Linear unit and system

Abstract

The invention relates to a linear unit (10) and a system (100) comprising such a linear unit (10). The linear unit comprises i) a housing (12), ii) a screw (14) rotatably mounted within said housing (12), iii) a nut (16) cooperating with said screw (14), iv) a carriage (18) supported on an outside of that housing (12) and being movable along said housing (12) by means of a guide assembly (20), and v) a coupling element (30) coupling said carriage (18) to said nut (16) such that upon the movement of said nut (16) along said screw (14), said carriage (18) is taken along.

Description

[0001] Linear unit and system

[0002] The invention relates to a linear unit and a system comprising such a linear unit.

[0003] For moving and positioning components such as machine parts, linear units are known in the art. Said linear units convert rotational motion, e.g. of an electric motor, into translational motion. To this end, a rotatable screw is provided which cooperates with a nut. Upon driving rotation of the screw, e.g. by means of the motor, the nut translates along the screw. The movement of the nut is transferred to the machine part, usually via a push tube.

[0004] Longevity of such linear units strongly depends, amongst others, on the loads exerted on the screw. Particularly radial loads, which may increase friction or even slightly deform the screw, severely reduce service life of the screw and / or nut. A common solution to prevent such radial loads on the screw is to ensure a tight guiding of the machine part along the longitudinal axis of the linear unit. In some cases, however, such guiding is not feasible, e.g. if the machine part does not exclusively moves along the longitudinal axis of the linear unit .

[0005] It is thus an object of the invention to provide an improved handling of radial loads acting on a linear unit, particularly to prevent or at least reduce radial loads acting on a screw of the linear unit.

[0006] This object is solved by the linear unit and the system according to the independent claims. Preferred embodiments are subj ect to the dependent claims and the following description .

[0007] The linear unit for converting the rotational motion into translational motion, according to a first aspect o f the invention, comprises i ) a housing, ii ) a screw rotatably mounted within said housing, iii ) a nut cooperating with said screw, iv) a carriage supported on an outside of that hous ing and being movable along said housing by means of a guide assembly, and v) a coupling element coupling said carriage to said nut such that upon the movement of said nut along said screw, said carriage is taken along .

[0008] An aspect of the invention is based on the approach of at least partially decoupling a screw of a linear unit from radial loads by coupling a nut cooperating with said screw with a carriage . Said carriage is preferably configured for attachment of an external component which is to be moved . A guiding arrangement for said carriage may then absorb the radial component of any load exerted by the external component . The carriage guided by the guiding arrangement can thus ef fectively separate radial loads from axial loads . Hence , axial load applied to the carriage may come through to the screw, while radial load is diverted to another path .

[0009] Here and in the following, "axial" and "axially" preferably refers to a direction parallel to a longitudinal axis of the linear unit , particularly parallel to the screw or an axis of rotation of said screw .

[0010] Accordingly, "radial" and "radially" preferably refer to a direction perpendicular to the longitudinal axis of the linear unit , particularly perpendicular to the screw or an axis of rotation of said screw . Alternatively or additional ly, "radial" and "radially" may refer to a direction perpendicular to a mounting surface of the guiding arrangement .

[0011] Preferably, the guiding arrangement is mounted on an outer side of a housing of the linear unit . The housing can ef fectively support the guiding arrangement and thus the carriage against radial loads . Any radial load applied to the carriage may thus be diverted through the outer structure of the linear unit without af fecting the screw . Preferably, the path for radial loads to the guiding arrangement and housing i s shorter than the path for radial loads to the nut . Therefore , radial load will advantageously first come through to the guiding arrangement and the housing before reaching the nut .

[0012] For coupling the nut arranged within the housing to the carriage arranged outside of the housing, a coupling element is provided . The coupling element preferably keeps the nut and the carriage axially at the same height . It is further preferred that the coupling element provides a sti f f connection between the nut and the carriage in the axial direction, such that movement of the nut can immediately af fect the axial position of the carriage .

[0013] This configuration is advantageous also due to its compactness . The coupling element can easily be integrated in the linear unit without using up signi ficant amounts of space .

[0014] The nut and the screw preferably cooperate by means of a plurality of planetary rollers radially arranged between them . The nut and the screw thus may form a planetary rol ler screw mechanism . Alternatively, the nut and the screw may cooperate by means of a plurality of balls , thus forming a ball screw mechanism . Preferred embodiments of the invention and further aspects thereof are described below, each of which, unless expressly excluded, may be combined with each other and with the aspects of the invention described below as desired .

