Force moment sensor
A force moment sensor for sensing forces and moments in a system through which forces and moments are transferred from an input member to an output member is disclosed. It includes a housing, an inner tube, a load plate, a plurality of elongate connectors and a plurality of dynamic deflection measuring devices. The housing has a base portion and an outer tube portion generally orthogonal to the base portion. The inner tube, a poled piezoceramic element, is operably connected to the base portion and spaced inwardly of the outer tube. The load plate is attached to the inner tube, spaced from the base portion and spaced from the outer tube. The plurality of elongate connectors are connected between the load plate and the outer tube portion. The plurality of dynamic deflection measuring devices are attached to the load plate for measuring dynamic flexible deflections of the load plate.
1. A computer implemented method of determining a force and moment measurement having six degrees of freedom for an external load applied to a force moment sensor having an inner tube, a load plate and a plurality of dynamics deflection measuring devices, the method comprising the steps of:
applying a current to the inner tube to excite the load plate through a plurality of definable frequencies;
extracting a plurality of resonant frequencies and associated dynamic shapes of the load plate from the plurality of definable frequencies and using the plurality of dynamics deflection measuring devices to measure deflection in six degrees of freedom;
comparing the plurality of extracted resonant frequencies and associated dynamic shapes to a plurality of calibration shapes, each corresponding to a defined force corresponding to the six degrees of freedom; and
determining the external loads corresponding to the six degrees of freedom forces.
2. The computer implemented method of claim 1 wherein the extracting step includes measuring acceleration of a plurality of locations on the load plate and calculating the resonant frequency and the dynamic shape of the load plate.
3. The computer implemented method of claim 2 wherein the calculating step is done using fast Fourier transform.
4. The computer implemented method of claim 2 wherein measuring the acceleration of a plurality of locations is measured through a plurality of dynamic deflection measuring devices; the plurality of dynamic deflection measuring devices being spaced apart on the load plate.
5. The computer implemented method of claim 4 wherein each dynamic measuring device is an accelerometer.
6. The computer implemented method of claim 1 wherein the inner tube includes a plurality of poled segments, and each of the poled segments are independently responsive to current.
7. The computer implemented method of claim 6 wherein each of the poled segments is poled in an axis parallel to the centre axis of the inner tube.
8. The computer implemented method of claim 6 wherein each of the poled segments is poled in an axis angled to the centre axis of the inner tube.
9. The computer implemented method of claim 6 wherein at least one poled segment is poled in an axis parallel to the center axis and at least another poled segment is poled in an axis angled to the centre axis.
10. The computer implemented method of claim 6 wherein the inner tube includes at least four poled segments.
11. The computer implemented method of claim 6 wherein a current is serially applied to each of the plurality of poled segments to create a cyclic, swirling excitation.
12. The computer implemented method of claim 11 wherein the cyclic, swirling excitation of the plurality of poled segments is continuously repeated to excite torsion mode of the external load.