Linear unit and system

Abstract

The present invention relates to a linear unit (10) and a system (100) comprising such a linear unit (10). The linear unit (10) comprises i) a housing (12), ii) a spindle (14) rotatably mounted in the housing (12), iii) a nut (16) cooperating with the spindle (14), and iv) two fastening assemblies (30) for fastening the housing (12) to an external structure (E). The fastening assemblies (30) each comprise at least two pins (32) arranged transversely to the spindle (14). The pins (32) are preferably movably mounted in bearing shells (34) arranged on opposite sides of the spindle (14).

Description

The present invention relates to a linear unit and a system comprising such a linear unit.Linear units for moving and positioning components such as machine parts are known in the art. Such linear units convert a rotational movement, e.g. of an electric motor, into a translatory movement. For this purpose, a rotatable spindle is provided which interacts with a nut. As the spindle rotates with the motor, the nut translates along the spindle. The movement of the nut is transmitted to the machine part, for example via a push tube.The longevity of such linear units is, among other things, highly dependent on the loads exerted on the spindle. In particular, the life of the spindle and / or nut is greatly reduced by radial loads which increase friction or can even easily deform the spindle. Such loads can arise not only due to inadequate (radial) guiding of the machine part, but also due to thermal expansion of components of the linear unit itself. Further, when the linear unit is fixedly attached to an external structure, deformation of the structure may cause deformation of the linear unit, i.e., components thereof, which may also result in such loads.Thus, an object of the invention is to increase the life of a linear unit, particularly to reduce the loads acting on the linear unit due to deformation of an external structure to which the linear unit is attached or due to thermal expansion of the linear unit.This object is achieved by a linear unit and a system comprising such a linear unit according to the independent claims.Preferred embodiments are the subject of the dependent claims and the following description.The linear unit for converting the rotational movement into a translatory movement according to a first aspect of the invention comprises i) a housing, ii) a spindle rotatably fixed in the housing, iii) a nut cooperating with the spindle, and iv) two fixing arrangements for fixing the housing to an external structure. The fastening arrangements each comprise at least two pins which are arranged transversely to the spindle, in particular to a rotational axis of the spindle. The pins are preferably movably mounted in preferably circular bearing shells which are arranged on opposite sides of the spindle, in particular on opposite sides of the axis of rotation of the spindle.One aspect of the invention is based on the approach of fastening the linear unit to an external structure in a flexible, in particular articulated manner, such that a deformation of the external structure is not transmitted to the linear unit, in particular to the spindle and / or a housing in which the spindle is arranged. For this purpose, the linear unit preferably comprises a fastening system for fastening the linear unit to the external structure, which allows the linear unit, in particular the spindle and / or the housing, to maintain its initial shape and / or initial orientation even if the external component deforms. The initial shape preferably corresponds to the shape without any load. For example, the attachment system may be configured to self-align the linear unit when the attachment points at which the linear unit is attached to the external structure are displaced due to deformation of the external structure. The linear unit, in particular the fastening system, can thus account for at least in part for any misalignment between the linear unit and the external structure caused by deformation of the external structure during operation. Furthermore, the linear unit, in particular the fastening system, can at least partially accommodate any changes in the distance between fastening points on the linear unit caused by thermal expansion of the linear unit itself.Preferably, the linear unit comprises two fastening arrangements for fastening the housing of the linear unit to the external structure, e.g. at four fastening points. The fastening arrangements are advantageously configured to hold the linear unit, in particular the nut and / or the housing, in an unloaded state, in particular independently of the position of the four fastening points with respect to the linear unit. In other words, the four attachment points can move with respect to the linear unit without applying any forces to the linear unit, at least to a certain extent that is to be expected in consideration of thermal expansion or deformation of the external structure due to external loads.For example, the two mounting arrangements may each comprise two pins movably mounted in respective bearing shells. The