Abstract:
The invention relates to a cover ( 20 ) for a secondary part ( 2 ) of an electrical linear motor ( 1 ), wherein the secondary part ( 2 ) includes at least one first and one second secondary partial element ( 12 ), and wherein each secondary partial element ( 12 ) comprises a toothed profile, and wherein the cover ( 20 ) extends over the toothed profiles of the first and second secondary partial elements ( 12 ), forming a continuous surface. The invention further relates to a secondary part ( 2 ) comprising a cover ( 20 ) and a linear motor ( 1 ) comprising a secondary part ( 2 ) and a cover ( 20 ).

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2008/053465, filed Mar. 25, 2008, which designated the United States and has been published as International Publication No. WO 2008/116857 and which claims the priority of German Patent Application, Serial No. 10 2007 014 396.8, filed Mar. 26, 2007, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a cover for a secondary part of an electrical linear motor, wherein the secondary part comprises at least one first and one second secondary part element, and wherein each secondary part element has a toothed profile. The invention also relates to a secondary part having a cover, and to a linear motor having a secondary part and a cover. 
     Electrical machines have a primary part and a secondary part. By way of example, the secondary part is a rotor of a rotary electrical machine or else a moving part of a linear motor. By way of example, the primary part is a stator or a stationary part with a single-phase or polyphase winding. In the case of linear motors, both the primary part and the secondary part may be moving parts. 
     In general, stators and rotors for electrical machines have a laminated core, comprising individual electrical laminates, wherein the winding or else permanent magnets for generation of magnetic fields is or are arranged on the laminated core. The individual laminates for stators and rotors are generally stamped individually and are joined together to form laminated cores, for example by stamping and packeting, welding or bracketing. 
     In order to guide the main magnetic flux between a stator and a rotor, toothed laminates are normally used in stators/rotors that are fitted with windings. The winding is arranged in the slots in the laminates and the laminated core. After the insulation of the slots, the winding is introduced, for example by drawing it in. 
     DE 10 2004 045 992 A1 discloses an electrical machine whose secondary part has no active means, such as windings through which a current can be passed or permanent magnets, for producing a magnetic field. In the case of a permanent-magnet synchronous linear motor with a secondary part without any permanent magnets, the primary part has windings through which a current can be passed and has permanent magnets, wherein the secondary part has only a toothed structure composed of a material which contains iron. 
     WO 2006/032255 A1 discloses a secondary part for an electrical linear motor, wherein the secondary part has no active means for generation of magnetic fields. Various embodiments are specified for a passive secondary part such as this. 
     Linear motors such as these are used in various fields of engineering as drives, in particular direct drives, for example for machine tools, processing machines such as automatic drilling, milling, turning, placement or bonding machines. 
     The physical length of the movement path depends on the purpose of the linear motor, and must be at least as long as the required movement distance plus the length of the rotor. In order to be flexible for the design of linear motors of different length, the secondary parts are, for example, formed from relatively short secondary part elements, which are arranged in a row to form the desired length. 
     The butt joints which are used in this case are, however, disadvantageous, particularly in severe operating conditions, in that dust, operating liquids, aggressive substances, etc. can accumulate in them. It is also impossible to prevent dirt and operating liquids, solid parts, tool pieces, etc. being deposited on the movement path. These foreign objects then, in particular, enter the air gap in the linear motor, thus enormously adversely affecting the life of the linear motor. Particularly in the case of movement paths which are arranged horizontally, it is impossible to prevent accumulation of dirt. Even if there is little dirt, it is only a question of time as to when the linear motor will fail. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a cover which protects a secondary part, which is free of active means for generation of magnetic fields, in particular in the air gap, reliably against foreign objects, which adversely affect the operation. Further objects are to provide a secondary part having a protective cover, as well as a linear motor having a secondary part such as this. 
