Rotary adjustment stage for a setup, in particular with an optical element

Abstract

Rotary adjustment stage for a setup, in particular an optical element, preferably a grating and / or mirror, comprising - at least one rotary table having at least one turntable - a drive connected to the rotary table, preferably comprising at least one motor and a gear and / or a motor-gear combination and a rotary mechanism wherein the rotary table is comprising an angle measuring system preferably directly mounted on the turntable to determine the angular position.

Description

[0001] Rotary adjustment stage for a setup, in particular with an optical element

[0002] The invention relates to a rotary adjustment stage for a setup, in particular an optical setup, in particular comprising an optical element preferably in the form of a grating and / or a mirror.

[0003] The rotary adjustment stages according to the invention are particularly suited for use in spectrometers or spectrographs, preferably in spectrometers having one or more grating and / or mirror elements. Applications of the invention in the wider field of optical instruments, such as microscopes or devices for adjusting a mirror, are also possible.

[0004] When used in an optical setup, for example a microscope or in particular a spectrometer, for which a high spectral resolution is required, precise positioning of the optical elements, for example of the mirrors or gratings of the spectrometer, is necessary. For the accuracy of the spectral calibration of a spectrometer, for example, it is crucial that the angle of rotation of the optical component, for example the optical grating, relative to the light impinging on the component, preferably the grating, is set and maintained precisely and reproducibly.

[0005] In the prior art, the rotary adjustment stages themselves are typically driven, via a screw and a bellows, by means of a stepper motor. The angle of rotation of the rotary plate, which comprises a turntable and is driven by the rotary adjustment stage is specified indirectly by moving the stepper motor by a known number of microsteps, thus indirectly controlling the rotation of the rotary plate via the reduction mechanism of the rotary adjustment stage. The microsteps are counted relative to a reference position attached to the rotary adjustment stage, for example by using a mechanical limit switch or a light barrier. In general, such simple setups for detecting the reference position suffer from poor resolution, which is further exacerbated in compact rotary tables having turntables, where small angle changes result in very small movements of the rotary table having turntables. For high resolutions in the arc-second range, additional information must therefore either be obtained from other sensors directly on the driving motor axis and therefore before the movement is mechanically reduced, or from extremely high-resolution and therefore more complex reference sensors. Directly in this case means that the other sensor is directly affixed to the drive axle of the motor and therefore senses the non-reduced movement of the motor. This further complicates the indirect exact control of the angular position of the rotary table that can be achieved. Furthermore, after commissioning the system, the reference position must first be approached and the system initialized. An initialization of the system has to be undertaken after a spectrometer is switched on since for the counting of the steps, a reference point is needed from which on is counted. The reference point is the light barrier position. Therefore after each switching on of the system, the light barrier position has to be found as a reference position.

[0006] Despite a reduction ratio of 100:1 to 500:1 , especially 100:1 to 1000:1 and thus 1 to 5 million stepper motor microsteps per rotary table revolution, such rotary adjustment stages, according to the prior art (for example the DV65-D37 rotary adjustment stage from OWIS, the ADT-65 rotary adjustment stage from Micos or the DT-80 rotary adjustment stage from the company Physik Instrumente), only have an accuracy of significantly worse than one arc second. Although it is possible to increase the accuracy by increasing the mechanical pretension of the components used in the reduction mechanism in order to minimize their mechanical play, it is also important to ensure that they run smoothly enough to avoid possible step losses of the motor when moving the rotary adjustment stage. Gears that are too stiff require powerful, large motors, which in turn introduce during movement a lot of heat and mechanical stress into the system, causing drift and relaxation processes and also preventing a compact design. Adjusting the pretension is therefore difficult and time-consuming. In general, the residual angular error can be reduced to a sinusoidal error of approx. 20-30 arc seconds, which is linked to the motor rotation. This is mainly caused by the worm drive, which according to the prior art approaches the target position always from the same direction to minimize the remaining gear play in the rotary adjustment stages. However, according to the prior art, in order to compensate for this residual mechanical error, it is necessary to measure said residual error during the calibration of the rotary adjustment stage and to fit the measurement data with a mathematical model of the rotary adjustment stage. This model is then used to approach the desired target position with a higher accuracy. For a worm gear per motor revolution a periodic error arises. In a model a sinusoidal curve of this error component can be assumed and the results of this calibration measurement can be fitted with a sinus signal in order to subtract this systematic error.

[0007] The disadvantage of the rotary adjustment stages and the prior art method for precisely positioning the rotary adjustment stages was therefore the relatively high adjustment and assembly effort required for the various and numerous components. Since the angular position of the rotary adjustment stage is only specified indirectly via the microstep position of the stepper motor, mechanical play in particular has a detrimental effect on the angular accuracy. In addition, despite the time-consuming adjustment and assembly work, the required accuracy was often not achieved and frequent recalibration was necessary.

[0008] From US 5,096,295 B1 a scanning monochromator using a pulse-driven microstepping motor to drive a spectral-dispersion element via a reduction-gear harmonic drive was made known whereby the motor is directly coupled to the input hub of the reduction gear-drive, and the output hub of the reduction-gear drive directly supports the spectral-dispersion element. According to US 5,096,295 B1 by selecting a motor with a great number of steps per revolution, and a harmonic drive with a great reduction ratio, a resolution of 5 million pulsed steps is available per single rotation of the output hub of the reduction-gear drive. This translates into more than 600,000 incremental angular-displacement steps over a usable 45° range of dispersion-element rotation.

[0009] US 9,551 ,612 B2 describes a monochromator including a light source and a diffraction grating. By using a diffraction grating having multiple, different dispersive surfaces, measurements of relatively high precision and quality may be taken throughout a wider spectral range. In another aspect of US 9,551 ,612 B2, the processing circuitry controls a sample drive motor to vary an angle of incidence of the dispersed wavelengths of light onto a sample for evaluation.