bearing shells or pins can thus move with deformation with the external structure or with thermal expansion with the linear unit without or with only partial transmission of this movement to the corresponding counter piece. In other words, by movably fastening the pins in the bearing shells, the pins and the bearing shells-and thus the linear unit and the external structure-are preferably movably decoupled, at least to a certain extent. Such a pin movably fastened in a bearing shell can be fastened in the bearing shell, for example, rotatably, pivotably and / or translationally (i.e. linearly movable). This means that the pin can rotate, pivot and / or move translationally with respect to the bearing shell. For this purpose, the pin can be accommodated by a corresponding seat in the bearing shell. The seat can be arranged rotatably and / or rotatably in the bearing shell, for example. Additionally or alternatively, the seat may allow for translatory (linear) movement of the pin relative to the bearing shell.By providing the linear unit with such a fastening system, in particular with two such fastening arrangements, functionality and reliability of the linear unit can be ensured even for long periods of time.The nut and spindle preferably cooperate by a plurality of planetary rollers radially interposed therebetween. The nut and the spindle can thus form a planetary roller screw drive. Alternatively, the nut and the spindle may cooperate by a plurality of balls, thus forming a ball screw.Preferred embodiments of the invention and further aspects thereof are described below, wherein all these can be combined with one another and with the aspects of the invention described below as desired, unless this is explicitly excluded.The two fastening arrangements are preferably arranged at opposite ends of the linear unit, in particular of the housing. Accordingly, the spindle, in particular an external thread of the spindle, is arranged axially between the two fastening arrangements such that the sum of the axial distances between the nut and each of the fastening arrangements is constant. This allows a particularly stable and robust attachment of the linear unit to the external structure.Here and in the following, unless expressly stated to the contrary, "axial" refers to a direction which runs parallel to a longitudinal axis of the linear unit, i.e. parallel to the spindle or its axis of rotation.In order to allow decoupling of the linear unit from a deformation of the external structure which has an effect on the alignment of the fastening points, i.e. of the components of the fastening arrangements which are fixedly attached to the external structure, the pins of at least one of the fastening arrangements are rotatably fastened in the respective bearing shells. For example, bending the external structure in a plane perpendicular to the pins may affect the orientation of the attachment points. Accordingly, it is preferred that the pins be rotatable about their longitudinal axes relative to the bearing shells.To allow decoupling from bending of the external structure in a plane parallel to the pins, the pins of at least one of the mounting arrangements are preferably axially translationally movable with respect to their respective bearing shell. For this purpose, the pins can have axial play with respect to their seat in the respective bearing shell. Here, "axial" refers to the longitudinal axis of the pins. Accordingly, the pins are advantageously located further in and / or out of their respective seat.In a further preferred embodiment, one of the mounting arrangements is arranged on a head piece of the linear unit, wherein the head piece is mounted on a front end plate of the housing. The front end plate can close the housing on its front side, e.g. in a region adjoining a free end of the spindle. Because the head piece is fastened to the front end plate, additional degrees of freedom are made possible for moving the fastening arrangement arranged on the head piece, in particular adjusting its orientation and / or axial position.For example, the head piece may be pivotably attached to the front end plate of the housing and / or axially translationally movable with respect to the front end plate of the housing. As a result, the orientation and / or position of the corresponding fastening arrangement can be changed without having an effect on the orientation and / or position of the housing.Such adaptive connection between the front end plate and the head can be achieved by providing a head comprising a cylindrical bore in which an axial protrusion of the front end plate is received.In some embodiments, the protrusion has a lateral surface with an annular convex curvature. The protrusion may be formed, for example, by a cylindrical pin having a spherical front end. The bulge of the protrusion advantageously contacts an inner wall of the central bore and can slide axially along the inner wall and / or pivot with respect to the wall.Alternatively, the axial protrusion may be cylindrical, i.e. have a completely planar lateral surface. In this case, the head piece preferably comprises