact with the bearing cage consistent, making it difficult to ensure roundness. Moreover, for each large thin-walled bearing cage product processed, it is necessary to repeatedly adjust the clamping force of each jaw, which is time-consuming and laborious. Due to the poor strength of large thin-walled bearing cage products themselves, it is difficult to ensure the flatness of the end face after end face turning machining. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a fixture for a bearing cage, which can solve the phenomenon of out-of-tolerance flatness and roundness caused by uneven clamping force during the lathe machining of large thin-walled bearing cage products.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] The fixture for a bearing cage includes a chuck, a mandrel seat, and a fastener. A plurality of jaws are provided on the chuck. The mandrel seat is clamped and fixed to the chuck through the plurality of jaws. An annular positioning groove is provided on the mandrel seat. The bearing cage is fixed in the annular positioning groove of the mandrel seat through the fixing component. The fastener is located between the outer diameter side of the annular positioning groove and the outer peripheral surface of the bearing cage. During positioning, the fastener abuts against the outer diameter side of the annular positioning groove and the outer peripheral surface of the bearing cage respectively.

[0006] Further, the positioning component includes a plurality of pressing blocks arranged circumferentially along the annular positioning groove. The outer diameter side of the annular positioning groove is a first tapered surface that expands outwards. A second tapered surface adapted to the first tapered surface is provided on the pressing block. A positioning surface for abutting against the outer peripheral surface of the bearing cage is provided on one side of the pressing block opposite to the second tapered surface. Each pressing block is axially adjustable and positioned in the annular positioning groove through a bolt. By screwing the bolt, the pressing block moves along the first tapered surface towards the bottom of the annular positioning groove, and the positioning surface on the pressing block presses against the outer peripheral surface of the bearing cage to clamp and fix the bearing cage.

[0007] Preferably, the positioning surface on the pressing block is an inwardly concave arc surface, and the inwardly concave arc surface is adapted to the outer circumferential surface of the bearing cage.

[0008] Furthermore, each of the pressing blocks is provided with a through hole parallel to the axial direction of the annular positioning groove. An axial threaded hole is provided on the bottom surface of the annular positioning groove. The diameter of the through hole is larger than the diameter of the fastening bolt. The threaded section of the fastening bolt passes through the through hole and is threadedly connected to the threaded hole. The nut of the fastening bolt abuts against the pressing block, and the pressing block can move along the conical surface towards the bottom of the annular positioning groove under the action of the downward pressure given by the fastening bolt.

[0009] Furthermore, a gasket is provided between the nut of the fastening bolt and the pressing block.

[0010] Furthermore, a bevel surface is provided between the positioning surface and the upper surface of the pressing block, and the bevel surface is inclined away from the bearing cage side.

[0011] Furthermore, there are six jaws, which are evenly distributed circumferentially on the chuck. A chute is provided on the chuck along the radial direction, and the jaws are movably arranged in the chute.

[0012] Furthermore, a chute is provided on the chuck along the radial direction, and the jaws are slidably arranged in the chute. The jaws are manual jaws. A positioning screw is provided on the outer end surface of the manual jaw, and a turbine is coaxially fixed at the front end of the positioning screw. A worm is provided on the chuck and is adapted to the turbine. Rotating the positioning screw realizes the clamping and positioning of the manual jaws.

[0013] Furthermore, the jaw includes a stepped positioning surface. The tire seat is positioned within the stepped positioning surface. Multiple clamping stepped positioning surfaces are arranged oppositely. The tire seat is clamped at the stepped positioning surface. The stepped positioning surface includes a first positioning surface that fits with the lower end surface of the bearing cage and a second positioning surface that abuts against the outer circumferential surface of the bearing cage. The second positioning surface is an arc surface, and the radian of the arc surface is adapted to the outer circumferential surface of the bearing cage.

[0014] Furthermore, the inner diameter of the annular positioning groove is smaller than the inner diameter of the bearing cage.

[0015] Furthermore, an annular positioning disc is provided between the inner circumferential surface of the bearing cage and the inner diameter side surface of the annular positioning groove. The annular positioning disc is detachably installed on the bottom surface of the annular positioning groove through a plurality of positioning screws, and the bearing cage is in clearance fit with the annular positioning disc.

