DE19928989C1 - Method for reducing the wobble movement in a freely suspended, rotating rotor body and device for carrying out the method - Google Patents

Abstract

The invention relates to a method for reducing wobbling of a rotating rotor body (1) which is mounted in a freely suspended manner and which comprises reflecting surfaces (13) on the outer periphery thereof. According to the inventive method, a measuring beam (5) having a predetermined point of incidence is reflected by the rotating reflecting surfaces (13) of the rotating rotor (1) and are directed onto a position detector (17) after having been reflected. The signals of said detector are fed to a computer (22). The computer determines the difference between the largest and smallest value of the signals output by the position detector (17) during a complete rotation of the rotor body (1), as well as the angular positions of the rotor body (1) corresponding to said values, and calculates control signals therefrom for the correcting device (16). This causes a change in the distribution of mass on the rotor body (1) during the rotation or a subsequent rotation of the same. This change in the distribution of mass is effected in a manner which contactless and which does not have an affect on the reflecting surfaces (13) such that the subsequently determined difference between the smallest and largest value of the signals output by the position detector (17) is less than the difference determined during the previous rotation. The invention also relates to a device for carrying out such a method.

Description

The invention relates to a method for reducing the wobble in one freely suspended, rotating rotor body, and a device for Implementation of such a procedure.

A rotating, freely suspended rotor body has a stable axis of rotation on, which is determined by its main axis of inertia when the angular momentum of the on it acting angular momentum coincides with the main axis of inertia and no other Interfering with him. If the rotor body is one rotationally symmetrical body, the main axis of inertia falls and thus the axis of rotation with its axis of symmetry together, provided that it is a perfect symmetry and the body has a completely homogeneous structure.

Real rotor bodies correspond to this ideal case due to the inevitable Material inhomogeneities, manufacturing inaccuracies and the given Skill tolerances are not. In contrast, they show more or less strong Deviations that lead to the main axis of inertia (as the axis of rotation at free, floating suspension) no longer with the axis of symmetry of the Rotor body matches. If there is a disturbance torque from outside on the overall system, this leads to an influence due to the preservation of the angular momentum of the overall system the position of the angular momentum axis, which migrates from the main axis of inertia. As long as none then act on the rotor body, the angular momentum axis is in their Alignment firmly in space. The main axis of inertia moves on the surface of one Cone, the so-called "nutation cone" around the angular momentum axis.

In practical systems, e.g. B. in polygon scanners, act through the system of Bearing, the drive and environmental forces constantly on the rotor body  a, which can lead to the effects described above, if not by a appropriate design and dimensioning of the bearings is counteracted.

If the rotor body is mounted on a rigid bearing axis, this turns it into the axis of rotation imprinted. As a rule, this axis of rotation agrees neither with the main axis of inertia, nor with the axis of symmetry. The rotor body then receives due to the difference in position Main axis of inertia is an "unbalance" and due to the position difference to the axis of symmetry one "Blow". It is now possible to change the mass distribution appropriately (Material shift) on the rotor body to eliminate the imbalance almost completely. Powers that impact on the rotor body due to imbalance can be absorbed by the bearing be the, with sufficiently stable bearings and high bearing damping Impact of an imbalance can be compensated.

If deviations occur between the axis of symmetry and the axis of rotation, these lead to a wobble error and thus z. B. to an undesirable sinusoidal beam deflection a mirror polygon scanner. It must therefore go through in the manufacture of the rotor body Compliance with the strictest possible manufacturing tolerances and through the manufacturing measures even ensure that there is a sufficiently good agreement of the axis of symmetry is reached with the axis of rotation of the rotor body. This is e.g. B. when using Mirror polygons are particularly important with regard to the optically effective mirror surfaces.

However, it turned out that despite considerable expenditure in the production of Mirror polygons the polygon scanner assemblies insufficiently meet the requirements meet that for the application in an image generation and in the application in the Printing technology.