[0015] In order to allow for a secure - and preferably axially sti f f - connection between the nut and the carriage , said coupling element preferably at least partially encloses said nut along a circumferential direction of said nut . For example , the coupling element may comprise a reception section for at least partially receiving the nut . The reception section, which advantageously forms a seat for the nut in said coupl ing element , may essentially have the shape of a pipe bisected along its middle axis .

[0016] The coupling element , particularly the reception section, is preferably connected to said nut by means of two , preferably cylindrical , trunnions . Advantageously, said trunnions are received in corresponding seats . By means of the trunnions , axial loads can directly and reliably be trans ferred between the nut and the coupling element .

[0017] Said trunnions may, for example , extend from said nut on two opposite sides . The trunnions may hence be received by slots in the coupling element , particularly in the reception section . This not only allows for a reliable mechanical coupling between the nut and the coupling element , but also facilitates assembly .

[0018] The two trunnions may be coaxial . The axes of the trunnions preferably cross a screw central axis . By this means , lever arm ef fects and rotation of the nut can be avoided or at least reduced . The slots in the coupling element , particularly the reception section, may be formed between two respective fingers of said coupling element . Hence , each trunnion is preferably received by said coupling element , particularly the reception section, between the two fingers of said coupling element .

[0019] Preferably, the immediate axial load trans fer between the nut and the coupling element is achieved by having the trunnions abut on seat walls , e . g . the fingers of the coupling element , in a direction parallel to the screw . In other words , it is preferred that the trunnions have an axial tight fit within their seats .

[0020] On the other hand, in order to prevent or at least reduce any radial load to be trans ferred from the coupling element to the nut , it is preferred that the trunnions have clearance with respect to the seats in a circumferential direction of the nut or reception section, respectively . Particularly, the trunnions may be arranged at a distance to the end of the respective slot .

[0021] In order to enable the absorption of e . g . vibrations or ( axial ) load spikes , it is preferred that the seats each include a damping element . Said damping elements preferably comprise two concentric sleeves with an elastic material arranged therebetween . Advantageously, the trunnions are seated in the inner one of the two concentric sleeves .

[0022] Alternatively, the trunnions are each rotationally mounted within their respective seat by means of the bearing . This may prevent or at least reduce friction and associated load when the coupling element slightly tilts about the trunnions in a plane parallel to the screw . In a similar manner, other low friction elements such as bushings may be used instead of bearings for rotational ly mounting the trunnions in the respective seat .

[0023] Instead of providing cylindrical trunnions , it can be considered to provide trunnions comprising a flat contact surface which contacts a complimentary flat seat surface . Preferably, said contact and seat surface each have a surface normal that is parallel to the screw, i . e . said surfaces are axially oriented . Preferably, the flat seat surfaces are formed by the seat walls , particularly the long side walls defining the slots . By having trunnions with flat contact surfaces , the force acting on the trunnions or the seats upon axial load trans fer between the nut and the coupling element can be distributed over a larger area . Hence , the acting pres sure can effectively be reduced, reducing strain and improving longevity of the components .

[0024] An alternative or additional option to allow for the reduction of surface contact pressure between trunnions their respective seats is to provide seats each including a seat insert . Advantageously, said seat inserts receive the respective trunnion . Preferably, said seat inserts are movably arranged between the two level opposite seat walls in a direction substantially tangential to the screw, e . g . between the two respective fingers of the coupling element . To this end, the seat inserts may comprise flat side surfaces , which advantageous ly form sliding surfaces sliding along the seat walls . Preferably, the side walls contact the flat seat surface , which is complimentary to the side surfaces . Said side surfaces and said seat surfaces advantageously each have a surface normal parallel to the screw . The seat inserts may also allow radial movement of the trunnions . Preferably, the ( cylindrical ) trunnions are received by complementary bores in the seat inserts so as to be rotatable with respect to the seat inserts .

[0025] In order to convert rotation of the screw into translation of nut , the nut has to sit on the screw in a torque-proof manner . To this end, the nut and the coupling element are preferably interlocking such that said nut cannot rotate relative to said coupling element . Particularly, the nut and the coupling element can form an interlocking assembly that trans fers torque between the nut and the coupling element . In contrast to common interlocking assemblies formed by e . g . nut and housing, designing the nut and the coupling element to be interlocking may be advantageous in terms of required space . Particularly, no additional space for arranging a dedicated interlocking assembly is required .