[0016] The beneficial effects of the present invention compared with the prior art are:

[0017] The fixture for bearing cages provided by the present invention includes a chuck, a seat and fasteners. A plurality of jaws are arranged on the chuck, and the seat is clamped and fixed to the chuck by the plurality of jaws. An annular positioning groove is arranged on the seat, and the bearing cage is fixed in the annular positioning groove of the seat through the fixing component. The fasteners are located between the outer diameter side of the annular positioning groove and the outer peripheral surface of the bearing cage. During positioning, the fasteners are respectively abutted against the outer diameter side of the annular positioning groove and the outer peripheral surface of the bearing cage. It fixes the bearing cage in the annular positioning groove of the seat through the fixing component, which can not only ensure that the bearing cage is uniformly stressed radially to meet the requirements of high-precision roundness and flatness, but also improve the replacement and adjustment time of different bearing cages. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic three-dimensional structure diagram of an embodiment of the present invention;

[0019] Figure 2 is Figure 1 a partial structure diagram of

[0020] Figure 3 is Figure 2 a schematic structure diagram of part C in

[0021] Figure 4 is a schematic three-dimensional structure diagram of another embodiment of the present invention;

[0022] Figure 5 is Figure 4 a partial structure diagram of

[0023] Figure 6 is Figure 5 a schematic structure diagram of part A in

[0024] Figure 7 is Figure 5 a schematic structure diagram of part B in

[0025] In the figure: 1. Jaw, 1.1. First positioning surface, 1.2. Second positioning surface, 2. Seat, 2.1. Annular positioning groove, 2.1a. First conical surface, 3. Pressure block, 3.1. Second conical surface, 3.2. Concave arc surface, 3.3. Through hole, 4. Fastening bolt, 5. Bearing cage, 6. Chuck, 6.1. Slide groove, 7. Annular positioning disc, 8. Gasket, 9. Inclined surface, 11. Positioning screw. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0027] Embodiment 1

[0028] As shown Figures 1-3 in the figure, the tooling fixture for the bearing cage includes a chuck 6, a base 2 and fasteners. A plurality of jaws 1 are arranged on the chuck 6. The base 2 is clamped and fixed to the chuck 6 by the plurality of jaws 1. In this embodiment, there are six jaws 1, which are circumferentially distributed on the chuck 6. A chute 6.1 is arranged on the chuck 6 in the radial direction. The jaws 1 are movably arranged in the chute 6.1. Specifically, the jaws 1 are manual jaws 1. A positioning screw is rotatably arranged on the outer end face of the manual jaw 1. A turbine is coaxially fixed at the front end of the positioning screw. A worm gear adapted to the turbine is arranged on the chuck 6. During use, the manual jaw is clamped and positioned by rotating the positioning screw to drive the turbine to engage with the worm gear. It should be noted that the chuck 6 in this embodiment can also be any automatic centering chuck in the prior art that can achieve a clamping function. During use, the chuck 6 is rotatably installed on a lathe.

[0029] The jaw 1 includes a stepped positioning surface. The base 2 is positioned within the stepped positioning surface. Specifically, the stepped positioning surfaces of the plurality of jaws 1 are oppositely arranged. The base 2 is clamped at the stepped positioning surface. The stepped positioning surface includes a first positioning surface 1.1 that fits the lower end surface of the bearing cage 5 and a second positioning surface 1.2 that abuts against the outer circumferential surface of the bearing cage 5. The second positioning surface 1.2 is an arc surface, and the radian of the arc surface is adapted to the outer circumferential surface of the bearing cage 5.

[0030] In this embodiment, an annular positioning groove 2.1 is arranged on the base 2. The bearing cage 5 is fixed in the annular positioning groove 2.1 of the base 2 through a fixing component. The fasteners are located between the outer diameter side surface of the annular positioning groove 2.1 and the outer peripheral surface of the bearing cage 5. During positioning, the fasteners respectively abut against the outer diameter side surface of the annular positioning groove 2.1 and the outer peripheral surface of the bearing cage 5.

[0031] Specifically, the positioning component includes a plurality of pressing blocks 3 arranged circumferentially along the annular positioning groove 2.1. The outer diameter side surface of the annular positioning groove 2.1 is a first conical surface 2.1a that expands outwards. A second conical surface 3.1 adapted to the first conical surface 2.1a is arranged on the pressing block 3. A positioning surface for abutting against the outer peripheral surface of the bearing cage 5 is arranged on one side of the pressing block 3 opposite to the second conical surface 3.1. Preferably, the positioning surface is an inner concave arc surface 3.2, and the inner concave arc surface 3.2 is adapted to the outer peripheral surface of the bearing cage 5.