a cavity with an inner wall region which is formed in a complementary manner to a spherical surface region of a central bearing disc. Thus, the central bearing disc is pivotable in the cavity. The central bearing disc advantageously comprises a central bore in which the axial cylindrical projection of the front end plate is axially translationally movable. Thus, the head and the central bearing disc may form a central spherical bearing which is axially translationally movable on the axial cylindrical protrusion of the front end plate.Preferably, the studs of at least one of the mounting arrangements comprise a mounting base for fixedly attaching the studs to the external structure. In this case, the bearing shells of one of the fastening arrangements are advantageously arranged in the head piece. The bearing shells are preferably formed at least in part by depressions in the head piece which receive the pins. Bushings may additionally be disposed in the recesses to allow rotation of the received pins relative to the head piece.Alternatively, the studs of one of the mounting arrangements extend from the header on opposite sides. In this case, the pins are preferably formed integrally with the head piece, i.e. integrally with the head piece. In order to improve the adaptability of the alignment of the head piece to a deformation of the external structure and / or thermal expansion of the linear unit, it is preferred that the pins in the bearing shells are fastened pivotably with respect to the bearing shell central axis. In particular, the bearing shells can form spherical bearings for the journals.The bearing shell central axis is preferably parallel to a surface normal of the opening of the bearing shell, i.e. a region surrounded by the bearing shell. When the bearing shells are secured to the external structure on a mounting surface, the bearing shell center axes are preferably perpendicular to the mounting surface.Another option for providing at least one additional degree of freedom for aligning and / or positioning the pins of the attachment assembly disposed on the header with respect to the external structure and / or housing is to provide a header that includes a bearing eye in which a central spherical bearing is disposed. This central spherical bearing may be formed by bushes with spherical contact surfaces in some embodiments.Preferably, the studs extend from the central spherical bearing on both sides of the bearing eye. In this case, the tenons on both sides of the head piece may be formed by a single rod which is received by the central spherical bearing, in particular an inner bushing, which is arranged in the bearing eye of the head piece. Here, the head piece is preferably formed integrally with the front end plate of the housing.To allow axial translatory movement of the pins relative to the housing, the pins preferably extend eccentrically from the central spherical bearing. For this purpose, the inner bushing can have a seat, for example a cylindrical bore, which accommodates the pins, in particular the only rod, which is arranged eccentrically with respect to a central longitudinal axis of the bushing. Due to this eccentric construction of the central spherical bearing, a rotational movement of the journals about a central axis of the bearing eye can have a translatory component in the axial direction.The movements of the external structure with respect to the linear unit due to a deformation of the external structure and / or thermal expansion of the linear unit or at least some components thereof are small compared to the dimensions of the linear unit, are e.g. in the range of a few millimeters. The central spherical bearing may be a deformable spherical bearing. The deformable spherical bearing advantageously comprises an elastic material surrounding an inner bushing in which the studs are fixed. In particular, the elastic material is arranged between an inner bushing and an outer bushing coaxial with the inner bushing. The sleeves may have spherical surface areas facing each other with the elastic material interposed therebetween. By inserting a deformable central spherical bearing, it is possible to absorb vibrations. Further, a certain degree of rigidity in a predefined direction may be provided as needed, which is advantageous for a standard operation of the linear unit.As mentioned above, the bearing shells may form spherical bearings for allowing pivotal movement of the pins in the bearing shells and thus further increasing the degrees of freedom for moving and / or aligning the linear unit with respect to the external structure. For this purpose, at least one of the fastening arrangements preferably comprises bearing disks which are rotatably fastened in the bearing shells of the fastening arrangement. Preferably, the bearing disks each have a mount which receives the respective journal. The bearing shells can each have a spherical inner surface region which is complementary to a spherical surface of the respective bearing disc. Thus, the bearing disks are pivotable in a cavity formed by the spherical inner surface of the bearing shells. Thus, when