It is known that the unbalance present in a rotor by rotating the rotor on a fixed shaft in a measuring device according to the angular position and size and then on the area of the area which has the unbalance or which is opposite the unbalance Rotor body by material removal (drilling, grinding or similar) or by material application (e.g. attaching balancing weights) eliminate the unbalance as far as possible. In one subsequent process step, it is determined whether sufficient material has been applied or has been removed or whether the procedure must be continued again. The whole The process is repeated until the unbalance that remains is below a predetermined size remains.  

Such a method is e.g. B. when balancing motor vehicle wheels, wherein here the imbalance is reduced or eliminated by attaching balancing weights.

DE 43 39 064 A1 describes a method for eliminating the unbalance on a rotor body known in which a material removal on the rotor body in an unbalance Measuring device is carried out by means of a laser device.

In these known methods, the balancing takes place in a separate measuring device, in which is assigned a fixed bearing axis to the rotor body, which, however, is used later for practical use of the balanced body given the storage conditions no longer corresponds exactly.

From US 4 096 988 it is known to eliminate the imbalance of a centrifuge, such as one fast-running gas centrifuge, the centrifuge body to be balanced is not in its own Measuring device, but to balance in its installed state, on which on a mounted rotor body by means of laser sensors the vibration behavior in the With regard to amplitude, frequency and phase of the vibrations recorded and from the obtained Results on a computer a material removal or a material order on one the rotor is pushed onto the ring by a suitable laser device.

In DD 299 546 A5 an arrangement is described with which the emigration of individuals Carrier screw blades of a helicopter can be measured, whereby to capture the Emigration a CCD array is used. This state of the art describes only that Obtaining corresponding measured values, which are then for a subsequent one, no further Correction of the position of the individual support screw blades of the helicopter described To be available.

From US 4,773,019 a method for balancing rotors is known, in which the Balancing is carried out in a separate balancing machine (measuring device). At that on a fixed bearing axis mounted rotor body by means of a measuring laser system Vibration behavior is detected and accordingly via a downstream computer Controlled laser for material removal on the rotor body, one at the same time Device for blowing away the material evaporating is provided to a to avoid unwanted condensation of the same on the rotor.

But should such a rotor body, for example in the form of a mirror polygon, be free with one floating storage can be used, for example as an active magnetic bearing Polygon scanner, the previous implementation of such a balancing procedure in a own facility with a fixed bearing axis does not prevent that in practice In the case of use in free-floating storage, a runout error still occurs which leads to Formation of a wobble leads.

Such a polygon scanner with a magnetic bearing is known from US Pat. No. 5,171,984 described, deflections of the polygon mirror detected when rotating and the Bearing magnets are controlled accordingly, so that the polygon mirror runs stably is always ensured. Balancing the polygon mirror in this document, however not received, so that here still a runout error and thus the occurrence of a Wobble occurs.  

Proceeding from this, the object of the invention is to propose a method with which an undesirable wobble in a freely suspended, itself can effectively reduce rotating rotor body.

According to the invention, this is achieved by a method for reducing the wobble movement with a freely suspended, rotating rotor body, which is attached to its Outer periphery has reflecting surfaces (mirror surfaces), with a measuring beam at a given single beam position the passing reflection surfaces (mirror surfaces) of itself at a speed that is not one of its Corresponds to resonance frequencies, rotating rotor body is reflected and after the reflection on a position detector is directed, the signals of which are fed to a computer which the difference between the largest and the smallest value of those during this complete Rotation of the rotor body from the position detector and signals to both Determined rotational positions of the rotor body belonging to values and control signals therefrom calculated, with which a correction device is controlled, the one or following rotation of the rotor body, a change in the mass distribution on the rotor body without contact and without influencing the reflecting surfaces (mirror surfaces) in such a way that in this following rotation of the rotor body determined difference between the smallest and largest value of the signals emitted by the position detector is smaller than that at the  previous revolution is certain difference until the difference found below a predetermined minimum value.

In the method according to the invention, the measures to reduce the Wobble directly on the freely suspended and rotating rotor body carried out without its axis of rotation being predetermined by a rigid bearing axis.