[0032] Each pressing block 3 is axially adjustably positioned in the annular positioning groove 2.1 through the fastening bolt 4. Specifically, each pressing block 3 is provided with a through hole 3.3 parallel to the axial direction of the opening of the annular positioning groove 2.1. An axial threaded hole is provided on the bottom surface of the groove at the opening of the annular positioning groove 2.1. The diameter of the through hole 3.3 is larger than the diameter of the fastening bolt 4. The threaded section of the fastening bolt 4 passes through the through hole 3.3 and is threadedly connected to the threaded hole. The nut of the fastening bolt 4 abuts against the pressing block 3. The pressing block 3 can move along the first conical surface 2.1a towards the bottom of the annular positioning groove 2.1 under the action of the downward pressure given by the fastening bolt 4. A gasket 8 is arranged between the nut of the fastening bolt 4 and the pressing block 3 in this embodiment. It should be noted that the setting of the gasket 8 can increase the contact area between the nut of the fastening bolt 4 and the pressing block 3 and ensure the fastening stability of the pressing block 3.

[0033] During use, the fastening bolt 4 is screwed to adjust the pressing block 3 to move along the first conical surface 2.1a towards the bottom surface of the annular positioning groove 2.1. The positioning surface (concave arc surface 3.2) on the pressing block 3 presses against the outer peripheral surface of the bearing cage 5, and the inner peripheral surface of the bearing cage 5 abuts against the inner diameter side surface of the annular positioning groove 2.1, thereby clamping and fixing the bearing cage 5. The fastening bolt 4 is screwed in the reverse direction to cancel the pressure applied by the fastening bolt 4 to the pressing block 3, and the pressing block 3 is taken out to release the clamping of the bearing cage 5.

[0034] It should be noted that the inner diameter of the annular positioning groove 2.1 is smaller than the inner diameter of the bearing cage 5, that is, there is a small gap between the inner diameter side surface of the annular positioning groove 2.1 and the inner peripheral surface of the bearing cage 5. This small gap not only enables self-centering when the bearing cage 5 is clamped and fixed by the pressing block 3 but also avoids the problem of out-of-roundness exceeding the tolerance after processing caused by the difficulty in adjusting the magnitude of the radial clamping force. In addition, it is necessary to ensure that after the small gap is compressed, the slight elastic deformation of the bearing cage 5 will not affect the final roundness of the bearing cage 5.

[0035] A slope 9 is arranged between the positioning surface (concave arc surface 3.2) and the upper surface of the pressing block 3 in this embodiment. The slope 9 slopes away from the bearing cage 5. The setting of the slope 9 is beneficial to processing.

[0036] The beneficial effects of this embodiment compared with the prior art are:

[0037] This solution mainly fixes the seat 2 once through the machine tool chuck 6 and the manual jaw 1. The lower end face of the large thin-walled bearing cage 5 product contacts the bottom of the annular positioning groove 2.1 on the seat 2 to play a supporting role. The inner diameter of the bearing cage 5 has a clearance fit with the stop of the seat 2 (that is, there is a clearance between the inner diameter side of the annular positioning groove 2.1 and the inner circumferential surface of the bearing cage 5) to play a radial positioning role. One side of the pressing block 3 is provided with a second conical surface 3.1, which cooperates with the first conical surface 2.1a on the annular positioning groove 2.1 of the seat 2. The fastening bolt 4 presses the pressing block 3 downward to generate a radially inward clamping force, so that the inner diameter of the bearing cage 5 abuts against and is fixed to the stop of the seat 2. This clamping method can not only ensure that the bearing cage 5 is uniformly stressed radially to meet the requirements of high-precision roundness and flatness, but also improve the time for replacing and adjusting different bearing cages 5.

[0038] Embodiment 2,

[0039] As Figures 4-7 shown, the fixture for the bearing cage includes a chuck 6, a seat 2 and a fastener. A plurality of jaws 1 are provided on the chuck 6. The seat 2 is clamped and fixed to the chuck 6 through the plurality of jaws 1. In this embodiment, there are six jaws 1, which are evenly distributed in a circle on the chuck 6. A chute 6.1 is provided on the chuck 6 along the radial direction, and the jaw 1 is movably arranged in the chute 6.1. Specifically, the jaw 1 is a manual jaw 1. A positioning screw is rotatably arranged on the outer end face of the manual jaw 1, and a turbine is coaxially fixed at the front end of the positioning screw. A worm gear adapted to the turbine is provided on the chuck 6. During use, the manual jaw is clamped and positioned by rotating the positioning screw to drive the turbine to mesh with the worm gear. It should be noted that the chuck in this embodiment can also be any automatic centering chuck in the prior art that can achieve a clamping function. During use, the chuck 6 is rotatably installed on a lathe.

