Spatial six-degree-of-freedom fully parallel mechanism with large swing angle output capacity

Abstract

The application discloses a space six-freedom-degree full-parallel mechanism with large swing angle output capacity, which comprises a fixed platform, three upper support chains, upper ends of the three upper support chains being connected with the fixed platform through upper-layer upper hinges, the three upper-layer upper hinges all passing through an upper imaginary circle, three lower support chains, upper ends of the three lower support chains being connected with the fixed platform through lower-layer upper hinges, the three upper-layer lower support chains all passing through a lower imaginary circle, the upper imaginary circle and the lower imaginary circle being arranged in parallel and at intervals, a movable platform, lower ends of the three upper support chains being connected with the movable platform through first lower hinges, and lower ends of the three lower support chains being connected with the movable platform through second lower hinges, and a machining main shaft arranged on the movable platform. The space six-freedom-degree full-parallel mechanism with large swing angle output capacity has the advantages of high rigidity, strong bearing capacity, good kinematic performance and large swing angle output capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of machining, in particular to a space six-degree-of-freedom full parallel mechanism with large swing angle output capacity. BACKGROUND

[0002] Multi-axis parallel mechanism is a closed-loop mechanism connected by multiple branch chains. Compared with serial mechanism, parallel mechanism has the characteristics of compact structure, high stiffness, high precision and high dynamic response.

[0003] In the related art, the more the number of branch chains, the better the stiffness performance, but the relative kinematics performance is more limited. In the related art, the number of branch chains is three to five. Compared with parallel mechanism with less degree of freedom, six-axis parallel machining mechanism has better stiffness performance, but the layout of hinges and branch chains is severely limited, which seriously restricts the improvement of kinematics performance of the mechanism and seriously affects the size of the high-quality attitude workspace of the mechanism. SUMMARY

[0004] The present application aims to solve at least one of the technical problems in the prior art. To this end, the present application proposes a space six-degree-of-freedom full parallel mechanism with large swing angle output capacity, which has the advantages of high stiffness, strong carrying capacity, good kinematics performance and large swing angle output capacity.

[0005] To achieve the above-mentioned purpose, according to the embodiment of the first aspect of the present application, a space six-degree-of-freedom full parallel mechanism with large swing angle output capacity is provided, which comprises: a fixed platform; three upper branch chains, the upper ends of the three upper branch chains are connected to the fixed platform through upper layer upper hinges, and the three upper layer upper hinges pass through an upper imaginary circle; three lower branch chains, the upper ends of the three lower branch chains are connected to the fixed platform through lower layer upper hinges, and the three lower layer upper hinges pass through a lower imaginary circle, and the upper imaginary circle and the lower imaginary circle are arranged in parallel and spaced apart; a moving platform, the lower ends of the three upper branch chains are connected to the moving platform through first lower hinges, and the lower ends of the three lower branch chains are connected to the moving platform through second lower hinges; a machining spindle, the machining spindle is arranged on the moving platform.

[0006] According to the embodiment of the present application, the space six-degree-of-freedom full parallel mechanism with large swing angle output capacity has the advantages of high stiffness, strong carrying capacity, good kinematics performance and large swing angle output capacity.

[0007] In addition, the space six-degree-of-freedom full parallel mechanism with large swing angle output capacity according to the above-mentioned embodiment of the present application can also have the following additional technical features:

[0008] According to one embodiment of the present application, the upper imaginary circle and the lower imaginary circle are coaxially arranged.

[0009] According to one embodiment of the present application, the three first lower hinges all pass through a first imaginary circle, the three second lower hinges all pass through a second imaginary circle, the first imaginary circle is located above the second imaginary circle and the first imaginary circle and the second imaginary circle are coaxially and parallelly arranged.

[0010] According to one embodiment of the present application, when the upper imaginary circle, the lower imaginary circle, the first imaginary circle and the second imaginary circle are coaxial, a projection of each upper branch chain in a plane where the upper imaginary circle is located is inclined to a radial direction of the upper imaginary circle, and a projection of each lower branch chain in a plane where the lower imaginary circle is located is inclined to a radial direction of the lower imaginary circle.

