Abstract:
A combined mechanical linkage and force-measuring assembly includes a central capacitive force sensor, in which force applied to the sensor causes the flexing of a diaphragm toward and away from a substrate, and a change in the capacitance between two conductive surfaces on the diaphragm and the substrate is sensed and processed to indicate the direction and magnitude of the force applied to the linkage. The linkage may have two parts coupled together by a flange which flexes under applied forces, to change the spacing of the conductive surfaces.

Description:
FIELD OF THE INVENTION 
     This invention relates to mechanical linkages with arrangements for sensing the amount of force applied to said linkage. 
     BACKGROUND OF THE INVENTION 
     Various systems for measuring the force applied to mechanical linkages have been proposed. However, by and large, the previously proposed linkage and sensor assemblies have not been sufficiently accurate and reliable, and/or have compromised the structural integrity of the linkage. Particularly for aircraft applications, the shortcomings noted above may become critical. 
     SUMMARY OF THE INVENTION 
     In accordance with one illustrative embodiment of the invention, a mechanical linkage includes first and second linkage members extending respectively from first and second external coupling points to an intermediate sub-assembly including a capacitive force measuring transducer. The first linkage member has a shaft extending from said first coupling point to said sub-assembly, and has a peripheral flange extending outwardly from said shaft at said sub-assembly; and the second linkage member has an inner opening or bore making a close sliding fit with the shaft of said first linkage member, and has an outer portion firmly secured to said peripheral flange, so that the first linkage member can move linearly toward and away from the second linkage member in accordance with the resilience of said flange. The sub-assembly also includes capacitive sensing arrangements for sensing the displacement of said shaft as said flange deflects or flexes as force is applied to the overall linkage. 
     The capacitive sensing arrangements preferably include a ceramic diaphragm mounted to flex with shaft position shifts, and a ceramic substrate fixed to the second linkage and spaced from the ceramic diaphragm, with conductive layers on the ceramic diaphragm and substrate to form a variable capacitor, the capacitance of which indicates the magnitude of the applied force to the overall linkage. 
     More generally, the capacitive sensing arrangements of the mechanical linkage described above include a pair of spaced conductive surfaces which form a capacitor, and wherein the relative movement of the first and second linkages and the flexing of the flange changes the spacing of the spaced conductive surfaces. 
     As a desirable advantage, the linkage assembly of the present invention does not change in length to any significant extent with changes in applied force, as the capacitive sensors are very sensitive to relatively small changes in the spacing of the capacitive plates. 
     Other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall view of a linkage assembly, illustrating the principles of the present invention; 
     FIG. 2 is an enlarged view of a central sensing portion of the assembly of FIG. 1; and 
     FIG. 3 is a cross-sectional view of another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring more particularly to the drawings, FIG. 1 shows a combined mechanical linkage and force measurement assembly. More particularly, the mechanical linkage of FIG. 1 has first and second mechanical coupling points  12  and  14 , and an intermediate force-measuring assembly  16 . Incidentally, FIG. 2 shows the central portion of the force-measuring assembly in greater detail. 
     Returning to FIG. 1, the shaft  18  makes a sliding fit in the cylindrical bore  20  as it is coupled to the circular part  22 . 
     The other end of the overall linkage includes the shaft  24  and the outer housing member  26 . The outer housing  26  is bonded or welded at the cylindrical area  28  to the circular member  22 . Secured to the shaft  18  and to the member  22  is the circular metallic member  30 , which flexes when force is applied to the overall linkage at the coupling points  12  and  14 . 
     A capacitive sensor, including a substrate  32  and a diaphragm  34 , forms the central sensing element for indicating the force between the coupling points  12  and  14 . Mounted on the rear of the substrate  32  is a semiconductor circuit  36 , which senses the changes in capacitance of the unit, including the diaphragm  34  and the substrate  32 , and provides a variable voltage which indicates this change in capacitance, and, of course, the force applied between the two coupling points  12  and  14  of the linkage. The diaphragm  34  is spaced apart from the substrate  32  by a relatively small distance, such as about 0.0005 to 0.020 of an inch, and is bonded and spaced from the substrate by the outer peripheral ring of glass frit  38 . On the facing surfaces of the diaphragm  34  and the substrate  32  are thin layers  50  of conductive material, such as gold, and these may be protected against engagement by a very thin layer of insulating material, such as glass, over at least one of the layers. 
     Leads  40  interconnect the conductive layers  50  to the circuit  36  through the bores  42  and are sealed within these bores by epoxy  43 . 
     Reference is made to several additional patents owned by the assignee of the present invention, and these include U.S. Pat. Nos. 4,388,668, 4,398,426 and 5,329,819, the disclosures of which are incorporated into this specification by reference. 
     In practice, as discussed above, when force is applied between the coupling points  12  and  14  of the overall linkage, the outwardly-extending part  30 , with its peripheral flange, is flexed somewhat, either inwardly or outwardly, depending on the direction of the force applied to the coupling points. The center of the part  30  is bonded to the center of the diaphragm  34  by epoxy  46 , so that as the center of the part  30  moves in or out, as indicated by the arrow  48 , the diaphragm  34  will be flexed inwardly or outwardly, to increase or decrease the capacitance between the two conductive plates  50  on the surfaces of the diaphragm  34  and the substrate  32 . 
     It may be noted that the assembly including the substrate  32  and the diaphragm  34  are held in position with the diaphragm adjacent the part  30 , by the shoulder  54  on the part  26 . 
     FIG. 3 shows an alternative embodiment in which a ceramic member  62  replaces the member  30 , as shown in FIGS. 1 and 2 of the drawings. On the exposed surface of the ceramic member  62  is a conductive layer  64 . In the arrangement as shown in FIG. 3, the diaphragm  34  may be dispensed with, and the part  62  may be directly bonded to and spaced from the substrate  32  by means of a peripheral layer of glass frit, as discussed above in connection with FIG. 2 of the drawings. Accordingly, the part  62  acts as the diaphragm, and the separate diaphragm may be dispensed with. 
     As a further, less preferred embodiment, the metal member  30  may serve as the diaphragm in an arrangement similar to that shown in FIG. 2, but with the diaphragm  34  omitted. 
     It may be particularly noted that in FIG. 2, the spacing between the conductive plates  50 , the thickness of the diaphragm  34  and the thickness of the bonding epoxy  46  are all exaggerated for clarity of disclosure, but would actually be much thinner than indicated in FIG.  2 . 
     As mentioned above, the spacing between the conductive plates on the diaphragm  34  and the substrate  32  is fairly small, preferably in the order of one-half of one thousandth of an inch to about twenty thousandths of an inch. Further, the thickness of the outwardly extending part is designed to flex so that the desired level of forces to be measured matches the spacing of the two conductive plates. With this configuration the assembly has the desired result that the length between the two coupling points changes very little with variable applied forces. 
     In closing, it is to be understood that the foregoing detailed description and the accompanying drawings relate to specific preferred illustrative embodiments of the invention. Various changes and alternative constructions may be implied without departing from the spirit and scope of the invention. Thus, by way of example, the diaphragm and the substrate are preferably made of alumina, but other ceramic or other insulating materials may be employed. Similarly, while the part  30  is shown as a somewhat mushroom-shaped part, it could be more of a spider construction with several individual arms extending outwardly and would still flex and produce the desired central movement to actuate the diaphragm  34 . It is also to be understood that other types of linkages, shorter, or longer, or with different types of coupling points could be employed. Accordingly, the present invention is not limited to the embodiments shown in the drawings and described in detail herein.