The fluid bearings that can preferably be used for free-floating storage, such as gas bearings or Liquid bearings, and especially magnetic bearings, can be dimensioned so that the bearing axis effective for the rotor body is not rigidly fixed geometrically and materially. Magnetic bearings can be used for this purpose, in which the axis of rotation of the Can set the rotor body freely within certain limits and thereby that of mechanical bearings Her known positive guidance of the axis of rotation in a bearing axis, through the bearings is determined, does not apply. The air gap in such magnetic bearings is similar to that in suitable fluid bearings, relatively large compared to usual deviations from the axis of rotation and Axis of symmetry, so that relatively large deviations are therefore also recorded can. This ultimately leads to the fact that the production of mirror polygons and their use in Polygon scanners, in particular for applications for image projection using a writing Laser beam, is associated with significant quality problems.

Here, the method according to the invention now creates a significant improvement in quality by it acts in such a way that the position of the axis of rotation of the rotor body and thus its (Identical position) main axis of inertia with the position of the axis of symmetry as good as possible Is matched, d. H. the axis of rotation is determined by the procedure Steps of the invention towards the best possible match with the location of the Axis of symmetry "drawn" towards this until an optimal run is achieved. Completely in Contrast this with conventional balancing methods in which the position of the axis of rotation the position of the main axis of inertia is determined unchanged by the mechanical mounting, which does not coincide with the axis of rotation there, as long as "pulled" to the axis of rotation until the bearing forces generated by the unbalance are minimized. This will, however, unlike the invention, did not achieve that the axis of rotation with the axis of symmetry in better agreement is brought.

The inventive method leads to the great advantage that the location of the The axis of rotation must be brought into good agreement with the position of the axis of symmetry can, so that an optimal run can be achieved. Since it is in the inventive  Ultimately, the process is an iterative process, in principle the question of what can be achieved The runout quality can be influenced and determined by the number of iteration steps carried out.

In addition, there is a further advantage in the method according to the invention that there Reduce the wobble on the free-floating, spinning Rotor body in a state (free floating) of the same that is completely identical to the state that this rotor body assumes in its subsequent use. It can under certain conditions, the method according to the invention with a rotating, floating rotor body can even be made while this is even in the Arrangement in which it is to be used.

The method according to the invention can with regard to how strong a difference in the Difference between the smallest and the largest value of the one emitted by the position detector Signals at two revolutions of the rotor body should be achieved in quite can be interpreted in different ways. So there is z. B. the possibility of the calculator interpret that he controls the correction device so that the occurring difference between the maximum and minimum values given by the position detector Signals is compensated for as completely as possible, so that with the next reference revolution this difference is already as small as possible. This will be particularly useful in cases if the rotor body has a relatively large mass and / or slow rotation, because in In this case, the change in the mass distribution to be brought about by the correction device Rotor body will be locally and quantitatively more extensive than in cases where small and rotating rotor bodies are used very quickly, such as. B. at extraordinary fast rotating polygon scanners. In the latter case, it is preferable if the calculator is like this is interpreted that the correction device only with each revolution of the rotor body acts for a short time, which gives the possibility of a difference occurring from the Position detector emitted minimum and maximum signals immediately at (one) of the following To compensate for revolution (s) as completely as possible is hardly given. Dependent on of the conditions of use, in particular also of the speed of rotation of the Rotor body, it may be advantageous in such cases to correct the mass distribution following turns so that the difference of the measured signals only by about 10%, 15% or 20% (or any other suitable percentage). there Although relatively small iteration steps are used, this ultimately results in one particularly good running accuracy can be achieved. Because the use of small iteration steps particularly suitable at high speeds of the rotor body, the iterative does Process in a relatively short time until a minimal then remaining is reached Residual difference of the signals from the position detector.  

In many cases, however, it should be advantageous if the computer is set so that the successively recorded differences in the signal values of the position detector each by approximately Half be reduced, which results in a sufficiently small choice of iteration steps a very good run can be achieved relatively quickly.

In this case, the rotations of the rotor body evaluated in succession can all immediately successive revolutions or only every second, third or similar revolution to Measurement and correction can be used.