[0010] RENISHAW PLC, New Mills, Wolton-under Edge, Gloucestershire, UK, has disclosed a rotary table with RENISHAW RESOLUTE absolute rotary encoders being used in machine tools which allow machine axes to resume after tool changes and setups for reduced production time.

[0011] Furthermore RENISHAW PLC disclosed a RESA and a REXA angle measurement system with high precision.

[0012] It is therefore an object of the invention to provide a rotary adjustment stage for a setup, in particular for optical elements, preferably a grating and / or a mirror, which avoids the relatively high adjustment and assembly efforts of rotary adjustment stages according to the prior art and makes it possible to measure the rotary position of the rotary adjustment stage directly, to adjust the rotary adjustment stage with high accuracy and to hold the rotary adjustment stage at a predetermined angular position.

[0013] According to the invention, this object is solved by a rotary adjustment stage having all the features of claim 1 .

[0014] By directly measuring the angular position of the rotary table of the rotary adjustment stage, it is possible in particular to detect and, optionally, compensate for position deviations that occur subsequently, such as thermal drift or mechanical relaxation.

[0015] It is a further object of the invention to provide a rotary adjustment stage that is compact in design and characterized by small dimensions, low weight and at the same time high precision and positioning accuracy. This further object of the invention is solved by a rotary adjustment stage with dimensions of less than 140mm x 125mm x 60mm in width, length and height for the rotary adjustment stage including drive, gear and angle measuring system. This means that preferred rotary adjustment stages which might be used e.g. in spectrometers fit in a cubus WxLxH with a dimension of 140 mm (W) x 125 mm (L) x 60 mm (H) including the glass scale. The dimensions of the motor and gear are WxLxH = 61x61x46 mm. In addition the angle measuring system comprises a glass scale and a sensor head. This means as said before that the dimensions of an exemplary complete system with all components including the glass scale and sensor head having dimensions of WxLxH: 140x123x57 mm which fit in a cubus of less than 140 mm x 125 mm x 60 mm as claimed before. This type of compact rotary adjustment stage has the advantage that it can be installed in spectrometer setups with a compact housing to save space and is easy to mount.

[0016] Although compact rotary adjustment stages being a little bit greater than the preferred cubus of 140 mm x 125 mm x 60 mm are possible, one has to take into account the fact that, if the rotary adjustment stages become significantly larger than 140 mm x 125 mm x 60 mm cubus size, problems due to thermal drift effects arise. Furthermore, the rotary adjustment stages warm up not equally. This leads further to twisting and distortion.

[0017] Compact and simple installation of compact rotary adjustment stages further allow the rotary adjustment stage to be replaced easily when servicing is required. Furthermore, rotary adjustment stages with such small dimensions as described are characterized by their low weight.

[0018] The rotary adjustment stage according to the invention, in particular the optical element set up such as a grating and / or a mirror, comprises at least one rotary table having at least one turntable and a drive connected to the turntable with preferably at least one motor and / or a motor-gear combination and a rotary mechanism as well as an angle measuring system for determining the angular position. In a preferred embodiment the angle measuring system is an absolute measuring system .

[0019] In a more preferred embodiment the system according to the invention, the angular position is detected directly on the turntable of the rotary adjustment stage, i.e. after the mechanical reduction, and thus as close as possible to the optical component to be positioned, due to the angle measuring system arranged directly on the turntable.

[0020] In principle, both incremental and absolute angle measuring systems are possible. According to the invention, it is provided that the angle measuring system is preferably an absolute measuring system. With the angle measuring system as an absolute measuring system, it is possible to determine the rotary position of the rotary adjustment stage directly and absolutely at any time, i.e. without prior reference travel, and to readjust the rotary adjustment stage from the determined rotary position until the desired angle of rotation is achieved. This offers particular advantages, as the grating or mirror does not have to be moved to a known reference position, from which the position can then be determined incrementally. Further incremental pulses cannot be lost due to interference in an absolute measuring system, which makes the measurement considerably more robust and therefore more accurate.

[0021] Preferably the rotary adjustment stage is situated in the spectrometer and therefore far away from a potentially heated sample. In a normal setup the microscope is connected to the spectrometer by 2 to 3 m long fibre optic cables.

[0022] To set the angle of rotation in a preferred embodiment, a control and / or regulating system or a control and / or regulating device is provided which, after determining the rotational position, controls the rotary adjustment stage in such a way that the rotary adjustment stage, which is preferably motor-driven, is moved to the desired rotational position, i.e. the desired angle of rotation. In particular, the control and / or regulating device is used to adjust the angle of rotation in such a way that a mechanical inaccuracy of the rotary mechanism is compensated for, for example an inaccuracy due to drift movement, mechanical stress relief or relaxation processes.

[0023] It is particularly preferable if the angle of rotation is adjusted, in particular with the aid of the control and / or regulating device, in such a way that an angular accuracy of better than one arc second, preferably better than half an arc second, is achieved. This is particularly advantageous because such accuracies are already achieved by tracking. In contrast to the prior art, no complex adjustment or use of non-linear fit routines are required. Active tracking also means that the need of frequent and costly recalibrations to ensure long-term accuracy is reduced or preferably avoided altogether.

[0024] In a further operating mode of the rotary adjustment stage, however, it is also possible to dispense with automated active tracking in the event of deviations below a predefined threshold value and instead allow small position deviations below the threshold value. The position deviations are only detected and noted over the course of time. The position deviations are taken into account for subsequent software correction of the measured spectra. An advantage of this operating modus is that the measurement can be made with the grating in resting position and the stepping motor has not to be supplied with electricity for a readjustment. Oscillating around the target position and entry of heat can be avoided.

