Abstract:
A measuring device for inspecting a hole, which can favorably be mounted on a riveting robot adapted to insert a rivet into the hole after inspection. The measuring device includes a test mandrel having a hollow housing and interacting means, whereby the relative position of the interacting means can be detected to determine characteristics of the inspected hole. The measuring device further includes a bushing which is arranged movable relative to the test mandrel.

Description:
CROSS-REFERENCE 
       [0001]    This application is a national phase application under 35 U.S.C. §371 of International Patent Application No. PCT/EP2015/080263, filed Dec. 17, 2015 (pending), which claims the benefit of European Patent Application No. 14307145.4 filed Dec. 22, 2014, the disclosures of which are incorporated by reference herein in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a measuring device for inspecting a hole, and in particular to a measuring device for inspecting a hole drilled or punched for fastening. 
       BACKGROUND 
       [0003]    Mechanical fasteners, such as rivets, are typically used to fasten work pieces and consist often of a cylindrical shaft with a head on one end. During the fastening process the fastener is placed in a hole which is punched out or drilled before. In the case of riveting, the shaft of the rivet expands, thereby holding the rivet in place. 
         [0004]    Riveting is commonly applied for the assembly of e.g. commercial and military aircrafts. The rivets thereby carry crucial loads from one part of the aircraft to an adjoining part. Especially for the manufacturing of aeronautic components, the provision of a correct hole diameter for riveting is of great importance and the manufacturing tolerances are very tight. If the hole diameter is too big, the rivets may not be held in place properly and may unfavorably become loose during later operation. On the other hand, if the hole diameter is too small, the rivets may be difficult to install therein, or may be preloaded in a non-optimal manner. This can cause unwanted noise or even create a joint which does not provide an optimal strength. A further point is, that if the head of the rivet is not placed perfectly within the hole or its counter sink air turbulences can occur, which increase the fuel need and therefore have to be avoided. 
         [0005]    During riveting, but also in many other fastening methods that make use of holes, the hole diameter is therefore typically checked with a measuring apparatus before installing a fastener, such as a rivet, therein. Thereby, a test mandrel (bore gauge) is inserted into the drilled or punched hole, and the lateral distance from the measuring rod to the walls of the hole is determined. This measurement is typically performed at high speed and with a high precision, i.e. in the range of μm. 
         [0006]    However, with the known measurement or check-methods, it is not possible to characterize the edge at the surface of the hole. While it can on the one hand be desired for some applications that the holes have a sharp edge, the provision of a counter sink is also often required. It is easy to imagine that in particular the depth of a counter sink is crucial for a proper placement of a fastener into the hole. For example, if the depth of the counter sink is not correct, the end of the fastener may protrude from the surface of the work piece further than desired. For aeronautic applications, such improperly seated fasteners can cause additional fuel consumption and may even have a negative impact on the airworthiness of the airplane. 
       SUMMARY 
       [0007]    In view of the above, it is an object of the present invention to provide a measuring device for inspecting a hole, and in particular for inspecting a hole drilled or punched for riveting, enabling both the measurement of the counter sink depth and the hole diameter of said hole. It is a further object of the present invention to provide a measuring device which can inspect a hole in a fast and preferably automated manner. It is another object of the present invention to provide a measuring device for inspecting a hole, whereby the measuring device can be provided on an effector for an industrial robot, for example for riveting work pieces. 
         [0008]    According to the present invention there is provided a measuring device for inspecting a hole, and in particular for inspecting a hole for riveting. The hole may be punched out or drilled into an object for placing or installing a fastener, such as a rivet, inside. The measuring device comprises a test mandrel, which in turn comprises a hollow housing and interacting means. The interacting means are arranged in the housing and can protrude partially from an outer surface of the hollow housing of the test mandrel and are movable relative to the hollow housing. Accordingly, the distance of the interacting means from the outer surface of the hollow housing can change. Furthermore, the relative position of the interacting means can be detected by suitable detection means assigned to the device. 