     This object is achieved according to the invention by a secondary part for a linear motor having at least two secondary part elements, wherein each secondary part element has a toothed profile. The toothed profiles face the air gap and a primary part of the linear motor. Each secondary part element is preferably formed by means of a laminated core which has a plurality of laminates, in particular electrical laminates. However, a secondary part element may also be unlaminated, for example in the form of a solid toothed rod. 
     The toothed profile can be formed by having various profile shapes, that is to say geometries. Examples of geometries are a rectangular shape, a triangular shape or a sinusoidal shape, etc. 
     According to the invention, a cover extends as one part or a plurality of parts over the toothed profiles of at least two secondary part elements, and forms a continuous surface. 
     In a first embodiment, the cover extends in the form of a plurality of parts over the toothed profiles of the at least two secondary part elements, that is to say each secondary part element has a separate cover, wherein the individual secondary part element covers overall produce one cover, and form a continuous surface. 
     The secondary part has a first and a second secondary part element, which are arranged in a row in a movement direction of the primary part, wherein one secondary part element in each case has one cover. This has the advantage that each secondary part element can be manufactured completely with its own cover. After the secondary part elements have been arranged and assembled to form a secondary part, the covers are connected to one another. 
     By way of example, one cover of one secondary part element is formed by means of a cured encapsulation compound. Encapsulation compounds such as these are, for example, casting resins. An encapsulation compound is advantageous since this has no adverse affect on the functionality of the linear motor. Furthermore, the toothed profile is covered completely, in particular in such a way that no dirt can accumulate in corners of the slots. 
     A further possibility is for one cover of one secondary part element to be formed by means of a corresponding laminate section. The secondary part element is formed by means of a laminated core, wherein a plurality of individual laminates are joined together to form the laminated core. The individual laminates are generally stamped individually and are then joined together to form laminated cores by means of stamping and packaging, welding or bracketing. In this case, it is now possible to design the laminate section for the individual laminates such that this results in a cover after the laminates have been joined together. Each individual laminate is stamped out so as to produce a narrow cover for each laminate. This solution is cost-effective, since the laminates must be stamped in any case, and the original for the laminate section need be adapted only once. However, this solution has magnetic disadvantages, since this impedes the guidance of the magnetic fluxes from the primary part to the secondary part. In addition, it is possible for dirt to accumulate in the slots, since they are partially exposed. 
     In addition, one cover for one secondary part element may be in the form of a flat covering plate and may be arranged on, that is to say attached to, the toothed profile of the secondary part. A flat covering plate such as this preferably has a small thickness in the region of tenths of a millimeter, for example 0.3 mm or 0.4 mm, as a result of which there is no adverse affect on the operation, in particular the guidance of the magnetic fields. By way of example, a covering plate such as this is produced from plastic. 
     In the embodied variants with regard to a cover which is formed from a plurality of parts or a plurality of pieces, butt joints and minimal intermediate spaces necessarily result, however, when the individual secondary part elements are arranged with their individual covers in a row. These intermediate spaces are advantageously filled by means of a filling material, wherein the covers can be connected to one another at the same time. By way of example, one such filling material is any suitable plastic, for example silicone. The filling material can connect not only the covers but also the secondary parts to one another. The filling material can be applied to one side of a secondary part element even during manufacture, and then fills the butt joint when the secondary part elements are arranged in a row. However, the filling material can just as well be introduced between the individual butt joints only during assembly of the individual secondary part elements to form a secondary part, for example by being sprayed in (silicone). 
     In a second embodiment, the cover is in the form of an integral covering plate and extends integrally over the toothed profiles, that is to say one integral cover extends over all the secondary part elements that have been arranged in a row, and forms a continuous surface. 
     The cover, which is in the form of a covering plate, can advantageously be attached by means of connecting elements to the toothed profiles of the individual secondary part elements. By way of example, holding elements or holding apparatuses are arranged or formed on the teeth of the toothed profiles, and the covering plate can be clipped, pushed or hooked into them. 
