Galvanometer drive having an insulating rotor bearing

Abstract

The invention relates to a galvanometer drive with a limited adjustment angle, said galvanometer drive comprising: a rotor (110) which can be rotated about an axis of rotation (R) which extends in the axial direction, wherein the rotor is supported by means of a bearing mechanism (140, 150) and has a magnet, wherein the bearing mechanism has at least two bearings; a stator (130) which surrounds the rotor and has a cylindrical opening which extends in the axial direction for receiving the rotor; and at least one electrical coil (125) which is attached to the stator and which, when excited, can impart a bidirectional torque to the rotor; and an angular position encoder for determining a rotational position of the rotor, said encoder being arranged at an end-face end of the rotor, wherein at least one bearing is a rolling bearing and the rolling bearing has an electrically insulating cover disk.

Description

[0001] SL 12-P39202PC00

[0002] Galvanometer drive with insulating rotor bearing

[0003] The invention relates to a galvanometer drive or rotary actuator, in particular to a galvanometer drive as used in laser applications for precisely directing the laser beam to the processing point. The galvanometers used typically have mirrors that are pivoted to direct the laser beam to the processing point within a limited angular range of less than ±45°, typically less than ±20°. Here, 'angular range' refers to the range within which the mirror can be pivoted, in contrast to the use of the term in optics in connection with galvanometers, where, due to the deflection of radiation at the mirror, the angular range is twice as large as a result of the pivoting. The precision requirements are high. The positioning error should preferably be less than 100 prad, and particularly less than 10 prad.

[0004] An example of such a galvanometer drive is described in DE 20 2013 000 369 U1, from which Figure 1 is taken to illustrate the basic structure of a galvanometer drive known in the prior art.

[0005] In Fig. 1, a rotor magnet containing a permanent magnet is arranged within a stator unit comprising a coil. When the coil is energized, the rotor magnet rotates about its central axis, which is perpendicular to the plane of the drawing. The designations "coil plus" and "coil minus" indicate the direction of current flow through the coil windings, representing currents flowing into and out of the plane of the drawing, respectively, according to the depicted state. Deviations from the figure are also possible.

[0006] SL 10 / PK / 19 December 2024 several coils may be present and / or the stator may have a toothed structure.

[0007] Galvanometer drives typically use pulse-width modulation (PWM) to control the stator coils. This can be achieved through common-mode or differential-mode operation. Although common-mode operation can lead to capacitive charging of the rotor, this mode is generally preferred because differential-mode operation can result in significant eddy current losses even when the rotor is stationary.

[0008] However, charging the rotor leads to a pulsed discharge as soon as the voltage difference exceeds the insulating capacity of the medium, e.g., the air between the rotor and stator. This can cause melting and, in some cases, material loss. The high temperatures can also damage the lubricant. All of this potentially leads to wear in the rotor bearing. In galvanometers, there is the additional problem that the aforementioned pulsed discharges (spark discharges) generally generate stochastic high-frequency electromagnetic interference, which can, for example, disrupt the position detector used to determine the angular position and, due to its stochastic occurrence, cannot be filtered, or can only be filtered very poorly.The problem is exacerbated by the fact that, due to increasing demands on the dynamics (acceleration capability) of galvanometer drives, increasingly higher pulse frequencies and higher voltages are being used, and consequently, position detectors (angular position sensors) with very high bandwidths are being employed, which are more sensitive to higher-frequency interference. Nevertheless, extremely high angular resolution remains crucial.

[0009] The object of the present invention is therefore to provide a galvanometer drive whose susceptibility to malfunctions is reduced compared to the prior art.

[0010] The problem is solved by a galvanometer drive according to claim 1 and a galvanometer scanner according to claim 6.

