Low non-repeatable runout rotation mount

Abstract

The rotation device (10) provides rotation of the position of interest about the axis of rotation and includes a first socket and a second socket, each having three contact points distributed about the axis of rotation. The contact points of each socket may be on a convex surface, and a spindle assembly (12) is held between the sockets facing each other along the axis of rotation. The spindle assembly (12) has a first convex surface centered about the axis of rotation that contacts the contact point of the first socket and a second convex surface that contacts the contact point of the second socket. The spindle assembly (12) also has a drive shaft (20) aligned with the axis of rotation. The linear stages (34, 36, 38) may be used to provide adjustment in one or more mutually perpendicular directions. Another embodiment uses a spindle (80) assembly (42) with two curved contact surfaces that are not aligned with the axis of rotation but contact respective curved surfaces adjacent the axis of rotation.

Description

[Technical field]

[0001] The present invention relates generally to the field of precision rotation components, and more specifically to rotatable sample supports. [Background technology]

[0002] 2. Description of Related Art In various applications, there is a need to rotate a component very precisely around a given axis while minimizing any displacement of the component, both radially or axially relative to the axis of rotation. Generally, motors and other drive mechanisms can provide rotation for mechanical actuation, but provide rotation within a certain tolerance regarding radial and axial displacement during rotation. That is, the rotated component remains approximately centered about the axis of rotation, but some radial or axial deviation during rotation is considered acceptable and usually has a negligible effect on the performance of the system. However, in a high precision environment, such tolerances are considered unacceptable since they would fundamentally impede the operation of the system.

[0003] An example of a system in which the rotation of a component must be performed with minimal radial and axial deviations is the examination of a sample using X-ray or electron diffraction. In such a system, a sample mounted on a goniometer is irradiated with an energy beam at a series of different rotation angles, allowing a three-dimensional characterization of the sample through the resulting diffraction images. However, due to the very small size of the sample, it is particularly difficult to keep the sample in the beam path. If a common center point of the sample is not maintained for the different rotation angles of the goniometer, or if a feature of interest on the sample is not at the center of all rotations, the sample feature will, upon rotation of the sample, precess through a finite volume, known as the "sphere of confusion", which represents the smallest spherical range covering all possible positions of an infinitely small object at all possible rotation angles. Minimizing the sphere of confusion necessarily requires minimizing the displacement of the sample due to the properties of the rotatable sample support, in particular the radial displacement relative to the direction of the irradiating energy beam. Some diffraction measurement systems require such high precision in the rotation of their samples that unintended displacements that may move regions of interest of the sample out of the beam path may need to be limited to the micron or submicron level. With such precision, even slight changes in the dimensions of rotating components or the presence of dust or lubricants can detrimentally increase the sphere of confusion.

[0004] When evaluating such radial or axial displacements, awareness is given to whether the displacement is repeatable or non-repeatable. Repeatable displacements, also known as repeatable runout, are an indication of persistent characteristics of a system that repeat with every revolution about a central axis. Such characteristics are therefore predictable and can be corrected using high precision linear stages, which achieve orders of magnitude more precise displacement than rotary devices. Non-repeatable displacements are deviations that do not reoccur and therefore cannot be compensated for except by real-time correction. Repeatable and non-repeatable displacements can occur in both radial and axial directions relative to a rotating axis. When operating a high precision rotating system, minimizing any displacement is important to the performance of the system. Summary of the Invention [Problem to be solved by the invention]

[0005] According to the present invention, a rotation device is provided that allows for precise rotation of a target area about an axis of rotation. [Means for solving the problem]

[0006] Summary of the Invention In a first embodiment of the invention, the rotating device includes a first and a second socket between which the spindle assembly is arranged. Each socket has three contact points distributed around the axis of rotation, the three contact points of the first socket facing a first axial direction relative to the axis of rotation, while the three contact points of the second socket facing a second axial direction opposite to the first axial direction relative to the axis of rotation. The first socket has a first axial position on the axis of rotation, while the second socket has a second axial position on the axis of rotation, and the target position is between the first axial position and the second axial position.