[0025] This operating mode offers particular advantages if the rotary adjustment stage is to remain completely at rest during the recording of spectra. The measuring accuracy of the angle measurement is significantly better than the achievable positioning accuracy of the rotary adjustment stage, which is limited by the mechanically reduced minimum motor movement of the rotary adjustment stage. The rotary adjustment stage is preferably adjusted using a stepper motor. In order to achieve a low synchronization error and a compact design, it is particularly preferable if the gear, especially the gear of the motor-gear combination, comprises a harmonic gear. A harmonic gear or a so-called "harmonic drive" is characterized by a high reduction ratio and zero backlash and thus high positioning and repeat accuracy.

[0026] Harmonic gears have three components:

[0027] 1. an elliptical steel disk (so-called "wave generator") in the center of the gear, wherein the gear has a centric hub as well as a thin, elliptically deformable special ball bearing,

[0028] 2. a flexspline, which is a deformable, cylindrical steel bushing with teeth arranged radially around the outside, and

[0029] 3. a circular spline, which is a rigid and cylindrical outer ring that surrounds both the wave generator and the flexspline and is equipped with an internal toothing.

[0030] The external toothing of the flexspline has fewer teeth than the internal toothing of the circular spline. This difference often amounts to two teeth. Typically, the wave generator is used as the input element, which is coupled to the motor, and the flexspline is used as the output element of the mechanism. As the driven element, the elliptical wave generator initiates the process of the harmonic gear and deforms the flexspline. This is in manual intervention with the internally toothed circular spline in the opposite areas of the large elliptical axis. The rotation of the wave generator shifts the large elliptical axis and thus also the intervention area. The decisive factor for the design and function of the harmonic gear is that the flexspline has fewer teeth than the circular spline. A difference of two teeth, for example, results in a relative movement between the flexspline and circular spline of one tooth after half a rotation of the wave generator. After a full rotation, the difference is already two teeth. This results in a high reduction ratio combined with high zero backlash and high torsional rigidity.

[0031] In order to determine the exact location in which the rotary table having a turntable is located and thus the optical element mounted on the rotary table, in particular the grating and / or the mirror, the angular positioning system of the invention has an angle measuring system or, in particular, a pitch circle angle measuring system. This can be a magnetically, inductively or preferably optically operating angle or pitch circle angle measuring system. The optical pitch circle angle measuring system is preferably in the form of a measuring tape, for example made of steel with periodically applied measuring markings, which are applied to a circumference, in particular of the rotary table, which carries the optical element, preferably the grating and / or the mirror. Optically operated systems are most preferred over e.g. magnetic systems because they are the most precise systems. Magnetically or inductively operated systems have advantages in case of pollution, which does not play a role in optically operated systems. Preferably, the angle measuring system or pitch circle angle measuring system in the form of a linear length measuring tape is glued and / or pressed onto the edge of the rotary table, for example. The length information can also be brought onto the circumference of the rotary table by a lithographic process or by etching or printing or engraving. Due to the round surface of the rotary table bringing the length information onto the circumference of the rotary table e.g. by a lithographic process is more difficult. The position of the rotary table can be determined via the measuring tape e.g. glued on the circumference of the rotary table with the aid of at least one sensor. The determination of the position of the rotary tape via a measuring tape and a sensor is not restricted to the usage of exactly one sensor. Also more than one sensor is possible.

[0032] The indirect determination of the rotary angle by length measurement at the circumference of the rotary table avoids very expensive angle measuring rings. Linear length measuring tapes are easier to manufacture and therefore cheaper. Further the length measuring tape levels the roughness on the circumference of the rotary table. Eccentricity of the rotational movement or uncertainties upon the determination of the diameter of the rotational table are transferred for small rotational movements into a gain error, which can be determined by calibrating the spectrometer with known calibration wavelengths. The gain error can be easily calculated out for small rotation angles of a grating as they are used in spectrometric applications. For such a downstream calibration a high reproducibility is necessary.

[0033] Since the change of the position at the circumference increases linearly with the diameter of the rotational table the further the measuring tape is situated from the centre (i.e. the pivot point), the more accurate is the angular resolution derived from the length measuring system. Therefore affixing the length measuring markings by means of a length measuring band to the circumference of the rotational table is preferred. By affixing the length measuring markings a ruler itself is affixed, the markings from the ruler are transferred and the ruler is used as a stencil mask.

[0034] Preferably, the sensor is an absolute sensor which detects the markings on the linear measuring tape and thus determines the position.

[0035] In one embodiment of the invention, the absolute sensor is an optical sensor. Preferably, the optical sensor comprises a photoelectric sensor with which the markings on the measuring tape are detected or, in particular, an extremely fast digital camera or digital line scan camera which continuously takes pictures of the measuring tape and the markings on it. The measuring tape bears clear markings so that the position of the section of the measuring tape read at the time of measurement is detected by the sensor head, similar to looking at a meter stick or a macroscopic measuring tape. The markings on the measuring tape are preferably stored in digital form and most preferably as contrast stripes in the form of barcodes with a nominal graduation period of 20-30pm. Special coding, such as 8B / 10B, 64B / 66B or 64B / 67 coding, ensures that there is always a sufficient number of contrast stripes and thus signal changes in the sensor's viewing window so that the sensor, which detects not only individual stripes but always a range of 20-100 contrast stripes simultaneously, can always determine a valid position. The exact mode of operation of such absolute sensors is described by the manufacturers of such sensors, for example the company Renishaw in (https: / / www.renishaw.de / de / funktionsweise-der-optischen-messsysteme-von- renishaw-36979) and is to be included in full in this application. Another embodiment would be a two track sensor. This means the system comprises two measuring standards: an incremental and an absolute standard. This makes coding more easier but more complex with regard to the hardware because two tracks have to be read out.

