Abstract:
A force sensor rod for an aircraft actuator system. The force sensor rod is constructed from a tube and a force sensing transducer. The force sensing transducer has a body containing a force responsive primary element and electronic circuitry. The force sensing transducer is provided with a protruding end composed of a material relatively harder than the tube material. The threads on the protruding end terminate in a plurality of axially spaced grooves adjacent to the force sensing transducer body and normal to the axis of the force sensing transducer. The tube is threaded onto the protruding end of the force sensing transducer and swaged onto the protruding end by causing the tube material to flow into the grooves.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to control rods used in aircraft actuator systems and more particularly to providing instrumented control rods. 
     Actuator systems are used within an aircraft to transmit a pilot&#39;s control inputs from controls in a cockpit to control surfaces on the exterior of the aircraft such as ailerons and rudders. In some actuator systems, the amount of force exerted by the pilot to the control in the cockpit is directly proportional to the amount of force required to operate the control surface. The amount of force applied by a pilot to a control is indicative of many things. For example, if a pilot must increase the amount of force applied to a control to operate a control surface, it may mean that a component of the actuator system linked to the control or the control surface itself is not working properly or has failed. Therefore, it would be useful to know how much force is being transferred between components within an actuator system in order to diagnose the actuator system during operation of the actuator system. More particularly, it would be beneficial to record the amount of force transferred between components in an actuator system in a flight recorder to help in diagnosing problems with actuator systems and control surfaces. 
     Putting force sensing and reporting components into an actuator system is difficult. In existing systems, there simply may not be enough space to accommodate a new component without completely restructuring the aircraft containing the actuator system. Even if the physical space is available for a new component, there may be significant amounts of EMF emissions in the area making the choice of sensing and reporting components difficult. Additionally, the only available space may have extreme thermal or environmental conditions that may cause premature failure of an exposed and sensitive measurement system. In new actuator systems, the introduction of a new component into an existing actuator system design may require a series of expensive design iterations where many different components within an aircraft are redesigned to accommodate the new component. 
     Therefore, a need exists for a method to integrate force sensing and recording components into existing and newly designed actuator systems in an unobtrusive and cost effective way. Preferably the integration method should be adaptable to many different kinds of actuator systems and not unduly increase the overall weight of the actuator system. The present invention meets such need. 
     SUMMARY OF THE INVENTION 
     A force sensor rod useful as a control rod in an aircraft actuator system is provided by the present invention. The force sensor rod is constructed from a tube and a force sensing transducer such as a load cell. The force sensing transducer has a body containing a force responsive primary element and the force responsive primary element&#39;s associated electronic circuitry. The force sensing transducer is provided with a protruding end composed of a material relatively harder than the tube material. The threads on the protruding end preferably terminate in a plurality of axially spaced grooves adjacent to the force sensing transducer body and normal to the axis of the force sensing transducer. The tube is threaded onto the protruding end of the force sensing transducer and swaged onto the protruding end by causing the tube material to flow into the grooves. 
     In one embodiment, the force sensing transducer includes a cable extending from the protruding end and the cable is routed through the tube. 
     In another embodiment, a second protruding end is provided. The second protruding end is bored and tapped creating a female threaded connection for a rod end. Alternatively, the second protruding end is threaded providing a male threaded connection for a rod end. 
     The force sensor rod is readily incorporated into an aircraft actuator system. The force sensor rod is operably coupled between two components of an actuator system. The force sensing transducer is connected to a signal conditioning module containing a power supply and a signal conditioner. The signal conditioning module supplies excitation power for the force sensing transducer and signal conditioning for an output signal from the force sensing transducer. The conditioned output signal is provided to a flight recorder for recording. 
     An advantage of a preferred force sensor rod is that it has a form factor similar to a conventional control rod making it suitable to retrofit existing actuator systems and easy to design into new actuator systems. Furthermore, the force sensor rod is easily adapted to different control rod ends without extensive modifications. 
     An additional advantage of a preferred force sensor rod is that the components are threaded and then swaged together creating a permanent and secure connection that does not require additional lock nuts or other kinds of connection locking mechanisms. This creates a lightweight and sleek design suitable for use in an aircraft. 