         [0009]    The measuring device further comprises a bushing in which the test mandrel is arranged. This bushing is arranged moveable relative to the test mandrel, i.e. test mandrel and bushing are movable relative to one another, between a first position and a second position. In the first position, the bushing covers the interacting means and is also in contact, and preferably in direct contact, with the interacting means, which as mentioned protrude at least partially from the outer surface of the hollow housing of the test mandrel. Preferably, the test mandrel tightly fits into the bushing. The bushing in the second position exposes the interacting means. In other words, the bushing is adapted to be moveable along the longitudinal extension of the test mandrel, thereby either covering or uncovering the interacting means. When the bushing is covering the interacting means, the bushing is contacting (i.e. interacting) with said interacting means. The relative position of the interacting means changes when the bushing is moved from the first position to the second position and vice versa. 
         [0010]    Accordingly, since the relative position of the interacting means can be detected, it is possible to detect whether the bushing is in contact with the interacting means or not. This allows the determination of the depth of sink holes as will be explained in the following and offers further advantages, in particular for automated inspection processes. When the test mandrel is inserted into a hole to be inspected, the bushing is moved—e.g. since it abuts the surface surrounding the hole to be inspected—to the second position relative to the test mandrel, whereby the interacting means are exposed. Thereby, the interacting means advantageously move to their outermost position with regard to the housing of the test mandrel, e.g. by means of suitable restoring means adapted to apply a reset force to the interacting means. This change in relative position can be detected and by generating a corresponding signal one can determine when the interacting means enter the space provided e.g. by the counter sink of the hole. 
         [0011]    Preferably, as mentioned briefly above, the test mandrel further comprises restoring means which are adapted to apply a reset force to urge the interacting means to protrude from the outer surface of the hollow housing, i.e. which urge the interacting means radially away from the hollow housing. Accordingly, the interacting means are urged to occupy a position in which the interacting means protrude from the outer surface of the hollow housing as far as practicable or as much as possible. In the first position of the bushing, the interacting means are thereby urged into contact with the inner wall of the bushing. When the bushing is in the second position and exposes the interacting means, the restoring means urge the interacting means to protrude further from the outer surface of the hollow housing. 
         [0012]    Preferably, the hollow housing of the test mandrel is a hollow tube. Further preferred, also the bushing is a hollow tube with an inner diameter which is greater than the outer diameter of the hollow housing of the test mandrel. When the bushing is in its first position it envelopes the test mandrel at least partially, e.g. at least in the area where the interacting means extend or protrude from the hollow housing of the test mandrel. Further preferred, the inner diameter of the bushing is smaller than the maximum extension of the interacting means. Accordingly, when the bushing is in its first position, it covers the interacting means and is in contact therewith. 
         [0013]    Preferably, the bushing comprises at least one recess or opening adapted to receive the interacting means at least partially when the bushing is in an initial position. Further preferred, when the bushing is moved from said initial position to another position, such as e.g. from the initial position to the first position, the relative position of the interacting means is changed. In other words, in the initial position of the bushing the interacting means are provided in said recess or opening and can thus protrude from the housing of the test mandrel to a large extend. When the bushing is moved the interacting means are forced out of the recess or opening inwardly into the bushing. As a result the (detectable) relative position of the interacting means is altered. 
         [0014]    In practice, the bushing is moved from the first position to at least the second position when a hole to be inspected is engaged, and in particular when the test mandrel is inserted into said hole. When engaging the hole, the bushing comes first into contact with the surface surrounding the hole (it abuts the surface and cannot be moved any further in the direction of the hole). When the measuring device is now moved even further towards or into the hole, the bushing moves relative to the test mandrel, until the bushing reaches the second position and exposes the interacting means. As explained above, this exposure can be detected. 
         [0015]    The measuring device according to the present invention is preferably configured to be employed at an end-effector for fastening work pieces, such as e.g. of a riveting robot, i.e. a machine which automatically performs all or some steps of a riveting process. 
         [0016]    According to the present invention there is further provided an end effector for fastening work pieces that comprises a measuring device as described above. 