[0026] One way of making the nut and the coupling element interlocking is to provide a nut or a coupling element comprising at least one elongate proj ection in a direction parallel to the screw, i . e . in the axial direction . Said elongate proj ection is advantageously received by a complimentary groove of the coupling element or nut , respectively . The proj ection and the groove have to be arranged necessarily on surfaces of the nut and the coupling element , particularly the reception section, that are facing each other . Hence , no additional space is required for forming such an interlocking assembly .

[0027] In order to enable improved stability of the coupling element against pivoting movement , it is conceivable to additionally make the nut and the housing interlocking as well . Preferably, said housing or said nut hence comprise at least one elongate proj ection in a direction parallel to the screw, wherein said elongate proj ection is received by a complimentary groove of said nut or said housing, respectively . Having the nut be interlocking with both the coupling element and the housing may hence even more ef fectively restrict movement of the coupling element to the axial direction .

[0028] Preferably, the web of the coupling element is movably mounted to the carriage . This may further add to ef fectively decoupling the nut from radial loads .

[0029] For example , the web may be radially movable with respect to the carriage , i . e . perpendicular to the screw and / or mounting surfaces of the guiding assembly . Alternatively or additionally, the web may be rotatable with respect to the carriage about a central axis of said web, which is advantageously extending radially, i . e . perpendicular to the screw and / or mounting surfaces of the guiding assembly .

[0030] To this end, it is preferred that the web comprises a web trunnion which extends perpendicular to the screw, i . e . radially . Advantageously, the web trunnion extends along the central axis of the web . Preferably, the web trunnion is received by a carriage seat in a floating manner, that e . g . allows rotation and radial translation of the web relative to the carriage .

[0031] The system, according to a second aspect of the invention, comprises a first component and a second component movable , particularly pivotable , relative to the first component . Preferably, a linear unit according to the first aspect of the invention is mounted to said first component . Further , said second component is preferably coupled to the carriage of said linear unit . Thereby, a connection between the second component and the nut can be established via the coupling element that does not or only to a very limited extend trans fers radial loads from the second component to the nut . Rather, radial load may be absorbed or diverted through the guide assembly and the housing . Keeping the nut - and hence the screw - substantial ly free of radial loads enables an increased service li fe .

[0032] The properties , features and advantages of the invention described above , as well as the manner in which they are achieved, will be explained in more detail in connection with the figures in the following description of examples . Where appropriate , the same reference signs are used in the figures for the same or corresponding elements of the invention . The examples serve to explain the invention and do not limit the invention to the combinations of features indicated therein, even with respect to functional features . Moreover, any of the features disclosed in the above description as well as in the examples below may be considered in isolation and suitably combined with the features of any of the above embodiments and their further aspects . In particular, each of the features described above and below may be combined alone or in conj unction with others of the described features with the linear unit according to the first aspect of the invention and the system according to the second aspect of the invention .

[0033] It is shown, in particular schematically, in

[0034] Fig . 1 an example of a linear unit in a cross-sectional side view;

[0035] Fig . 2 an example of a coupling element in a side view; Fig. 3 the coupling element of figure 2 in a cross-sectional view;

[0036] Fig. 4 an example of a force acting on a carriage;

[0037] Fig. 5 an example of a flexibly mounted trunnion;

[0038] Fig. 6 an example of a rotatably mounted trunnion;

[0039] Fig. 7 an example of a system;

[0040] Fig. 8 an example of a seat including a seat insert; and

[0041] Fig. 9 an example of a coupling element being movably mounted to a carriage.

[0042] Figure 1 shows an example of a linear unit 10 for converting rotational motion into translational motion in a cross-sectional side view. The linear unit 10 comprises a housing 12, a screw 14 rotatably mounted within said housing 12, a nut 16 cooperating with said screw 14, a carriage 18 supported on the outside of said housing 12 by means of a guide assembly 20, and a coupling element 30 coupling said carriage 18 to said nut 16. The screw 14 is driveable by means of a motor 22. Upon rotation of the screw 14, the nut 16 travels along the screw 14. Due to the coupling element 30 connecting the nut 16 and the carriage 18, the carriage 18 moves synchronously with the nut 16. The carriage 18 comprises an attachment structure 24 for attaching an external component, e.g. a machine part, to be moved.