[0007] The spindle assembly has a first convex surface centered about the axis of rotation and in contact with the three contact points of the first socket. The spindle assembly also has a second convex surface centered about the axis of rotation and in contact with the three contact points of the second socket, such that the spindle assembly is held between the first and second sockets. A drive shaft of the spindle assembly is aligned with the axis of rotation and extends away from the first and second convex surfaces of the spindle assembly to an axial location on the axis of rotation that is on a side of the first socket away from the target location. Thus, the drive shaft of the spindle assembly can be rotated to rotate the spindle assembly relative to the first and second sockets.

[0008] The three contact points of the first and second sockets may be located on the convex surfaces of their respective sockets, although it is also possible to use a substantially flat surface with the sockets providing the three contact points. In an exemplary version of this embodiment, the first socket comprises a plurality of first socket balls, each of which provides one of the three convex surfaces of the first socket, and the first socket balls are held in the housing of the first socket, such as by a press fit. Similarly, the second socket may have a plurality of second socket balls, each of which provides one of the three convex surfaces of the second socket, and the second socket balls may be of a common size and material with the first socket balls. The material may be a hardened material, such as a ceramic, that provides a relatively low degree of friction, wear, and deflection. Typically, the contacting material will have a Mohs hardness of less than 9.0 and a surface finish of Ra 0.02 (micrometer) or better.

[0009] In an exemplary embodiment, the first and second convex surfaces of the spindle assembly may be formed by first and second spindle balls axially disposed on either side of a location of interest that may include a sample support for a sample to be analyzed. The first and second sockets may be mounted on a linear stage configured to allow adjustment of the position of the first and second sockets and the spindle assembly in a first adjustment direction. The linear stage may be one of a plurality of linear stages to which the first and second sockets are connected and that allow adjustment of the position of the first and second sockets and the spindle assembly in a plurality of mutually orthogonal directions. A chassis for the rotation device is also provided, the chassis may include a resilient mechanism biased to urge the first and second sockets toward each other and that allows for small changes in the relative axial position of the first and second sockets while the spindle is rotated. Rotation of the spindle assembly may be provided by a motor that rotates a drive shaft of the spindle assembly.

[0010] In another embodiment of the invention, the spindle assembly is provided with two partially spherical contact surfaces, but the support structures they contact are located to the side of the axis of rotation, rather than along the axis of rotation. The first support structure has at least two contact points located adjacent a first axial location on the axis of rotation and evenly distributed around a first radial direction perpendicular to the axis of rotation. The second support structure has at least two contact points located adjacent a second axial location on the axis of rotation and evenly distributed around a second radial direction perpendicular to the axis of rotation. The contact points on the first and second support structures may be located on curved surfaces that may take different shapes. In one version of this embodiment, at least one of the first and second support structures may be a socket having three convex surfaces evenly distributed around the first radial direction, and the socket may use three socket balls, each of which provides one of the three convex surfaces. In another version of this embodiment, at least one of the first and second support structures can be two parallel rods, each of which provides one of two outwardly curved surfaces.

[0011] In this embodiment, the spindle assembly has first and second partially spherical surfaces, each rotationally symmetric about an axis of rotation. The first partially spherical surface contacts a contact point of a first support structure and the second partially spherical surface contacts a contact point of a second support structure. The spindle assembly has a drive mechanism by which the spindle assembly can be rotated.

[0012] This embodiment also provides a retention mechanism that maintains the first and second partially spherical surfaces of the spindle assembly in contact with the first and second support structures, respectively. The retention mechanism may include a rolling bearing through which the spindle assembly passes axially and that may be spring-loaded to provide a resilient force urging the spindle assembly toward the first and second support structures. When the first partially spherical surface contacts a support structure having two contact points, such as a pair of parallel rods, movement of the first partially spherical surface is constrained in a radial direction perpendicular to the axis of rotation by the action of the retention mechanism. When the first partially spherical surface contacts a support structure having three contact points, movement of the first partially spherical surface is constrained in both the axial and radial directions by the action of the retention mechanism.