[0011] SL 10 / PK / 19 December 2024 A galvanometer drive according to the invention with a limited angle of rotation comprises: a rotor rotatable about an axis of rotation (R) extending in the axial direction, wherein the rotor is supported by a bearing mechanism and has a magnet, wherein the bearing mechanism has at least two bearings; a stator surrounding the rotor with a cylindrical opening extending in the axial direction for receiving the rotor and at least one electrical coil attached to the stator, which, when excited, can impart a bidirectional torque to the rotor; an angular position sensor for determining a rotational position of the rotor, which is arranged at an end face of the rotor, wherein at least one bearing is a rolling bearing comprising an outer ring, an inner ring and a plurality of rolling elements between the inner ring and the outer ring, wherein the outer ring and / or the inner ring is at least partiallypreferably made entirely of metallic material and the rolling elements consist at least partially, preferably entirely, of ceramic material, wherein the rolling bearing has an electrically insulating cover plate.

[0012] A rotary actuator, or galvanometer actuator, according to the present invention differs from a conventional electric motor in that the rotor is only movable within a limited angular range. This is due, for example, to the fact that the galvanometer actuator according to the invention has a two-pole stator, whereby the generated torque decreases with the cosine of the actuator angle and is constant at ±90°. 0 has dropped to zero. Accordingly, the galvanometer drive is operated with two poles. Furthermore, a stop element is typically used in the operation of rotary actuators or galvanometer drives to ensure that a certain maximum angle of rotation (e.g., + / -30°) is not exceeded. 0) cannot be exceeded. Accordingly, a winding scheme is adapted to the limited rotation range or adjustment angle range.

[0013] Preferably, the rotor consists entirely or at least substantially entirely of permanent magnetic material. However, the use of a coil is also conceivable.

[0014] SL 10 / PK / 19 December 2024 for the magnetization of the rotor. In one embodiment of the invention, the rotor is provided with grooves around the axis of rotation on its outer surface, which is separated from the stator's inner surface by an air gap, and which preferably have substantially the same radial spacing from one another.

[0015] The axial direction is the direction in which the axis of rotation runs around which the rotor is rotatably mounted. The axial direction and the axis of rotation run parallel to the longitudinal axis of the rotor and, in particular, coincide with this longitudinal axis. Specifically, the axis of rotation can be an axis of symmetry of the essentially cylindrical rotor. The term "bearing mechanism" here does not refer only to a single bearing arranged at a specific location in the axial direction, especially a rolling bearing. Rather, it encompasses a plurality of bearings arranged at different locations in the axial direction, preferably including two bearings arranged at the ends of the rotor in the axial direction.

[0016] Given a specific polarity of the permanent magnet, the direction of the torque is usually coupled to the direction of the current flowing through the electrical coil.

[0017] The bearing mechanism is located between the rotor and the stator. In this context, elements rigidly connected to the stator are also considered components of the stator. For example, such an element rigidly connected to the stator could be a flux guide, which is understood to be a component located outside the coil that serves to guide the magnetic flux of the magnetic field generated by the coil, and in particular to create a closed magnetic circuit. Furthermore, an outer casing of the stator can also be considered an element rigidly connected to the stator, even if it has no or only a very minor effect on the magnetic flux generated by the coil. In short, when it is mentioned that an object is attached to or arranged relative to the stator, this object can refer in particular to the stator.

[0018] SL 10 / PK / 19 December 2024 a rigidly connected element to the stator, e.g. a flux guide in the stator or an outer casing of the stator.

[0019] The wall of the stator's cylindrical opening can be considered the inner wall of a hollow cylinder, where the term "cylinder" is not limited to circular cylinders but is used in a mathematical sense. In particular, recesses or projections (grooves) may be present on the inner wall.

[0020] The excitation of the at least one coil, preferably exactly one coil, can be carried out by means of the pulse width modulation or pulse duration modulation (PWM) mentioned above in common-mode or differential-mode operation.

[0021] The angular position sensor (position detector) is preferably arranged via a shaft at one end face of the rotor, in line with the rotor's axis of rotation. Since the arrangement of the angular position sensor must not impair the rotational movement, structural modifications to a galvanometer drive are generally not as easy to implement compared to a conventional electric motor.