the bearing shells are fixedly attached to the external structure, the pins received by the sockets of the bearing disks may be pivotable with respect to the external structure.Additionally or alternatively, in order to compensate for compression or elongation of the external structure and / or of the linear unit, the pins of at least one of the fastening arrangements can be moved in translation preferably in the bearing shells in a direction running perpendicular to the longitudinal axis of the pins, in particular parallel to the spindle.For example, at least one of the mounting arrangements may include bearing washers rotatably mounted in the bearing shells, the bearing washers each having a socket that receives one of the pins. Preferably, the studs have two parallel flat surfaces that contact opposite inner surfaces of the sockets. Advantageously, the sockets are elongated so that the pins in the sockets are translationally movable. For example, the sockets may be formed by elongated holes in the bearing disks. Accordingly, each of the pins can translate independently within its bearing shell perpendicular to its longitudinal axis.Alternatively, a translatory movement of the journals within the bearing shells can be realized by providing at least one fastening arrangement which comprises bearing disks rotatably fastened in the bearing shells, wherein the bearing disks each have a mount which accommodates one of the journals. Advantageously, the mounts are arranged eccentrically on the bearing disks. A rotation of the journals about a central axis of the bearing disks or of the bearing shells also has a component in the axial direction, i.e. parallel to the spindle.The system according to a second aspect of the invention comprises a first component and a second component which is movable, in particular pivotable, with respect to the first component. Preferably, a linear unit according to the first aspect of the invention is fastened to the first component by the fastening system, in particular the two fastening arrangements, and the second component is coupled to the nut of the linear unit.In this configuration, the linear unit is preferably freely floatingly attached to the first component. In particular, this configuration can prevent or at least considerably reduce the effect of loads caused by a deformation of the first component and / or thermal expansion of the linear unit on the linear unit, in particular its spindle. In other words, deformations of the first component, such as bending, torsion and / or compression / extension, are not transferred to the linear unit.As a result, the service life of the linear unit, in particular of its spindle, can be extended considerably.The characteristics, features and advantages of the invention described above, as well as the manner in which they are achieved, are explained in more detail in connection with the figures in the following description of examples. Where appropriate, the same reference numerals are used in the figures for the same or corresponding elements of the invention. The examples are intended to illustrate the invention and do not limit the invention to the combinations of features given herein, even with respect to functional features. Moreover, any of the features disclosed in the above description and the examples below can be considered individually and correspondingly combined with the features of one of the above embodiments and their further aspects. In particular, each of the features described above and below can be combined with the linear unit according to the first aspect of the invention and the system according to the second aspect of the invention alone or in combination with other of the features described.They show, in particular schematically: FIG. 1 shows an example of a linear unit comprising two mounting arrangements; FIG. 2 shows an example of a head piece in a cross-sectional view; FIG. 3 shows a cross-sectional view of a further example of a head piece; FIG. 4 shows a still further example of a head piece in a three-dimensional view; FIG. 5 shows an example of two fastening arrangements in a side view; FIG. 6 shows a further example of two fastening arrangements in a side view; FIG. 7 shows an example of a flexible spherical bearing; and FIG. 8 shows an example of a system comprising two components and a linear unit for pivoting the two components with respect to each other.FIG. 1 shows an example of a linear unit 10 for converting a rotational movement, for example a motor 18, into a translatory movement. The linear unit 10 includes a housing 12, a spindle 14 rotatably mounted in the housing 12, a nut 16 cooperating with the spindle 14, and two mounting assemblies 30 for mounting the linear unit 10, particularly the housing 12, to an external structure (not shown). The two fastening assemblies 30 may form a fastening system.The motor 18 is operatively coupled to the spindle 14 through a gear box disposed in a gear box 20. The gear box 20 is disposed at a distal or rear end 12 bof the housing 12. By rotating the spindle 14, the nut 16 is moved translationally along the spindle 14. The nut 