[0013] As with other embodiments, the rotation apparatus may include one or more linear stages to which the sockets and support structures are attached. The linear stages are configured to allow adjustment of the position of the first and second support structures and the spindle assembly in a first adjustment direction. Other linear stages may also be included to allow adjustment of the position of the first and second support structures and the spindle assembly in other directions perpendicular to the first adjustment direction. A sample support for a sample to be analyzed in a diffractometer or other measurement instrument may be at the location of interest, and a motor may be used to rotate the spindle assembly.

[0014] The rotation device may also include a chassis to which the first and second support structures are mounted, the chassis including a resilient mechanism, such as a leaf spring, that flexes to accommodate slight changes in the relative axial positions of the first and second sockets as the spindle assembly is rotated. In one version of this embodiment, the first and second partially spherical surfaces each have a convex portion on a side facing away from the position of interest, each of which contacts a respective rigid flat surface during rotation of the spindle assembly to limit axial movement of the spindle assembly. In this version, at least one of the rigid flat surfaces has a resilient connection to the chassis, the resilient connection allowing for slight changes in the relative axial positions of the rigid flat surfaces as the spindle assembly is rotated. [Brief description of the drawings]

[0015] [Figure 1] 1 is a perspective view of a rotation device according to the present invention; [Diagram 2] 2 is a perspective view of an isolated spindle assembly of the rotating device shown in FIG. 1, in a reversed orientation compared to FIG. 1; [Diagram 3] FIG. 2 is a front view of one of the two trihedral sockets of the rotating device shown in FIG. 1. [Figure 4] FIG. 4 is a perspective view of the tripod socket shown in FIG. 3. [Diagram 5] FIG. 2 is a perspective view of the rotational device of FIG. 1 mounted on a chassis having three linear stages. [Figure 6] FIG. 13 is a perspective view of an alternative embodiment of the present invention in which a spindle assembly having two partially spherical surfaces is spring-loaded into contact with a trihedral socket and a pair of stiffened support rods. [Figure 7] FIG. 7 is a perspective view of an alternative embodiment of the invention that uses a spindle assembly similar to that of FIG. 6, but in which each of the partially spherical surfaces is in spring-loaded contact with a trihedral socket. [Figure 8]FIG. 13 is a perspective view of an alternative embodiment of the present invention having a spindle with partially spherical ends, each end resting against a hardened surface, and each end supported by a pair of hardened support rods. [Figure 9] 13A-13C are perspective views of alternative embodiments of sockets used in various embodiments of the present invention, where a flat surface of the socket provides a contact point with a cooperating spindle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Detailed Description A perspective view of a rotation device 10 according to the invention is shown in FIG. 1. The device is intended for use at low rotational speeds, such as with stop-start rotation of samples mounted in an analytical system, and does not use rolling or sleeve bearings, avoiding what might otherwise be a significant source of non-repetitive runout. Instead, a spindle assembly 12 with hardened balls 14 at both ends is mounted between two trihedral sockets 16, each socket containing three precision-machined contact balls 17 that establish three contact points between the socket 16 and a respective engaged spindle ball 14. A sample holder 18 is placed in the central region of the spindle assembly 12, and a sample on the sample holder will be rotated with the rotation of the spindle assembly. During rotation, the trihedral socket 16 remains stationary, while the rotation of the spindle assembly is controlled by a drive shaft 20, which may be driven by, for example, a stepper motor or a piezoelectric motor, extending through a housing 22 of the proximal socket 16.