[0022] The angular position sensor preferably detects the current position angle with a high measurement rate in the kHz to MHz range. The galvanometer drives are preferably designed to accommodate rotational accelerations in the range of 1 to 10⁻⁶. 5 rad / s 2 , in some cases up to over 1 ■ 10 6 rad / s 2 Furthermore, performance can be achieved that is one or more orders of magnitude higher than with conventional electric motors.

[0023] Bearings with steel bearing rings are typically used. In combination with steel rolling elements, such as balls, an electrical contact usually forms between the balls and the outer and inner rings of the bearing when the rotor is stationary.

[0024] This grounds the rotor and prevents sparking. However, as soon as the rotor starts rotating, the balls float in the lubricant (oil or oil in a grease matrix) once a certain rotational speed is reached.

[0025] SL 10 / PK / 19 December 2024 and the electrical contact breaks. At this moment, a spark is generated, which vaporizes a small portion of the metal at the contact point. With frequent, oscillating movements, typical for galvanometer scanners, this causes the raceways to erode, which can lead to bearing failure after only a short time.

[0026] The occurrence of bearing currents is already known for conventional electric motors. The primary concern here is the problem of bearing wear. However, the inventors have observed that this problem is more pronounced in galvanometer drives. With an oscillating drive, the thickness of the lubricant film changes in each cycle. This can lead to frequent arcing (spark discharges) at points where the lubricant layer is particularly thin. The challenge of high-precision position detection combined with an oscillating, highly accelerated movement, and thus regular and frequent alternation between electrical insulation and lubricant film breakdown, likely only arises in galvanometer scanners. In particular, for high-precision position accuracy, interference signals must not be coupled into the signals supplied by the position detector (angular position sensor).To reduce the susceptibility to malfunctions of galvanometer drives, the bearing mechanism itself, and not merely the lubricant used in the bearing mechanism, is therefore designed to be electrically insulating according to the invention.

[0027] A known remedy from the prior art is to use insulating rolling elements, e.g., ceramic balls, which are available as standard from bearing manufacturers. However, the inventors have found that short-term discharges (spark discharges) still occur in the bearings during operation with modern, high-performance power amplifiers. A more detailed analysis has shown that these discharges occur between the bearing's outer ring and the inner ring. Here, the insulating capacity is only provided by a narrow air gap and can be further reduced by contamination or abrasion in the bearing oil. The inventors were also able to determine that the occurrence of spark discharges is correlated with the magnitude of the supply voltage or its rate of rise when the coil(s) are driven. This can

[0028] SL 10 / PK / December 19, 2024 explains that the higher the supply voltage, the greater the charge on the rotor and thus the probability of arcing through the insulating gap between the cover plate and the inner ring. While these arcs do not directly damage the raceways, the vaporized material can still enter the bearing and the lubricant, leading to increased wear. It can also reach the position detector, which, for reasons of minimal inertia, is located close to one of the bearings. If the vaporized material settles there, the accuracy of the position detector can degrade over time. In particular, the arcing also generates an electromagnetic pulse that can couple into the high-precision position detector and severely disrupt it.As the inventors have discovered, this disturbance is interpreted by the highly dynamic control system of a galvanometer scanner as a mispositioning, leading to uncontrolled, jerky movements of the scan mirror. The stochastic occurrence of the spark discharges prevents the signals from being filtered.

[0029] In this rolling bearing, the inner ring is attached to the rotor and the outer ring to the stator. A rolling element cage is optional. Suitable ceramic materials for the rolling elements (e.g., balls) include silicon nitride (SisN4) or zirconium oxide (ZrÜ2). If only part of the rolling elements is made of ceramic, for example, a steel core can be coated with ceramic material. Of course, all other components of the rolling bearing could also be made of ceramic. However, this would result in a very high price for the bearing. The inventors have found that, in a galvanometer drive, it is possible to manufacture the inner and / or outer bearing rings from metallic material while still ensuring a sufficient reduction in stochastic spark discharges, thereby reducing susceptibility to malfunctions and improving positioning accuracy.The partial construction of the bearing inner ring and / or the bearing outer ring from metal (for example, if both are made entirely of steel) has the further advantage that the bearing's load-bearing capacity and resistance to sudden temperature changes are better compared to all-ceramic bearings. Bearings are frequently used to reduce radial...