     A further advantage of a preferred force sensor rod is that the force sensing transducer is coupled to the tube with a swaged connection creating a hermetically sealed enclosure protecting the cable exiting the force sensing transducer. This adapts the force sensing transducer for use in hostile environments where solvents, hydraulic fluids, and corrosive liquids are used. Furthermore, routing the cable through the tube provides electrical shielding and mechanical protection as well. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
     FIG. 1 is an illustration of using a force sensor rod of the present invention in an aircraft control linkage; 
     FIG. 2 is a side view of a sensor prepared for use in constructing the force sensor rod; 
     FIG. 3 is a side view of a rod end used in the force sensing rod; 
     FIG. 4 is a side view of a threaded tube prepared for use as a rod body of the force sensor rod; 
     FIG. 5 is an exploded view of a sensor rod; 
     FIG. 6 is a cross-sectional view of a swaged connection of the force sensor rod; and 
     FIG. 7 is a perspective view of a force sensor rod according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Control rods are elements used in actuator systems to transfer forces and loads between components within the actuator system. For example, control rods are often used to transfer control inputs from the pilot into the actuator system. Replacing a control rod in an actuator system with a force sensor rod adapts the actuator system for measurement and recording of the forces transferred between components in the actuator system. FIG. 1 is an illustration of using a force sensor rod of the present invention in an aircraft control linkage to measure and record control forces applied by a pilot to a control surface or actuator system. Control lever  1002  comprises top end  1032 , bottom end  1034 , and control lever pivot attachment point  1004  located between the top end and the bottom end. The control lever is pivotally attached to first fixed member  1026  at the control lever pivot attachment point within an aircraft. The control lever is moveably attached at the bottom end to force sensor rod  1000  at first sensor rod end  1006 . The force sensor rod is moveably attached to control arm  1028  at second sensor rod end  1008 . The control arm comprises a first attachment point  1036 , a second attachment point  1012 , and a control arm pivot attachment point  1010 . The control arm is pivotally attached at the control arm pivot attachment point to second fixed member  1030  within the aircraft. The control linkage arm is moveably attached to control rod  1014  at attachment point  1012 . 
     Application of a control force to top end  1032  of control lever  1002  causes the control lever to pivot about control lever pivot attachment point  1004  at first fixed member  1026 . This pivoting motion transfers the control force to control arm  1028  through force sensor rod  1000  attached to bottom end  1034  of the control lever. The control force causes the control arm to pivot about control arm pivot attachment point  1010  transferring the control force to control rod  1014 . The force sensor rod is thus an integral component of the control linkage and is subjected to the control forces applied by a pilot to the control lever. 
     Force sensor rod  1000  contains force sensing transducer  1100  aligned to respond to the control force transferred through the force sensor rod. The force sensing transducer is operably coupled to signal conditioning module  1038  via sensor cable  1016 . The signal conditioning module contains power supply  1018  for excitation of the force sensing transducer and signal conditioner  1020  for reception and amplification of force response signals transmitted by the sensing element. The signal conditioner is operably coupled to flight recorder  1022  for recording the amplified force response signals. 
     Application of a control force to control lever  1032  applies the control force to force sensor rod  1000  as previously described. Power supply  1018  in signal conditioning module  1038  excites force sensing transducer  1100  in the force sensor rod such that the force sensing transducer is enabled to transform the applied control force into an output signal proportional to the applied control force. The output signal is transmitted to signal conditioner  1020  and the signal conditioner amplifies the output signal and sends the amplified output signal to flight recorder  1022  for recording. Those skilled in the art of instrumentation will recognize that many different configurations of signal conditioning modules and flight recorders may be used to excite the force sensor rod and condition and record the resultant output signal. 
     FIG. 2 is a side view of a sensor prepared for use in constructing the force sensor rod. Force sensing transducer  1100  is a load cell comprising body  1116 . The body contains a force responsive primary element and strain gauge resistive elements fixedly attached to the force responsive primary element and configured as a temperature compensated Wheatstone bridge. The load cell responds to both tensile and compressive forces. The force sensing transducer further comprises a first protruding end  1102  with extending excitation and signal cable  1106 , and a second protruding end  1108 . Those skilled in the art of instrumentation will recognize that any number of force sensing transducers may be used alone or in combination within a force sensor rod to measure linear, bending, and rotary forces experienced by the force sensor rod. 
     First protruding end  1102  of force sensing transducer  1100  has external screw threads  1112  having a major diameter and a minor diameter. The external screw threads extend from a free end of the first protruding end, along the length of the first protruding end, towards body  1116  of the force sensing transducer. The threaded length of the first protruding end is commensurate with the intended maximum force to be applied to the a force sensor rod comprising the force sensing transducer. At the body end of the external screw threads, at least one row of grooves  1114  are disposed. The grooves are preferably disposed in a direction parallel to the axis of the force sensing transducer and at right angles to any turning moment tending to rotate the force sensing transducer relative to any threaded element receiving the first protruding end of the force sensing transducer. 
     Second protruding end  1108  of force sensing transducer  1100  has internal screw threads  1110  having a major diameter and a minor diameter. The threads extend from an open end of the second protruding end along the length of the second protruding end of the force sensing transducer towards the body of the force sensing transducer. In one embodiment, the external thread is a 7/16-28 UNJEF and the internal thread is a 3/8-24 UNJF. 
