Abstract:
A scanning device scans a dimensional standard which is situated on a guide rail which extends in a longitudinal direction, and has a body with a cross-section that is essentially U-shaped so that it may grip around the guide rail, at least one cover being provided on the outside of the scanning device and is designed as a profiled element, the cross section of which is U-shaped, having a base and two U-shaped legs, the cross-sectional shape of the cover being matched to the cross-sectional shape of the scanning device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2008 022 312.3 filed on May 6, 2008. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a scanning device and to a linear bearing including a scanning device of this type. 
         [0003]      FIG. 4  shows a known linear bearing  10  which is composed of a guide rail  20  which extends in a longitudinal direction  21 , on which a guide carriage  11  is supported in a longitudinally displaceable manner. Four tracks  23  for spherical rolling elements (not depicted) which circulate endlessly in guide carriage  11  are provided on guide rail  11  which is composed of hardened roller bearing steel. A deflection assembly  13  which transfers the endlessly circulating rolling elements from the carrying zone into a return channel (not depicted) in guide carriage  11 , and vice versa, is provided on each of the two longitudinal front sides of guide carriage  11 . 
         [0004]    A scanning device  30  which encloses guide rail  20  and guide carriage  11  in a U-shaped manner is mounted on one of the deflection assemblies  13 . A separate sensor  39  which is designed as described in DE 10 2007 009 994 is provided in the scanning assembly. Sensor  39  is used to scan a dimensional standard  22  which is situated between two tracks  23  on a lateral surface of guide rail  20 . Dimensional standard  22  is designed in the shape of a strip of sheet metal in which a large number of periodically arranged, rectangular cut-out sections is provided which are scanned inductively by sensor  39  using a plurality of electrical coils in order to determine the position of guide carriage  11  relative to guide rail  20 . The design of dimensional standard  22  is described in detail in EP 1 052 480 B1. The mode of operation of sensor  39  is described in EP 1 164 358 B1. The attachment of separate scanning device  30  to guide carriage  11  is designed as described in DE 103 47 360 A1. 
         [0005]    Reference is made to adapter plate  14  which is fixedly connected to deflection assembly  13 , and which is detachably connected to scanning device  30 . A planar mating surface for scanning device  30  which is oriented exactly at a right angle to the direction of motion, i.e. longitudinal direction  21  of linear bearing  10 , is provided on adapter plate  14 , so that sensors  39  are therefore oriented exactly parallel to dimensional standard  22 . An end seal  15  which prevents dirt from entering scanning device  30  and guide carriage  11  is provided on the front side of scanning assembly  30 . Connecting cable  36  for connecting scanning device  30  to a higher-order control device is merely suggested in the illustration. A further sensor (not depicted) is provided on the side opposite sensor  39 , with which reference marks or an absolute dimensional standard is scanned in order to determine an approximate position. 
         [0006]    Two lateral covers  59  and one top cover  60  are provided to facilitate installation of sensors  39  and evaluation electronics  40  (depicted in a basic schematic manner), lateral covers  59  and top cover  60  each being attached using four fastening screws  41  to a main body  33  which has been milled out of a metallic solid body. To prevent fluids from penetrating evaluation electronics  40  and sensors  39  from the outside, inner space  43 ;  44  of scanning device  30  is filled with a casting compound in the form of a liquid polyurethane resin which hardens in scanning device  30  and encloses the components mentioned above in a fluid-tight manner. 
         [0007]    The casting compound is applied as described below. With lateral cover  59  open, lateral spaces  43  are filled with as much casting compound as possible. To prevent the casting compound from escaping through the gap between sensor  30  and main body  33 , it is sealed with latex (a “latex shell”). After this first casting step, lateral covers  59  are installed, and the gap between lateral covers  59  and main body  33  are also sealed using latex. Next, with top cover  60  removed, casting compound is filled into top space  44  of main body  33 , and the casting compound may then flow via connecting channels (not depicted) into lateral spaces  43  and fill them completely. Upper space  44  is not filled completely, but rather only to the extent that evaluation electronics  40  and all cables connected therewith are completely covered by the casting compound. Finally, top cover  60  is installed, and the latex shells which were applied previously are removed. Main body  33  is tilted in various positions relative to the direction of gravity during the process of applying the casting compound described above, in order to ensure that the casting compound reliably fills all opens spaces in main body  33 . 