         [0017]    There is further a method provided for inspecting a hole, in particular for inspecting a hole for rivets or similar fasteners, wherein a measuring device as described above is provided and moved towards a hole in a work piece until the bushing comes in abutment with a surface of the work piece surrounding said hole. When this is achieved the measuring device is further moved (the whole movement is preferably done without any stop) towards the hole, such that the test mandrel is moved relative to the bushing in the direction of the hole and finally into the hole. Upon the movement of the measuring device, the test mandrel will move relative to the bushing, since the bushing is in abutment with the work piece and can therefore not move any further. When the test mandrel is moved to some extend relative to (and out of) the bushing, the interacting means exit the bushing and become exposed. When the interacting means are no longer covered by the bushing, this is detected with the detection means and a signal S 1  is generated. Upon further movement, the interacting means come into contact with the inner walls of the hole and this contact is then again detected with the detection means and a signal S 2  is generated. Based on the signals S 1  and S 2  it is now possible to determine the distance the test mandrel covered between generating of the signals S 1  and S 2 . This can for example be facilitated by a means that accurately measures the amount of movement of the test mandrel: when signal S 1  is generated, the actual position of the test mandrel is e.g. determined by said means. The position can for example be the actual position in a predefined reference frame and could e.g. be the position in relation to the bushing. When the signal S 2  is generated, again the actual position of the test mandrel is determined, whereby a comparison of the position at signal S 1  and the position at signal S 2  allows a precise determination of the distance traveled by the test mandrel. In case of a hole with a counter sink, this distance traveled can e.g. correspond to the depth of the counter sink. 
         [0018]    Depending on the dimensions of the measuring device and the hole to be inspected, it is also e.g. possible to measure the shape and in particular the chamfer angle of a counter bore. If e.g. the interacting means protrude to a sufficient extend from the outer surface of the test mandrel, it is possible to measure the outer (major or maximum) diameter of the counter sink, and by forwarding the test mandrel deeper into the hole, also the contour of the counter sink, if the interacting means stay in contact with the walls of the counter sink and are thus continuously pushed inwards when the test mandrel is pushed deeper into the bore. 
         [0019]    If the chamfer angle of the counter sink is known, it is also possible to calculate the outer diameter of the counter sink, once the depth of the counter sink is determined and the diameter of the entrance of the bore is measured (the diameter of the entrance of the bore corresponds to the inner or smallest diameter of the counter sink). 
         [0020]    In use of the measuring device, it is particular advantageous when the test mandrel is turned or rotated within the bore and to take a plurality of signals. This allows a more precise measurement of the diameter of the bore and to check e.g. if the bore is circular and not (for example) oval or elliptical. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the following the invention is described exemplarily with reference to the enclosed figures. 
           [0022]      FIGS. 1 to 5  show schematic illustrations of a cross section of a measuring device for inspecting a hole according to the present invention at different working positions relative to a hole to be inspected. 
           [0023]      FIG. 6  is a schematic illustration of another measuring device according to the present invention. 
           [0024]      FIG. 7  shows the measuring device of  FIG. 6  in another configuration. 
           [0025]      FIG. 8  shows a detailed view of a section of the measuring device of  FIG. 6 . 
           [0026]      FIG. 9  shows a detailed view of a section of the measuring device of  FIG. 6  in another configuration. 
           [0027]      FIG. 10  shows in a schematic illustration an industrial robot with an end effector comprising the measuring device. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIGS. 1-5  schematically illustrate different steps of inspecting a hole with an exemplary measuring device  10  according to the present invention. The function of measuring device  10  will be explained in the following by this example. 
         [0029]      FIG. 1  shows a schematic illustration of a cross section of measuring device  10  which is adapted for inspecting a hole  21 . The hole  21  was prepared, i.e. drilled or punched into a work piece or object  20 . Around the hole  21 , the object  20  features a planar outside surface  22 , while the hole  21  features a counter sink  21 ′ with a counter sink depth t CS . The hole  21  has an inner diameter d h  that corresponds to the inner diameter d CSi  of the counter sink  21 ′. The outer diameter (or major/maximum diameter) of the counter sink  21 ′ is denoted as d CSO  and in the shown example the counter sink  21 ′ has a chamfer angle α of 90 degrees. 