The change in the mass distribution on the rotor body by the correction device can intensity and / or locally in any desired manner. The change in the process according to the invention is particularly preferably carried out Mass distribution on the rotor body, however, within localized areas, namely by local mass removal or mass order.

The change in mass distribution on the rotor body can be carried out in any suitable manner Way. However, it is particularly preferred by laser radiation, Electron irradiation and / or ion irradiation carried out, with, again preferred, the used radiation is pulsed. The radiation is advantageously synchronized with Speed of the rotor body pulsed.

The pulse time and / or the pulse length and / or the pulse frequency and / or the pulse power, depending on the signals supplied by the position detector set the calculator. The design of the computer becomes one for the application particularly suitable systematics. Is very particularly preferred in the The inventive method, the pulse regime of the radiation used with the signal of Triggered position detector, which is a simple synchronization between the Speed of the rotor body and the pulsing of the radiation can be reached.

A further advantageous embodiment of the method according to the invention also consists in that the orientation of the radiation used relative to the rotor body via the control signals of the computer is set so that the correction device from the same starting point the radiation used on different impact points on the rotor body or on can align different positions of the reflective surfaces.

The correction device is preferably deactivated in the method according to the invention, if and as long as the difference found between the smallest and the largest value of the  signals emitted by the position detector have a predetermined lower limit falls short, d. H. when a specified runout accuracy is reached.

The method according to the invention can basically be done on the rotating rotor body Run at any speed that is not exactly one of its resonance frequencies. Especially however, it is preferably carried out when the rotor body during the measurement and the Change in mass distribution rotates with its nominal speed.

The free-floating bearing of the rotor body used can be of any suitable type and Way to run. The rotor body is advantageously in a passively superconducting Magnetic bearings stored. The rotor body could equally as well be actively magnetically supported his.

The method according to the invention is particularly preferably carried out with a rotor body, which is designed as a mirror polygon or as a polygon scanner; in principle, however, it is any type of rotor body can be executed.

Any suitable measuring beam can be used as the measuring beam in the method according to the invention are used, but a laser beam is particularly preferably used as the measuring beam becomes.

The invention also relates to an arrangement with which the method according to the invention can be carried out in a particularly advantageous manner. According to the invention, these are an arrangement with a rotatable by a drive rotor body, the has outer surfaces of reflection surfaces, further with a bearing device for free floating bearing of the rotor body when rotating, a light source for generating a can be aligned to the passing reflection surfaces of the rotating rotor body Measuring beam, a position detector for detecting the from the reflection surfaces reflected measuring beam, a device for the continuous detection of the rotational angle positions of the rotor body, a correction device by means of which the mass distribution on the rotor body is contactlessly changeable, and with a computer at the input of which Position detector and the device for continuously detecting the rotational angle position of the Rotor body are connected and the control signals to the correction device such provides that these contact the mass distribution on the rotor body in a suitable manner changed.  

In the arrangement according to the invention, preference is given to a correction device preferably pulsed laser generator is provided, which, again preferably, as a ne YAG laser generator or is designed as an Eximer laser generator.

Any suitable for this purpose can be used as a position detector in the arrangement according to the invention Device can be used. However, a position detector is very particularly preferred CCD array selected.

Preferably, in the arrangement according to the invention, the light source is also used Generation of the measuring beam also uses a laser generator. The is preferred Light source for generating the measuring beam arranged so that the orientation of the Irradiation position on the reflective surfaces is adjustable.

In the arrangement according to the invention, a rotor body is advantageously used Mirror polygon or a polygon scanner and a passive superconducting as storage device Magnetic bearings or an active magnetic bearing provided. In certain applications However, it may also be desirable to free another suitable storage facility for one use floating storage, e.g. B. a fluid bearing (such as a gas bearing).

The invention is explained in more detail below by way of example with reference to the figures. It demonstrate:

Figure 1 is a (schematic) sectional view through an arrangement with an actively magnet-mounted, disk-shaped mirror polygon as a rotor body.

