Drive system for rotary shafts, which are to be driven eccentrically, in a vacuum chamber having at least one feedthrough

Abstract

The invention relates to a drive system for rotary shafts, which are to be driven eccentrically, in a vacuum chamber (6) which comprises at least one feedthrough (3). The drive system primarily comprises at least one bellows (2) having two ends, wherein a first end is open and can be arranged in a vacuum-tight manner in a feedthrough (3) of a vacuum chamber (6), and wherein the bellows (2) can be folded at least in one axis, and wherein the bellows (2) are closed at a second end. The drive system further comprises a motor (5) which indirectly or directly rotates a screw nut (4), and to a lead screw (1) which is parallel to the fold axis of the bellows (2) and is linked to the bellows (2) on a first side of the closed end of the bellows (2), and wherein the screw nut (4) is arranged on the lead screw (1). The drive system also comprises a coupling rod (8) which is linked at a first end to a second side of the closed end of the bellows (6), and the coupling rod can be linked at a second end to a rotary shaft (9) which is to be driven eccentrically.

Description

[0001] Designation

[0002] Drive system for eccentrically driven rotary axes in a vacuum chamber with at least one feedthrough

[0003] Technical area

[0004] The invention relates to a drive system for rotating optics in a vacuum, such as is used, for example, for monochromators for X-ray radiation at synchrotron radiation sources.

[0005] State of the art

[0006] The optics that are rotated by the drive systems concerned by the invention relate in particular to those that are used in monochromators, such as plane grating monochromators, and are known from the prior art, for example from article 1 by F. Senf et al. (A plane-grating monochromator beamline for the PTB undulators at BESSY II; Journal of Synchrotron Radiation Vol. 5, 1998, pp. 780-782). In the monochromators, the light or X-rays are diffracted by means of a plane grating or crystal for diffraction, thereby achieving monochromatization. Monochromatization here is understood to mean a restriction in the spectral width AA around a specific wavelength A for which the diffraction conditions at the plane grating are met. The quality of the monochromatization depends, among other things, on the achievable spectral width of the diffracted X-ray beam.By means of the line density N (lines / mm) of the plane grating or the grating spacing in a crystal, a specific wavelength A can be selected by setting a corresponding total deflection angle 29 on the mirror or crystal and, in the case of plane grating monochromators, additionally by changing the diffraction angle ßö of the incident beam, whereby this beam is monochromatized for a diffraction order “m” in the further beam path. A = (sin.

[0007] By using a plane mirror, the light is shifted in height in the further beam path.

[0008] The monochromators are typically housed in an evacuable housing with entrance and exit windows or slits for the radiation. Each monochromator is equipped with a drive system that allows them to rotate around an axis perpendicular to the incident beam and located in the plane of the plane grating or offset parallel to the plane mirror. To record the currently set angles of the drives, they are equipped with angle decoders, which can also be provided with absolute scales. The rotation of the axes of rotation of the monochromators, particularly those of the type covered by the invention, is eccentric, and the rotation typically occurs within an angular range that does not encompass complete rotations, usually only a few degrees.

[0009] In addition to the alignment or adjustment of the plane grating and the plane mirror to each other, to the beam and any other optics in the beam path or target locations, as well as the resolution to be achieved, the quality of the monochromatization also depends on the accuracy (also referred to as correctness) of the angle settings with which a total deflection angle 26 through the mirror or a specific diffraction angle β through the plane grating, for setting a specific wavelength of monochromatization, can be set on the plane grating and the plane mirror. During operation, a value for the diffraction angle and thus, via the grating equation (1), a specific wavelength or energy is assigned through calibration to a motor position of a drive of the plane grating or plane mirror. The accuracy is then the degree of agreement between the displayed (read) and the "correct value."In addition to accuracy, the reproducibility and achievable resolution of the position control are also crucial for the quality of a monochromator.

[0010] Drive systems for rotating optics in a vacuum are also known in various designs from the state of the art. O. Müller et al. (Quick scanning monochromator for millisecond in situ and in operando X-ray absorption spectroscopy, Review of Scientific Instruments, Vol. 86, 2015, p. 093905-1 - 8) presents a drive system for rotating the optics of a monochromator in which the drive of a motor located outside the vacuum chamber of the monochromator is transmitted into the vacuum chamber and onto the rotation axis of the monochromator via a coaxial rotary feedthrough with an inner and outer shaft. This type of feedthrough is known to be suitable for ultra-high vacuum ranges of p < 10'. 9mbar are unsuitable, as they sometimes break the vacuum, which is undesirable. The monochromator's optics, in this case pairs of crystals, are rotated together around an axis.