       SUMMARY OF THE INVENTION 
       [0008]    The object of the present invention is to simplify the installation of the cover. At the same time, the installation space provided for the sensor and the evaluation electronics will be increased. In addition, the casting of the scanning device will be simplified. 
         [0009]    It is provided that the cover is designed as a profiled element, the cross section of which is U-shaped, having a base and two U-shaped legs, the cross-sectional shape of the cover being matched to the cross-sectional shape of the scanning device. 
         [0010]    Given that only one cover is provided, the number of fastening means may be minimized, thereby simplifying assembly. In addition, the assigned counter-fastening means in the main body of the scanning device may be eliminated, thereby creating additional installation space. Another result of the fact that the counter-fastening means are eliminated is that the receiving space for the sensors and the evaluation electronics is much less angular. Accordingly, it is considerably easier to apply the casting compound in a manner such that the entire interior of the scanning device is completely filled with casting compound. 
         [0011]    The cover may be extruded, preferably being extruded out of aluminum. The cover may be manufactured particularly cost-effectively in this manner. 
         [0012]    Even though it is feasible to manufacture the cover out of plastic via extrusion, it is preferable to use an electrically conductive aluminum cover. This allows the evaluation electronics to be protected particularly well against electromagnetic interferences which act on the scanning devices from the outside. At the same time, aluminum is highly resistant to the fluids used in the vicinity of the scanning device, e.g., coolants in machine tools. 
         [0013]    The length of the U-shaped legs may be essentially equal to the height of the scanning device. It is therefore possible to provide the largest possible opening for the interior space of the evaluation device, thereby simplifying the installation of the sensors and the evaluation electronics. It is preferable to terminate the U-shaped legs of the cover in a flush manner with the underside of the scanning device without the front surface of the U-shaped legs abutting the main body of the scanning device. The length of the U-shaped legs may therefore be manufactured in a relatively inaccurate manner via extrusion without impairing the accurate fit of the cover on the main body. 
         [0014]    The longitudinal front surfaces of the cover may be planar in design and preferably oriented perpendicularly to the longitudinal direction, in which case they bear against a planar counter-surface on the adjacent component, preferably the main body, of the scanning device. The longitudinal front surfaces of the cover are still machined in a material-removing manner when the extruded raw profile is trimmed. They may therefore be manufactured in a highly accurate manner. The length of the cover, in particular, may be manufactured in a highly accurate manner. Accordingly, the sealing gap between the longitudinal front surface of the cover and the planar counter-surface of the adjacent component may be particularly narrow in design, which is why the scanning device is very well protected against fluids which penetrate from the outside. The longitudinal front surfaces and the counter-surface are planar in design, thereby enabling them to be manufactured particularly easily. The orientation of the longitudinal front surface transversely to the longitudinal direction is preferred, because the cover may then be easily installed on the scanning device using a straight-line installation motion transversely to the longitudinal direction. 
         [0015]    The scanning device may be filled with a casting compound, the cover being secured on the scanning device in a form-fit manner via the casting compound. The cover is therefore fixedly connected to the rest of the scanning device via casting, which must be carried out anyway. The large number of screws known from the prior art may be eliminated. With the cover installed on the scanning device, the liquid casting compound is filled into the scanning device and hardens therein. The minimally angled receiving space for the sensor and the evaluation electronics, which is made possible via the U-shaped cover, is particularly significant in this embodiment, since it ensures that the interior of the scanning device will be completely filled with casting compound. A visual inspection of the casting for unfilled spaces, which may not be performed with the cover in place, may be eliminated. 