         [0030]    The measuring device  10  features a test mandrel  11 , which comprises a hollow housing  12 , which in turn features an inner wall  13  and an outer wall  14 , which again in turn define the outer and inner diameter of the hollow housing  12 . The test mandrel  11  further comprises interacting means  15 ,  16 , which are provided in form of spherical elements arranged essentially inside the hollow housing  12 . The skilled person thereby understands that the term “essentially inside” means that at least 50% of the spherical elements are arranged inside the hollow housing  12 . 
         [0031]    The interacting means  15 ,  16  partially extends through a circular opening of said hollow housing  12  and protrude from the housing. Since the diameter of the circular opening is less than the diameter of the spherical elements, the latter cannot completely drop out of the hollow housing  12 . The skilled person understands that the interacting means  15 ,  16  can also be provided in different forms, such as e.g. in form of cones, wedges, and the like. The skilled person further understands that the interacting means  15 ,  16  can also be prevented from dropping out of the hollow housing  12  in different manners, such as e.g. by pinning the interacting means  15 ,  16  in a flexible manner inside the hollow housing  12 . 
         [0032]    The test mandrel  11  further features restoring means  17 , which are adapted to apply a reset force to urge the interacting means  15 ,  16  to protrude from the outer surface of the hollow housing  12 . Preferably, the restoring means  17  is pushed by means of a compression spring  17 ′ (shown in  FIG. 1 ) towards the tip of the test mandrel. In the shown embodiment, the restoring means  17  has a conical shaped tip, such that when the interacting means  15 ,  16  are moved radially inwards, they push the restoring means  17  to the left in the figures. Accordingly, when the restoring means  17  is moved to the left in the figures, the interacting means are urged radially outwardly. In the situation of  FIG. 1 , the interacting means  15 ,  16  push against the inner walls of a bushing  30 , which is arranged moveable relative to the test mandrel  11 . 
         [0033]    The test mandrel  11  further comprises detection means  18  which are coupled to the restoring means  17  and are adapted to indicate the relative position of the interacting means  15 ,  16 , since the relative position of the means  15 ,  16  are directly coupled to the position of the restoring means  17 . Accordingly, when the relative position of the interacting means  15 ,  16  changes due to a displacement resulting from e.g. a force applied from outside the test mandrel  11  onto the interacting means  15 ,  16 , the interacting means  15 ,  16  interact with the restoring means  17  and move the restoring means  17  to the right in  FIG. 1 . This movement of the restoring means  17  is detected by the detection means  18  and the same is able to generate a signal in response. 
         [0034]    The measuring device  10  of  FIG. 1  further features a bushing  30 , which is surrounding the test mandrel  11 . The inner diameter of the bushing  30  is such that the bushing  30  is in contact with the interacting means  15 ,  16  when the bushing  30  is covering them. The skilled person thereby understands that the inner diameter of the bushing  30  can vary. However, a defined portion of the bushing  30  should have an inner diameter such that the bushing  30  contacts the interacting means  15 ,  16  when in first position. The outer diameter of the bushing  30 , or the overall dimensions of bushing  30  is larger than the counter sink width of hole  21  to be inspected. Accordingly, when the measuring device  10  is engaging the hole  21 , the bushing  30  is not able to penetrate the hole  21  or the counter sink of hole  21 . 
         [0035]    As illustrated in  FIG. 2 , when beginning inspection of hole  21 , the measuring device  10  approaches the object  20  until the bushing  30  is in contact with the outer planar surface  22  of the object  20 . The test mandrel  11  is aligned with hole  21 . The bushing  30  is still in the first position of  FIG. 1 , where it is in contact with the interacting means  15 ,  16 . 