[0036] The absolute sensor determines the absolute position on the measuring tape with a resolution of less than 100 nm and preferably less than 50 nm. An evaluation unit then calculates the angular position of the rotary adjustment stage from the absolute position determined and the diameter of the measuring scale. For example, if the diameter of the turntable is 100 mm and the measuring tape was mounted on the circumference of the turntable, an angular resolution of less than 0.5 arc seconds is achieved, which is significantly better than one arc second. If the pivot point of the rotational table only deviates slightly from its center, the resulting measurement error of the sensor is periodic to the rotation of the rotary table. For small rotation angles this error proportional to the rotation, which can be corrected easily with spectral calibration using known gas spectral lines. The same holds true for not perfectly glued metal strips with markings or metal strips with markings where the strip is glued and the glue thickness varies.

[0037] A particularly high positioning accuracy and compactness is achieved if the gear is designed as a harmonic gear as described above, wherein the harmonic gear preferably comprises a flexspline and a circular spline and has a high reduction ratio of at least 80:1 and preferably at least 100:1 .

[0038] In addition to the rotary adjustment stage, which is characterized by a particularly high accuracy according to the invention, the invention also provides a device for Raman microscopy, in particular confocal Raman microscopy and / or fluorescence microscopy and / or spectroscopy, wherein the device comprises a rotary adjustment stage according to one of the previously described designs and an optical element arranged on the rotary adjustment stage, in particular a mirror and / or a grating.

[0039] With the aid of the rotary adjustment stage according to the invention, extremely precise angular positioning can be achieved, particularly within a spectrometer. With the rotary adjustment stages according to the invention, reproducibilities in the range of significantly less than one arc second are achieved.

[0040] The advantages of using a rotary adjustment stage according to the invention in a spectrometer are described below. For example, in a spectrometer with a focal length of 600 mm, the CCD camera used to record the spectra is also 600 mm away from the optical grating. In spectrometry, the gratings are typically used in reflection mode. An error in the angular positioning of the grating or mirror therefore has a twofold effect, namely on the angle of the incident light and the angle of the reflected light. In the exemplary embodiment shown, an error of one arc second in the angular positioning of the grating at a distance of 600 mm on the CCD camera causes a shift of approx. 5.6 pm. The CCD cameras used in such spectrometers typically have pixel sizes in the range of 15-26 pm. To ensure that the error caused by the angular positioning remains smaller than one CCD pixel, the angular positioning must therefore be better than 3-5 arc seconds. Smaller CCD pixels are technically possible, but collect an insufficient number of photons per time unit and become too insensitive to light. However, the spectral resolution of spectrometers is not usually limited by the CCD pixel size. Typical spectral lines in a spectrometer are usually mapped onto several CCD pixels. Interpolation in the CCD sub-pixel range is enabled by fitting spectral lines, for example using a Gaussian or Lorentzian function and determining the spectral center of gravity. This fitting of spectral lines allows spectral resolutions of the spectrometer in the order of less than 1 % of typical CCD pixel dimensions. Angular positioning errors of the grating in the range of arc seconds are therefore clearly visible which, if not corrected, can significantly distort spectral measurements. Reducing the value of angular positioning errors to the sub-arcsecond range is very advantageous because only then is the increase in resolution achieved by the fitting process no longer significantly obscured by errors and thus can be utilized. It is necessary to fit the spectral lines, as otherwise the pixel size of the CCD camera limits the spectral resolution. At the same time, the CCD pixels must not become too small to overcome the readout noise such that the signal to noise ratio has an unacceptable level.

[0041] In addition to the rotary adjustment stage for different optical elements, the invention also claims an optical device, in particular a spectrometer having such a rotary adjustment stage, and a method for setting an angle of rotation of a rotary adjustment stage with a rotary table and said method utilizing an angle measuring system or alternatively a pitch circle measuring system either of which is arranged thereon.

[0042] According to a preferred embodiment of the invention, the optical device, especially the device for Raman, in particular confocal Raman and / or Fluorescence microscopy and / or spectroscopy, comprises at least one optical element and at least one rotary adjustment stage onto which at least one optical element is arranged, especially mounted. A particular technical benefit of the invention is that it enables the design of said optical device to be very compact, especially in one preferred embodiment in which the length L and the width W of the rotary adjustment stage being preferably smaller than L<125 and W<140 mm.

[0043] Preferably the height H of the rotary adjustment stage is less than 60 mm.

[0044] In the following, the invention will be described by way of example and without limitation with reference to the enclosed drawings, wherein:

[0045] Fig. 1 : shows a rotary adjustment stage for an optical element according to the invention, in particular a grating for use in a spectrometer; Fig. 2: shows a rotary adjustment stage according to the invention with applied pitch circle measuring tape, sensor, drive and evaluation devices;

[0046] Fig. 3: shows a schematic setup of the assembly of a rotary adjustment stage according to the invention consisting of rotary adjustment stage, pitch circle measuring tape, sensor and motor with directly mounted harmonic gear;

[0047] Fig. 4: shows a schematic setup of a harmonic gear;

[0048] Fig. 5: shows a section of the markings (bar code from contrast stripes; where the absolute positions are stored in the bar code as a coarse position in coded form; the fine position is determined by interpolation of the bars) on a measuring tape according to the invention;

[0049] Fig. 6: shows a schematic setup of the detector for reading the pitch circle measuring tape;

[0050] Fig. 7: shows the dimensions of the fully assembled rotary adjustment stage according to the invention with length L, width W and height H;

[0051] Fig. 8: shows the calibration result achieved for a 600 mm spectrometer equipped with a rotary adjustment stage according to the invention; the graph shows the residual error after calibration in pixels (16 pm) in relation to the various positions of the CCD chip.