16 is coupled to a carriage 22 disposed outside the housing 12 so that the carriage 22 is carried along as the nut 16 moves. The movement of the carriage 22 along the housing 12 is guided by guide rails 24 disposed on an upper side of the housing 12. The carriage 22 comprises a fastening structure 26 for fastening a component, for example a machine part, to the carriage 22.The mounting arrangements 30 each comprise two pins 32 which are movably mounted in bearing shells (not visible in FIG. 1 ). The two pins 32 of each fastening arrangement 30 extend perpendicular to a longitudinal axis L of the linear unit 10, in particular to the spindle 14. Advantageously, the two pins 32 of each fastening arrangement 30 are arranged on opposite sides of the linear unit 10, in particular the spindle 14. The linear unit 10 can thus be fastened to the external structure at four fastening points.Each stud 32 includes a mounting base 32a for fixedly attaching the respective stud 32 to the external structure. The mounting bases 32 amay include through holes 32 cto screw the pins 32 to the external structure (for clarity, only one through hole 32 cis indicated with a reference numeral).One of the mounting assemblies 30 is disposed at the rear end 12 bof the housing 12. The other attachment assembly 30 is disposed on a head 40 of the linear unit 10, the head 40 being attached to a proximal or forward end 12 aof the housing 12.Preferably, the studs 32 of the mounting arrangement 30 disposed at the rear end 12b are rotatably mounted only in their respective bearing shells. In other words, the components of the mounting assembly 30 are all axially fixed. However, the studs 32 of the mounting arrangement 30 disposed on the head piece 40 are preferably movably mounted in their respective bearing shells such that movement of the head piece 40 is permitted with respect to additional degrees of freedom, i.e., not only rotation, but also axial and radial movements. Alternatively or additionally, the header 40 may be attached to the housing 12 such that at least a portion of the additional degrees of freedom are provided.Accordingly, in the example of FIG. 1, the pins 32 follow any movement caused by deformation of the external structure. Because the pins 32 of the front mounting assembly 30 are movably mounted in their bearing shells and / or the head 40 is movably mounted to the front end 12a, the linear unit 10 can maintain its initial orientation. In other words, by moving the pins 32 in the respective bearing shell and / or the head piece 40 with respect to the housing 12, any deformation, e.g. bending, torsion and / or compression / extension, of the external structure can be compensated. Likewise, by moving the pins 32 with respect to the respective bearing shell, a thermal expansion of the linear unit 10 or of some of its components, in particular of its spindle 14, can be compensated. In this regard, the linear unit 10 may be freely suspended to the external structure at its front end 12a by the mounting assemblies 30. Due to the inherent stiffness of the components of the linear unit 10, particularly the housing 12, the mounting assemblies 30 may be considered self-aligning.FIG. 2 shows an example of such a head piece 40 in a cross-sectional view. Here, the head 40 is movably attached to a front end plate 50 of the housing 12. The front end plate 50 closes the housing 12 at its front end 12a in the vicinity of a free end of the spindle 14.The head 40 includes a cylindrical bore 42 that receives an axial protrusion 52 of the front end plate 50. The axial protrusion 52, which preferably extends along the longitudinal axis L, is axially movable within the cylindrical bore 42. This may allow compensating for, e.g., thermal expansion of the linear unit or extension / compression of the external structure E due to external loads.Additional degrees of freedom for positioning and / or aligning the external structure E with respect to the linear unit can be made possible by providing the axial protrusion 52 with a convex, preferably spherical, annular surface region 54 a. The surface region 54 amay be formed by a curvature 54 of the lateral surface 52 aof the protrusion 52. Preferably, under load, surface portion 54a contacts an inner wall of cylindrical bore 42 in a point-like manner. This type of point-like contact between the axial protrusion 52 and the head 40 allows the head 40 to pivot about the axial protrusion 52, and also allows translation along the spindle axis.In the example shown in FIG. 2, the pins 32 are fixedly attached to the external structure E via the attachment bases 32 a. In particular, the linear unit is arranged between two walls of the external structure E, wherein the pins 32 extend through openings in the walls. The pins 32 are received in recesses 44 of the head piece 40. Here, the depressions 44 form the bearing shells 34 of the fastening arrangement 30, which is arranged on the head piece 40. To enable the pins 32 to be rotated in the bearing shells 34, bushings 36 can optionally be arranged in the bearing shells 34 / depressions 44.Preferably, the studs 32 have axial play D in