[0017] An isolated view of the spindle assembly 12 is shown in Figure 2 (in a reversed orientation compared to Figure 1). The components of the spindle assembly are aligned along an axis of rotation 24, with the distal end of the drive shaft 20 fixed to the center point of the proximal of the spindle assembly's two balls 14. In the embodiment shown, each ball 14 is rigidly connected to a cylindrical flange 26, which in turn is rigidly connected to the sample support 18 between the flanges 26. The balls 14 and flanges 26 are also aligned to ensure that the entire spindle assembly rotates uniformly about axis 24, although in the exemplary embodiment, the drive shaft 20 is sufficiently flexible that slight misalignment would not be an issue.

[0018] In this embodiment, each ball 14 is a perfect sphere, making it easier to manufacture and / or supply. Because of the flexibility of precision manufacturing of such balls, the contact between the ball 14 of the spindle assembly and the ball 17 of the socket 16 is unlikely to cause axial runout during rotation, and any such axial runout tends to be a repeatable runout that is relatively easy to correct using a linear stage (described further below). An advantageous material for the balls is ceramic, particularly silicon nitride, which is widely available in grades 3 and 5. Such materials exhibit particularly low friction and resilience. Overall, the materials used for the spindle assembly and any support structure should have a low coefficient of thermal expansion to minimize sensitivity to temperature. In addition to silicon nitride ceramic, a possible material choice could be Invar®, although ceramic may be preferred if the invention is to be used in a system where the presence of metal would impede operation of the system. However, those skilled in the art will recognize that as an alternative to ball 14, a surface that is only partially spherical (in the vicinity of the contact points with the respective sockets) may be used, and that ball 14 and each flange may even be a single, integral component, so long as the device maintains three contact points between the partial spherical surfaces and the corresponding sockets.

[0019] A front view of one of the trihedral sockets along the axial direction is shown in Figure 3. The socket housing 22 is generally annular with three curved recesses 28 equally spaced along its inner surface. Each of these recesses receives one of the socket's three contact balls 17. The outer surface 30 of the housing prevents axial movement of the contact balls 17 when pressure is applied by the spindle assembly, and firm contact is maintained at the three contact points between the contact balls 17 and adjacent spindle balls 14. In this embodiment, the press fit of the balls within the housing prevents them from moving when the spindle is rotated.

[0020] As shown in FIG. 3, the recess 28 of the housing has a nominal inner radius that is slightly smaller than the radius of the contact ball, so that when the ball 17 is pressed into the recess 28, the socket housing flexes, allowing the ball to be fully secured within the recess. The resilience of the socket housing 22 then provides pressure on the outside of the ball, preventing it from moving relative to the housing 22. In another embodiment, the radius of the ball could be matched to the inner radius of the recess 28, and optionally, in either embodiment, an adhesive could be used to secure the ball to the socket housing 22. Also shown in FIG. 3 is the central hole 32 in the outer surface 30 that receives the drive shaft 20 of the spindle assembly 12 and is aligned with the axis of rotation 24. In FIG. 4, a perspective view of one of the housings 22 is shown, showing the relative thickness in the axial direction of the housing, which must be sufficient to accommodate the contact ball 17.

[0021] FIG. 5 shows the rotational device 10 mounted on a chassis 35 having three linear stages 34, 36, 38, each movable in three mutually orthogonal directions. In the embodiment shown in FIG. 5, the linear stage 34 can be adjusted along a rotational axis, defined here as the "y-direction", and the linear stage 36 can be adjusted along an axis perpendicular to the y-direction, defined here as the "x-direction". The third linear stage 38 can move the device in the "z-direction", which is perpendicular to the x- and y-directions and, in this embodiment, the direction of an illumination beam (indicated by arrow 37), such as an X-ray or electron beam of a diffractometer. In such an embodiment, the system is less sensitive to errors in the z-direction, especially if the beam is collimated. For this reason, another embodiment of the system may have only linear stages 34, 36, if compensation for the direction of the beam 37 is deemed unnecessary.