[0052] Fig. 1 shows the schematic setup of a spectrometer, for example a Raman spectrometer as known from WO 2018 / 158 136 A1 or WO 20117131 311 A1 , having a rotary adjustment stage 1 according to the invention and an optical element 3, for example a grating or mirror arranged on the rotary adjustment stage. The disclosure content of WO 2018 / 158 136 A1 and WO 2011 / 131311 A1 is fully incorporated into the present application. In a spectrometer, in particular a Raman spectrometer, an optical grating is illuminated by a light beam 5 from a light source through an entrance slit 2 or pinhole. The pinhole can also preferably be formed by the end of an optical fiber. Preferably, the coupled light is Raman scattered light, i.e. essentially a light source that also contains non-monochromatic light components in addition to the excitation wavelength. The light beam 5 hits the optical element arranged on a rotary adjustment stage 1 , e.g. a grating, and is deflected in the direction 7, e.g. onto a camera 9. This can be achieved by diffraction in the case of a grating and by reflection in the case of a mirror. The distance between the camera 9 and the optical element, e.g. the grating 3, on the rotary adjustment stage is preferably around 300 mm to 600 mm. The grating arranged on the rotary adjustment stage is preferably a grating spectral filter of a spectrometer. In a Raman spectrometer, the beam is expanded using suitable optics. The expanded beam then hits the grating spectral filter, which is mounted on the rotary adjustment stage. The grating spectral filter diffracts the light in different directions according to its wavelength so that a spectral signal can be recorded on a CCD chip, for example, depending on the location. For example, the CCD chip may have 1024 channels, wherein the 1024 channels of the CCD chip can record light of different wavelengths. The rotary adjustment stage is designed in such a way that a minimum error of less than 1 arc second, preferably less than half an arc second, is achieved. For this purpose, the angle of rotation of the rotary adjustment stage is measured, then evaluated with the aid of a control and regulating device and finally the angular position is readjusted with the aid of the control and / or regulating device in such a way that a mechanical inaccuracy of the rotary mechanism is compensated for and an angular accuracy of better than 1 arc second, preferably better than half an arc second, is achieved. This is a very high accuracy since the harmonic drive gear without any sensor and rotary adjustment has only an accuracy of 20 to 30 arc seconds.

[0053] Fig. 2 shows the entire system of a rotary adjustment stage according to one embodiment of the invention. The embodiment in Fig. 2 is a system with only one sensor. This system with one sensor is only an exemplary system, but not restricted thereto. A further embodiment of the invention may comprise multiple sensors, e.g. two sensors which are positioned in proximity to or at the measuring tape. Preferably, these two sensors can be positioned on opposite sides of the pivot point. The usage of two sensors instead of one increases the accuracy.

[0054] An optical element, e.g. a grating or grating spectral filter, is arranged on the turntable 4 of the rotary adjustment stage. A pitch circle measuring scale in the form for example of a measuring tape 11 with an imprint (not shown) is applied to the edge of the rotary table of the rotary adjustment stage, for example by gluing. The pitch circle measuring scale contains coded length or angle information, which is evaluated via the sensor 10 and is used to sense the rotary position of the rotary adjustment stage in order to then, depending on the detected rotary position of the rotary adjustment stage, adjust it by motor until the desired angle of rotation is reached. Preferably the length information is evaluated by the sensor, because this evaluation is easier. A grating or grating spectral filter 3 is arranged on the turntable 4 which can also be denoted as rotation table of the rotary adjustment stage.

[0055] In order to sense the rotary position achieved by the rotary adjustment stage, a sensor 10 records the absolute position of the rotary adjustment stage via the measuring scale on the measuring tape. The position of the rotary adjustment stage is passed to a control / regulating device 14. A digital microcontroller is the central part of the control / regulating device 14. From the rotary position of the rotary adjustment stage, which was determined with the absolute angle measuring system, the rotary plate 4 of the rotary adjustment stage 1 can be readjusted in such a way that the desired angle of rotation is achieved and maintained. The pitch circle angle measuring system is applied to the rotary plate, e.g. by gluing, wherein a precise angular position can be determined with the angle measuring system. The control / regulating device 14 allows the angle of rotation to be adjusted via the motor 13 and the gear 12 of the rotary adjustment stage in such a way that any mechanical inaccuracies of the rotary mechanism are compensated for. The angles determined with the angle measuring system according to the invention have an angular accuracy of for example 5 to 0.01 arc second, especially 1 to 0.5 arc second. This accuracy can be achieved without complex adjustment or fit routines. The angle measuring system according to the invention is an absolute measuring system in which the light barriers previously required for reference positions and time-consuming reference runs to these reference positions for initialization after commissioning the system, as required for incremental sensors, can be dispensed with. This greatly simplifies the setup and operation of the system. Another advantage is the increased robustness of such an absolute system, as individual incorrect measurements caused by dirt or vibrations, for example, cannot influence subsequent measurements and thus distort them (for example by integrating previous measurement errors).

[0056] Fig. 3 shows the schematic assembly of the components of a rotary adjustment stage according to the invention. The turntable 4, which can also be denoted as rotary plate of the rotary adjustment stage is placed directly on the gear flange 111 of the harmonic gear 12, wherein the gear is also mounted directly on the motor flange, so that the motor and gear form a compact motor-gear combination and the motor axle and gear axle are connected directly to each other. The measuring scale 11 of the angular pitch circle measuring system is glued or pressed onto the circumference of the turntable 4 and is evaluated via a sensor 10.

[0057] Fig. 4 shows a top view of the main parts of a harmonic gear as used in the drive of the rotary adjustment stage 1. The harmonic gear, also known as a "harmonic drive", as shown in Fig. 4 comprises an elliptical disk 100 in the center of the gear, which has a centric hub and a thin, elliptically deformable special ball bearing. Furthermore, the harmonic gear consists of a flexspline 110 with a toothing 112 arranged radially around the outside and a circular spline 120 with an internal toothing 122. The number of teeth is significant in the "harmonic drive", wherein the external toothing of the flexspline 110 has fewer teeth than the internal toothing 122 of the circular spline 120. This results in the reduction ratio of the gear. The elliptical "wave generator" 100 initiates the process of the harmonic gear as a driven element and deforms the initiating flexspline 110. The flexspline is in engagement with the internally toothed circular spline 120 in the opposite areas situated on either end of the large elliptical axis. The rotation of the "wave generator" shifts the large elliptical axis and thus the tooth engagement area. The decisive factor is that the flexspline always has fewer teeth than the circular spline. When the circular spline is fixed, the flexspline rotates in the opposite direction to the drive as the output element.