the recesses 44. Thus, the studs 32 can translate along their longitudinal axis A, thereby allowing self-alignment of the attachment assembly 30 to the header 40 upon bending of the external structure E in the figure plane of FIG. 2.FIG. 3 shows a cross-sectional view of a further example of a head piece 40. Similar to the example shown in FIG. 2, the header 40 is movably attached to the front end plate 50 of the housing 12.However, the head piece 40 here comprises a preferably spherical cavity 46, in which a central bearing disc 48 is accommodated. An inner surface portion 46a of the cavity 46 is formed complementary to the spherical surface portion 48a of the center bearing disc 48. The central bearing disc 48 is thus pivotable within the cavity 46. In other words, the head piece 40 and the central bearing disk 48 form a spherical bearing.Preferably, the central bearing disc 48 includes the cylindrical bore 42 in which the axial protrusion 52 of the front end plate 50 is received. Here, the axial protrusion 52 is cylindrical, i.e., has a planar lateral surface 52 a, so that it is linearly translationally movable only within the cylindrical bore 42.Further, unlike the example shown in FIG. 2, the studs 32 of the mounting assembly 30 are fixedly attached to the header 40. In particular, the pins 32 are formed integrally with the head piece 40, i.e. integrally with the head piece 40. The free ends of the pins 32 are movably mounted in the bearing shells 34, and the bearing shells 34 may be fixedly mounted on the external structure E.In the present example, the pins 32 are not only rotatably but also pivotally mounted in the bearing shells 34, particularly with respect to a bearing shell center axis X (indicated by a dashed line). For this purpose, the fastening arrangement 30 comprises bearing disks 38 which comprise a seat for the free ends of the pins 32. The bearing disks 38 each comprise a spherical surface region 38 a. An inner surface region 34 aof the bearing shells 34 is of complementary design, such that the bearing shells 34 and the bearing disks 38 together form a spherical bearing.The bearing shells 34 further comprise bores 38b which receive the pins 32. The bores 38b thus form the seats for the pins 32 in the bearing shells 34.Preferably, the pins 32, at least their free ends, are axially movable in the bores 38b, i.e. along their longitudinal axis A (indicated by a dash-dotted line) - and thus, when the bearing shells 34 are attached to a mounting surface of the external structure E, are movable perpendicular to the mounting surface.FIG. 4 shows yet another example of a head piece 40 in a three-dimensional view. Here, the head 40 is fixedly secured to the front end plate 50 of the housing 12. The head piece 40 comprises a bearing eye 64, in which a central spherical bearing 56 is arranged. Preferably, the pins 32 extend from the central spherical bearing 56 on both sides of the bearing eye 64. the spherical bearing 56 may allow not only rotation of the pins 32 but also pivoting about the central axis of the bearing eye 64.In this example, the studs 32 may be formed by a single rod 58 passing through the bearing eye 64 and the seat provided by the spherical bearing 56.FIG. 5 shows an example of two fastening arrangements 30 in a side view. A linear unit 10 is fixed to an external structure E by the fixing assemblies 30.One of the mounting assemblies 30 is disposed at a rear end 12 bof a housing 12 of the linear unit 10. The mounting assembly 30 includes two pins 32 (only one of which is seen) rotatably mounted in bearing shells 34 (only one of which is seen). To enable rotation, a bushing 36 is radially disposed between each pin 32 and the corresponding bearing shell 34.The other of the fastening arrangements 30 is arranged on a head piece 40 of the linear unit 10. The head 40 is fixed to the housing 12, more specifically, to a front end plate thereof (not shown), at a front end 12 aof the housing 12. Studs 32 of the mounting assembly 30 are also movably mounted in bearing shells 34.In contrast to the fastening arrangement 30 at the rear end 12 b, the pins 32 of the fastening arrangement 30 on the head piece 40 are not only rotatable in the respective bearing shell 34 but also pivotable. For this purpose, the journals 32 are seated in bearing disks 38. The bearing disks 38 form spherical bearings with the corresponding bearing shells 34, as was explained in more detail in connection with FIG. 3.In addition, the pins 32 are also translationally movable in their bearing shells 34 in a direction perpendicular to a longitudinal axis of the pins 32 (which is perpendicular to the figure plane in FIG. 5 ). In particular, the pins 32 can be translationally movable in a direction running parallel to a longitudinal axis L of the linear unit 10.To this end, the studs 32 of the mounting assembly 30 on the head piece 40 include two parallel flat surfaces 32b that contact inner surfaces 60a of a socket 60 in the bearing washers 38. The sockets 60 thus define the seats of the studs 32 in the bearing shells 34.Advantageously, the sockets 60 are elongated and the pins 32 have play in