     In another embodiment, the second protruding end is externally threaded. 
     In another embodiment, the second protruding end is externally threaded and grooved in a manner similar to the first protruding end. 
     In a further alternative embodiment, the rod end is threaded into the second protruding end of the force sensing transducer with an adhesive sealer coating the threads. An overlap swaging operation is performed, creating a swaged connection over a portion the threaded connection. 
     FIG. 3 is a side view of a rod end used in the force sensing rod. Rod end  1200  is a connector to a push-pull load, such as an eye bolt, clevis, or the like. The rod end has rod end external screw threads  1202 . The rod end external screw threads extend from a free outer end portion of the rod  1204  toward an inner end portion. The rod end external screw threads are of appropriate size for mating with internal threads  1110  of second protruding end  1108  of force sensing transducer  1100  (all of FIG.  2 ). The rod end further comprises a connector terminating in eye  1206  with antifriction bearing  1208 . Alternatively, the rod end may terminate in a manner suitable for attachment to another element such as a threaded or socketed connector. 
     FIG. 4 is a side view of a threaded tube prepared for use as a rod body of the force sensor rod. Tube  1300  has cable opening  1308  for exit of excitation and signal cable  1106  (FIG. 2) of force sensing transducer  1100  (FIG.  2 ). The tube is preferably composed of a softer material than external screw threads  1112  of first protruding end  1102  (all of FIG. 2) of the force sensing transducer. The tube has an internally threaded bore  1304  for mating with the external screw threads of first protruding end of the force sensing transducer. Entrance portion  1306  to the internally threaded bore has a diameter substantially equal to the major axis of the external screw threads and thus the external screw threads are readily threaded into the internally threaded bore without interference until grooves  1114  (FIG. 2) of the force sensing transducer are aligned with the entrance portion. In one embodiment, the entrance portion to the internally threaded bore has a diameter not greater than the major axis of the external screw threads. 
     Referring again to FIG. 2, in a further alternative embodiment of a sensor used in a sensor rod, the rod end is threaded and grooved similarly to the first protruding end of the force sensing transducer. The second protruding end  1108  of force sensing transducer  1100  is provided with an entrance portion similar to the entrance portion of the tube. Once threaded together, the female threaded end of the force sensing transducer is swaged onto the rod end. In this way, the force sensing transducer and the rod end are fixedly connected using a swaged connection. 
     FIG. 5 is an exploded view of a sensor rod. Rod end  1200  is threaded into internally threaded second protruding end  1108  of force sensing transducer  1100 . As previously described, the force sensing transducer has excitation and signal cable  1106  extending from a first protruding end. The excitation and signal cable is inserted through internally threaded bore  1304  into the interior of tube  1300  exiting the tube through cable exit opening  1308 . The force sensing transducer is threaded into the internally threaded bore of the tube. 
     FIG. 6 is a cross-sectional view of a swaged connection. A swaging force is applied to the external surface of tube  1300 . Preferably the contact of the swaging tool with the tube is limited to the external area of the tube opposite entrance portion  1306  aligned with grooves  1114  of first protruding end  1102  of a force sensing transducer. With proper swaging, metal from the tube is caused to flow into the grooves of the first protruding end of the force sensing transducer. 
     In an alternative embodiment, the tube is threaded onto the first protruding end of the force sensing transducer with an adhesive sealer coating the threads. An angle swaging operation is performed, creating a swaged connection. 
     In a further alternative embodiment, the tube is threaded onto the first protruding end of the force sensing transducer with an adhesive sealer coating the threads. An overlap swaging operation is performed, creating a swaged connection over a portion the threaded connection. 
     FIG. 7 is a perspective view of a force sensor rod according to the present invention. Force sensor rod  1000  comprises rod end  1200  connected to force sensing transducer  1100  that is fixed to tube  1300 . Excitation and signal cable  1106  of the force sensing transducer exits the body of the tube via cable hermetically sealed exit opening  1308 . 
     Alternatively, the excitation and signal cable exits directly from the body of the force sensing transducer. 
     The preceding description has been presented with reference to specific embodiments of the invention shown in the drawings. Workers skilled in the art and technology to which this invention pertains will appreciate that alteration and changes in the described processes and structures can be practiced without departing from the spirit, principles and scope of this invention. 
     Accordingly, Although this invention has been described in certain specific embodiments, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that this invention may be practiced otherwise than as specifically described. Thus, the present embodiments of the invention should be considered in all respects as illustrative and not restrictive, the scope of the invention to be determined by the claims supported by this application and their equivalents rather than the foregoing description.