[0058] A significant advantage of the harmonic gear over conventional gears is the high reduction ratio that can be achieved and the absolute freedom from backlash over the service life as well as the high torsional rigidity over the entire torque range. Furthermore, the gear type is characterized by small dimensions and low weight compared to conventional gear types. Furthermore, the high reduction ratio and zero backlash provide high positioning and repeat accuracy.

[0059] The compact design of the gear also allows the gear to be mounted directly on the flange of the stepper motor, wherein the motor axle and gear axle can be connected directly to each other. This results in very compact motor-gear combinations that can be easily replaced if necessary and that do not require additional axle couplings, such as the bellows that are otherwise often necessary to compensate for axle misalignment, which further simplifies the overall design and avoids the mechanical backlash of the entire system, for example caused by possible torsion of long drive axles.

[0060] Fig. 5 shows the markings, in particular the contrast stripes, which form a barcode and contain the position or angle information in coded form.

[0061] In this embodiment, the single-track measuring tape has full-width contrast stripes based on a nominal 30 pm graduation period. The absence of multiple parallel tracks gives the system important immunity to yaw angle errors in sensor head alignment and greater lateral tolerance.

[0062] The barcodes are preferably generated by feedback shift registers, as these methods for generating the barcode are self-synchronizing and also ensure that signal changes in the bit sequences occur with sufficient frequency to ensure that the barcodes are sufficiently dense.

[0063] Fig. 6 schematically shows the beam path of the optical pitch circle measuring system. To read the measuring scale 11 , a light source 202, for example an LED, briefly illuminates an area of the measuring scale 11 opposite the sensor 200 at the time of reading via the illumination beam path 204. A prism or mirror 205 is used to direct the beam path and ensures that the illumination and detection beam paths 203 illuminate or detect the same area on the measuring scale. This enables a fast digital camera 201 to capture an image of the illuminated section of the measuring standard via the detection beam path 203 through the exit window 206 of the sensor, which covers a range of 40-100 contrast stripes of the barcode. Each contrast stripe is mapped onto a plurality of neighboring camera pixels so that the position of each contrast stripe can be determined with sub-pixel resolution by interpolation. This image is digitized and evaluated by digital signal processing.

[0064] A first algorithm then determines the number stored in the barcode in coded form and thus the absolute rough position. Meanwhile, another routine calculates a fine position with high resolution by interpolating the exact positions of the individual bars in the camera image, which is then combined with the rough position to provide an absolute position with a very high resolution.

[0065] Fig. 7 shows the compactness of a fully assembled rotary adjustment stage according to the invention. All components are located within a cube with length L, width W and height H. As is shown in Fig. 7 the size of the fully assembled rotary adjustment stage could be very small. In a preferred embodiment the length L of the dimensions of the rotary adjustment stage is smaller than 125 mm and / or the width W of the rotary adjustment stage is smaller than 140 mm and / or the height H smaller than 60 mm. These numbers for length, width and height are only exemplary and not restricting. Fig. 8 shows the residual error after calibration of a spectrometer equipped with a rotary adjustment stage according to the invention. In order to demonstrate the great potential of the rotary adjustment stage, a spectrometer with a long focal length (600 mm) was used on the one hand and a grating with a very high dispersion capacity (2400 g / mm) was installed in the spectrometer on the other hand. The long focal length ensures that the position error of the rotary adjustment stage is amplified (12x in this case). For gratings with a high dispersion capacity, a large angular range of the rotary adjustment stage (here 38°) must be used at the same time in order to image the desired spectral range onto the CCD chip (here 1650 pixels at 16pm).

[0066] Light sources with a known emission spectrum are generally used for spectrometer calibration. The emission lines of gas discharge lamps are particularly suitable here, as the lines have a very narrow spectral widths which can be in the order of 0.0001 nm. The lines (404.6565nm (301 ); 435.8335nm (302); 546.0750nm (303); 576.961 Onm (304); 696.5431 nm (305); 738.3980nm (306)) of a mercury-argon gas discharge lamp were used for this calibration.

[0067] When recording the calibration data, each spectral line is positioned at different positions (in this case 15 positions) on the CCD chip by the rotary adjustment stage and its exact position on the chip is measured.

[0068] The data obtained (angle of the rotary adjustment stage, wavelength of the emission line and position on the chip) can be adapted to a mathematical model that contains the optical and geometric properties of the spectrometer. The deviation from this mathematical model is the residual error, which is plotted against the chip position shown in Fig. 9.

[0069] As the position determination of the spectral lines according to this method only has an accuracy of approx. 1 / 10 pixel, the actual positioning error of the rotary adjustment stage is likely to be even smaller. With this invention, a rotary adjustment stage is disclosed for the first time, in particular for use in spectrometers or microscopes, which do not require an initial reference run and is characterized by high accuracy and small dimensions and weight and in that it can be used to set and hold very precise angular positions of an optical component, e.g. a grating. Furthermore, it is no longer necessary to move to a home position with several light barriers, for example. In the prior art after the spectrometer was activated, a reference drive for finding the light barrier was necessary. The additional time needed for this step was approximately 40 seconds. This is avoided in the claimed inventive system.

[0070] Furthermore a device for Raman, in particular confocal Raman and / or fluorescence microscopy and / or spectroscopy with a rotary adjustment stage according to the invention is provided. Moreover also a method for setting an angle of rotation of a rotary adjustment stage according to the invention is disclosed.