[0011] Another type of drive for rotating the optics of a monochromator is presented in 5. Narayanan et al. (Initial Characterization and Design of an UHV-Compatible Artificial Channel-Cut Monochromator, AIP Conference Proceedings, Vol. 879, 2007, pp. 911-914), in which the rotational motion of the axis that rotates the crystal pairs that serve as the monochromator's optics is generated by linear drives that drive a rotary shaft. Here, the drive components are largely housed within the monochromator's vacuum chamber, resulting in unfavorably large dimensions of the chamber.

[0012] In M. Ramanathan et al. (Multipurpose monochromator for the Basic Energy Science Synchrotron Radiation Center Collaborative Access Team beamlines at the Advanced Photon Source x-ray facility, Review of Scientific Instruments, Vol. 66, 1995, pp. 2191-2194) the rotation axis of the optics of the monochromator is driven directly by an axis rotation drive in the form of a goniometer, which is arranged in a connected vacuum chamber.

[0013] Another disadvantage of the motor, which acts directly on an axis for rotation, is the low resolution of the angles of rotation A0 and A / ? and the associated resolution of the monochromatizable wavelengths, as can be seen from can be assessed.

[0014] (Results from the relationship for the resolution

[0015] All formulas are explained and derived in detail in the article by F. Eggenstein et al. "New UHV angle encoder for high resolution monochromators, a modern spare part for the Heidenhain UHV RON 905" (Nuclear Instruments and Methods in Physics Research, A, 2021, 165645 1-8).

[0016] A solution for driving the rotation of the optics of a monochromator, also with a linear drive, which here acts on the axis of rotation, is shown by MR Howells (Plane Grating Monochromators for Synchrotron Radiation, Nuclear Instruments and Methods, Vol. 177, 1980, pp. 127-139).

[0017] Another alternative method for a drive to rotate the optics of a monochromator is to use a linear drive to eccentrically deflect the mount of an optic and thus rotate the optics about an axis, as disclosed, for example, in O. Schwarzkopf et al. (High-resolution constant length Rowland circle monochromator at BESSY, Review of Scientific Instruments, Vol. 69, 1998, pp. 3789 - 3793).

[0018] A monochromator, which would be particularly suitable for use with a drive system of the generic type according to the invention, is disclosed in DE 3045931 A1. A planar grating monochromator operating with grazing incidence is disclosed, which comprises a planar diffraction grating, a planar front mirror projecting a beam of wave radiation to be spectrally dispersed onto the diffraction grating with grazing incidence, an exit slit, a concave mirror for focusing the radiation dispersed by the diffraction grating onto the exit slit, and an adjustment mechanism coupled to the front mirror and the diffraction grating, which effects a predetermined adjustment of the angle of incidence and reflection of the radiation with respect to the plane of the diffraction grating depending on the wavelength of the dispersed radiation focused by the concave mirror onto the exit slit, producing essentially monochromatic radiation.

[0019] The object of the present invention is to provide a drive for the eccentric rotation of the rotation axes of the optics of a monochromator in a vacuum chamber with at least one feedthrough, which has a reduced space requirement compared to the prior art, while at the same time providing high precision, accuracy and resolution as well as good UHV compatibility and increased rotation speed.

[0020] The problem is solved by claim 1. Advantageous embodiments are the subject of the dependent claims.

[0021] The drive system according to the invention for eccentrically driven rotary axes in a vacuum chamber with at least one feedthrough is to be described in its features as follows.

[0022] Vacuum chambers which are considered for the application of the invention within the meaning of the invention include all chambers which can be pumped out, ie evacuated, and which can be used in particular up to the ultra-high vacuum range (pressures < 10' 9mbar). Such vacuum chambers are equipped with special feedthroughs, which can be provided, for example, for contact between the inside and outside, but also for manipulators and the like that can be operated from outside inside the chamber. The feedthroughs are usually designed as a so-called "flange", which facilitates the attachment of functional components while simultaneously providing a seal. A flange is usually provided as a tube that is arranged, for example, on a vacuum chamber to form the feedthrough. This flange has a ring at the open end that is usually provided with holes for screwing. The ring is used for the flange-mounting of components that have a counterpart to the ring. Seals between the rings serve to seal the vacuum chamber.