[0022] The linear stages 34, 36, 38 help compensate for repeatable runout that may occur despite tight system tolerances and may also be used to position the sample. Repeatable runout errors are displacements that occur with each revolution of the spindle and are therefore predictable. The primary error of concern is radial runout, but axial runout errors may also occur. Because of the predictability of repeatable runout errors, the linear stages 34, 36, 38 may be controlled using software or hardware routines that adjust their linear position in the x, y, or z directions by an amount equal and opposite to the predicted error, based on the rotation angle of the spindle. It is also possible to use the linear stages 34, 36, 38 to compensate for non-repeatable runout errors, but because they are less predictable, the control of the stage must be responsive to a means of detecting deviations in the position of the sample holder. For example, when used in a diffractometer, detected errors in the diffraction pattern introduced by movement along the Z axis may be compensated for using the linear stages 38. Depending on the application, it is possible to use both coarse and fine linear stages in any of three orthogonal directions, allowing more precise compensation of run-out errors.

[0023] Also shown in Figure 5 is the use of spring loading of the system in the axial direction. In this embodiment, the two trihedral sockets 22a, 22b are identical and, when assembled, each socket is fixed to the chassis support below it. However, the support below socket 22b consists of two parts interconnected by a leaf spring 39, which is biased axially towards the interior of the assembly, so that socket 22b exerts a force on the spindle in the direction of socket 22a. The leaf spring 39 thereby provides preload for the spindle / socket assembly while remaining flexible enough to compensate for axial displacements that may be caused by thermal expansion / contraction, axial runout, etc.

[0024] Rotating systems often use lubricants to reduce friction, but in systems requiring sub-micron accuracy, lubricants can be a source of non-repeatable runout errors. Thus, in this embodiment, lubricants are preferably avoided. However, low rotational speed systems are less susceptible to heat buildup due to friction, and because the present invention relies not only on precision point contact between rotating components, but also on hardened balls as the contact surface, excessive friction and associated heat buildup is avoided. The lack of lubricants also allows the device to operate in a high vacuum environment. With selected materials, the device can be operated in a range of temperatures from below zero up to several hundred degrees Celsius. The runout compensation tables or algorithms used to compensate for runout errors in the system may also include compensation for system errors caused by temperature changes.

[0025] In the embodiment shown, a 12.7 mm diameter Grade 5 silicon nitride ball was used with a spindle assembly having an overall length of 3.8 cm, measured from the outside of one ball to the outside of the other. The balls at both ends of the spindle assembly were the same size as the balls in the trihedral socket, although the diameter of the spindle ball or socket ball could be altered to accommodate a particular application. The length of the spindle could also be adapted to the application, but generally a longer spindle would reduce runout error.

[0026] Another embodiment of the present invention is shown in FIG. 6. In this embodiment, a rotation device 40 uses a spindle assembly 42 with two rounded portions 44, 46 centered about a rotation axis 48. The rounded portions are partially spherical and each contacts an underlying support structure. In particular, the rounded portion 44 rests on a trihedral socket 50, which in turn is mounted on a chassis 52. The trihedral socket 50 may have the same structure as the trihedral socket shown in FIGS. 3 and 4, but does not intersect with the rotation axis 48. Rather, the three balls of the trihedral socket reside on one side of the rotation axis 48, providing low-friction support for the spindle. The rounded portion 44 simultaneously contacts each ball of the trihedral socket 50 and rests in the space formed between them. This positioning of the rounded portion 44 axially constrains the spindle assembly 42 while allowing low-friction rotation.

[0027] Since the axial position of the spindle assembly 42 is constrained by the contact of the rounded portion 44 with the trihedral socket 50, it is only necessary to constrain the rounded portion 46 radially. Thus, this embodiment uses a pair of parallel rods 54 that simultaneously contact the rounded portion 46. In this embodiment, the rods are cylindrical, but those skilled in the art will understand that the rods 54 do not need to be perfectly cylindrical, provided that the surfaces that contact the rounded portion 46 are curved and the contact between each rod 54 and the rounded portion 46 is limited to one point. The socket 50 and the pair of rods 54 are placed adjacent to the axis of rotation 48, but the respective contact points are evenly distributed around a radial direction perpendicular to the axis of rotation. The three contact points of the socket 50 are evenly distributed around the radial direction 51, and the two contact points of the pair of rods 54 are evenly distributed around the radial direction 53.