[0043] The guide assembly 20 is preferably mounted to the housing 12 on an outer side 12a, for example a top side, of said housing 12. In order to enable for the coupling element 30 to couple the nut 16 to the carriage 18 , the housing 12 is at least partially open to the outside at said outer side 12a . For example , the housing 12 may comprise an opening 12b in said outer side 12a through which said coupling element 30 extends . This opening 12b is indicated in figure 1 by the dashed lines .

[0044] By arranging the carriage 18 movably on the guide assembly 20 , for example a pair of guide rails , supported by the housing 12 , radial loads exerted of the carriage 18 e . g . by the external component attached to the attachment structure 24 are not or at least not fully trans ferred to the nut 16 , but diverted via the housing 12 . Substantially only axial loads are transferred between nut 16 and carriage 18 by means of the coupling element 30 . The structure of the linear unit 10 shown in figure 1 thus ef fectively separates axial and radial loads .

[0045] Figure 2 shows an example of a coupling element 30 in a side view . The coupling element 30 couples a nut 16 to a carriage 18 such that upon axial movement of the nut 16 , the carriage 18 is taken along .

[0046] The nut 16 is received in a reception section 32 of the coupling element 30 . The reception section 32 thus forms a seat for the nut 16 . The reception section 32 is connected to the carriage 18 via a web 34 . Reception section 32 and web 34 are preferably integral , i . e . formed as a single piece .

[0047] In order to allow trans fer of axial loads between the nut 16 and the coupling element 30 , the coupling element 30 is coupled to the nut 16 via trunnions 36 received in respective seats 38 . In the present example , the trunnions 36 are arranged on opposite sides of the nut 16 and extend radially from a lateral surface 16a of the nut 16 . Accordingly, the seats 38 are formed by the coupling element 30 , particularly in the reception section 32 . In the present example , the seats 38 are formed by slots 40a in the coupling element 30 , particularly the reception section 32 . The slots 40a - and thus the seats 38 - are each formed between two fingers 40 o f the coupling element 30 . The slots 40a ( and fingers 40 ) extend in a circumferential direction of the reception section 32 and are preferably open at a lower end 42a of the coupling element 30 . Said lower end 42a is opposite to an upper end 42b of the coupling element 30 . At the upper end 42b, the coupling element 30 is coupled to the carriage 18 .

[0048] The trunnions 36 are cylindrical in shape and preferably coaxial . Thus , the coupling element 30 may pivot relative to said nut 16 about the trunnions 36 , i . e . a central axis of said trunnions 36 . This may be facilitated by providing the seats 38 with bearings or other low friction elements as shown in figure 6 and described in more detail below .

[0049] The trunnions 36 preferably have a tight seat in their respective seat 38 in the axial direction, i . e . they axially contact the coupling element 30 . Therefore , axial loads can be immediately trans ferred between nut 16 and coupling element 30 and thus between nut 16 and carriage 18 .

[0050] On the other hand, the trunnions 36 preferably have clearance with respect to the seats 38 in a circumferential direction of the nut 16 or reception section 32 , respectively . That is , the trunnions 36 advantageously do not contact the coupling element 30 in the circumferential direction . This may help in even more reliably decoupling the nut 16 from radial loads , as even i f a radial force is acting on the coupling element 30 , the coupling element 30 may move perpendicular to the longitudinal axis of the nut 16 without exerting any forces on the nut 16 . Due to their cylindrical shape and the clearance in their seats 38 , the contact between the trunnions 36 and the coupling element 30 is substantially a line contact . This may reduce friction when the coupling element 30 moves perpendicular to the longitudinal axis of the nut 16 , and thus reduces radial load on the nut 16 , or when the coupling element 30 tilts about an axis parallel to the trunnion axes , thus e f fectively rotating about the trunnions 36 .

[0051] Figure 3 shows the coupling element 30 of figure 2 in a cross- sectional view . Additionally, a housing 12 is shown in which the nut 16 is arranged . The nut 16 cooperates with a screw 14 by means of a plurality of planetary rollers 14a radially arranged between the screw 14 and the nut 16 . On a top side of the housing 12 , a guide assembly 20 comprising a pair of guide rails 20a is arranged, by means of which the carriage 18 is movably mounted to the housing 12 . On said top side , the housing 12 comprises an opening 12b to allow coupling o f the carriage 18 to the nut 16 . To this end, the coupling element 30 , particularly the web 34 , extends through the opening 12b .