         [0016]    The form-fit connection between the cover and the casting compound may be brought about by the fact that the cover includes—as viewed in the cross section—at least one inwardly oriented projection which engages in the casting compound. The inwardly oriented projection may be manufactured directly via extrusion and, therefore, without additional costs. The projection preferably extends across the entire length of the cover, thereby resulting in a particularly inwardly-oriented and fixed connection to the hardened casting compound. 
         [0017]    To prevent the U-shaped legs from bending during operation of the evaluation device, the shape of the projection may be selected such that the casting compound reaches behind the projection. The rearward attachment also makes it difficult for the cover to be removed from the scanning device. To form the rearward attachment, a preferred approach is to design the inwardly oriented projection as a segment which is slanted relative to the U-shaped leg, or as a hook-type, T-shaped, or Y-shaped—as viewed in the cross section—segment. 
         [0018]    At least one inlet opening may be provided in the scanning device, via which the casting compound may be applied when the cover has been placed on the scanning device, the inlet opening being closed via an electrically conductive closing means which engages in the cover and in an adjacent component of the scanning device. Via the electrically conductive engagement of the closing means with the cover and the adjacent component of the scanning device, preferably the main body, an electrically conductive connection between these components is established in a reliable manner. The aim is to connect the cover to ground potential in particular, thereby ensuring that the cover is shielded in an optimum manner from electromagnetic interferences that act from the outside. At the same time, the inlet opening is closed tightly by the closing means. In addition, the cover is secured against displacement relative to the adjacent component. In this manner, it is possible to prevent the two components which are engaged with the closing means from becoming accidentally displaced while the casting compound is hardening. 
         [0019]    It should be pointed out that electrical contact between the cover and the main body may also occur since the two components are in direct contact with one another. This electrical contact is eliminated in some cases, however, by the casting compound which penetrates the particular joining gap. This problem may be reliably prevented using the closing means which are installed after casting. 
         [0020]    The closing means are preferably a self-tapping screw bolt, thereby making it possible to eliminate threads—which are costly to produce—in the cover and in the adjacent component. In addition, via the self-tapping thread, the electrical contact between the screw bolt and the associated counter-piece is improved. A “self-tapping screw bolt” refers to a screw bolt which forms the associated internal thread during the screw-in process using material-removing cutting processes or material deformation. 
         [0021]    It is possible to provide at least one undercut recess on the inside of the cover, the undercut recess being connected in a fillable manner to the inlet opening, and the closing means being enclosed, in sections, by the undercut recess. Using the undercut recess, it is possible to create—in a cost-effective manner—a connection in the profiled cover between the internal thread which is assigned to the closing means and the inner space of the evaluation device, which is enclosed by the cover, so that the casting compound may flow from the inlet opening into the interior space of the evaluation device. It should be pointed out that this embodiment—in conjunction with the self-tapping screw bolt—has the disadvantage that the chips which are produced during the shaping of the internal thread may reach the evaluation electronics, thereby possibly resulting in a short circuit. The undercut recesses are therefore provided with an internal thread using a separate working step, so that the chips which are produced may be reliably removed from the cover before it is installed on the scanning device. 
         [0022]    The undercut recess may be situated in a corner region between the base and a U-shaped leg of the cover. Using this configuration it is possible to apply the casting compound easily and reliably in the upper space in the region of the base, and in the lateral space in the region of the U-shaped legs. Preferably, an undercut recess is provided in both corner regions between the base and the two U-shaped legs, so that both lateral spaces may be reliably filled with casting compound in the region of the two U-shaped legs of the cover. 
         [0023]    At least one arresting means which may engage in counter-arresting means on an adjacent component of the scanning device may be provided on the cover. The arresting means are used to prevent the cover and the adjacent component from becoming displaced before the casting compound is applied and the closing means are installed. The cover is therefore secured against displacement relative to the adjacent component while the latex shield is installed and the casting compound is applied. 