[0011] According to one embodiment of the present application, two of the three first lower hinges are oppositely arranged in a radial direction of the moving platform and the other first lower hinge is arranged in a normal direction of an imaginary connecting line of the two oppositely arranged first lower hinges, and two of the three second lower hinges are oppositely arranged in a radial direction of the moving platform and the other second lower hinge is arranged in a normal direction of an imaginary connecting line of the two oppositely arranged second lower hinges.

[0012] According to one embodiment of the present application, imaginary connecting lines of the three upper upper hinges and a center of the upper imaginary circle respectively coincide with projections in a horizontal plane of imaginary connecting lines of the three lower upper hinges and a center of the lower imaginary circle one by one.

[0013] According to one embodiment of the present application, imaginary connecting lines of the three upper upper hinges and a center of the upper imaginary circle respectively coincide with projections in a horizontal plane of imaginary connecting lines of the three lower upper hinges and a center of the lower imaginary circle one by one.

[0014] According to one embodiment of the present application, each of the upper branch chain and the lower branch chain comprises a motor and a screw rod, the motor is in transmission connection with the screw rod, and the screw rod is driven to rotate along a central axis and move in an axial direction by rotation of the motor.

[0015] According to one embodiment of the present application, each of the upper layer upper hinge and the lower layer upper hinge is a Hooke joint and comprises: a mounting outer ring mounted on the fixed platform; a rotating middle ring rotatably arranged in the mounting outer ring; a mounting inner ring rotatably arranged in the rotating middle ring, the mounting inner ring being perpendicular to the rotating middle ring relative to the rotating axis of the rotating middle ring, the motor being mounted in the mounting inner ring, each of the first lower hinge and the second lower hinge being a Hooke joint and comprising: a mounting seat mounted on the movable platform; a rotating column rotatably connected with the mounting seat along a central axis; a U-shaped piece rotatably connected with the rotating column and having a rotating axis perpendicular to the axial direction of the rotating column, the lower end of the lead screw being connected with the U-shaped piece.

[0016] According to one embodiment of the present application, the movable platform has a main shaft sleeve, the machining main shaft being fitted in the main shaft sleeve.

[0017] Additional aspects and advantages of the present application will be given, partially in the following description, partially become obvious from the following description, or be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0019] Figure 1 is a structural schematic diagram of a spatial six-degree-of-freedom full-parallel mechanism with large swing angle output capacity according to one specific embodiment of the present application.

[0020] Figure 2 is a partial exploded view of a spatial six-degree-of-freedom full-parallel mechanism with large swing angle output capacity according to one specific embodiment of the present application.

[0021] Figure 3 is a structural schematic diagram of a spatial six-degree-of-freedom full-parallel mechanism with large swing angle output capacity according to another specific embodiment of the present application.

[0022] Figure 4 is a partial exploded view of a spatial six-degree-of-freedom full-parallel mechanism with large swing angle output capacity according to another specific embodiment of the present application.

[0023] Figure 5 is a structural schematic diagram of a spatial six-degree-of-freedom full-parallel mechanism with large swing angle output capacity according to another specific embodiment of the present application.

[0024] Figure 6is a partial exploded view of a spatial six-degree-of-freedom full parallel mechanism with large swing angle output capability according to another specific embodiment of the present application.

[0025] Figure 7 is a partial exploded view of a spatial six-degree-of-freedom full parallel mechanism with large swing angle output capability according to an embodiment of the present application.

[0026] Fig. 1 is a partial exploded view of a spatial six-degree-of-freedom full parallel mechanism with large swing angle output capability according to an embodiment of the present application. DETAILED DESCRIPTION

[0027] The present application is made based on the discovery and realization of the inventors on the following facts and problems:

[0028] The more the number of branch chains in the parallel machining mechanism in the related art, the better the stiffness performance, but the relative kinematic performance is more limited. The number of branch chains in the parallel machining mechanism in the related art is three to five. Compared with the parallel machining mechanism with less degrees of freedom, the six-axis parallel machining mechanism has better stiffness performance, but the layout of the hinge and the branch chain is severely limited, which seriously restricts the improvement of the kinematic performance of the mechanism and seriously affects the size of the high-quality posture working space of the mechanism.