FIG. 2 shows a top view of the mirror polygon in FIG. 1, showing the beam path of the reflected measuring beam;

Figure 3 is a (basic) sectional view through an arrangement comprising a passive and axial magnetic bearings mirror polygon as a rotor body.

Figure 4 is a graphical representation of the components of the pyramidal error of a rotating mirror polygon.

Fig. 5 shows the graph corresponding to FIG. 4, however, after compensation of the wobble error, and

Fig. 6 shows the pulse train of a pulsed laser source of the correction device and the pulse train of laser radiation for laser ablation in the method.

In Fig. 1, an arrangement is shown in principle, in which a polygon scanner is used as the rotor body 1 , which is arranged in a housing 2 . This consists of an annular central part 3 ( FIG. 2) in which a plane-parallel plate 4 is arranged as a transparent window for a measuring beam 5 to be deflected from a light source 6 (only indicated in principle in FIG. 1), for example a laser generator ( FIG . 2).

The permanently magnetic mirror polygon 7 inserted in the polygon scanner is inserted into the cavity of the central part 3 , after which the central part 3 is closed in a vacuum-tight manner by a base plate 8 and a cover plate 9 .

The base plate 8 and the cover plate 9 are made of glass and carry the magnet coils 10 for a magnetic bearing, the magnet coils 11 for a drive and permanent magnets 12 .

Due to the permanent magnet system used, the mirror polygon 7 bears on the base plate 8 or on the cover plate 9 , as a result of which damage to the mirror surfaces 13 attached to the circumference of the mirror polygon 7 as reflection surfaces is excluded.

For commissioning, the axial position of the device is first set precisely and then the electromagnetic rotating field is excited, which sets the mirror polygon 7 in rotation. With the rotating mirror polygon 7 , an axis of rotation AA is always set such that it corresponds to the main axis of inertia of the mirror polygon 7 , the position of the axis of rotation AA relative to the housing 2 always being reproducible in the same way with a stable generated magnetic field. However, the desired high-precision 90 ° orientation of the surface normal N ( FIG. 2) of the mirror surfaces 13 to the main axis of inertia, which is the axis of rotation AA, of the mirror polygon 7 is generally not sufficiently ensured, as a result of which a wobbling movement of the mirror surfaces 13 of the mirror polygon 7 is caused .

The distribution of the magnetic coils 10 , 11 and the permanent magnets 12 on the base plate 8 and the cover plate 9 is advantageously carried out completely symmetrically.

The arrangement is also such that there are free areas 15 through which the end face 27 of the mirror polygon 7 can be suitably reached for an ablation radiation for the purpose of position measurement or for influencing the mass distribution of the mirror polygon 7 . This is initially the case in the center of rotation of the mirror polygon 7 , where a distance measuring device 14 is provided in the example shown, which is based on an optical principle, e.g. B. according to US Pat. No. 5,171,984, works and detects the alignment of the mirror polygon 7 , a signal for active control of the axial directional components of the magnetic bearing being obtained from the measurement results.

In addition, outside of the magnetic coils 10 for the magnetic bearing and the magnetic coils 11 for the drive, a free area 15 can be created which is permeable to the laser light from a correction device 16 , which consists of a pulsed laser generator.

This free area 15 is used for the passage of the laser radiation from the laser generator as a correction device 16 (as a processing laser), with which laser ablation can be carried out on surface areas 23 of the mirror polygon 7 during its operating state (preferably rotation at nominal speed). Appropriate control of the pulse regime of the laser radiation results in partial material removal on the top of the mirror polygon 7 , the control being carried out in such a way that the position of the main axis of inertia of the mirror polygon 7 is influenced such that the periodic deviation of the position of the perpendicular N on the mirror surfaces 13 to the main axis of inertia AA, ie the "wobble error" is minimized.

With the method of laser ablation used in the example, z. B. when using an Eximer laser at 1 kHz repetition rate on quartz glass removal rates of 1 × 10 ^-7 mm ³ per pulse achieved, which corresponds to a mass change of 2.2 × 10 ^-7 g / s.

When using an Nd-YAG laser, removal rates of 1 × 10 ^-7 mm ^{3 are also} achieved with a pulse duration of 100 ns and a repetition rate of 10 kHz for metals and silicon.