[0040] The jaw 1 in this embodiment includes a stepped positioning surface, and the seat 2 is positioned within the stepped positioning surface. Specifically, the stepped positioning surfaces of the plurality of jaws 1 are oppositely arranged, and the seat 2 is clamped at the stepped positioning surface. The stepped positioning surface includes a first positioning surface 1.1 that fits the lower end face of the bearing cage 5 and a second positioning surface 1.2 that abuts against the outer circumferential surface of the bearing cage 5. The second positioning surface 1.2 is an arc surface, and the radian of the arc surface is adapted to the outer circumferential surface of the bearing cage 5.

[0041] In this embodiment, the placenta 2 is provided with an annular positioning groove 2.1. The bearing cage 5 is fixed in the annular positioning groove 2.1 of the placenta 2 through a fixing component. The fastener is located between the outer diameter side of the annular positioning groove 2.1 and the outer peripheral surface of the bearing cage 5. During positioning, the fastener abuts against the outer diameter side of the annular positioning groove 2.1 and the outer peripheral surface of the bearing cage 5 respectively. An annular positioning disc 7 is arranged between the inner peripheral surface of the bearing cage 5 and the inner diameter side of the annular positioning groove 2.1 in this embodiment. The annular positioning disc 7 is detachably fixed and installed on the bottom surface of the annular positioning groove 2.1 through a plurality of positioning screws 11. The bearing cage 5 and the annular positioning disc 7 are in clearance fit. It should be noted that different annular positioning discs 7 can be matched according to the specifications and models of the bearing cage 5 during use.

[0042] Specifically, the positioning component includes a plurality of pressing blocks 3 arranged circumferentially along the annular positioning groove 2.1. The outer diameter side of the annular positioning groove 2.1 is a first tapered surface 2.1a that expands outwards. The pressing block 3 is provided with a second tapered surface 3.1 adapted to the first tapered surface 2.1a. On one side of the pressing block 3 opposite to the second tapered surface 3.1, there is a positioning surface for abutting against the outer peripheral surface of the bearing cage 5. Preferably, this positioning surface is an inner concave arc surface 3.2, and the inner concave arc surface 3.2 is adapted to the outer peripheral surface of the bearing cage 5.

[0043] Each pressing block 3 is axially adjustable and positioned in the annular positioning groove 2.1 through a fastening bolt 4. Specifically, each pressing block 3 is provided with a through hole 3.3 parallel to the axial direction of the annular positioning groove 2.1 opening. On the bottom surface of the annular positioning groove 2.1 opening, there is an axial threaded hole. The aperture of the through hole 3.3 is larger than the diameter of the fastening bolt 4. The threaded section of the fastening bolt 4 passes through the through hole 3.3 and is threadedly connected to the threaded hole. The nut of the fastening bolt 4 abuts against the pressing block 3. The pressing block 3 can move along the first tapered surface 2.1a towards the bottom of the annular positioning groove 2.1 under the downward pressure given by the fastening bolt 4. A gasket 8 is arranged between the nut of the fastening bolt 4 and the pressing block 3 in this embodiment. It should be noted that the setting of the gasket 8 can increase the contact area between the nut of the fastening bolt 4 and the pressing block 3 and ensure the fastening stability of the pressing block 3.

[0044] During use, the fastening bolt 4 is screwed to adjust the pressing block 3 to move along the first tapered surface 2.1a towards the bottom surface of the annular positioning groove 2.1. The positioning surface (inner concave arc surface 3.2) on the pressing block 3 presses against the outer peripheral surface of the bearing cage 5, and the inner peripheral surface of the bearing cage 5 abuts against the outer peripheral surface of the annular positioning disc 7, thereby clamping and fixing the bearing cage 5. The fastening bolt 4 is screwed in the reverse direction to cancel the pressure exerted by the fastening bolt 4 on the pressing block 3, and the pressing block 3 is taken out to release the clamping of the bearing cage 5.

[0045] It should be noted that the bearing cage 5 is in clearance fit with the annular positioning disc 7, that is, there is a small gap between the outer circumferential surface of the annular positioning disc 7 and the inner circumferential surface of the bearing cage 5. This small gap not only enables self-centering when the bearing cage 5 is clamped and fixed by the pressing block 3, but also avoids the problem of out-of-roundness exceeding the tolerance after machining caused by the difficulty in adjusting the magnitude of the radial clamping force. In addition, it is necessary to ensure that after the small gap is compressed, the slight elastic deformation of the bearing cage 5 will not affect the final roundness of the cage.

[0046] In this embodiment, a bevel 9 is provided between the positioning surface (concave arc surface 3.2) and the upper surface of the pressing block 3, and the bevel 9 slopes away from the bearing cage 5. The provision of the bevel 9 is beneficial to machining.

