Method and system for monitoring position of a fluid actuator employing microwave resonant cavity principles

Claim 1

An actuator system (10) comprising a fluid-driven actuator (12, 14, 16 or 18) having a cylinder (12b, 14b, 16b or 18b) coupled to a source (20) of motive fluid, a piston (12a, 14a, 16a or 18a) axially slidable within said cylinder as a function of fluid pressure within said cylinder and actuator means - (12c, 14c, 16c or 18c) for coupling said piston to an actuator load, and means (22) for monitoring position of said actuator means and load as a function of position of said piston within said cylinder, said monitoring means comprising a swept frequently oscillator (46) for generating microwave radiation over a preselected range, an antenna (30) coupled to said oscillator (46) and positioned in said cylinder (12b, 14b, 16b or 18b) to inject said microwave energy into said cylinder such that at least one resonance is developed within said cylinder as said oscillator sweeps said frequency range, means (66 through 70) coupled to said antenna (30) for detecting occurrence of said at least one resonance, means (78) coupled to said detecting means (66 through 70) and to said oscillator (46) for identifying resonant frequency of said microwave radiation at which said at least one resonance occurs, and means (56) for determining position of said piston (12a, 14a, 16a or 18a) within said cylinder as a function of said resonant frequency, characterized in that said antenna is constructed such that said at least one resonance is of a single preselected normal cylindrical mode of microwave propagation, and in that said means (56) for determining position of said piston comprises means (82 through 92) responsive to said oscillator and to said detecting means for identifying the order of said single preselected mode of propagation associated with said at least one resonance, and means (82 through 92) for determining position of said piston within said cylinder as a combined function of said resonant frequency and said order.

Claim 6

The system (10) set forth in any preceeding claim wherein said cylinder (12b, 14b, 16b or 18b) has a predetermined fixed geometry and said piston (12a, 14a, 16a or 18a) has predetermined limits of travel therewithin, and wherein said oscillator comprises means (60) for generating said microwave radiation over a frequency range preselected to generate at least one resonance at alf positions of said piston within said travel limits, and to generate only resonances of said single preselected normal cylindrical propagation mode at all positions of said piston between said limits.

Claim 7

The system (10) set forth in any preceeding claim wherein said resonance detecting means (66 through 70) comprises a microwave detector (66) coupled to said antenna (30) for providing a detection signal as a function of microwave energy absorbed at said cylinder (12b, 14b, 16b or 18b), and a peak detector (70) responsive to said detector signal for detecting resonance conditions upon occurrence of peaks in said detection signal, characterized in that said resonant frequency identifying means (78) comprises storage means coupled to said oscillator (46) and to said peak detector - (70) for storing information indicative of microwave frequency at said oscillator upon occurrence of peaks in said detector signal.

Claim 10

The system (10) set forth in any preceeding claim further comprising means (98) for selectively establishing desired limits of travel of said actuator load, and means (94) responsive to said limit- establishing means (98) and to said position-determining means (82 through 92) for indicating travel of said actuator load to said limits.

Claim 11

A method of monitoring axial position of a piston (12a, 14a, 16a or 18a) within a right circular cylinder (12b, 14b, 16b or 18b) between predetermined minimum and maximum limits of travel within said cylinder, said method comprising the steps of: (a) injecting microwave radiation into said cylinder, (b) sweeping said microwave radiation over a frequency range preselected to generate at least one resonance of a preselected normal cylindrical resonant mode within said cylinder at said minimum limit of travel and multiple resonances of differing order of the same said preselected resonant mode at said maximum limit of travel, (c) detecting occurrence of at least one resonance condition within said cylinder as said radiation is swept through said frequency range, (d) identifying the frequency of said microwave radiation at which said at least one resonance occurs, (e) identifying the order of said preselected resonant mode at which said at least one resonances occurs, and (f) determining position of said piston within said cylinder as a combined function of resonant frequency identified in said step (d) and said order identified in said step (e).

Claim 12

A method of monitoring axial position of a piston (12a, 14a, 16a or 18a) within a right circular cylinder (12b, 14b, 16b or 18b) between predetermined minimum and maximum limits of travel within said cylinder, said method comprising the steps of: (a) injecting microwave radiation into said cylinder, (b) sweeping said microwave radiation over a frequency range preselected to generate at least one resonance of a preselected normal cylindrical resonant mode within said cylinder at said minimum limit of travel and multiple resonances of differing order of the same said preselected resonant mode at said maximum limit of travel, (c) detecting occurrence of at least one resonance condition within said cylinder as said radiation is swept through said frequency range, (d) identifying the frequency of said microwave radiation at which said at least one resonance occurs, (e) identifying the order of said preselected resonant mode at which said at least one resonances occurs, and (f) determining position of said piston within said cylinder as a combined function of resonant frequency identified in said step (d) and said order identified in said step (e).