It is important that the material is removed over a large area and that there are no grooves which could otherwise lead to notch stresses which adversely affect the strength of the rapidly rotating mirror polygon 7 . The method of laser ablation has the great advantage over the other conceivable and possible methods for material displacement, such as evaporation, vapor deposition, sputtering, sputtering, chemical conversion (oxidation, nitration), ion implantation, etc., that there is practically no influence on the material properties and material composition of the mirror polygon 7 takes place, which is essential since thermal treatment or thin layers always cause strength problems under the extreme loads to which a rapidly rotating mirror polygon 7 is exposed. In principle, however, such other methods for changing the material distribution on the rotor body 1 could also be used.

There is also no difficulty in the laser beam of the processing laser of the correction device 16 at a nominal speed of the mirror polygon 7 of z. B. 1.3 kHz to control so that the laser pulses selectively hit a predetermined area 23 on the end face 27 of the mirror polygon 7 and cause material removal there. If this is done at the nominal speed of the mirror polygon 7 , this has the advantage that the state of the mirror polygon 7 is absolutely the same as in later operation. However, the material removal does not necessarily have to take place at the nominal speed of the mirror polygon 7 , the rotational speed of which does not influence the position of the main axis of inertia, which represents the axis of rotation AA. So z. B. with extremely fast rotating mirror polygons 7, the laser ablation takes place well below their nominal speed, but care must be taken that the set speed does not correspond to any resonance speed of the mirror polygon 7 .

In the exemplary embodiment shown, there is also the possibility of synchronizing the rotation of the mirror polygon 7 with the pulse behavior of the processing laser, with no overly high accuracy requirements for the synchronization having to be met, because it is practically irrelevant whether the material removal takes place exactly at the maximum amplitude of the wobble error or in a slight deviation from the same (+/- 10 °). Due to the large number of necessary laser impulses, averaging occurs anyway and the measurements carried out continuously during the material removal immediately provide proof of the process success.

To measure the position of the normal N on the mirror surfaces 13 , the measuring laser used as the light source 6 is fixed in its position relative to the polygon scanner (rotor body 1 ). The measuring beam 5 is reflected by each moving mirror surface 13 of the mirror polygon 7 onto a receiver line of a position detector 17 in the form of a CCD array. With a pixel spacing of the CCD receiver line of 7 µm, a resolution is achieved that is better than an angular second. A measured value is supplied for each mirror surface 13 .

On the central part 3 of the housing 2 of the polygon scanner (rotor body 1 ), a sensor 18 is also provided at a suitable point for determining the facet timing of the circumferential, reflecting facets (mirror surfaces 13 ), which provides information on the current angular position of the mirror polygon 7 .

The graphic representation in FIG. 4 shows the course of the measured values W for the so-called "pyramidal error" of the mirror polygon 7 used . This pyramidal error consists of a portion that is due to a fixed angular error 19 from mirror surface 13 to mirror surface 13 and the superimposed sinusoidal wobble error 20 of the rotating rotor body 1 (shown in dotted lines in FIG. 4). Both errors are collectively referred to as "pyramidal errors".

In the illustration of FIG. 4, the X-axis indicates the angular position φ of the mirror polygon 7 and the Y-axis measured by the position detector 17 (CCD array) associated amplitude W of the detection signal again.

As FIG. 4 shows, the wobble error 20 represents the sinusoidal component of the overall signal.

A computer 22 is also shown in FIG. 1, into which the output signal of the position detector 17 and the sensor 18 for angle detection is input. On the basis of the detected measured values, the computer 22 first determines the difference D between the largest measured value W _max and the smallest measured value W _min (see FIG. 4) that occurs during a complete revolution of the polygon mirror 7 , as well as the rotary positions X ₁ and X _{2 of} the rotor body 1 and uses this to determine control signals for transmission to the correction device 16 . By means of the laser beam 24 directed from this onto the area 23 on the upper side 27 of the mirror polygon 7 , material is then removed from the area 23 such that the difference D _i then measured is smaller than that previously during the (or a subsequent) rotation of the mirror polygon 7 measured difference D is. At the same time, the computer 22 , if the newly determined difference D _{i is} greater than a predetermined minimum value, in turn controls the correction device 16 , which performs a new laser ablation before the or a further complete revolution in such a way that the subsequently measured difference between the maximum and the minimum measured value becomes smaller again. These steps are repeated until this difference ultimately becomes smaller than the specified minimum value.