[0052] The coupling element 30 , particularly the reception section 32 , at least partially encloses the nut 16 . Particularly, an inner surface 32a of the reception section 32 may be formed complementary to the lateral surface 16a of the nut 16.

[0053] Preferably, the lateral surface 16a of the nut 16 does not contact the inner surface 32a . Particularly, the nut 16 may have radial clearance in the seat 38 formed by the reception section 32 . This allows a mechanical decoupling of the nut 16 from the coupling element 30 in the radial direction . In order to lock the nut 16 against rotation, the nut 16 and the coupling element 30 are interlocking . To this end, the nut 16 comprises an elongate proj ection 16b that extends in the axial direction ( i . e . perpendicular to the figure plane ) and is received by a complementary groove 44 of the coupling element 30 . The nut 16 is thus received by the reception section 32 in a torque-proof manner . Proj ection 16b and groove 44 form an interlocking assembly .

[0054] In the present example , the nut 16 is additionally interlocking with the housing 12 . Accordingly, the nut 16 comprises a second elongate proj ection 16b that extends in the axial direction and is received by a complementary groove 12c of the housing 12 . Again, second proj ection 16b and groove 12c form an interlocking assembly .

[0055] Preferably, the two proj ections 16b of the nut 16 are arranged on opposite sides of the nut 16 . Particularly, the two proj ections 16b may advantageously extend in a plane perpendicular to the opening 12b .

[0056] In the present example , the trunnions 36 radially extend from the nut 16 and are received by the seats 38 in the coupling element 30 . However, it is also conceivable that the trunnions 36 extend from the coupling element 30 and are received by seats 38 in the nut 16 . In this case , the seats 38 may be formed by recesses in the nut body .

[0057] Figure 4 shows an example of a force F acting on a carriage 18 . Said carriage 18 is movably mounted to a housing (not shown) by means of a guide assembly 20 indicated by dashed lines . The carriage 18 is coupled to a nut 16 by means of a coupling element 30 that comprises seats 38 for two trunnions 36 extending radially from the nut 16 on opposite s ides . The force F has two components: an axial component Fa and a radial component Fr . The axial component Fa is transferred to the nut 16 via the coupling element 30. Particularly, the axial component Fa is transferred to the nut 16 at the region where the trunnions 36 contact the coupling element 30. The radial component Fr, however, is at least partially diverted via the guide assembly 20 to the housing, as indicated by arrows A. The radial component Fr thus does not (substantially) act on the nut 16. This may be facilitated by the nut 16 having clearance in a reception section 32 of the coupling element 30, and the trunnions 36 having clearance in the seats 38 in a circumferential direction of the nut 16 or reception section 32, respectively.

[0058] For immediate axial load transfer between nut 16 and coupling element 30, the trunnions 36 preferably have a tight seat in their respective seat 38 in the axial direction, i.e. they contact the coupling element 30. In the shown example, the trunnions 36 are not cylindrical, but have two flat contact surfaces 36a. These contact surfaces 36a contact complementary flat seat surfaces 38a. By this means, the axial component Fa may be transferred to the nut 16 via a larger area (that is, the area of the contact surfaces 36a) and thus reduce the strain compared to a transfer via a line contact.

[0059] Figure 5 shows an example of a trunnion 36 flexibly mounted within a seat 38 of a coupling element 30. To this end, the seat 38 includes a damping element 46, e.g. two concentrically arranged sleeves with an elastic material 46a arranged therebetween. Preferably, the trunnion 36 is received within the inner one of said sleeves. This may not only reduce vibrations, but also prevent or at least reduce load spikes when transferring load in an axial direction. Figure 6 shows an example of a trunnion 36 rotatably mounted within a seat 38 of a coupling element 30 . To facil itate rotation of the trunnion 36 relative to its seat 38 , the trunnion 36 may be mounted in the seat 38 by means of a bearing 48 . Alternatively, other types of low friction elements such as bushings may be utili zed . Rotatably mounting the trunnion 36 within the seat 38 ef fectively allows pivoting of the coupling element 30 relative to a nut comprising said trunnion 36 about said trunnion 36 , i . e . about a central axis of said trunnion 36 (perpendicular to the figure plane ) .

[0060] Figure 7 shows an example of a system 100 comprising a first component 102 and a second component 104 pivotably mounted at the first component 102 . The system 100 further comprises a linear unit 10 mounted to the first component 102 . A carriage 18 of the linear unit 10 is coupled to the second component 104 , such that upon linear translation of the nut , the second component 104 pivots about a j oint 106 relative to the first component 102 . The connection between the carriage 18 and the second component 104 may be established by means of a connector 108 attached to an attachment structure 24 o f the carriage 18 at one end and to the second component 104 at the opposite end .