         [0024]    The arresting means may be formed by an arresting projection which is located on the end—that faces away from the base—of at least one U-shaped leg, and preferably on both U-shaped legs, at least one detent recess which is matched to the arresting projection being provided in the adjacent component. The arresting projection may be manufactured particularly easily and without generating additional costs by extruding the cover. In addition, the arresting projection does not weaken the relatively thin-walled cover. An arresting projection on the end of the U-shaped leg also has the advantage that the elasticity of the U-shaped legs is utilized particularly well for the arresting effect. A relatively large arresting projection may therefore be provided without this resulting in an excessive increase in the installation force of the cover. 
         [0025]    A U-shaped main body of the scanning device may be manufactured via metal-injection molding. In metal-injection molding, which is known per se, a mixture of fine metal particles and plastic is brought into the desired shape using the known, cost-effective plastic forming procedures, e.g. injection molding. The “green product” is then subject to thermal treatment, in which the plastic is broken down and the metal particles are welded to one another. The shrinkage that occurs in this process must be taken into account when the green product is sized. Using the method which is provided, it is possible to manufacture the main body—which is formed in a complicated manner—of the scanning device in a cost-effective manner and with the required accuracy. 
         [0026]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  shows a perspective view of an evaluation device according to the present invention; 
           [0028]      FIG. 2  shows a first embodiment of the cover, in a cross-sectional view; 
           [0029]      FIG. 3  shows a second embodiment of the cover, in a cross-sectional view; and 
           [0030]      FIG. 4  shows a known linear bearing which includes a known scanning device. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    A scanning device according to the present invention is labelled in general with reference numeral  30  in  FIG. 1 . Scanning device  30  is provided for use with the linear bearing which was described with reference to  FIG. 4 . It is intended to replace the scanning device provided therein. 
         [0032]    Scanning device  30  includes a main body  33  which is manufactured using the metal-injection method, and which has a U-shaped design overall, inner contour  35  of main body  33  being designed essentially equidistantly to the assigned guide rail of the linear bearing. A sensor  39  for scanning an assigned dimensional standard is situated on each of the U-shaped legs of main body  33 . The two sensors are essentially designed as described in DE 10 2007 009 994. A front plate  45  is situated on each end of main body  33 , being formed as a single piece therewith. Contact surfaces  47  of front plates  45 , which are designed to bear against longitudinal front surfaces  61  of cover  50 , are planar in design, thereby enabling cover  50  to be sawed off of an extruded aluminum profile using one straight cut. Cover  50  is slid onto main body  33  so far that base  52  touches stop  47  on main body  33 . 
         [0033]    Front surface  63  of U-shaped leg  53  does not bear against main body  33 , so cover  50  bears against main body  33  in the vertical direction which is determined statically. The length of lateral U-shaped legs  53  of the cover is matched to main body  33  in a manner such that lateral space  43  is completely covered. Evaluation electronics  40  (depicted in a basic schematic manner) are located in upper space  44  in the region of the base of main body  33 . Upper space  44  and two lateral spaces  43  are designed such that the casting compound may flow back and forth, essentially unhindered, between the two spaces during filling, thereby ensuring that the two spaces  43 ;  44  may be completely filled with casting compound. 
         [0034]    A through-bore  34   b  for an electrically conductive screw bolt  42  made of steel is provided in both front plates  45 , thereby enabling screw bolt  42  to engage in assigned longitudinal passage  62  in cover  50  in order to establish an electrically conductive connection between cover  50  and main body  33 , and to fixedly connect the parts mentioned above to one another.  FIG. 1  shows a cover  50  according to a first embodiment which is depicted in greater detail in  FIG. 2 . In this embodiment, two separate filling openings  34   a  for the casting compound are provided; they are depicted in  FIG. 1  in a basic schematic manner. Separate filling openings  34   a  are closed using separate closing means (not depicted) in the form of screw bolts. 