Finally, FIG. 5 shows the diagram from FIG. 4, the wobble error 20 having virtually disappeared completely through a large number of steps carried out in this way (in the case of successive measurements) and material removal (mostly the process becomes when the wobble error 20 has reached a predetermined minimum residual level canceled), in which case only the fixed angular error 19 from mirror surface 13 to mirror surface 13 is present ( FIG. 5).

The illustration of FIG. 6 shows the control of the pulse sequence of the laser processing of the correction means 16 (pictured above) and the force acting on the surface 27 of the polygon mirror 7 laser pulse sequence (bottom) in principle.

According to the arrangement from FIG. 2, the transmission of the pulse sequence of the processing laser of the correction device 16 is an integral multiple of T compared to the position of the detected maximum of the wobble error. ¾ (with T = revolution time for one revolution) shifted in time. In practice, the procedure is such that the deflection of the measuring beam 5 in accordance with the beam path, as shown in FIG. 2, is further measured with the rotating mirror polygon 7 during the material removal and the process of measuring and removal is terminated as soon as the measured difference D _{i is} below one predetermined limit has dropped.

Fig. 3 finally shows the basic structure of a polygon mirror 7 in a passive superconducting magnetic bearings (this in principle sectional view), the polygon mirror 7 surrounding housing is not shown.

Here, the rotor body 1 consists of layered permanent magnets 12 and a mirror polygon 7 . A stator part 25 surrounding it consists of a superconducting material which is cooled below its critical temperature by a cooler 26 . The magnetic coils 11 for the drive generate a magnetic field which acts on the rotary body 1 and sets it in rotation.

Such a passive magnetic bearing has the advantage that here the position of the rotor body 1 does not have to be stabilized by regulation. The "frozen" state of the currents induced in the superconducting material of the stator part 25 by the permanent magnets 12 guides the rotor body 1 in a stable, interference-resistant and exactly reproducible manner.

The arrangement shown in principle in FIG. 3 also has the advantage that the free area 15 on the end face 27 of the mirror polygon 7 is practically not restricted by any structures.

Claims (25)