[0029] Specifically, the connection hinges of the fixed platform and the six branch chains in the six-axis parallel machining mechanism in the related art are all distributed in the same plane, which limits the layout of the hinge and the branch chain, restricts the kinematic performance of the parallel machining mechanism, and further affects the size of the high-quality posture working space of the mechanism.

[0030] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0031] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the features defined as "first" and "second" can be explicitly or implicitly included one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0032] In the description of the present application, it needs to be understood that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] The spatial six-degree-of-freedom parallel mechanism 1 with large swing angle output capability according to the embodiment of the present application is described below with reference to the drawings.

[0034] As shown in Figures 1-7 The spatial six-degree-of-freedom parallel mechanism 1 with large swing angle output capability according to the embodiment of the present application includes a fixed platform 10, three upper branch chains 20, three lower branch chains 30, a moving platform 40 and a machining spindle 50 (the upward and downward directions are shown by arrows in the drawings and are only for the convenience of description, and are not a limitation on the actual arrangement direction).

[0035] The upper ends of the three upper branch chains 20 are connected to the fixed platform 10 through upper layer upper hinges 21, and the three upper layer upper hinges 21 all pass through an upper imaginary circle. The upper ends of the three lower branch chains 30 are connected to the fixed platform 10 through lower layer upper hinges 31, and the three lower layer upper hinges 31 all pass through a lower imaginary circle, and the upper imaginary circle and the lower imaginary circle are arranged in parallel and spaced apart. The lower ends of the three upper branch chains 20 are connected to the moving platform 40 through first lower hinges 22, and the lower ends of the three lower branch chains 30 are connected to the moving platform 40 through second lower hinges 32. The machining spindle 50 is arranged on the moving platform 40.

[0036] According to the space six-degree-of-freedom parallel mechanism 1 with large swing angle output capacity provided by the embodiment of the present application, by arranging three upper support chains 20 and three lower support chains 30, a total of six support chains, compared with parallel structures with less number of support chains, the space six-degree-of-freedom parallel mechanism 1 can have high stiffness and high bearing capacity.

[0037] In addition, by arranging the three upper layer upper hinges 21 of the fixed platform 10 to pass through the upper imaginary circle and the three lower layer upper hinges 31 to pass through the lower imaginary circle, and arranging the upper imaginary circle and the lower imaginary circle to be parallel and spaced, the three upper layer upper hinges 21 are arranged on the upper layer and the three lower layer upper hinges 31 are arranged on the lower layer, so that the six upper hinges are arranged in two layers, which can alleviate the layout limitation of the hinges and the support chains, facilitate the adjustment of the arrangement position of the upper hinges, and greatly improve the kinematic performance of the space six-degree-of-freedom parallel mechanism 1, so as to adjust the hinge layout according to the processing requirements to fully exert the kinematic performance and obtain larger swing angle output capacity, and the additional torsional freedom can be used to avoid interference and singularity in real time, so as to further improve the kinematic performance and expand the high-quality attitude workspace.

[0038] Therefore, the space six-degree-of-freedom parallel mechanism 1 with large swing angle output capacity provided by the embodiment of the present application has the advantages of high stiffness, strong bearing capacity, good kinematic performance, large swing angle output capacity, etc.

[0039] The space six-degree-of-freedom parallel mechanism 1 with large swing angle output capacity according to the embodiment of the present application will be described below with reference to the accompanying drawings.

[0040] In some embodiments of the present application, as shown in Figures 1-7 The space six-degree-of-freedom parallel mechanism 1 with large swing angle output capacity provided by the embodiment of the present application includes a fixed platform 10, three upper support chains 20, three lower support chains 30, a moving platform 40, and a processing spindle 50.