     In a further refinement, the secondary part elements each have a cured encapsulation compound, wherein the covering plate can then be attached to the encapsulation. The encapsulation compound itself provides a continuous surface in the form of a cover for the individual secondary part elements, wherein the covering plate is then placed over the encapsulated toothed profiles. The covering plate has holding elements, for example clips or barbs, which are pressed into the encapsulation compound. This on the one hand creates a continuous cover, while on the other hand fixing the secondary part elements and partially connecting them to one another. In particular, the holding elements are arranged at a predeterminable distance apart from one another on the side of the covering plate which faces the toothed profiles and, in particular, the holding elements are pressed in the area of the butt joints, thus connecting and fixing the secondary part elements. 
     It is also possible to encapsulate the individual secondary part elements and to provide the cured encapsulation with a slot in each case on two opposite sides, and to plug or insert the covering plate into the slots. The slots may be arranged both on the sides parallel to a movement direction and the sides transversely with respect to a movement direction of the primary part. By way of example, the covering plate has attachments by means of which the covering plate is pushed into the slots. Surprisingly, it has been found that a cover according to the invention of the secondary part does not adversely affect the operation of the linear motor, and provides adequate protection against dirt and foreign objects. Furthermore, a choice can be made between the individual variants of the cover depending on the field of use of the linear motor. It is also possible to retrofit a cover to linear motors which are already in use, without major effort. If it becomes dirty or worn, a detachably attached cover can also be replaced. 
     The linear motor according to the invention is preferably in the form of a synchronous machine, wherein the secondary part is the stationary component, and the primary part is the moving component. The secondary part has no active means for production of magnetic fields while, in contrast, the primary part has at least two active means for production of magnetic fields, in particular in the form of windings through which a current can be passed, and permanent magnets. 
     The physical length of the movement path, that is to say of the secondary part, depends on the purpose of the linear motor, and it must be at least as long as the required movement distance plus the length of the rotor (primary part). In order to be flexible for the design of linear motors of different lengths, the secondary parts are formed from relatively short secondary part elements, which are arranged in a row to form the desired length. In this case, any desired number of secondary part elements can be arranged in a row in any desired direction. The secondary part elements can be arranged in a row both in a movement direction of the primary part and transversely with respect to the movement direction of the primary part. The cover according to the invention forms a continuous surface, at least over two secondary part elements. However, the cover may extend over any desired number of secondary part elements, wherein different embodiments of cover can be combined with one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Further features and details of the invention will be explained in more detail in the following description on the basis of exemplary embodiments and in conjunction with the attached drawings. In this case, features and relationships which are described in individual variants can in principle be transferred to all the exemplary embodiments. In the drawings: 
         FIG. 1  shows an outline illustration of a linear motor with a toothed secondary part; 
         FIG. 2  shows a cross-sectional view of the linear motor shown in  FIG. 1 ; 
         FIG. 3  shows a secondary part with a cover, which is formed by means of an encapsulation compound; 
         FIG. 4  shows a secondary part with a cover, which is formed by means of a laminate section; 
         FIG. 5  shows a secondary part with a cover, which is in the form of a covering plate having a plurality of parts; 
         FIG. 6  shows a secondary part having a cover, which is formed from one part and is attached to toothed profiles; 
         FIG. 7  shows a secondary part having a cover, which is formed from one part and is pushed into slots in encapsulation; 
         FIG. 8  shows a secondary part having a cover, which is formed from one part and is attached to the encapsulation; and 
         FIG. 9  shows a detailed view of the attachment shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows an outline illustration of a linear motor  1  having a toothed secondary part  2  and having a primary part  3 . The primary part  3  has a winding  4 , permanent magnets  5  and a laminated core  6 . The movement direction of the primary part  3  is indicated by means of a double-headed arrow  7 , which runs in the longitudinal direction of the linear motor  1 . The laminated primary part  3  has the permanent magnets  5  on the side facing the secondary part  2 . The permanent magnets  5  are fitted such that their magnetization alternates. The permanent magnets  5  produce a magnetic flux whose alignment alternates transversely with respect to an air gap  8 . The winding  4  surrounds the winding teeth  10 , with the winding  4  forming an end winding  11 . The air gap  8  between the primary part  3  and the secondary part  2  forms an air gap plane, wherein the secondary part  2  has teeth  9  which are adjacent to the air gap  8 . The winding  4  of the primary part  3  is a first active means for production of a first magnetic field, and the permanent magnets  5  are a second active means for production of a second magnetic field. The secondary part  2  has no active means for production of magnetic fields. 