[0061] Preferably, the carriage 18 is movably mounted to a housing (not shown) of the linear unit 10 by means of a guide assembly, guiding the movement in a direction parallel to a longitudinal axis of the linear unit 10 . Movement of the carriage 18 is driven by a nut (not shown) cooperating with a rotatable screw, wherein connection between the nut and the carriage 18 is established by means of a coupling element (not shown) . This configuration allows at least a partial decoupling of loads exerted e . g . by the connector 108 on the carriage 18 in a direction perpendicular to the direction of movement of the carriage 18 from the nut .

[0062] Figure 8 shows an example of a seat 38 including a seat insert 50 receiving a trunnion 36 of a nut 16 . The seat insert 15 is received between two fingers 40 of a coupling element 30 . The seat insert 50 is preferably rectangular and movably arranged within a slot 40b formed by the two fingers 40 . Particularly, the seat inserts 50 comprises two opposite flat side surfaces 50a which are in flat contact with complementary flat seat surfaces 38a of seat walls , i . e . flat surfaces of the sidewalls of said fingers 40 .

[0063] The seat insert 50 comprises a central bore 52 which receives the trunnion 36 . In the shown example , the trunnion 36 is cylindrical and thus rotatable with respect to the seat insert 50 .

[0064] Figure 9 shows an example of a coupling element 30 being movably mounted to a carriage 18 , wherein said carriage 18 is movable along an outer side of a housing (not shown) o f a linear unit by means of a guide assembly 20 . The coupling element 30 couples a nut 16 cooperating with a screw 14 to the carriage 18 . To this end, the coupling element 30 comprises a reception section 32 forming a seat for the nut 16 . The nut 16 is coupled to the reception section 32 by means of trunnions 36 received by respective seats 38 . I f the trunnions 36 are cylindrical , as in the present example , the coupling element 30 may be pivotable about a longitudinal axis of the trunnions 36 , i . e . an axis perpendicular to the figure plane .

[0065] The coupling element 30 extends from the reception section 32 , i . e . nut 16 , to the carriage 18 by means of a web 34 . The web 34 preferably extends perpendicular to the screw 14 or a longitudinal axis of the reception section 32 and / or the nut 16 , respectively .

[0066] At its end opposite to the reception section 32 , the web 34 comprises a web trunnion 54 . The web trunnion 54 extends along a central axis 30a of the coupling element 30 , said central axis 30a being perpendicular to the screw 14 and to the direction of movement of the carriage 18 along the guide assembly 20 .

[0067] The web trunnion 54 , which is preferably cylindrical , is received by a respective carriage seat 56 . Said carriage seat 56 is preferably arranged at a bottom side of said carriage 18 facing the nut 16 . The carriage seat 56 may be formed e . g . by a, preferably cylindrical , recess on the bottom side of the carriage 18 .

[0068] Preferably, the web trunnion 54 has axial clearance inside the carriage seat 56 . The coupling element 30 is thus axially movable with respect to the carriage 18 . Here , "axial" and "axially" refer to a direction parallel to the web central axis 30a, i . e . perpendicular to the screw 14 .

[0069] I f the web trunnion 54 is cylindrical , it may also be rotatably received by the carriage seat 56 , such that the coupling element 30 is rotatable about the web central axis 30a relative to the carriage 18 .

[0070] I f the coupling element 30 also does not tightly sit on the nut 60 , e . g . because the trunnions 36 are received between two fingers of the coupling element 30 as shown in figures 2 and 8 , the coupling element 30 ef fectively establishes a free- floating connection between the nut 16 and the carriage 18 . The mechanical decoupling of the nut 16 from the carriage 18 achievable by this configuration ef fectively and reliably prevents radial loads from acting on the nut 16 .