[0041] Specifically, the upper imaginary circle and the lower imaginary circle are coaxially arranged. In this way, the stress of the fixed platform 10 can be more uniform, and the arrangement of the multiple upper hinges can be facilitated.

[0042] In some embodiments, as shown in Figures 1-4As shown, the three first lower hinges 22 all pass through a first imaginary circle, the three second lower hinges 32 all pass through a second imaginary circle, the first imaginary circle is located above the second imaginary circle and the first imaginary circle and the second imaginary circle are coaxially and parallelly spaced. In this way, the lower hinges connecting the branch chains and the moving platform 40 are also divided into two layers, which further facilitates the improvement of the kinematic performance and the realization of greater swing angle output capacity, and the hinge positions of the fixed platform 10 and the moving platform 40 can be designed and adjusted according to the processing requirements, further avoiding the restriction on the arrangement of the hinges and the branch chains, further improving the kinematic performance of the spatial six-degree-of-freedom parallel mechanism 1 and obtaining a larger high-quality attitude workspace.

[0043] Specifically, as shown in Figures 1-4 , when the upper imaginary circle, the lower imaginary circle, the first imaginary circle and the second imaginary circle are coaxial, the projection of each upper branch chain 20 in the plane where the upper imaginary circle is located is inclined to the radial direction of the upper imaginary circle, and the projection of each lower branch chain 30 in the plane where the lower imaginary circle is located is inclined to the radial direction of the lower imaginary circle. In this way, the two hinges of each branch chain are circumferentially offset and biased, further avoiding the restriction of the branch chain itself on the hinge position, so as to facilitate the adjustment and design of the hinge layout according to the processing requirements to fully exert the kinematic performance and obtain greater swing angle output capacity, and the additional torsional freedom can be used to avoid interference and singularity in real time, thereby further improving the kinematic performance and expanding the high-quality attitude workspace.

[0044] In some embodiments, as shown in Figure 5 and Figure 6 , two of the three first lower hinges 22 are arranged opposite to each other in the radial direction of the moving platform 40, and the other first lower hinge 22 is arranged in the normal direction of the imaginary line connecting the two opposite first lower hinges 22, two of the three second lower hinges 32 are arranged opposite to each other in the radial direction of the moving platform 40, and the other second lower hinge 32 is arranged in the normal direction of the imaginary line connecting the two opposite second lower hinges 32. Specifically, Figure 5 The moving platform 40 is shown moving to a horizontal machining position, and the moving platform 40 can also move to a vertical machining position under the drive of the six branch chains. In this way, the end swing capability of the moving platform 40 can be greatly improved, and the moving platform 40 can be converted between the vertical and horizontal machining modes.

[0045] In some embodiments, as shown in Figure 1 , Figure 2 , Figure 5 and Figure 6As shown in

[0046] In some embodiments, as shown in Figure 3 and Figure 4 the three upper-layer upper hinges 21 and the three lower-layer upper hinges 31 are staggered by a predetermined angle. Specifically, the predetermined angle can be 60 degrees. In this way, the motion accuracy and flexibility of the moving platform 40 can be improved, and interference and singularity can be avoided.

[0047] Specifically, as shown in Figures 1-4 the three first lower hinges 22 and the three second lower hinges 32 are staggered by a specific angle. In some embodiments, as shown in Figure 1 and Figure 2 the specific angle is 60 degrees. In some embodiments, as shown in Figure 3 and Figure 4 the specific angle is 30 degrees. In this way, the motion accuracy and flexibility of the moving platform 40 can be further improved, and interference and singularity can be avoided.

[0048] Figures 1-7 A spatial six-degree-of-freedom parallel mechanism 1 with large swing angle output capability according to some examples of the present application is shown. As shown in Figure 1 , Figure 3 , Figure 5 and Figure 7 Each upper branch 20 and lower branch 30 includes a motor 61 and a lead screw 62, the motor 61 is in transmission connection with the lead screw 62, and the rotation of the motor 61 drives the lead screw 62 to rotate along the central axis and move axially. Specifically, the motor 61 is provided with a nut, and the lead screw 62 is in threaded cooperation with the nut to convert the rotation of the lead screw 62 into axial movement of the lead screw 62. In this way, the telescopic drive of the upper branch 20 and the lower branch 30 can be facilitated.