         [0035]    Main body  33  shown in  FIG. 1  may also be used in conjunction with a second embodiment of cover  50 , which is shown in greater detail in  FIG. 3 . In this embodiment, instead of longitudinal passage  62 , undercut recesses  47  are provided for engagement with screw bolts  42 . The casting compound may therefore be applied via inlet openings in the form of through-bore  34   b  in scanning device  10 , the inlet openings being provided anyway for screw bolts  42 . In this case, screw bolts  42  are used simultaneously as closing means for inlet opening  34   b . Independently of the embodiment of the cover, the casting compound may be applied to the scanning device, in the form of a polyurethane resin, e.g. using a plunger syringe to which a thin cannula has been attached, via inlet opening  34   a  or  34   b . The scanning device which has been filled with liquid casting compound is swiveled and tilted slightly to ensure that all cavities to be filled are completely filled with casting compound. After the casting compound has been applied, inlet openings  34   a  or  34   b  are closed to allow the casting compound to harden. 
         [0036]      FIG. 2  shows a first embodiment of cover  50 , in a cross-sectional view. Cover  50  is manufactured as a single piece out of aluminum via extrusion. The cross-sectional profile shown is constant across the entire length of cover  50 . Cover  50  includes a base  52  and two U-shaped legs  53  which project therefrom at right angles, each of which having an essentially constant wall thickness. A longitudinal passage  62  is provided on each inner side  51  of cover  50  in the region of the corners between base  52  and the two U-shaped legs  53 , longitudinal passage  62  being open only toward both longitudinal front surfaces of cover  50 . Longitudinal passage  62  is used to screw in screw bolts (number  42  in  FIG. 1 ) which establish the electrical contact between the cover and the main body. In this case, the screw bolts are designed to be self-tapping. Since longitudinal passage  62  is not open toward the lateral space and upper space (numbers  43  and  44  in  FIG. 1 ), the chips which are produced when the screw bolts are turned are prevented from reaching the evaluation electronics, where they could cause a short circuit. 
         [0037]    A projection  56  which engages in hardened casting compound in a form-fit manner is provided on each of the two U-shaped legs. Since projection  56  is designed to slant relative to U-shaped legs  53 , the undercut that results prevents U-shaped legs  53  from bending in the lateral direction. This could cause gaps to form between the hardened casting compound and cover  50 , into which fluid, e.g. coolant in machine tools, could enter, which is undesired. 
         [0038]      FIG. 3  shows a second embodiment of cover  50 , in a cross-sectional view. Since this cover is designed essentially identical to the first embodiment, only the differences from the first embodiment will be described below. 
         [0039]    An undercut recess  57  for engagement with the screw bolts (number  42  in  FIG. 1 ) which establish the electrical contact between cover  50  and the main body is provided in the corners between base  52  and the two U-shaped legs  53 . Undercut recess  57  is essentially circular in design, as viewed in the cross section. Since undercut recess  57  is open toward the upper space and the lateral space (numbers  43  and  44  in  FIG. 1 ), they may be used for application of the casting compound. In this embodiment of cover  50 , the thread in undercut recess for engagement with the screw bolts mentioned above is preferably created in advance, so that the chips which are produced may be reliably removed from cover  50  before it is installed on the scanning device. 
         [0040]    An arresting projection  58  is provided on each end—which faces away from base  52 —of U-shaped leg  53 , which may snap into a matching arresting recess in the main body of the scanning device. It is thereby ensured that cover  50  remains securely in the desired position relative to the main body while the casting compound is being applied. 
         [0041]    Projection  57  is slanted in the opposite direction compared with the first embodiment. Via this orientation of projection  57 , cover  50  is better prevented, by the casting compound, from being removed in the upward direction. In contrast, the cover according to the first embodiment may be slid onto the main body more easily. 
         [0042]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
         [0043]    While the invention has been illustrated and described as embodied in a scanning device with unshaped cover, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
         [0044]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.