[0071] List of reference signs

[0072] 10 linear unit

[0073] 12 housing

[0074] 12a outer side

[0075] 12b opening

[0076] 12c groove

[0077] 14 screw

[0078] 14a planetary roller

[0079] 16 nut

[0080] 16a lateral surface

[0081] 16b proj ection

[0082] 18 carriage

[0083] 20 guide assembly

[0084] 20a guide rail

[0085] 22 motor

[0086] 24 attachment structure

[0087] 30 coupling element

[0088] 32 reception section

[0089] 32a inner surface

[0090] 34 web

[0091] 36 trunnion

[0092] 36a contact surface

[0093] 38 seat

[0094] 38a seat surface

[0095] 40 finger

[0096] 40a slot

[0097] 42a lower end

[0098] 42b upper end

[0099] 44 groove

[0100] 46 damping element

[0101] 46a elastic material

[0102] 48 bearing 50 seat insert

[0103] 50a side surface

[0104] 52 bore

[0105] 54 web trunnion 56 carriage seat

[0106] 100 system

[0107] 102 first component

[0108] 104 second component 106 j oint

[0109] 108 connector

[0110] F force

[0111] Fa axial component Fr radial component

[0112] A arrow

Claims

Claims1. A linear unit (10) for converting rotational motion into translational motion, comprising- a housing ( 12 ) ,- a screw (14) rotatably mounted within said housing (12) ,- a nut (16) cooperating with said screw (14) ,- a carriage (18) supported on the outer side (12a) of said housing (12) and being movable along said housing (12) by means of a guide assembly (20) , and- a coupling element (30) coupling said carriage (18) to said nut (16) such that upon a movement of said nut (16) along said screw (14) , said carriage (18) is taken along.

2. The linear unit (10) according to claim 1, wherein said coupling element (30) at least partially encloses said nut (16) along a circumferential direction of said nut (16) .

3. The linear unit (10) according to claim 1 or 2, wherein said coupling element (30) is connected to said nut (16) by means of two trunnions (36) , said trunnions (36) being received in corresponding seats (38) .

4. The linear unit (10) according to claim 3, wherein said trunnions (36) extend from said nut (16) on two opposite sides, each trunnion (36) being received by said coupling element (30) between two fingers (40) of said coupling element (30) .

5. The linear unit (10) according to claim 3 or 4, wherein said trunnions (36) abut on seat walls in a direction parallel to the screw (14) , and have clearance with respect tothe seats (38) in a circumferential direction of the nut (16) .

6. The linear unit (10) according to any one of claims 3 to 5, wherein said seats (38) each include a damping element (46) , said damping element (46) comprising two concentric sleeves with an elastic material (46a) arranged therebetween .

7. The linear unit (10) according to any one of claims 3 to 5, wherein said trunnions (36) are each rotationally mounted within their respective seat (38) by means of a bearing (48) .

8. The linear unit (10) according to any one of claims 3 to 5, wherein said trunnions (36) comprise a flat contact surface (36a) which contacts a complimentary flat seat surface (38a) , said contact surface (36a) and seat surface (38a) each having a surface normal parallel to the screw ( 14 ) .

9. The linear unit (10) according to any one of claims 3 to 6, wherein said seats (38) each include a seat insert (50) receiving the respective trunnion (36) , said seat inserts (50) being movably arranged between two level opposite seat walls in a direction substantially tangential to the screw (14) and comprising flat side surfaces (50a) which contact a complimentary flat seat surface (38a) , said side surface (50a) and seat surface (38a) each having a surface normal parallel to the screw (14) .

10. The linear unit (10) according to any one of the preceding claims, wherein said nut (16) and said coupling element (30) are interlocking such that said nut (16) cannot rotate relative to said coupling element (30) .

11. The linear unit (10) according to claim 9, wherein said nut (16) or said coupling element (30) comprises at least one elongate projection (16b) in a direction parallel to said screw (14) , said elongate projection (16b) being received by a complementary groove (44) of said coupling element (30) or said nut (16) , respectively.

12. The linear unit (10) according to any one of claims 9 and 10, wherein in addition to said coupling element (30) and said nut (16) being interlocking, said housing (12) or said nut (16) comprises at least one elongate projection (16b) in a direction parallel to said screw (14) , said elongate projection (16b) being received by a complementary groove (12c) of said nut (16) or said housing (12) , respectively.

13. The linear unit (10) according to any of the preceding claims, wherein a web (34) of the coupling element (30) is movably mounted to the carriage (18)14. The linear unit (10) according to claim 13, wherein the web (34) comprises a web trunnion (54) , said web trunnion (54) extending perpendicular to said screw (14) and being received in a carriage seat (56) in a floating man- ner .

15. 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 one of the preceding claims is mounted to said first compo- nent (102) , and said second component (104) is coupled to the carriage (18) of said linear unit (10) .

Images