[0071] The invention includes aspects which are the subject matter of the following sentences but are not claims according to J 15 / 88:

[0072] Sentences

[0073] 1. Rotary adjustment stage (1 ) for a setup, in particular an optical element (3), preferably a grating and / or mirror, comprising

[0074] - at least one rotary table having at least one turntable,

[0075] - a drive connected to the rotary table, preferably comprising at least one motor and a gear and / or a motor-gear combination and a rotary mechanism, wherein the rotary table comprises an angle measuring system directly affixed to the turntable to determine the angular position, wherein the angle measuring system is preferably an absolute measuring system.

[0076] 2. Rotary adjustment stage (1 ) according to sentence 1 , Wherein a control and / or regulating device is provided.

[0077] 3. Rotary adjustment stage (1 ) according to one of the sentences 1 to 2, wherein the angle of rotation is readjusted from the determined angular position with the aid of the control and / or regulating device (14) in such a way that a mechanical inaccuracy of the rotary mechanism, caused, for example, by drift movements, mechanical stress build-up or relaxation processes, can be compensated for.

[0078] 4. Rotary adjustment stage (1 ) according to one of the sentences 1 to 3, characterized in that the angle of rotation is adjusted with the aid of the control and / or regulating device in such a way that an angular accuracy of better than 1 arc second, preferably better than half an arc second, is achieved. 5. Rotary adjustment stage (1 ) according to one of the sentences 1 to 4, wherein the drive comprises a stepper motor.

[0079] 6. Rotary adjustment stage (1 ) according to one of the sentences 1 to 5, wherein the angle measuring system comprises a pitch circle angle measuring system.

[0080] 7. Rotary adjustment stage (1 ) according to sentence 6, wherein the pitch circle angle measuring system comprises a measuring tape (20), preferably a measuring tape made of steel, most preferred of a reflective material with measuring markings, which is preferably affixed to an edge, in particular of the rotary table, preferably glued and / or pressed on it.

[0081] 8. Rotary adjustment stage (1 ) according to one of the sentences 1 to 7, wherein the angle measuring system comprises at least one sensor, preferably an absolute sensor, in particular an optical sensor, preferably a digital camera or digital line scan camera.

[0082] 9. Rotary adjustment stage (1 ) according to one of the sentences 1 to 8, wherein the gear, in particular the motor-gear combination, has a reduction ratio of at least 80:1 and preferably at least 100:1 , in a most preferred embodiment of 320:1.

[0083] 10. Rotary adjustment stage (1 ) according to one of the sentences 1 to 9, wherein the gear is mounted directly on the motor flange. Rotary adjustment stage (1 ) according to one of the sentences 1 to 10, wherein the gear and the motor axle are mounted directly onto and aligned parallel to the axle. Rotary adjustment stage (1 ) according to one of the sentences 1 to 11 , wherein the rotary table of the rotary adjustment stage is mounted directly on the gear. Rotary adjustment stage (1 ) according to one of the sentences 1 to 12, wherein the motor-gear combination comprises a harmonic gear. Rotary adjustment stage (1 ) according to sentence 13, wherein the harmonic gear comprises a flexspline (110) with teeth arranged radially around the outside and a circular spline (120) with an internal toothing. Rotary adjustment stage (1 ) according to sentence 13, wherein the external toothing of the flexspline (110) has fewer teeth than the internal toothing of the circular spline (120). Device for Raman, in particular confocal Raman and / or fluorescence microscopy and / or spectroscopy, having at least one optical element, in particular a grating and / or mirror, and at least one rotary adjustment stage (1 ), wherein the optical element is arranged on the rotary adjustment stage (1). Device according to sentence 16, wherein the rotary adjustment stage (1) is a rotary adjustment stage according to one of the sets 1 to 12. Device according to one of the sentences 15 to 17, wherein the device comprises a housing that accommodates the rotary adjustment stage with the optical element. Device according to one of the sentences 15 to 17, wherein the rotary adjustment stage comprises a rotary table and the dimensions of the rotary adjustment stage are characterized by a length, a width and a height. Device according to sentence 19, wherein the length L and the width W of the rotary adjustment stage are less than L<125 mm and W<140 mm. Device according to one of the sentences 19 to 20, wherein the height is less than 60 mm. Method for setting an angle of rotation of a rotary adjustment stage with a rotary table and at least one measuring scale or pitch circle measuring scale attached thereto, which has coded length or angle information, comprising the following steps: a sensor (10) is used to determine the absolute rotary position of the rotary adjustment stage based on the coded length or angle information, - the absolute position is transmitted to a control / regulating device

[0084] - due to the absolute rotary position, the rotary adjustment stage is preferably adjusted by means of the control / regulating device via motor and gear until the desired angle of rotation is reached and mechanical inaccuracies of the rotary mechanism are compensated for. Method according to sentence 22, wherein the angle of rotation is set with an angular accuracy of better than 5 arcseconds, preferably better than 1 arcsecond, in particular preferably better than 0.5 arc seconds.