         [0036]      FIG. 3  shows a following step during inspection of hole  21 . Preferably, the measuring device  10  comprises an automated actuating means which is adapted to move the test mandrel in longitudinal direction. Accordingly, the automated actuating means can move the test mandrel  11  to penetrate the hole  21  to be inspected. As can be seen in  FIG. 3 , the bushing  30  is moved relative to the test mandrel  11  due to the contact of the bushing  30  with the side walls  22  of object  20 . As soon as the interacting means  15 ,  16  are no longer covered by the bushing  30 , the relative position of the interacting means  15 ,  16  changes because the restoring means  17  urge the interacting means  15 ,  16  to protrude further from the hollow housing  12 . The restoring means  17  moves forward (to the left in the figure) and this movement is detected by the detection means  18 , which generates a signal in response. Thereby, the change in relative position of the interacting means  15 ,  16  is detected. The corresponding signal is denoted as signal S 1  in the following. 
         [0037]      FIG. 4  shows a following step in inspecting hole  21 . Compared to the situation of  FIG. 3 , the test mandrel  11  is moved further into the hole  21 , and the interacting means  15 ,  16  are now in contact with the object  20 . When moving the test mandrel further into the hole  21 , the interacting means  15 ,  16  will be pushed back into or towards the hollow housing  12  of the test mandrel  11 . Due to the coupling with the conical shape of restoring means  17 , the restoring means  17  is moved thereby to the right in  FIGS. 1 to 5 . This movement of the restoring means  17  is detected by the detecting means  18  and thus the change of the relative position of the interacting means  15 ,  16 . Thus, when the interacting means  15 ,  16  enter the hole  21  itself, this is detected by the detecting means  18  and the means  18  outputs a new signal, which is denoted as signal S 2  in the following. 
         [0038]      FIG. 5  shows the situation where the test mandrel  11  is further inserted into the hole  21  to be inspected. The interacting means  15 ,  16  are now in contact with the inner walls of the hole  21 , and the detection means  18  is able to indicate the relative position of the interacting means  15 ,  16 . A corresponding signal is denoted as signal S 3  in the following. 
         [0039]    Accordingly, since the geometry and dimensions of the measuring device are known, and also the amount of linear movement of the test mandrel, one can determine the depth of the counter sink and also the diameter of the hole  21  from the provided signals S 1 , S 2  and S 3 . In particular, on the basis of signals S 1  and S 2 , one can determine the depth of the counter sink, while signal S 3  allows for determining the diameter of the hole  21 . It is hence advantageously possible to measure both properties in one operation. As also the angle of the counter sink is known, the person skilled in the art can also easily determine or calculate the outside diameter d CSO  of the counter sink.  FIG. 6  shows a measuring device  10 ′, comprising a test mandrel  11 ′, a bushing  30 ′ and automated actuating means  40 ′ for moving the test mandrel  11 ′ in longitudinal direction. The bushing  30 ′ comprises two recesses or openings  31 ′,  32 ′, which are adapted to receive the interacting means  15 ′,  16 ′ (see detail view of  FIG. 9 ) at least partially when the bushing  30 ′ is in an initial position covering the test mandrel  11 ′. The initial position corresponds to the idle position of the measuring device  10 ′, i.e. when the test mandrel  11 ′ is not penetrating a hole to be inspected. The initial position further differs from a first position of the bushing  30 ′, in which the inner walls of the bushing  30 ′ are contacting the interacting means  15 ′,  16 ′. The bushing  30 ′ is favorably moved to the first position when the bushing  30 ′ is coming in first contact with an object, similar to the situation illustrated in  FIG. 2 . 
         [0040]      FIG. 7  shows the measuring device of  FIG. 6  in another configuration, i.e. with the test mandrel  11 ′ being moved in longitudinal direction due to an operation of the automated actuating means  40 ′. 
         [0041]    The illustration of  FIG. 8  shows a detailed view of the tip of measuring device  11 ′ of  FIGS. 6 and 7 . The bushing  30 ′ covers the test mandrel  11 ′, and the interacting means  15 ′,  16 ′ are provided in the openings  31 ′,  32 ′. Hence the bushing  30 ′ is in its initial position. 
