1. Field of the Invention
The present invention relates to monitoring loads in load bearing members, and more particularly to sensors for monitoring loads in landing gear torque links.
2. Description of Related Art
There is a need to monitor loading in landing gear structures of aircraft to determine if the load bearing members are ever overloaded. The application of a landing gear overload detection system to an aircraft landing gear requires measurement of loading in six dimensions or degrees of freedom, namely three linear dimensions and three rotational dimensions. These six dimensions or degrees of freedom are identified in FIG. 1. One particular loading dimension of interest is rotation about the main axis of the landing gear strut (MV in FIG. 1), where there is a rotational moment applied to the strut from the action of the wheels on the ground. A torque linkage is typically provided to bear this rotational moment, preventing rotation between telescoping strut members, and measurement of the resulting moment can be accomplished in a number of ways. In the laboratory, a foil strain gage can be bonded to the strut piston in a position advantageous to monitoring pure shear due to torsion. Foil strain gages, however, are not reliable over the long term, so other means have been devised to measure the applied rotational moment.
One approach to this problem has been to mount a linear capacitive sensor capsule to one of the torque links. The torsional loading on the torque link puts the web of the torque link in tension. The resultant linear strain on the link can be measured in a linear capacitive sensor capsule by monitoring the change in capacitance as the capacitor plates are moved away from or toward each other under the strain motion in the torque link. Such sensors have typically been sensitive and accurate. In some applications, the most desirable location for this type of sensor with respect to sensitivity, is unfavorable with respect to exposure to the elements and to the hazards of flying debris. Positive fixation, e.g., by fasteners, when mounting such sensors may not be practical in applications where it is preferred not to form holes in the loaded elements. In such applications, sensors of this type are typically mounted in place by an adhesive bond that is not as robust as positive fixation by typical fasteners.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for capacitive sensors that allow for sensitive and accurate monitoring of loads while being robust under exposure to the elements and/or flying debris as in landing gear applications, for example. There also remains a need in the art for such sensors that are easy to make and use. The present invention provides a solution for these problems.