[0085] List of reference symbols:

[0086] 1 : Rotary adjustment stage

[0087] 2: Entrance slit or pinhole

[0088] 3: Optical element (optical grating or mirror)

[0089] 4: Turntable

[0090] 5,7: Light beam

[0091] 9: Camera

[0092] 10: Sensor

[0093] 11 : Measuring scale

[0094] 12: Gear

[0095] 13: Motor

[0096] 14: Control and regulating device

[0097] 15: Coded position information

[0098] 100: Elliptical disk (driven by the motor)

[0099] 110: Flexspline (gear output)

[0100] 111 : Gear flange (connected to flexspline)

[0101] 112: External toothing of flexspline

[0102] 120: Circular spline (gear housing)

[0103] 121 : Gear housing (connected to circular spline)

[0104] 122: Internal toothing of circular spline

[0105] 130: Centric hub

[0106] 200: Sensor

[0107] 201 : Camera

[0108] 202: Lighting source

[0109] 203: Detection beam path

[0110] 204: Illumination beam path

[0111] 205. Prism or mirror

[0112] 206: Exit window

[0113] 301 : Measured deviation of the peak position at 404.6565nm 302: Measured deviation of the peak position at 435.8335nm 303: Measured deviation of the peak position at 546.0750nm : Measured deviation of the peak position at 576.961 Onm: Measured deviation of the peak position at 696.5431 nm: Measured deviation of the peak position at 738.3980nm

Claims

Set of claims1. Rotary adjustment stage (1 ) for a setup, in particular an optical element (3), preferably a grating and / or mirror, comprising- at least one rotary table having at least one turntable- a drive connected to the rotary table, preferably comprising at least one motor and a gear and / or a motor-gear combination and a rotary mechanism, wherein- the rotary table is comprising an angle measuring system preferably directly mounted on the turntable (4) to determine the angular position.

2. Rotary adjustment stage according to claim 1 wherein the angle measuring system is an absolute measuring system.

3. Rotary adjustment stage for a set up, in particular an optical element, wherein the angle measuring system is an indirect measuring system in which the angular position is determined by measuring a length at the circumference of the rotary table.

4. Rotary adjustment stage (1 ) according to claim 1 or 3, wherein a control and / or regulating device is provided.

5. Rotary adjustment stage (1 ) according to claim 4, wherein the angle of rotation is readjusted from the determined angular position with the aid of the control and / or regulating device (14) preferably in such a way that a mechanical inaccuracy of the rotary mechanism caused, for example,by drift movements, mechanical stress build-up or relaxation processes is compensated for.

6. Rotary adjustment stage (1 ) according to one of claims 1 to 5, wherein the angle of rotation is adjusted with the aid of the control and / or regulating device preferably in such a way that an angular accuracy of better than 1 arc second, preferably better than half an arc second, is achieved.

7. Rotary adjustment stage (1 ) according to one of claims 1 to 6, wherein the drive comprises a stepper motor.

8. Rotary adjustment stage (1 ) according to one of claims 1 to 7, wherein the angle measuring system comprises a pitch circle angle measuring system .

9. Rotary adjustment stage (1 ) according to claim 8, wherein the pitch circle angle measuring system comprises preferably periodic measure markings with reflective properties different to the one of adjacent material surfaces and is preferable applied to an edge, in particular of the rotary table.

10. Rotary adjustment stage according to one of the claims 1 to 8, wherein the material of the rotary table is preferably a metal especially steel with preferably periodically applied measure markings, which are preferably applied to an edge, in particular of the rotary table, preferably glued and / or pressed on and / or deposited onto and / or etched into.11 . Rotary adjustment stage according to one of the claims 1 to 9 wherein the rotary adjustment stage comprises a metal strip comprising the measure markings preferably glued and / or pressed on the circumference of the rotary table.

12. Rotary adjustment stage (1 ) according to one of claims 1 to 11 , wherein the angle measuring system comprises at least one sensor, preferably an absolute sensor, in particular an optical sensor, preferably a digital optical sensor or digital line scan camera.

13. Rotary adjustment stage (1 ) according to one of claims 1 to 12, wherein the gear, in particular the motor-gear combination, has a reduction ratio at least 50:1 , especially 80:1 and preferably at least 100:1.

14. Rotary adjustment stage (1 ) according to one of the claims 1 to 13, wherein the gear is mounted directly on the motor flange.

15. Rotary adjustment stage (1 ) according to one of the claims 1 to 14, wherein the gear and the motor axle are mounted directly onto and aligned parallel to the axle.

16. Rotary adjustment stage according to one of the claims 1 to 15, wherein the rotary table of the rotary adjustment stage is mounted in direct contact with the gear.

17. Rotary adjustment stage (1 ) according to one of the claims 1 to 16, wherein the motor-gear combination comprises an harmonic gear.

18. Device for Raman, in particular confocal Raman and / or fluorescence microscopy and / or spectroscopy, having at least one optical element, in particular a grating and / or mirror, and at least one rotary adjustment stage, wherein the optical element is arranged on the rotary adjustment stage (1).

19. Device according to claim 18, wherein the rotary adjustment stage (1 ) is a rotary adjustment stage according to one of the claims 1 to 17.

20. Device according to one of the claims 18 to 19, wherein the device comprises a housing that accommodates the rotary adjustment stage and the optical element.21 . Device according to one of the claims 18 to 20, wherein the rotary adjustment stage comprises a rotary table and the dimensions of the rotary adjustment stage are characterized by a length L, a width W and a height H.

22. Device according to claim 21 , wherein the length L and the width W of the rotary adjustment stage are less than L<125 mm and W<140 mm.

23. Device according to one of the claims 21 to 22, wherein the height H is less than 60 mm.

24. Method for setting an angle of rotation of a rotary adjustment stage with a rotary table and at least one measuring scale or pitch circle measuring scale attached thereto, which has coded length or angle information, comprising the following steps:- a sensor (10) is used to determine the absolute rotary position of the rotary adjustment stage based on the coded length or angle information,- the absolute rotary position is transmitted to a control / regulating device- due to the absolute rotary position, the rotary adjustment stage is preferably adjusted by means of the control / regulating device via motor and gear until the desired angle of rotation is reached and mechanical inaccuracies of the rotary mechanism are compensated for.

25. Method according to claim 24, wherein the angle of rotation is set with an angular accuracy of better than 5 arc seconds, preferably better than 1 arc second, in particular preferably better than 0.5 arc seconds.

26. Method of at least one of the claims 24 to 25, wherein the angle measuring system is an indirect measuring system and an angular position of the rotary table is determined by measuring a length at the circumference of the rotary table.

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