[0030] SL 10 / PK / December 19, 2024 The bearing race is also pressed onto the rotor or into the bearing seat, which is only possible with metallic bearing rings. Ceramic rings would break due to the brittleness of the material.

[0031] It should be mentioned in passing that, theoretically, the build-up of electrical charges on the rotor relative to the stator could be prevented by establishing an electrical connection between them. On the stator side, charges can be prevented, for example, by placing the stator at a defined potential, such as by connecting it to ground. Similarly, the rotor could also be placed at a defined potential, specifically the stator potential. The problem here, however, is that the rotor's movement would necessitate the use of sliding contacts. Besides the fact that sparking also occurs in sliding contacts, these contacts also produce wear, which reduces long-term stability. Furthermore, sliding contacts introduce mechanical resistance that must be overcome during movement.

[0032] The latter, in turn, negatively impacts the required motion precision and thus the control accuracy of a galvanometer drive. An alternative method of attaching the electrical connection to the end face of the rotor, for example using a wire, is impractical because the position detector (angular position sensor) for determining the rotor's rotational position is typically located there in a galvanometer drive. Furthermore, the wire could break over time due to the constant movement.

[0033] The use of a conductive lubricant in conjunction with steel balls would also be conceivable. However, the lubricants currently available (e.g., Klüberelectric BQ72-72) have a relatively high resistance. This does not sufficiently prevent stochastic discharges. Furthermore, steel balls often wear out faster. According to the invention, the susceptibility to malfunctions of galvanometer drives is therefore reduced by designing the bearing mechanism to be electrically insulating.

[0034] A very cost-effective method that combines most of the advantages is the insulation of the bearing cover plates. That would also be conceivable.

[0035] SL 10 / PK / December 19, 2024, mentions all-ceramic bearings, ceramic guide shafts, or additional insulation layers or insulated mounting of the bearings. However, all-ceramic bearings have the disadvantage of being expensive, brittle, and sometimes difficult to obtain, making the aforementioned press-fitting of the bearings impossible. Another advantage of insulating the cover plate is that no forces are transmitted through it. Therefore, it can also be made of an inexpensive material such as plastic. This is not possible with guide shafts, for example. On the one hand, the lack of rigidity of plastic would lead to delayed force transmission at the high accelerations that occur; on the other hand, plastic deformation and thermal expansion under temperature cycling would lead to unwanted rotor movements and thus to reduced positioning accuracy.

[0036] With insulated shields, the distance between the metallic elements in the bearing is so large that further insulation measures are generally unnecessary. In principle, this distance could be increased even further by using a non-conductive cage instead of a metallic one. The rolling element cage can be made of plastic (e.g., PTFE or PEEK, which is very temperature-resistant). Alternatively, the same or a similar ceramic material as that used for the rolling elements can be used for the rolling element cage.

[0037] A galvanometer scanner according to the invention has a galvanometer drive according to the invention and an optical element connected to the rotor in such a way that the optical element and the rotor together can perform a rotational movement about the axis of rotation (R).

[0038] The optical element can be, in particular, a rotating mirror for deflecting a laser beam, for example, when the galvanometer scanner is used in a laser processing device. Preferably, the optical element is arranged on a shaft extending along the extension of the rotor's axis of rotation at a front end of the rotor, preferably at the end of the rotor opposite the end where the position sensor is located.

[0039] SL 10 / PK / 19 December 2024 The outer surface of the inner ring may be designed to be electrically insulating.

[0040] Electrical insulation on the outside of the inner ring can be achieved, for example, by coating the inner ring (e.g., made of steel) on its outside with a ceramic coating (e.g., aluminum oxide-based).

[0041] The inner surface of the outer ring can be designed to be electrically insulating.

[0042] Electrical insulation on the inside of the outer ring can be achieved, for example, by coating the outer ring (e.g., made of steel) at least on its inside with a ceramic coating (e.g., aluminum oxide-based).