[0049] Specifically, as shown in Figure 7As shown, each of the upper-layer upper hinges 21 and the lower-layer upper hinges 31 is a Hooke joint and comprises a mounting outer ring 71, a rotating middle ring 72 and a mounting inner ring 73. The mounting outer ring 71 is mounted on the fixed platform 10. The rotating middle ring 72 is rotatably arranged in the mounting outer ring 71. The mounting inner ring 73 is rotatably arranged in the rotating middle ring 72, and the rotation axis of the mounting inner ring 73 is perpendicular to the rotation axis of the rotating middle ring 72 relative to the mounting outer ring 71. The motor 61 is mounted in the mounting inner ring 73. In this way, the upper hinges have two rotation degrees of freedom perpendicular to each other, facilitating the motion of the branch chains relative to the fixed platform 10.

[0050] More specifically, as shown, Figure 7 each of the first lower hinges 22 and the second lower hinges 32 is a Hooke joint and comprises a mounting seat 81, a rotating column 82 and a U-shaped piece 83. The mounting seat 81 is mounted on the movable platform 40. The rotating column 82 is rotatably connected to the mounting seat 81 along a central axis. The U-shaped piece 83 is rotatably connected to the rotating column 82 and has a rotation axis perpendicular to the axial direction of the rotating column 82. The lower end of the lead screw 62 is connected to the U-shaped piece 83. In this way, the lower hinges have two rotation degrees of freedom perpendicular to each other, facilitating the motion of the branch chains relative to the movable platform 40.

[0051] Advantageously, as shown, Figure 2 , Figure 4 and Figure 6 the movable platform 40 has a main shaft sleeve 41, and the machining spindle 50 is fitted in the main shaft sleeve 41. In this way, the installation of the machining spindle 50 can be facilitated.

[0052] Specifically, the spatial six-degree-of-freedom parallel mechanism 1 with large swing angle output capacity can be used as an independent machining device to carry out milling, drilling and other operations on small and medium-sized structural parts, or can be used as a machining module loaded on a movable device to realize efficient machining of large structural parts.

[0053] That is, the spatial six-degree-of-freedom parallel mechanism 1 with large swing angle output capacity according to the embodiments of the present application can alleviate the problem of limited layout of hinges and branch chains, so that the positions of the upper hinges on the fixed platform 10 and the movable platform 40 can be flexibly adjusted according to machining requirements, to improve the kinematic performance of the parallel mechanism, obtain greater swing angle output capacity, and facilitate the use of additional torsional degrees of freedom to avoid interference and singularity in real time, thereby further improving the kinematic performance and expanding the high-quality posture workspace.

[0054] Other configurations and operations of the spatial six-degree-of-freedom parallel mechanism with large swing angle output capacity according to the embodiments of the present application are known to those skilled in the art and will not be described in detail here.

[0055] In the description of the specification, reference to "one embodiment", "some embodiments", "an exemplary embodiment", "an example", "a specific example", or "some examples" means that a particular feature, structure, material, or characteristic being described is included in at least one embodiment or example of the application. The appearances of the phrases "in one embodiment", "in some embodiments", "in an exemplary embodiment", "an example", "a specific example", or "some examples" in various places in the specification are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0056] Although embodiments of the application have been shown and described, it will be appreciated that those skilled in the art can make various changes, modifications, substitutions and alterations thereto without departing from the principles and scope of the application, which are defined by the claims and their equivalents.