       FIG. 2  shows a cross-sectional view of the linear motor  1  shown in  FIG. 1 . The cross-sectional plane runs parallel to or along the movement direction  7  of the primary part  3 . The secondary part  2  is formed from one part and has the teeth  9 . The primary part  3  has the winding  4  as well as the permanent magnets  5 , wherein the winding  4  surrounds winding teeth  10 . End windings  11  are illustrated symbolically by curves. The secondary part  2  is laminated, wherein a large number of individual electrical laminates are layered and joined together parallel to the movement direction  7 . 
       FIG. 3  shows a secondary part  2  with a cover  20  which is formed by means of cured encapsulation compounds  21 . The secondary part  2  has a first and a second secondary part element  12 , which are arranged in a row in the movement direction  7  of the primary part  3  (see  FIG. 2 ), wherein one secondary part element  12  in each case has one cover  20 . Each secondary part element  12  has a toothed profile which is formed by the teeth  9  and slots  13 . 
     After the secondary part elements  12  have been arranged to form an entire secondary part  2 , the covers  20  are connected to one another. According to this embodiment, the cover  20  is formed from a plurality of pieces or a plurality of parts and extends over the toothed profiles of the secondary part elements  12 , that is to say a plurality of partial covers result overall in one cover  20 , and form a continuous surface. 
     One cover  20  of one secondary part element  12  is formed by means of a cured encapsulation compound  21 . Encapsulation compounds  21  such as these are, for example, casting resins. The toothed profile is covered completely, as a result of which no dirt can accumulate, in particular in corners of the slots  13 . 
       FIG. 4  shows a secondary part  2  with a cover  20  which is formed by means of a laminate section  22 . The secondary part elements  12  are each formed by means of a laminated core, wherein a plurality of individual laminates are joined together to form the laminated core. The individual laminates are generally stamped individually and are then assembled by stamping and packaging, welding or bracketing to form laminated cores. It is now possible in this case to design the laminate section  22  for the individual laminates so as to create a cover  20  when the laminates have been joined together. The laminate section  22  may, for example, be designed such that the teeth  9  are each connected to one another by means of a web  30 . In this case, the slots  13  have a rectangular cross section. However, the slots  13  may also have a different cross section, corresponding to the configuration of a web  30 , for example being oval, rounded, semicircular or circular. 
       FIG. 5  shows a secondary part  2  having a cover  20  which is in the form of a covering plate  23  comprising a plurality of parts. The covering plate  23  is attached or fixed to the toothed profile of the secondary part  2 . The covering plate  23  is as thin as possible, with a thickness in the tenths of millimeter range, as a result of which there is no adverse affect on operation, and in particular on the guidance of the magnetic fields. A covering plate  23  such as this is produced, for example, from plastic and is adhesively bonded to the teeth  9  of the secondary part elements  12 . 