[0028] To maintain contact between the spindle assembly 42 and the trihedral socket 50 and cylindrical rod 54, a spring-loaded rolling bearing 56 is provided that restrains radial movement of the spindle assembly 42. A bracket 58 fits over the bearing 56 and is secured by two springs 60 connected to the chassis 52. The springs 60 are under tension and urge the bearing, and thus the spindle assembly 42, towards the chassis 52, thus maintaining contact between the rounded portion 44 and the trihedral socket 50, and between the rounded portion 46 and the pair of rods 54. The bearing provides sufficient radial flexibility to have little or no effect on the radial runout of the spindle assembly 42, which rests in firm contact with the trihedral socket 50 and rods 54.

[0029] The embodiment shown in FIG. 7 uses essentially the same spindle assembly 42 as that of FIG. 6, but it is shown in a different orientation relative to that of FIG. 6. Similarly, the bearings 56, brackets 58, and springs 60 are identical, but the machine chassis and supports are different. In FIG. 7, the partially spherical portions 44, 46 of the spindle assembly 42 each rest on a socket similar to the socket 50 of FIG. 6. Because these trihedral sockets each limit axial movement, the system also uses axial spring loading to accommodate any slight axial variations during rotation. Socket 50a is fixed to the machine chassis 70, while socket 50b is not, but instead is connected to two leaf springs 72a, 72b, each of which is independently fixed to the chassis 70.

[0030] The leaf springs 72a, 72b in the embodiment of Figure 7 are fixed on opposite sides of the socket 50b in a position that maintains the socket elevated above the surface of the chassis 70. That is, the socket 50b is suspended by the springs 72a, 72b above the chassis 70 and is therefore free to move in the axial direction defined by the spindle assembly 42. The flexibility of the leaf springs 72a, 72b is selected relative to the tension of the spring 60 (which maintains contact between the spindle assembly and the socket) such that relative axial displacement of the spindle assembly portions 44 and 46 during rotation will result in bending of the leaf springs 72a, 72b before any interruption of contact between the spindle portions 44 and 46 and their respective sockets 50a, 50b can occur. Thus, the suspension of socket 50b by leaf springs 72a, 72b enables any slight axial errors in the spindle assembly to be absorbed by the support arrangement, eliminating the risk of radial misalignment of one of the part-spherical portions that might otherwise occur.

[0031] Another alternative embodiment of the invention is shown in FIG. 8. In this version of the invention, the spindle 80 has two partially spherical portions 82a and 82b and is supported by two pairs of cylindrical rods 84a, 84b similar to the cylindrical rods 54 of the embodiment of FIG. 6. However, in FIG. 8, it is not just one of the partially spherical portions 82a, 82b of the spindle 80 that is supported by a cylindrical support, but both of them. As in the embodiments of FIGS. 6 and 7, a spring-loaded rotary bearing 86 is provided that prevents radial movement of the spindle 80. A bracket 88 fits over the bearing 86 and is secured by two springs 90 connected to the chassis of the device. The springs 90 are under tension and urge the bearing, and thus the spindle 80, towards the chassis, thus maintaining contact between the rounded portions 82a, 82b and the rod pairs 84a, 84b.

[0032] Because the rods of the rod pairs 84a, 84b are aligned parallel to the axis of rotation, they prevent radial movement of the spindle assembly, but provide no such restriction in the axial direction. Thus, the rounded portions 82a, 82b at each axial end of the spindle 80 assembly are contacted by respective hardened stops 92a, 92b, which provide a hard, flat, low-friction surface against which a corresponding one of the rounded portions 82a, 82b of the spindle assembly presses. Because the contact surfaces of the hardened stops 92a, 92b are flat, there is a single point of contact between each rounded portion 82a, 82b and its respective stop 92a, 92b. Thus, the hardened stops axially restrain the spindle 80 as it is rotated.