[0043] In particular, the electrically insulating cover plate can be in mechanical contact with the electrically insulated inner surface of the outer ring along its entire circumference.

[0044] Mechanical contact can be established, for example, by the edge of the cover plate engaging in a recess, preferably an electrically insulating one, on the electrically insulating inner surface of the outer ring. Preferably, the electrically insulating cover plate is made of an electrically insulating material, in particular plastic, ceramic, or a composite material.

[0045] Alternatively, the electrically insulating cover plate can be made of metallic material whose surface has been coated with an electrically insulating layer. Such electrically insulating cover plates can be obtained, for example, by coating a metal cover plate with a non-conductive (insulating) layer, such as a plastic, ceramic, or anodized layer. Surface oxidation of the metal is also a possible method.

[0046] Preferably, the rolling bearing has an outer ring whose contact surface to the bearing seat in the stator is electrically insulating and / or an inner ring whose contact surface to the rotor is electrically insulating.

[0047] SL 10 / PK / 19 December 2024 To achieve electrical insulation, the inside of the inner ring and / or the outside of the outer ring can be provided with an insulating coating (e.g., plastic, ceramic, anodized, oxide). Alternatively or additionally, the insulating coating can be applied to the rotor-side contact surface with the bearing and / or to the stator-side contact surface with the bearing, or, for example, an insulating adhesive layer can be inserted between the inner ring and rotor and / or the outer ring and stator instead of or in addition to a coating.

[0048] Preferably, an insulating element made of electrically insulating material is inserted between the outer ring and the stator and / or between the inner ring and the rotor.

[0049] The insulating element can be, in particular, an insulating ring or an insulating sleeve made of, for example, plastic, ceramic, or a composite material. Alternatively, the insulating element can also have a different, particularly more complex, geometry, for example, if components of devices for reducing the radial movement of the bearing in the bearing seat simultaneously function as an insulating element.

[0050] Preferably, the section of the rotor adjacent to the bearing and / or the section of the stator adjacent to the bearing are made entirely of electrically insulating material.

[0051] The section adjacent to the bearing in the rotor and stator refers in particular to that area of ​​the rotor or stator in which the bearing is accommodated, i.e. the bearing seat.

[0052] A barrier made of electrically insulating material is preferably arranged at least partially between the section of the rotor adjacent to the bearing and the rest of the rotor and / or between the section of the stator adjacent to the bearing and the rest of the stator.

[0053] SL 10 / PK / 19 December 2024 There may be cases where it is not possible to construct the sections of the rotor and stator adjacent to the bearing from electrically insulating material. In these cases, it is possible to insert one or more barriers to current flow between the rotor and stator into the rotor and / or stator. This can be achieved by inserting layers of electrically insulating material (e.g., ceramic, plastic, an oxide, or an electrically insulating adhesive) or by providing a gap in the rotor and / or stator material.

[0054] Preferably, the electrical insulation between rotor and stator is designed such that no spark discharge occurs up to a potential difference of 30 V, preferably 48 V, even more preferably 120 V.

[0055] Resistance to spark discharges can be determined experimentally in a similar manner to the dielectric strength of materials for which the IEC 60243 series of standards has been established. Preferably, a typical rotational motion sequence during the operation of a galvanometer is also specified for the determination; this sequence is typically present in a particular application for which the resistance is to be determined.

[0056] Preferably, the galvanometer drive has a control unit designed to control at least one electrical coil attached to the stator by means of pulse width modulation (PWM), wherein the control voltage is determined as a function of the rotational position of the rotor determined by the angular position sensor.

[0057] A galvanometer scanner according to the invention comprises a galvanometer drive according to the invention and an optical element, wherein the optical element is connected to the rotor in such a way that the optical element and the rotor together can perform a rotational movement about the axis of rotation (R).

[0058] SL 10 / PK / 19 December 2024 Further features and advantages of the invention will become apparent from the description of exemplary embodiments with reference to the accompanying drawings.