[0047] The beneficial effects of this embodiment compared with the prior art are as follows:

[0048] The lower end surface of the large thin-walled bearing cage 5 product contacts the bottom of the annular positioning groove 2.1 on the platen 2 to play a supporting role; the outer diameter of the annular positioning disc 7 fixed to the platen and the inner diameter of the large thin-walled bearing cage are in radial positioning through a small clearance fit; the radial force generated by adjusting the position of the pressing block 3 through the fastening bolt 4 on the outer diameter of the large thin-walled bearing cage 5 realizes the clamping of the bearing cage 5. The support of the bottom plane of the annular positioning groove 2.1 on the platen 2 effectively avoids the problem of out-of-flatness exceeding the tolerance after machining caused by the axial deformation of the bearing cage 5 due to insufficient strength during clamping. The clearance fit between the outer diameter of the annular positioning disc 7 and the inner diameter of the bearing cage 5 ensures self-centering of the product and, together with the pressing block 3, clamps the bearing cage 5, avoiding the problem of out-of-roundness exceeding the tolerance after machining caused by the difficulty in adjusting the magnitude of the radial clamping force. This design can realize rapid workpiece replacement without repeated positioning, which not only improves production efficiency, but also effectively reduces the labor intensity of the operator, improves the machining accuracy of the large thin-walled bearing cage 5 product, and reduces the scrap rate.

[0049] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "front", "center", "both ends", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0050] In the present invention, unless otherwise clearly defined or limited, terms such as "installation", "setting", "connection", "fixation", "rotation connection", etc. shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] Although the embodiments of the present invention have been shown and described above, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Fixture for bearing cage, characterized in that: It includes a chuck, a placenta and fasteners. A plurality of clamping jaws are provided on the chuck. The placenta is clamped and fixed to the chuck by the plurality of clamping jaws. An annular positioning groove is provided on the placenta. The bearing cage is fixed in the annular positioning groove of the placenta by the fasteners. The fasteners are located between the outer diameter side surface of the annular positioning groove and the outer peripheral surface of the bearing cage. During positioning, the fasteners are respectively in contact with the outer diameter side surface of the annular positioning groove and the outer peripheral surface of the bearing cage; The fasteners include a plurality of pressing blocks arranged circumferentially along the annular positioning groove. The outer diameter side surface of the annular positioning groove is a first conical surface that expands outwards. A second conical surface adapted to the first conical surface is provided on the pressing block. A positioning surface for contacting the outer peripheral surface of the bearing cage is provided on one side of the pressing block opposite to the second conical surface. Each pressing block is axially adjustable and positioned in the annular positioning groove by a fastening bolt. By screwing the fastening bolt, the pressing block moves along the first conical surface towards the bottom of the annular positioning groove, and the positioning surface on the pressing block presses against the outer peripheral surface of the bearing cage to clamp and fix the bearing cage; A through hole parallel to the axial direction of the annular positioning groove is provided on each pressing block. An axial threaded hole is provided on the bottom surface of the annular positioning groove. The diameter of the through hole is larger than the diameter of the fastening bolt. The threaded section of the fastening bolt passes through the through hole and is threadedly connected to the threaded hole. The nut of the fastening bolt abuts against the pressing block. The pressing block can move along the first conical surface towards the bottom of the annular positioning groove under the action of the downward pressure given by the fastening bolt; An annular positioning disc is provided between the inner peripheral surface of the bearing cage and the inner diameter side surface of the annular positioning groove. The annular positioning disc is detachably mounted on the bottom surface of the annular positioning groove by a plurality of positioning screws. The bearing cage is in clearance fit with the annular positioning disc.

2. The tooling fixture for a bearing cage according to claim 1, wherein: The positioning surface on the pressing block is a concave arc surface, and the concave arc surface is adapted to the outer circumference of the bearing cage.

3. The fixture for the bearing cage according to claim 1, wherein: A gasket is provided between the nut of the fastening bolt and the pressing block.

4. The tooling fixture for a bearing cage according to claim 1, wherein: A slope is provided between the positioning surface of the pressing block and the upper surface of the pressing block, and the slope inclines away from the bearing cage.

5. The tooling fixture for a bearing cage according to any one of claims 1-4, characterized in that: The clamping jaw includes a stepped positioning surface. The placenta is positioned in the stepped positioning surface. A plurality of clamping stepped positioning surfaces are arranged oppositely. The placenta is clamped at the stepped positioning surface. The stepped positioning surface includes a first positioning surface that fits with the lower end surface of the placenta and a second positioning surface that abuts against the outer circumference of the placenta. The second positioning surface is an arc surface, and the radian of the arc surface is adapted to the outer circumference of the placenta.

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