[0023] The drive system initially comprises a bellows. In the sense of the invention, a bellows is an elastic hose that can be folded together like an accordion, with the folding occurring along the axis of the hose. For use in the invention, the bellows is made in particular from stainless steel suitable for ultra-high vacuums. The bellows as a hose also has two ends, a first end of which is open and the second closed. The closed end in particular has a component that can also be provided to close off the bellows itself and which in particular comprises fastening means that are accessible from a first side and a second side opposite the first side. The side to be referred to as the first side of the closed second end of the bellows lies inside the bellows (i.e. the hose) and the second side lies on the outer side of the closed second end of the bellows.The open first end of the hose can be arranged in a feedthrough of a vacuum chamber. For this purpose, the bellows must be equipped with a connecting means at the open first end, which serves to connect the bellows in the feedthrough to the vacuum chamber. Such connecting means are usually means that interact with the design of a feedthrough, such as the use of O-rings or other seals and flanges provided for this purpose (e.g. KF flanges with external or internal centering rings, chamber flanges, fixed flanges, so-called CF flanges for use in UHV with copper flat gaskets, and the like) or other means. When arranged in a feedthrough with its open end, the bellows closes off the feedthrough with its closed end, whereby the closed end can be moved along the fold axis due to the accordion-like folding.

[0024] The drive system also includes a rotary table with a coaxial bore into which a spindle or screw nut and threaded rod can be accommodated, allowing the screw nut to be rotated. An electric motor can also directly or indirectly transmit the rotation to the rotary table and thus to the spindle nut via a pinion or spur gear. According to one embodiment, the entire rotary table and motor can advantageously be realized by a hollow-shaft torque motor.

[0025] The screw nut is rotated via the rotary table along a threaded rod which is prevented from rotating on its own and can therefore only move in a translational manner. The transmission as a rotary movement to a mirror, grating or crystal is achieved, for example, by a sine drive, whereby the screw nut is firmly connected to the rotary table or, for example, the rotary table takes on the function of the screw nut. Other indirect and direct transmissions of the rotary movement are possible. The rotary table is advantageously arranged directly on the feedthrough on which the bellows is also arranged, so that a threaded spindle which is arranged parallel to the folding axis of the bellows and is linked to the bellows on a first side of the closed end of the bellows inside, ideally coincides with the rotation axis of the rotary table. Due to the fact that the rotary table orWhen the screw nut, which is arranged on the threaded spindle, is rotated by the motor, the threaded spindle is merely translated, i.e., it is guided in a linear motion without rotation, which the bellows follows along its folding axis, which ideally coincides with the threaded spindle. Depending on the direction of rotation of the rotary table or the spindle nut, the threaded spindle is moved into or out of the bellows. If the drive system is arranged on a vacuum chamber according to the invention, the linear movement of the threaded spindle occurs together with the bellows into or out of the vacuum chamber.

[0026] A coupling rod, which is connected to a second side of the closed end of the bellows, then transmits the linear movement of the threaded spindle to an eccentrically rotating axis of rotation, whereby the coupling rod can be eccentrically connected to a rotation axis.

[0027] The components which protrude into a vacuum chamber when arranged in a vacuum chamber, such as the bellows, a bellows end and the coupling rod or articulated rod (see below) as well as any required connecting elements, must be selected with regard to their suitability for vacuum or UHV.

[0028] The advantage of the drive system according to the invention lies, on the one hand, in the possible space-saving arrangement of the threaded rod and screw nut on the rotary table with motor, which enables a linear feedthrough into a vacuum chamber directly by means of a bellows. Furthermore, the transmission of the movement, in this case the linear movement, into a vacuum chamber is possible without the need for rotary bearings or similar, but a feedthrough in a vacuum chamber can be closed off by the bellows of the drive system, which is a major advantage for evacuating the vacuum chamber. A small pitch of the spindle thread can increase the accuracy of the drive, and the combination of a torque motor enables high power transmission and high linear speed.