1. A method for reducing the wobble movement in a freely suspended, rotating rotor body ( 1 ) which has reflection surfaces (mirror surfaces 13 ) on its outer circumference, a measuring beam ( 5 ) having a predetermined irradiation position on the passing reflection surfaces (mirror surfaces 13 ) of the a rotational speed, which does not correspond to one of its resonance frequencies, reflects the rotating rotor body ( 1 ) and, after reflection, is directed at a position detector ( 17 ), the signals of which are fed to a computer ( 22 ) which measures the difference between the largest and the smallest value of the During each complete revolution of the rotor body ( 1 ), the signals emitted by the position detector ( 17 ) and the rotational positions of the rotor body ( 1 ) belonging to both values are determined and control signals are calculated therefrom, with which a correction device ( 16 ) is actuated, which is used in one or the following Rotation of the rotor body ( 1st ) a change in the mass distribution on the rotor body ( 1 ) without contact and without influencing the reflection surfaces (mirror surfaces 13 ) in such a way that the difference between the smallest and largest value of the signals emitted by the position detector ( 17 ) during this rotation of the rotor body ( 1 ) is less than is the difference determined in the previous revolution. 2. The method according to claim 1, wherein the change in the mass distribution on the rotor body ( 1 ) is carried out within locally limited areas ( 23 ). 3. The method according to claim 1 or 2, wherein the mass distribution on the rotor body ( 1 ) is changed by local mass removal or mass application. 4. The method according to any one of claims 1 to 3, wherein the mass distribution on the rotor body ( 1 ) is changed by laser radiation, electron radiation and / or ion radiation. 5. The method according to claim 4, wherein the radiation ( 24 ) used to change the mass distribution on the rotor body ( 1 ) is pulsed. 6. The method of claim 5, wherein the radiation used to change the mass distribution on the rotor body (1) (24) is pulsed in synchronism to the rotation speed of the rotor body (1). 7. The method according to claim 5 or 6, in which the pulse time and / or the pulse length and / or the pulse frequency and / or the pulse power are set as a function of the signals supplied by the position detector ( 17 ). 8. The method according to claim 7, wherein the pulse regime of the radiation used ( 24 ) with the signal of the position detector ( 17 ) is triggered. 9. The method according to any one of claims 4 to 8, wherein the orientation of the radiation used ( 24 ) relative to the rotor body ( 1 ) is set via the control signals of the computer ( 22 ). 10. The method according to any one of claims 1 to 9, wherein the correction device ( 16 ) is deactivated when and as long as the determined difference between the smallest and the largest value of the signals emitted by the position detector ( 17 ) no longer exceeds a predetermined limit value. 11. The method according to any one of claims 1 to 10, wherein the rotor body ( 1 ) rotates at its nominal speed during the measurements and the change in the mass distribution on it. 12. The method according to any one of claims 1 to 11, wherein the rotor body ( 1 ) is mounted in a passive superconducting magnetic bearing (permanent magnet 12 , stator part 25 ). 13. The method according to any one of claims 1 to 12, in which a mirror polygon ( 7 ) is used as the rotor body ( 1 ). 14. The method according to any one of claims 1 to 13, in which a laser beam is used as the measuring beam ( 5 ). 15. Arrangement for carrying out the method according to claim 1, with a rotor body ( 1 ) which can be rotated by a drive and has reflection surfaces (mirror surfaces 13 ) on its outer circumference, a bearing device (magnetic coil 10 , permanent magnet 12 ; permanent magnet 12 , stator part 25 ) for free-floating mounting of the rotor body ( 1 ) when rotating, a light source ( 6 ) for generating a measuring beam ( 5 ) which can be aligned with the reflection surfaces (mirror surfaces 13 ) of the rotating rotor body ( 1 ), a position detector ( 17 ) for detecting the of the Reflection surfaces (mirror surfaces 13 ) of the reflected measuring beam ( 5 ), a device ( 18 ) for continuously detecting the rotational angle positions of the rotor body ( 1 ), a correction device ( 16 ) by means of which the mass distribution on the rotor body ( 1 ) can be changed without contact, and with a computer ( 22 ), at the input of the position detector ( 17 ) and the device ( 18 ) for continuously detecting the angular position of the rotor body ( 1 ) are connected and the control signals to the correction device ( 16 ). 16. The arrangement as claimed in claim 15, in which a laser generator is provided as the correction device ( 16 ). 17. The arrangement as claimed in claim 16, in which an Nd-YAG laser generator or an eximer laser generator is provided. 18. The arrangement according to claim 15 or 16, wherein a pulsed laser generator is provided. 19. Arrangement according to one of claims 15 to 18, in which a CCD array is provided as position detector ( 17 ). 20. Arrangement according to one of claims 15 to 19, wherein the light source ( 6 ) for generating the measuring beam ( 5 ) is a laser generator. 21. Arrangement according to one of claims 15 to 20, in which the light source ( 6 ) for generating the measuring beam for aligning its irradiation position on the reflection surfaces (mirror surfaces 13 ) is arranged in an adjustable position. 22. Arrangement according to one of claims 15 to 21, wherein the rotor body ( 1 ) is a mirror polygon ( 7 ). 23. Arrangement according to one of claims 15 to 22, in which a passive superconducting magnetic bearing (permanent magnet 12 , stator part 25 ) is provided as the bearing device. 24. Arrangement according to one of claims 15 to 21, wherein the rotor body ( 1 ) is an actively magnet-mounted polygon scanner. 25. Arrangement according to one of claims 15 to 22, in which a fluid bearing as the bearing device is provided.