     In the refinements shown in  FIG. 3 ,  FIG. 4  and  FIG. 5 , the cover  20  is in each case formed from a plurality of pieces or a plurality of parts. When the secondary part elements  12  are joined together, this necessarily results in butt joints with minimal intermediate spaces  24 . These intermediate spaces  24  are filled by means of a filling material  25 , with the covers  20  being connected to one another at the same time. By way of example, a filling material  25  such as this is any suitable plastic, for example silicone. In addition to the covers  20 , the filling material  25  can also connect the secondary part elements  12  to one another. The filling material  25  may be applied to one side of a secondary part element  12  even during manufacture, and then fills the intermediate space  24  of a butt joint when the secondary part elements  12  are arranged in a row. However, the filling material  25  can just as well be introduced between the individual intermediate spaces  24  during assembly of the individual secondary part elements  12  to form a secondary part  2 , for example by being sprayed in. 
       FIG. 6  shows a secondary part  2  with a cover  20  which is formed integrally or from one part, and is attached to the teeth  9 . The cover  20 , which is in the form of a covering plate, is attached by means of connecting elements  26  to a predeterminable number of teeth  9  of the secondary part elements  12 . By way of example, holding elements  27  such as slots are arranged or formed on the teeth  9 , and the cover  20  is clipped, pushed or hooked onto them. As shown in  FIG. 6 , the teeth  9  do not all have holding elements  27 . It is possible to provide any desired number of teeth  9  with holding elements  27 , for example corresponding to the purpose of the secondary part  2 .  FIG. 6  also shows that the number of holding elements  27  is not equal to the number of connecting elements  26 . In the present case, there are fewer connecting elements  26  than holding elements  27 . For example, all the teeth  9  could be provided with holding elements  27 , although corresponding connecting elements  26  engage only in selected holding elements  27 . 
     The cover  20  is in the form of a flat covering plate and extends integrally over the secondary part elements  12 , forming a continuous surface. In this case as well, the cover  20  is as thin as possible, with a thickness in the tenths of millimeter range, as a result of which there is no adverse affect on operation, and in particular on the guidance of the magnetic fields. 
       FIG. 7  shows a secondary part  2  with a cover  20  which is formed integrally and is pushed into slots  28  in encapsulation  21 . The secondary part  2  is illustrated from an end face, that is to say from a face transversely with respect to the movement direction  7  (see  FIG. 2 ). The individual secondary part elements  12  (which are arranged one behind the other in this illustration, that is to say on the plane of the drawing) are encapsulated, wherein the cured encapsulation  21  is in each case provided with a slot  28  on two opposite sides, and the covering plate  20  is pushed into and fixed in the slots  28  from one end face. The slots  28  may be arranged both on the sides parallel to the movement direction  7  (as illustrated in  FIG. 7 ) and on the sides transversely with respect to the movement direction  7  of the primary part  3  (not shown). By way of example, the covering plate  20  has attachments  29 , by means of which the covering plate  20  is pushed into the slots  28 . 
       FIG. 8  shows a secondary part  2  with a cover  20  which is formed integrally and is attached to the cured encapsulation  21 . The secondary part elements  12  each have encapsulation  21 , wherein the cover  20  is then attached to the encapsulation  21 . The encapsulation compounds  21  themselves from a continuous surface, in the form of a cover for the individual secondary part elements  12 , with the cover  20 , which is in the form of a covering plate, then being placed over the encapsulated toothed profiles. The covering plate has connecting elements  26 , such as clips or barbs, which are pressed into the encapsulation compound  21 . In consequence, a continuous cover  20  is created on the one hand, while the secondary part elements  12  are fixed and partially connected to one another, on the other hand. In particular, the holding elements  26  are arranged at a predeterminable distance apart on the side of the cover  20  facing the toothed profiles, and in particular the holding areas  26  are pressed in the area of the butt joints  24 , as a result of which the secondary part elements  12  are connected and fixed. 
       FIG. 9  shows a detailed view of a holding element  26  as shown in  FIG. 8 . As can be seen, the holding element  26  is in the form of a pin or plug, wherein the holding element  26  has a friction-increasing structure or a barb structure, such that the holding element  26  can be pressed in one direction, specifically into the encapsulation compound  21 , and is then hooked in the encapsulation compound  21 , producing a non-detachable connection.