[0033] In the embodiment of FIG. 8, the hardened stop 92b is rigidly attached to a side wall 94b of the rotating device chassis. However, at the opposite end, the side wall 94a is not fixedly attached to the chassis, but rather is connected to the chassis via a leaf spring 96. The leaf spring 96 is axially flexible, and any slight changes in the effective length of the spindle assembly 80 will be accommodated by the flexing of the spring 96. Because the spindle assembly terminates in rounded ends 82a, 82b that press against the hardened stops 92a, 92b, in this embodiment, there is no drive shaft that extends axially beyond the spindle 80. As such, a drive motor 98 is positioned between the rounded ends 82a, 82b and is used to rotate the spindle as needed.

[0034] In each of the embodiments described above, the socket or cylindrical rod that contacts the spherical or partially spherical surface of the spindle assembly is curved outwardly and the contact is between opposing curved surfaces. However, the contact could also be between a curved surface and a flat surface, and the contact would also be at a single point and therefore relatively low friction. For example, the trihedral socket used in any of the above embodiments could be replaced with the socket 100 shown in FIG. 9, which would still provide contact at three contact points between the spindle and the socket.

[0035] While the sockets of the previous embodiments use convex surfaces to contact the spindle at certain points, the socket 100 of FIG. 9 has flat surfaces that engage one of the curved surfaces of the spindle according to the present invention. These flat surfaces could be integral parts of a larger socket component or even flat portions of a socket having a single integral structure, but the socket of FIG. 9 uses inserts 102 that are rigidly fixed to the support portion of the socket. The use of such inserts simplifies preparation of the insert surface that contacts the curved surface of the spindle, since the insert surface should be as flat and smooth as possible to minimize friction during rotation of the spindle. Similar hard materials could be used for the flat surfaces as described above.

[0036] In the embodiment shown, the insert 102 is positioned at a relative angular position of 120° around the circumference of the socket, but other relative positions of the surfaces may be used as long as the surfaces constrain radial movement of the spindle as it rotates. Similarly, the pitch of the surfaces is selected to provide sufficient restriction of such radial movement by the spindle, although one skilled in the art will recognize that such design details may be selected depending on the particular application and the respective contact forces between the spindle assembly and the surfaces. It is also possible to use more than two surfaces, but typically additional surfaces would increase positional instability between the spindle assembly and the socket. It is not necessary for the surfaces to be perfectly flat, so long as each surface has a single point of contact with the spindle.

Claims

1. 1. A rotation device for precise rotation about an axis of rotation of a position of an object having a predetermined axial position on said axis, said rotation device comprising: a first socket having three contact points distributed around the axis of rotation and oriented in a first axial direction relative to the axis of rotation, the first socket having a first axial position on the axis of rotation; a second socket having three contact points distributed around the axis of rotation and facing in a second axial direction opposite to the first axial direction with respect to the axis of rotation, the second socket having a second axial position on the axis of rotation, the target position being located between the first axial position and the second axial position; a spindle assembly having a first convex surface centered about the axis of rotation and contacting the three contact points of the first socket, and a second convex surface centered about the axis of rotation and contacting the three contact points of the second socket, the spindle assembly being held between the first and second sockets, the spindle assembly further having a drive shaft extending away from the first and second convex surfaces of the spindle assembly, via which the spindle assembly may be rotated.

2. 2. The rotating device of claim 1, wherein the three contact points of the first socket are located on three substantially flat areas that contact the first convex surface of the spindle assembly.

3. 2. The rotating device of claim 1, wherein the three contact points of the first socket are disposed on three convex surfaces that contact the first convex surface of the spindle assembly.

