US4737705A
Expired / Lapsed
US
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Linear position sensor using a coaxial resonant cavity
Assignee: Mid-America Commercialization Corp
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Filing: 1986-11-05
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Granted: 1988-04-12
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Expires: 2006-11-05
Abstract
Abstract Known linear position sensors suffer from inaccuracies owing to severe environmental conditions, such as temperature and humidity. Physical damage to sensors exposed to rugged work conditions is a limiting factor in the expected life of sensors used, for example, in the heavy equipment industry. A pair of loop antennas mounted internal to an extensible coaxial cavity respectively transmit and receive electromagnetic signals in the radio frequency range exciting a transverse electromagnetic field in the cavity when the frequency of the signal corresponds to the resonant frequency of the cavity. The resonant frequency of the cavity is primarily dependent upon the longitudinal length of the cavity. Therefore, a voltage controlled oscillator acts under the control of a sawtooth voltage waveform of a function generator to controllably deliver a variable frequency signal to the first loop antenna. An RF detector monitors the second loop antenna for an indication that the resonant frequency has been reached. At resonance a microprocessor samples the output of the VCO and correlates the resonant frequency to the length of the coaxial cavity. The sensor is particularly suited for use in the heavy equipment industry for detecting the extended length of hydraulic cylinders as it is highly insensitive to environmental conditions and protected from the work environment.
Inventors
- 👤 Ali Bitar
- 👤 Adam J. Gudat
- 👤 Brian D. Huggins
- 👤 Wesley E. Jacobson
- 👤 John F. Szentes
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 22:46
CPC Classifications
F; F15; F15B; F15B15/00; F15B15/20; F15B15/28; F15B15/2815; F15B15/2869; G; G01; G01D; G01D5/00; G01D5/48; G01R; G01R23/00; G01R23/02; G01R23/06; G01R23/07; H; H01; H01P; H01P7/00; H01P7/04
Claims Analysis
Total Claims: 32
Claim 1
Independent Claim
203 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, said piston and piston rod being movable within said housing and defining a variable length coaxial resonant cavity, comprising: means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving said first signal and delivering a second signal of a preselected frequency in response to the magnitude of said first signal; first coupling means for receiving said second signal and delivering an electromagnetically radiated signal into said coaxial cavity; second coupling means for receiving electromagnetic wave signals within said coaxial cavity and delivering a third signal in response to receiving said electromagnetic wave signals; detector means for receiving said third signal and delivering a fourth signal in response to the magnitude of said third signal exceeding a preselected setpoint; means for resetting said first signal delivering means to said minimum value in response to receiving said fourth signal; and means for receiving said second signal, determining the frequency of said second signal, and determining the linear position of said piston and piston rod relative to said housing in response to the determined frequency of said received signal.
Claim 2
Independent Claim
203 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, said piston and piston rod being movable within said housing and defining a variable length coaxial resonant cavity, comprising: means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving said first signal and delivering a second signal of a preselected frequency in response to the magnitude of said first signal; first coupling means for receiving said second signal and delivering an electromagnetically radiated signal into said coaxial cavity; second coupling means for receiving electromagnetic wave signals within said coaxial cavity and delivering a third signal in response to receiving said electromagnetic wave signals; detector means for receiving said third signal and delivering a fourth signal in response to the magnitude of said third signal exceeding a preselected setpoint; means for resetting said first signal delivering means to said minimum value in response to receiving said fourth signal; and means for receiving said second signal, determining the frequency of said second signal, and determining the linear position of said piston and piston rod relative to said housing in response to the determined frequency of said received signal.
Claim 3
Dependent Claim
58 words
An apparatus, as set forth in claim 1, wherein said first coupling means includes processing means for receiving at least a portion of said second signal, determining the frequency of said received second signal in response to receiving said fourth signal, and determining the linear position of said piston in response to the frequency of said second signal.