[0059] Fig. 1 shows the schematic structure of a galvanometer drive known in the prior art in a section plane perpendicular to the axis of rotation.

[0060] Fig. 2 shows a schematic section in axial direction through an embodiment of a galvanometer drive according to the invention.

[0061] Fig. 3 shows a schematic representation of a rolling bearing.

[0062] Fig. 4 shows a schematic representation of a variant according to the invention of the bearing shown in Fig. 3.

[0063] Fig. 5 shows a schematic representation of a variant according to the invention of the bearing shown in Fig. 4.

[0064] Fig. 6 shows a schematic representation of a modification of the galvanometer drive shown in Fig. 2.

[0065] Fig. 7 shows a possible embodiment of the galvanometer drive according to the invention in a galvanometer scanner.

[0066] Fig. 2 shows a schematic axial section through a galvanometer drive according to an embodiment of the invention, containing the rotor's axis of rotation R. A rotor 110, consisting of a diametrically magnetized permanent magnet, is arranged inside a stator 130, which essentially has the shape of a hollow cylinder to accommodate the rotor 110 in a cylindrical opening. The inner wall of the stator forms the outer boundary of this opening. The rotor is held by means of two bearings 140 and 150 such that it can rotate about an axis of rotation R, which in Fig. 1 runs horizontally through the center of the rotor, relative to the stator unit 130. In the present application,

[0067] SL 10 / PK / 19 December 2024 the direction of the axis of rotation R is referred to as the axial direction and directions perpendicular to this axis as radial directions.

[0068] A change in current is effected in the coil 125 of the stator unit 130 via electrical connection elements 300. As a result of a change in the magnetic field of the coil, the rotor 110 containing the magnet rotates relative to the flux guide 120 of the coil 125 or relative to the stator unit 130. The change in current in the coil is effected by means of the pulse width modulation or pulse duration modulation (PWM) mentioned above, in common-mode or differential-mode operation.

[0069] To prevent the rotor's thermal expansion from causing mechanical stress, the bearing 150 in this embodiment is designed as a floating bearing, unlike the fixed bearing 140. This is achieved by having the outer ring 150a of the bearing 150 form a clearance fit with the bearing seat in the stator unit 130. A wave spring 200 is mounted under preload, allowing the bearing 150 to move within certain limits in the event of thermal movement (size changes) of the rotor 110. The wave spring 200 fixes the axial position of the bearing 150, so that it only changes this axial position during thermally induced movements.

[0070] The invention is described below by way of example with reference to one of the bearings 140, 150 (for example, the floating bearing 150). It should be emphasized that the present invention can be implemented as a fixed or floating bearing regardless of the configuration of the bearings 140 and 150, and can also be implemented in embodiments in which no wave spring 200 is present. In particular, the inventive approach is preferably implemented not only in one bearing, but in all bearings with which the rotor 110 is supported relative to the stator 130.

[0071] According to the invention, improved, preferably complete, isolation of the rotor from the stator is provided. This is achieved by first using insulating materials.

[0072] SL 10 / PK / 19 December 2024 Measures at the storage facility(ies) themselves are described, followed by isolating measures outside the storage facility(ies).

[0073] Fig. 3 schematically shows the basic structure of a rolling bearing 300 with, in this example, spherical rolling elements 301, which are positioned between an inner bearing ring 302 and an outer bearing ring 303. When the inner ring 302 rotates relative to the outer ring 303, the rolling elements 301 roll on the inner ring running surface 302a (outer surface of the inner ring 302) and the outer ring running surface 303a (inner surface of the outer ring 303). The distance between the spherical rolling elements 301 is defined by a bearing cage 304. Shielding washers 305 (also called sealing washers) are attached to the end faces of the rolling bearing and are separated from the inner ring 302 by a narrow gap 307.

[0074] To improve the electrical insulation of the rotor 110 from the stator 130, the rolling elements (balls) 301 in the present invention are made of a non-conductive material. Due to its hardness, ceramic material is particularly suitable for this purpose. However, it would also be conceivable to use steel balls with a ceramic coating. In Figure 3, the insulating effect of the balls 301 is indicated by the addition of the reference numeral 301 i ("i" for "insulating") in brackets.