[0029] With the drive system according to the invention, an angular range of eccentric rotation of an axis of more than 25° is possible, which represents a further improvement over conventional systems.

[0030] In a first embodiment of the invention, the coupling rod is formed from an articulated rod (also referred to as a gear rod). The articulated rod comprises cardanic joints or joints in a cardanic arrangement at both ends, ideally symmetrically. A first end of the articulated rod is linked to the second side of the closed end of the bellows, as in the case of the coupling rod, and a second end can be linked to an eccentrically driven rotary axis. The articulated rod also comprises at least one adjusting screw, ideally with two threads with opposite directions of rotation, for length adjustment. The cardanic suspension, which is provided by the cardan joints of the articulated rod and the possibility of adjusting the length of the articulated rod, enables it to be mounted and moved with almost no play.If, as provided in another embodiment, the universal joints are also equipped with cross-spring joints, the virtually play-free assembly is further improved, even during movement. The precision of the adjustable angles is thus increased.

[0031] Example

[0032] The invention will be explained in more detail using an embodiment and four figures.

[0033] The figures show:

[0034] Fig. 1: Schematic representation of a cross-section of a drive system according to the invention in a first angular position of 25°; Fig. 2: Schematic representation of a cross-section of a drive system according to the invention in a second angular position of 3°;

[0035] Fig. 3: Schematic representation of the embodiment for an articulated rod in two different views: 1. View a) and second view b) which is rotated 90° around the axis of the articulated rod to a);

[0036] Fig. 4: Schematic representation of a cross-section of the embodiment for a motor with spindle rod and bellows mounted on a flange of a vacuum chamber.

[0037] 1 and 2 show an exemplary embodiment of a drive system according to the invention for eccentrically driven rotary axes 9 in a high-vacuum chamber 6, having at least one feedthrough 3 in two different angular positions of rotation of an eccentrically rotating rotary axis 9 (Fig. 1: 25° and Fig. 2: 3°). The illustration is based on a cross-section through the installed drive system. In addition to the drive system, a portion of the wall of a high-vacuum chamber 6 is also shown, which has a feedthrough in the form of a flange 3 in which the drive system is arranged. Also shown is a section of an eccentrically rotating rotary axis 9 in the vacuum chamber 6, wherein the section is the cantilever 9 arranged on the rotary axis for eccentric rotation. In the exemplary embodiment, the vacuum chamber is a high-vacuum chamber of a plane grating monochromator.The eccentrically rotating axis 9 relates to the rotation axis of the mirror (not shown) of the monochromator. A drive system identical to that in the exemplary embodiment is also provided for rotating the plane grating of the plane grating monochromator (not shown). The flange 3 and the vacuum chamber 6 are made of common, commercially available CF components (stainless steel). The bellows 2 provided according to the invention, also made of stainless steel, projects into the flange and thus into the vacuum chamber 6. The bellows 2 has an open end, which is flange-mounted to the flange 3 from the inside (with respect to the vacuum chamber) with a sealing ring in a vacuum-tight manner. The bellows 2 further has a second end, which is closed by a blind flange 7' (see Fig. 4 for details). Due to the arrangement of the bellows 2 in the flange 3, the vacuum chamber is vacuum-tightly closed at this passage.The side referred to as the first side of the closed second end of the bellows lies inside the bellows 2 (i.e. the hose) and the second side lies on the outer side of the closed second end of the bellows 2. At this closed, second end, an eyelet 7 is arranged on the second, outer side, via which an articulated rod 8 (as a coupling rod) is coupled to the bellows at a first end. At the closed, second end of the bellows 2, a threaded rod 1 is coupled to the bellows 2 on the first, inner side. The articulated rod 8, in turn, is coupled at a second end to the boom of the eccentrically rotating axis 9. A rotary table 5, which is driven by a motor (not shown), is arranged on the flange 3 from the outside (with respect to the vacuum chamber) as a feedthrough of the vacuum chamber 6. This form of attachment, which is made possible by the invention, offers the advantage of being space-saving.The motor in the exemplary embodiment is a torque motor. The rotary table 5 is firmly connected to a screw nut 4, so that when the rotary table 5 rotates due to the motor, the screw nut 4 is also rotated. The screw nut 4 is arranged on the threaded rod 1. When the screw nut 4 is rotated, the articulated rod is translated along its axis, whereby it is particularly noteworthy that this translation occurs without any rotational movement of the threaded rod 1 itself. The translation of the threaded rod 1 causes the bellows 2 to expand or contract along the fold axis of the bellows 2. The translation of the threaded rod 1 is transmitted as a movement without translation directly to the articulated rod 8, which in turn is eccentrically coupled to the axis of rotation 9, so that the rotation of the rotary table 5 acts on the axis of rotation in an eccentric rotation of the same.This operative connection is established via the closed bellows 3 without any vacuum attack in the vacuum chamber, which represents a particular advantage of the invention. In the exemplary embodiment, the threaded rod 1 is designed with a thread with a pitch of mp = 1 mm. The screw nut 4 is selected to match the thread. The torque motor in the exemplary embodiment has the following characteristics: speed ry = 240 rpm, acceleration o = 240 rpm / 0.3 s = 13.3 rpm. 2 = 48000 rpm 2 , positioning accuracy d(p = 36071945600 = 0.66" and torque M = 3.4 Nm. The axial force F a on the threaded rod is at an efficiency of 0.85: F a = 3.4 Nm*2n*0.85 / l mm = 18 kN. A 110 mm stroke via a sinusoidal drive via the motor allows a mirror rotation of 27°. The positioning accuracy A0 of the mirror is therefore:

[0038] A0 = ((27°) / (110 mm) • 1 mm / (360°)) ■ 0.66" = 0.00045“ which results in an angular velocity a)0 at the mirror of a>0= (27° / (110 / 240)min) • 1 min / 60 s = 0.98° / s and an angular acceleration a e from a e = (0.98° / s) / 0.3 s = 3.27° / s 2 .

[0039] Fig. 3 shows the articulated rod 8 of the exemplary embodiment in detail. The articulated rod 8 is equipped at each end with a pair of joints 8a, 8a', 8b, 8b', which are arranged in a cardanic manner. The joints 8a, 8a', 8b, 8b' are each equipped with cross-spring joints. Additionally, an adjusting screw 8c with two threads 8c', 8c" with opposite directions of rotation is arranged in the center of the articulated rod for length adjustment. This design advantageously enables a virtually play-free arrangement of the articulated rod, which is maintained even during movement, particularly thanks to the cross-spring joints.

[0040] Fig. 4 shows a detailed view of the arrangement of the bellows 2 and the rotary table 5 in or on the flange 3 (not shown here, see Fig. 1). Two sealing elements 3', 3" are used to position the bellows 2. The rotary table 5 is sealed with two seals 5', 5" on each side. The closed, second end of the bellows 2 is also closed with a blind flange 7', on which the eyelet 7 for coupling the articulated rod is arranged. The threaded rod 2 and the screw nut 4 are also shown.

Claims

Patent claims 1. Drive system for eccentrically driven rotary axes in a vacuum chamber (6) with at least one passage (3), at least comprising a. a bellows (2) with two ends, a first end being open and vacuum-tight and being able to be arranged in a passage (3) of a vacuum chamber (6), the bellows (2) being foldable in at least one axis, the bellows (2) being closed at a second end, and b. a motor (5) which directly or indirectly rotates a screw nut (4), and c. a threaded spindle (1) which is arranged parallel to the folding axis of the bellows (2) and is linked to the bellows (2) on a first side of the closed end of the bellows (2), the screw nut (4) being arranged on the threaded spindle (1), and d.a coupling rod (8) which is connected to a first end on a second side of the closed end of the bellows (6), and wherein the coupling rod can be connected to a second end with an eccentrically driven rotational axis (9).

2. Drive system according to claim 1, characterized in that the coupling rod (8) is provided by an articulated rod (8) and the articulated rod (8) comprises symmetrical cardan joints (8a, 8a', 8b, 8b') at both ends, of which a first end is linked to the second side of the closed end of the bellows (2) and a second end can be linked to an eccentrically driven rotational axis (9) and the articulated rod (8) comprises at least one adjusting screw (8c) for length adjustment.

3. Drive system according to claim 2, characterized in that the cardan joints (8a, 8a', 8b, 8b') of the articulated rod are equipped with cross spring joints.

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