4. 4. A rotating device according to claim 1 or 3, wherein at least one of the first socket and the second socket comprises three socket balls, each socket ball providing one of the three contact points of the first socket.

5. 5. The rotating device of claim 4, wherein the three socket balls are retained within a housing of at least one of the first socket and the second socket.

6. 6. The rotating device of claim 5, wherein the three socket balls are retained within a housing of at least one of the first socket and the second socket by a press fit.

7. 7. A rotating device according to claim 1, wherein the first and second convex surfaces of the spindle assembly are formed by first and second spindle balls arranged axially on either side of the target position.

8. 8. A rotating device according to any one of the preceding claims, characterized in that the location of interest comprises a sample support for a sample to be analysed in a measuring instrument.

9. 9. A rotation device according to claim 1, further comprising a linear stage to which the first socket and the second socket are mounted, the linear stage being configured to enable adjustment of the positions of the first and second sockets and the spindle assembly in an adjustment direction.

10. 10. A rotating device according to claim 1, further comprising a chassis to which the first socket and the second socket are mounted, the chassis including a resilient mechanism biased to urge the first and second sockets towards each other and allowing the relative axial position of the first and second sockets to change while the spindle assembly is rotated.

11. 1. A rotation device for precise rotation about an axis of rotation of a position of interest having a predetermined axial position on the axis of rotation, said rotation device comprising: a first support structure disposed adjacent a first axial location on the axis of rotation and having at least two contact points evenly distributed about a first radial direction perpendicular to the axis of rotation; a second support structure disposed adjacent a second axial location on the axis of rotation and having at least two contact points evenly distributed around a second radial direction perpendicular to the axis of rotation, the second support structure being disposed between the first axial location and the second axial location; a spindle assembly having a first partial spherical surface that is rotationally symmetric about the axis of rotation and that contacts the contact point of the first support structure, and a second partial spherical surface that is rotationally symmetric about the axis of rotation and that contacts a contact point of the second support structure; a retention mechanism for maintaining the first and second partial spherical surfaces of the spindle assembly in contact with the first and second support structures, respectively.

12. 12. The rotating device of claim 11, wherein the first support structure has two surfaces that contact the first partial spherical surface of the spindle assembly at the two contact points of the first support structure, and the two surfaces prevent movement of the first partial spherical surface of the spindle assembly in a radial direction perpendicular to the rotation axis by the action of the retention mechanism.

13. 13. A rotating device according to claim 11 or 12, wherein at least one of the first and second support structures comprises a socket having three convex surfaces evenly distributed around the first radial direction, each of the convex surfaces providing one of the contact points of the support structure.

14. 14. A rotating device according to claim 13, wherein said socket comprises three socket balls, each of said socket balls providing one of said three convex surfaces of said socket.

15. 14. The rotating device of claim 13, further comprising a chassis to which the first and second support structures are mounted, the chassis including a resilient mechanism that allows small changes in the relative axial position of the first and second sockets as the spindle assembly is rotated.

16. 16. A rotating device according to any one of claims 11 to 15, characterized in that at least one of the first and second support structures includes two parallel rods, each of which provides one of the two contact points of the support structure.

17. 17. A rotating device according to claim 11, wherein the retention mechanism comprises a rotary bearing through which the spindle assembly passes along the axial direction.

18. 18. The rotating device of claim 11, wherein the retention mechanism is spring loaded to provide a resilient force urging the spindle assembly in a direction toward the first and second support structures.

19. 19. A rotating device according to any one of claims 11 to 18, wherein the first and second partial spherical surfaces of the spindle assembly each have a convex portion on a side facing away from the target position, each of the convex portions contacting a respective rigid flat surface of a hardened stopper during rotation of the spindle assembly to limit axial movement of the spindle assembly.

20. 20. The rotation device of claim 19, further comprising a chassis to which the first and second support structures and the rigid planes are mounted, at least one of the rigid planes having a resilient connection to the chassis that allows for small changes in relative axial position of the rigid planes as the spindle assembly is rotated.

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