[0075] For high operating voltages of the galvanometer drive and applications where high dynamics (acceleration) are required, it is advantageous to use additional insulation measures besides the insulating rolling elements.

[0076] Fig. 4 is very similar to Fig. 3. However, unlike Fig. 3, those structural features that can be electrically insulating in addition to the rolling elements 301 i are provided with reference numerals to which the letter "i" has been appended. Otherwise, the numerals of the reference numerals correspond to the reference numerals chosen in Fig. 3 for the respective structural features.

[0077] SL 10 / PK / December 19, 2024 In principle, there is a possibility that a discharge may occur via the cover plates, which are normally made of metallic material, in which the current flows through the narrow gap 307 between the inner ring 302 and the cover plate 305. A remedy for this is the use of electrically insulated cover plates 305i. These can either be made of insulating material (plastic or ceramic) or metallic cover plates can be selected whose surfaces are provided with an insulating coating (plastic, ceramic, anodized).

[0078] As shown in Fig. 4, it is also possible to design the rolling bearing cage 304i from electrically insulating material (e.g., plastic (especially PTFE or PEEK) or ceramic). Furthermore, at least one of the two running surfaces 302ai and 303ai of the rolling balls 301i on the inner ring 302 or outer ring 303, in particular both, can be designed to be electrically insulating, e.g., by providing the inner ring 302 on its outer surface or the outer ring 303 on its inner surface with an insulating coating (e.g., with a ceramic or plastic layer).

[0079] Fig. 5 illustrates an additional advantageous measure for reducing or preventing spark discharges when electrically insulating cover plates are present. Fig. 5 is very similar to Fig. 4. The difference is that the contact points of the cover plate 305i with the outer ring 303 are designated by reference numeral 306. In the figure, there are recesses in the inner surface of the outer ring 303 into which the cover plate 305i engages. The additional measure consists of electrically insulating this contact point with the cover plate 305i. If the contact points of the cover ring 305 to the outer ring 303 are treated as described, the entire area containing the lubricant can be encased in an electrically insulating sheath.

[0080] It should be emphasized that all the described insulation measures can be achieved cumulatively if the entire bearing is made entirely of ceramic. However, this would entail high costs for the bearing, and furthermore, the inner ring 302 and outer ring 303 would have to be made of metal.

[0081] SL 10 / PK / 19 December 2024 (especially steel) advantages regarding stability, which is why, according to the invention, the inner bearing ring 302 and the outer bearing ring 303 are made of metal (especially steel).

[0082] In addition to the described measures for the electrical insulation of the rolling bearings themselves, measures for the electrical insulation of the bearing's surroundings can reduce spark discharges. For example, electrical insulation can be applied to the inside of the inner ring 302 and / or the outside of the outer ring 303. This is illustrated in Fig. 5 by reference numerals 372i and 373i. This creates barriers for the current from the rotor to the stator. The electrical insulation can be achieved, for example, by means of an insulating coating (e.g., plastic, ceramic, anodized aluminum, oxide) on the inside of the inner ring 302 and / or the outside of the outer ring 303. Alternatively or additionally, the insulating coating can be applied to the rotor side at the contact surface with the bearing and / or to the stator side at the contact surface with the bearing (the bearing seat).Alternatively or additionally to the insulating coating, an insulating ring made of insulating material (e.g., plastic, ceramic, or a composite material) can also be attached to the inside of the inner bearing ring 302 and / or the outside of the outer bearing ring 303 for electrical insulation. Instead of an insulating ring, an insulating component with a more complex geometry can also be used, for example, components of devices for reducing the radial movement of the bearing in the bearing seat.

[0083] The aforementioned measures for isolating the bearings are also shown in Fig. 6, but for the sake of clarity, only for bearing 150. This does not, however, preclude their application in conjunction with the other bearing 140. Furthermore, Fig. 6 also shows additional isolation measures that can be implemented on the stator side and / or the rotor side.

