High accuracy optical position sensing system

In an aircraft including a flight controller for controlling flight of the aircraft, the combination comprising:

• electro-optical means for outputting a modulated optical signal and a chirped radio frequency signal, an envelope of the modulated optical signal having a phase that has a known relation to the phase of the chirped radio frequency signal;
• light guide means optically coupled to said electro-optical means for receiving and transmitting the modulated optical signal along a plurality of optical paths;
• a plurality of position sensor heads for sensing different parameters on the aircraft, each sensor head having a displaeable element which is displaced in dependence of changes in a respective one of the parameters, each displaceable element being disposed in one of said plurality of optical paths for reflecting the modulated optical signal to provide a position sensing optical signal, and each sensor head further including reference reflecting means disposed in the optical path upstream of the corresponding displaceable element for partially reflecting the modulated optical signal to provide a reference optical signal;
• and
• position detecting means having an input optically coupled for receiving the position sensing optical signals and the reference optical signals, another input electrically coupled to said electro-optical means for receiving the chirped radio frequency signal, and processing means for processing the position sensing optical signals, reference optical signals and chirped radio frequency signal for outputting to the flight controller a plurality of signals representing the respective positions of the displaceable elements of the sensor heads at sufficient rates, sufficient accuracies and sufficiently short lag times to enable the flight controller to control flight of the aircraft.

A fiber optic position sensing system, comprising:

• source means for producing a chirped radio frequency signal;
• optical modulating means coupled to said source means for receiving the chirped radio frequency signal and producing a modulated optical signal in accordance with the chirped radio frequency signal;
• optical fiber means coupled to said optical modulating means for receiving and transmitting the modulated optical signal along an optical path;
• sensor head means disposed in the optical path of the modulated optical signal transmitted by said optical fiber means for receiving the modulated optical signal and for outputting a reference optical signal in dependence of a position of a reference object and a target optical signal in dependence of a position of a target object;
• transducing means optically coupled to the output of said sensor head means for producing an electrical signal from the reference optical signal and the target optical signal which have, respectively, first and second times delay with respect to the radio frequency chirped signal;
• mixing means having an output and inputs coupled, respectively, to said source means and said transducing means for mixing the chirped radio frequency signal from said source means and the electrical signal from said transducing means and for producing a multi-frequency signal with first and second frequencies corresponding to the first and second time delays, respectively, at the output of said mixing means;
• and
• frequency estimating means coupled to the output of said mixing means for estimating a difference frequency corresponding to the difference between the first and second frequencies of the multi-frequency signal, the difference frequency representing a distance between the reference object and the target object.

A fiber optic position sensing system comprising:

• source means for producing a chirped radio frequency signal;
• radio frequency splitter means coupled to said source means for receiving and splitting the chirped radio frequency signal into a first chirped radio frequency signal and second chirped radio frequency signal;
• optical modulating means for receiving the first chirped radio frequency signal and producing a modulated optical signal in accordance with the first chirped radio frequency signal;
• optical fiber means coupled to said optical modulating means for receiving and transmitting the modulated optical signal along an optical path;
• reference reflecting means disposed in the optical path of the modulated optical signal transmitted by said optical fiber means for partially reflecting the transmitted modulated optical signal to provide a reference optical signal;
• reflector means fixed to a displaceable element and disposed optically downstream of said reference reflecting means in the optical path of the transmitted modulated optical signal for reflecting the transmitted modulated optical signal to provide a target optical signal in dependence of the position of a target;
• optical coupling means having an output and an input for receiving the reference optical signal and the target optical signal and coupling the reference optical signal and the target optical signal to the output of said optical coupling means;
• transducing means optically coupled to the output of said optical coupling means for producing an electrical signal including first and second signal components representing first and second time delays of the reference optical signal and the target optical signal, respectively, with respect to the chirped radio frequency signal;
• mixing means having an output and inputs coupled, respectively, to said radio frequency splitter means and said transducing means for mixing the first chirped radio frequency signal and the electrical signal and for outputting a multi-frequency signal including first and second frequencies corresponding to the first and second time delays, respectively;
• means for acquiring an initial difference frequency corresponding to the difference between the first and second frequencies;
• and
• means for tracking subsequent difference frequencies resulting from movement of the displaceable element.

A high speed position sensing system for sensing the position of a displaceable element, comprising:

• radio frequency source means for producing a chirped radio frequency signal having a series of radio frequency chirps each having an end of chirp time;
• controllable light source means having a modulating input coupled to the chirped radio frequency signal for producing a modulated optical signal having a signal envelope with a phase that has a known relationship to the phase of the chirped radio frequency signal;
• optical fiber means coupled to said light source means for receiving and transmitting the modulated optical signal along an optical path for reflection off a surface of the displaceable element to provide a position sensing optical signal;
• transducing means having an input optically coupled to said optical fiber means for receiving the position sensing optical signal with a time delay in dependence of the position of the displaceable element and an output for producing an electrical signal which is a function of the position sensing optical signal;
• mixing means, having an output and two inputs coupled, respectively, to said radio frequency source means and the output of said transducing means, for mixing the chirped radio frequency signal and the electrical signal and producing a signal at the output of said mixing means with a frequency corresponding to the time delay of the position sensing optical signal;
• and
• frequency detecting means coupled to the output of said mixing means for detecting and outputting, within 0.5 ms of the end of chirp time, the frequency which corresponds to the time delay as representing the position of the displaceable element.

A method for determining the position of a displaceable element, comprising:

• producing a chirped radio frequency signal;
• producing a modulated optical signal having an envelope of modulation with a phase that is known with respect to the phase of the chirped radio frequency signal;
• transmitting the modulated optical signal along an optical path and reflecting the modulated optical signal off a surface of the displaceable element to provide a position sensing optical signal;
• partially reflecting the transmitted optical signal at a point in the optical path prior to the surface of the displaceable element to provide a reference optical signal;
• producing an electrical signal as a function of first and second time delays of the position sensing optical signal and the reference optical signal, respectively, with reference to the chirped radio frequency signal;
• mixing the chirped radio frequency signal and the electrical signal to produce a multi-frequency signal with first and second frequencies corresponding to the first and second time delays, respectively;
• and
• detecting a difference frequency of the multi-frequency signal corresponding to the difference between the first and second frequencies, the difference frequency representing the position of the displaceable element.