Claims

1. A spatial six-degree-of-freedom fully parallel mechanism with large swing angle output capability, characterized in that, The machine comprises: a fixed platform; three upper chains, upper ends of the three upper chains being connected to the fixed platform through upper upper hinges, the three upper upper hinges all passing through an upper imaginary circle; three lower chains, upper ends of the three lower chains being connected to the fixed platform through lower upper hinges, the three lower upper hinges all passing through a lower imaginary circle, the upper imaginary circle and the lower imaginary circle being arranged in parallel and at intervals; a movable platform, lower ends of the three upper chains being connected to the movable platform through first lower hinges, lower ends of the three lower chains being connected to the movable platform through second lower hinges; a machining spindle, the machining spindle being arranged on the movable platform, the three first lower hinges all passing through a first imaginary circle, the three second lower hinges all passing through a second imaginary circle, the first imaginary circle being located above the second imaginary circle and the first imaginary circle and the second imaginary circle being coaxially arranged in parallel and at intervals, when the upper imaginary circle, the lower imaginary circle, the first imaginary circle and the second imaginary circle are coaxial, a projection of each of the upper chains in a plane in which the upper imaginary circle is located is inclined to a radial direction of the upper imaginary circle, and a projection of each of the lower chains in a plane in which the lower imaginary circle is located is inclined to a radial direction of the lower imaginary circle.

2. The spatial 6-DOF fully parallel mechanism with large swing angle output capability according to claim 1, characterized in that, The upper imaginary circle and the lower imaginary circle are coaxially arranged.

3. The spatial 6-DOF fully parallel mechanism with large swing angle output capability according to claim 1, characterized in that, Two of the three first lower hinges are arranged in opposition in a radial direction of the movable platform, and the other first lower hinge is arranged in a normal direction of an imaginary connecting line of the two first lower hinges in opposition, two of the three second lower hinges are arranged in opposition in the radial direction of the movable platform, and the other second lower hinge is arranged in a normal direction of an imaginary connecting line of the two second lower hinges in opposition.

4. The spatial 6-DOF fully parallel mechanism with large swing angle output capability according to claim 1, characterized in that, Imaginary connecting lines of the three upper upper hinges and a center of the upper imaginary circle respectively coincide with projections in a horizontal plane of imaginary connecting lines of the three lower upper hinges and a center of the lower imaginary circle one by one.

5. The spatial 6-DOF fully parallel mechanism with large swing angle output capability according to claim 1, characterized in that, Imaginary connecting lines of the three upper upper hinges and the center of the upper imaginary circle respectively deviate from projections in a horizontal plane of imaginary connecting lines of the three lower upper hinges and the center of the lower imaginary circle by a predetermined angle.

6. The spatial 6-DOF fully parallel mechanism with large swing angle output capability according to claim 1, characterized in that, Each of the upper chains and the lower chains comprises a motor and a screw rod, the motor being in transmission connection with the screw rod and driving the screw rod to rotate along a central axis and move in an axial direction through rotation of the motor.

7. The spatial 6-DOF fully parallel mechanism with large swing angle output capability according to claim 6, characterized in that, Each of the upper upper hinges and the lower upper hinges is a Hooke joint and comprises: an installation outer ring, the installation outer ring being installed on the fixed platform; a rotating middle ring, the rotating middle ring being rotatably arranged in the installation outer ring; an installation inner ring, the installation inner ring being rotatably arranged in the rotating middle ring, an axis of rotation of the installation inner ring relative to the rotating middle ring being perpendicular to an axis of rotation of the rotating middle ring relative to the installation outer ring, the motor being installed in the installation inner ring, Each of the first lower hinges and the second lower hinges is a Hooke joint and comprises: a mounting seat, the mounting seat being installed on the movable platform; a rotating column, the rotating column being rotatably connected to the mounting seat along a central axis; A U-shaped piece is rotatably connected with the rotating column and the rotating axis is perpendicular to the axial direction of the rotating column, and the lower end of the screw rod is connected with the U-shaped piece.

8. The spatial 6-DOF fully parallel mechanism with large swing angle output capacity according to claim 1, characterized in that, The movable platform has a main shaft sleeve, and the machining spindle is fitted in the main shaft sleeve.

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