the elongated sockets 60 transverse to their longitudinal axis.FIG. 6 shows a further example of two fastening arrangements 30 in a side view. As in FIG. 5, a linear unit 10 is attached to an external structure E by the attachment assemblies 30.The fastening arrangements 30 correspond to the fastening arrangements shown in FIG. 5. The only difference is that the translational movability of the pins 32 of the mounting arrangement 30 arranged on the head piece 40 is not achieved by elongated mountings but by an eccentric arrangement of the mountings 60 on the bearing disks 38. in other words, the mountings 60 receiving the pins 32 are arranged at a distance from a centre point of the bearing disks 38. As a result, upon rotation of the bearing disks 38, the pins 32 follow a curved path in the bearing shells 34 and move translationally perpendicular to their longitudinal axis. This translatory movement along the curved path also has a component parallel to the longitudinal axis L of the linear unit 10.In the example shown, the center point of the bearing shells 34 of the fastening arrangement 30 on the head piece 40, and thus the pivot point or the pivot axis of the bearing disks 38 in the bearing shells 34, is offset O radially from the longitudinal axis L. The offset O is preferably selected such that the pins 32 are at the same height, i.e. are arranged in a plane running parallel to the longitudinal axis, in a neutral position of the linear unit 10 with respect to the external structure E, i.e. without deformation of the external structure E and without thermal expansion of the linear unit 10. In particular, the longitudinal axis L and the center of the studs 32, or at least their seats 60, lie in the same plane.FIG. 7 shows an example of a flexible spherical bearing in cross section. This type of spherical bearing may be used as, for example, a center spherical bearing (reference numeral 56 in FIG. 4 ). The flexible spherical bearing comprises two coaxially aligned bushes 62a, 62b, between which an elastic material 66 is arranged. The inner bushing 62a has a circumferential surface which is at least partially convex, preferably spherical. The outer bushing 62 bhas a complementary, at least sectionally concave, preferably spherical, inner surface. However, in an alternative embodiment, the sleeves 62a, 62b may have planar circumferential or inner surfaces. By using such a flexible spherical bearing, radial rigidity required for standard operation can be provided, and radial, torsional, axial and conical degrees of freedom are obtained by the elastic material 66 in predetermined directions as required.In addition to or alternatively to using the flexible spherical bearing as a central spherical bearing, such flexible spherical bearings may also be used to movably attach studs to an external structure. In particular, such flexible spherical bearings can replace in principle the spherical bearings formed by bearing disks and bearing shells, for example as shown in FIG. 3. For example, the bearing washers and bearing shells shown in FIG. 3 may be provided with the flexible material 66 disposed between them.FIG. 8 shows an example of a system 100 that includes a first component 102 and a second component 104 pivotally attached to the first component 102. The system 100 further comprises a linear unit 10 attached to the first component 102 by two attachment assemblies 30. A nut (not shown) of the linear unit 10 is coupled to the second component 104 such that the second component 104 pivots about a joint 106 relative to the first component 102 upon linear translation of the nut. The connection between the nut and the second component 104 may be accomplished by a carriage having a mounting structure 26 (see FIG. 1 ) and a connector 108 attached at one end to the mounting structure 26 and at the opposite end to the second component 104.By the two fastening arrangements 30, the linear unit 10 can be decoupled from deformations of the first component 102, which are caused, for example, by a load exerted by the second component 104. Likewise, one of the mounting arrangements 30 can align itself during thermal expansion of the linear unit 10, so that no load is generated.List of reference characters10 Linear unit 12 Housing 12 aFront end 12 bBack end 14 Spindle 16 Nut 18 Motor 20 Gear 22 Slide 24 Guide rail 26 Fixing structure 30 Fixing assembly 32 Trunnion 32 a Base 32 b Flache surface 32 cThrough holes 34 Lagerschale shell 34 a Innenflächen surface area 36 Bushing 38 Lager disk 38 a Sphärisch surface area 38 b Bore 40 Head piece 42 Bore 44 Depression 46 Cavity 46 a Innenflächen surface area 48 Mittige disk 48 a Sphärisch surface area 50Front end plate 52 Projection 52 a Laterale surface 54 Wölbung 54 a Konvex annular surface area 56 Mittige spherical bearing 58 Rod 60 Mount 60 a Innenfläche surface 62 a Innere bushing 62 b Äußere bushing 64 Bearing eye 66 Elastic material 100 System 102 First component 104 Second component 106 Joint 108 Connector E Externe structure L Longitudinal axis a longitudinal axis X bearing shell central axis D play O offset

Claims