         [0042]    When the bushing  30 ′ is in the following moved relative to the test mandrel  11 ′ it is moved from the initial position to the first position, whereby the interacting means move out of their respective openings  31 ′,  32 ′ and come into contact with the inner walls of the bushing. In other words, the interacting means are pushed radially inwardly by the inner walls of the bushing and this change in position can be detected similar or identical as with the device of  FIGS. 1 to 5 . Accordingly, when the interacting means  15 ′,  16 ′ are exiting the openings  30 ′,  31  and are moved or pressed in the hollow housing  12  via the contact with the bushing  30 ′ a signal is generated at the detection means. This signal will be denoted as signal S 0  in the following. 
         [0043]    This signal S 0  indicates that the bushing  30 ′ is moved away from its initial position, i.e. that the bushing  30 ′ has moved relative to the test mandrel  11 ′. Thereby, it is possible to determine when the measuring device  10 ′ comes into contact with e.g. the surface  22 , which is highly advantageous in automated inspection processes, when the measuring device is e.g. operated by an industrial robot. Accordingly, signal S 0  indicates that the measuring device is in contact with the surface of the object to be inspected. Based on said information, the speed of the longitudinal movement, i.e. the speed induced by the automated actuating means, can for example be altered. It is hence possible to e.g. engage the hole with a high speed and to perform the inspection or actual measurement of the counter sink depth and hole diameter at a reduced velocity. Alternatively or in addition also other parameters can be altered based on signal S 0 . The following steps are analogous to the steps described with reference to  FIGS. 1 to 5 ; i.e. also with the device of  FIGS. 6 to 9  it is possible to determine the depth of a sink hole. 
         [0044]      FIG. 9  illustrates the measuring device  10 ′ with its test mandrel  11 ′ being completely uncovered, as the bushing  30 ′ is fully pushed back. Accordingly, the interacting means  15 ′,  16 ′ are uncovered and extend from the housing  12 ′ of the test mandrel  11 ′ as far as possible (maximum protrusion). Case  50 ′ contains recovering means which are adapted to apply a reset force to urge the bushing  30 ′ into the initial position. By way of example, the recovering means can comprise a spring or similar. The skilled person understands that the recovering means can be selected irrespective of whether the bushing features openings  31 ′,  32 ′ or not. 
         [0045]    The person skilled in the art further understands that the figures discussed above are not drawn to scale, and that for example the interacting means can be of different forms. The skilled person thereby understands to choose appropriate components in order to achieve the desired resolution of the measuring device. Further on, it will be appreciated that the person skilled in the art understands to set the maximum extension of the interacting means according to the holes to be inspected and the expected quality and manufacturing tolerances of the holes. 
         [0046]      FIG. 10  shows in a purely schematic illustration an industrial robot  70  with an end effector  60  comprising the measuring device as described herein. The robot can be used for automatically inspecting holes or the end effector  60  may comprises additional tools for the automatic installation of mechanical fasteners, in particular rivets. 
         [0047]    While the present invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features shown and described herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit and scope of the general inventive concept. 
       REFERENCE CHART 
       [0000]    
       
           10 ,  10 ′ measuring device 
           11 ,  11 ′ test mandrel 
           12 ,  12 ′ hollow housing 
           13  inner wall of hollow housing 
           14  outer wall of hollow housing 
           15 ,  16 ,  15 ′,  16 ′ interacting means 
           17  restoring means 
           17 ′ compression spring 
           18  detection means 
           20  object 
           21  hole in object 
           21 ′ counter sink 
           22  outer surface of object 
           30 ,  30 ′ bushing 
           31 ′,  32 ′ opening in bushing 
           40 ′ actuating means 
           50 ′ case comprising recovering means 
           60  end effector 
           70  robot 
         d h  diameter of holed 
           CSi  inner diameter of counter sink 
         d CSo  outer diameter of counter sink 
         t CS  depth of counter sink 
         α chamfer angle of counter sink