[0084] For example, in Fig. 6 an electrically insulating barrier 150i can be seen, which is arranged on the side of the bearing 150 facing the stator 130. Likewise, a

[0085] SL 10 / PK / December 19, 2024 shows an electrically insulating barrier 140i, which is arranged on the end face of the bearing 140 facing the coil 120. Both insulating barriers support the electrical isolation of the respective bearing from the stator. Although, as a rule, due to other design requirements, the bearing seat in the stator cannot be completely electrically isolated from the stator, the barriers still have a beneficial effect with regard to reducing spark discharges. With barrier 140i, it is particularly evident that improved isolation of the entire bearing can also be achieved by electrically insulating the entire section of the stator in which the bearing 140 is located. An electrically insulating barrier can be achieved by inserting electrically insulating intermediate elements or adhesive layers.Furthermore, a surface of a section of the stator can be provided with an insulating coating where the section borders another section.

[0086] Finally, individual sections of the stator, e.g., the one in which the bearing is located, can also be made entirely of electrically insulating material.

[0087] On the rotor side, it is possible to construct the sections of the rotor adjacent to the bearings, typically sections 1100 and 1101 adjacent to the rotor magnets at the end faces, also known as guide shafts, entirely from insulating material, e.g., ceramic or composite material (CFRP, etc.). Alternatively, electrically insulating barriers can be inserted where the guide shafts adjoin the rotor magnets. This can again be achieved by inserting electrically insulating intermediate elements or adhesive layers. Alternatively, a surface of the guide shaft and / or the rotor magnet can be provided with an insulating coating, at least where they adjoin each other.

[0088] Fig. 7 shows by way of example the use of the rotary actuator shown in Fig. 2 in a galvanometer scanner, in that a mirror 1000 is attached to the end face of the rotor 110, by rotating the mirror a laser beam hitting the mirror can be directed to another location.

[0089] SL 10 / PK / 19 December 2024

Claims

Patent claims 1. Galvanometer drive with limited angle of rotation comprising: a rotor rotatable about an axially extending axis of rotation (R), wherein the rotor is supported by a bearing mechanism and has a magnet, the bearing mechanism having at least two bearings; a stator surrounding the rotor with an axially extending cylindrical opening for receiving the rotor and at least one electrical coil attached to the stator, which, when excited, can impart a bidirectional torque to the rotor; an angular position sensor for determining a rotational position of the rotor, which is arranged at an end face of the rotor, wherein at least one bearing is a rolling bearing (300) comprising an outer ring (150a, 303), an inner ring (150b, 302) and a plurality of rolling elements (301i) between the inner ring and the outer ring, wherein the outer ring (150a, 303) and / or the inner ring (150b, 302) is at least partiallypreferably are made entirely of metallic material and the rolling elements (301 i) consist at least partially, preferably entirely, of ceramic material, wherein the rolling bearing has an electrically insulating cover plate (305i).

2. Galvanometer drive according to claim 1, wherein the electrically insulating cover plate (305i) consists of an electrically insulating material, in particular plastic, ceramic or a composite material.

3. Galvanometer drive according to claim 1, wherein the electrically insulating cover plate (305i) consists of metallic material whose surface has been provided with an electrically insulating coating. SL 10 / PK / 19 December 2024 4. Galvanometer drive according to one of the preceding claims, wherein the electrical insulation between rotor and stator is designed such that no spark discharge occurs up to a potential difference of 30 V, preferably 48 V, more preferably 120 V.

5. Galvanometer drive according to one of the preceding claims, comprising a control unit designed to control the at least one electrical coil attached to the stator by means of pulse width modulation (PWM), wherein the control voltage is determined as a function of the rotational position of the rotor determined by the angular position sensor.

6. Galvanometer scanner comprising: a galvanometer drive according to one of claims 1 to 5 and an optical element (1000) connected to the rotor (110) in such a way that the optical element (1000) and the rotor (110) can jointly perform a rotational movement about the axis of rotation (R). SL 10 / PK / 19 December 2024

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