A linear unit (10) for converting a rotational movement into a translatory movement, comprising: - a housing (12), - a spindle (14) rotatably fixed in the housing (12), - a nut (16) cooperating with the spindle (14), and - two fixing arrangements (30) for fixing the housing (12) to an external structure (E), wherein the fixing arrangements (30) each comprise at least two pins (32) arranged transversely to the spindle (14), the pins (32) being movably fixed in bearing shells (34) arranged on opposite sides of the spindle (14).The linear unit (10) of claim 1, wherein the pins (32) of at least one of the mounting assemblies (30) are rotatably mounted in their respective bearing shells (34).Linear unit (10) according to claim 1 or 2, wherein the pins (32) of at least one of the fastening arrangements (30) are axially translatory movable with respect to their respective bearing shells (34).The linear unit (10) of any preceding claim, wherein one of the mounting assemblies (30) is disposed on a head (40) of the linear unit (10), the head (40) being mounted on a front end plate (50) of the housing (12).The linear unit (10) of claim 4, wherein the head (40) is pivotally attached to the front end plate (50) of the housing (12) and / or is axially translationable with respect to the front end plate (50) of the housing (12).The linear unit (10) of claim 5, wherein the head (40) comprises a cylindrical bore (42) in which an axial protrusion (52) of the front end plate (50) is received, the protrusion (52) having a lateral surface (52a) with an annular convex curvature (54).The linear unit (10) of claim 5, wherein the head (40) comprises a cavity (46) having an inner surface portion (46a) complementary to a spherical surface portion (48a) of a central bearing disc (48) such that the central bearing disc (48) is pivotable within the cavity (46), and the central bearing disc (48) comprises a cylindrical bore (42) in which an axial cylindrical protrusion (52) of the front end plate (50) is axially translationally movable.The linear unit (10) according to any one of claims 4 to 7, wherein the pins (32) of at least one of the fastening arrangements (30) comprise a fastening base (32a) for fixedly attaching the pins (32) to the external structure (E), and the bearing shells (34) of one of the fastening arrangements (30) are arranged in the head piece (40).The linear unit (10) of any of claims 4 to 7, wherein the pins (32) of one of the mounting assemblies (30) extend from the head (40) on opposite sides and are pivotally mounted in the bearing shells (34) with respect to the bearing shell center axis (X).The linear unit (10) of claim 9, wherein the head piece (40) comprises a bearing eye (64) in which a central spherical bearing (56) is arranged, the pins (32) extending from the central spherical bearing (56) on both sides of the bearing eye (64).The linear unit (10) of claim 10, wherein the pins (32) extend eccentrically from the central spherical bearing (56).Linear unit (10) according to any of claims 10 or 11, wherein the central spherical bearing (56) is a deformable spherical bearing comprising an elastic material (66) surrounding an inner bushing (62a) in which the studs (32) are fixed.The linear unit (10) of any preceding claim, wherein at least one of the mounting assemblies (30) comprises bearing washers (38) rotatably mounted in the bearing shells (34) of the mounting assembly (30), the bearing washers (38) each having a socket (60) receiving the respective journal (32), and the bearing shells (34) each having a spherical inner surface area (34a) complementary to a spherical surface area (38a) of the respective bearing washer (38) to form spherical bearings.Linear unit (10) according to one of the preceding claims, wherein the pins (32) of at least one of the fastening arrangements (30) in the bearing shells (34) can be moved in translation in a direction running perpendicular to a longitudinal axis (A) of the pins (32).The linear unit (10) of claim 14, wherein at least one of the mounting assemblies (30) comprises bearing washers (38) rotatably mounted in the bearing shells (34), the bearing washers (38) each having a socket (60) that receives one of the pins (32), and the pins (32) have two parallel flat surfaces (32b) that contact opposing inner surfaces (60a) of the sockets (60), and the sockets (60) are elongated such that the pins (32) are translationally movable in the sockets (60).The linear unit (10) of claim 14, wherein at least one of the mounting assemblies (30) comprises bearing washers (38) rotatably mounted in the bearing shells (34), the bearing washers (38) each having a socket (60) that receives one of the pins (32), and the sockets (60) are eccentrically disposed on the bearing washers (38).A system (100) comprising a first component (102) and a second component (104) movable relative to the first component (102), wherein a linear unit (10) according to any of the preceding claims is attached to the first component (102) with the two attachment arrangements (30), and the second component (104) is coupled to the nut (16) of the linear unit (10).

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