Claim 4
Dependent Claim
29 words
An apparatus, as set forth in claim 1, including means for holding the magnitude of said first signal at a preselected value in response to receiving said fourth signal.
Claim 5
Dependent Claim
25 words
An apparatus, as set forth in claim 1, wherein said fourth signal is delivered to said first signal delivering means after a preselected time delay.
Claim 6
Dependent Claim
114 words
An apparatus, as set forth in claim 2, wherein said processing means includes means for receiving at least a portion of said second signal and delivering a frequency divided signal; means for receiving said frequency divided signal, counting the number of cycles occurring within a preselected duration of time in response to receiving a control signal, and delivering a count signal having a magnitude responsive to the count; and microprocessor means for delivering a control signal to said counting means in response to receiving said fourth signal, receiving said count signal, determining the linear position of said piston and piston rod relative to said housing in response to the magnitude of said count signal.
Claim 7
Dependent Claim
17 words
An apparatus, as set forth in claim 1, wherein said first coupling means includes a loop antenna.
Claim 8
Dependent Claim
23 words
An apparatus, as set forth in claim 1, wherein said second coupling means includes a loop antenna and a radio frequency signal detector.
Claim 9
Dependent Claim
21 words
An apparatus, as set forth in claim 1, wherein the frequency of said second signal is within the radio frequency spectrum.
Claim 10
Independent Claim
203 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, said piston and piston rod being movable within said housing and defining a variable length coaxial resonant cavity, comprising: means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving said first signal and delivering a second signal of a preselected frequency in response to the magnitude of said first signal; first coupling means for receiving said second signal and delivering an electromagnetically radiated signal into said coaxial cavity; second coupling means for receiving electromagnetic wave signals within said coaxial cavity and delivering a third signal in response to receiving said electromagnetic wave signals; detector means for receiving said third signal and delivering a fourth signal in response to the magnitude of said third signal attaining a peak value; means for resetting said first signal delivering means to said minimum value in response to receiving said fourth signal; and means for receiving said second signal, determining the frequency of said second signal, and determining the linear position of said piston and piston rod relative to said housing in response to the determined frequency of said received signal.
Claim 11
Independent Claim
203 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, said piston and piston rod being movable within said housing and defining a variable length coaxial resonant cavity, comprising: means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving said first signal and delivering a second signal of a preselected frequency in response to the magnitude of said first signal; first coupling means for receiving said second signal and delivering an electromagnetically radiated signal into said coaxial cavity; second coupling means for receiving electromagnetic wave signals within said coaxial cavity and delivering a third signal in response to receiving said electromagnetic wave signals; detector means for receiving said third signal and delivering a fourth signal in response to the magnitude of said third signal attaining a peak value; means for resetting said first signal delivering means to said minimum value in response to receiving said fourth signal; and means for receiving said second signal, determining the frequency of said second signal, and determining the linear position of said piston and piston rod relative to said housing in response to the determined frequency of said received signal.
Claim 12
Dependent Claim
65 words
An apparatus, as set forth in claim 9, wherein said first coupling means includes processing means for receiving at least a portion of said second signal, determining the frequency of said received second signal in response to receiving said fourth signal, and determining the linear position of said piston and piston rod relative to said housing in response to the frequency of said second signal.
Claim 13
Dependent Claim
29 words
An apparatus, as set forth in claim 9, including means for holding the magnitude of said first signal at a preselected value in response to receiving said fourth signal.
Claim 14
Dependent Claim
25 words
An apparatus, as set forth in claim 9, wherein said fourth signal is delivered to said first signal delivering means after a preselected time delay.
Claim 15
Dependent Claim
114 words
An apparatus, as set forth in claim 10, wherein said processing means includes means for receiving at least a portion of said second signal and delivering a frequency divided signal; means for receiving said frequency divided signal, counting the number of cycles occurring within a preselected duration of time in response to receiving a control signal, and delivering a count signal having a magnitude responsive to the count; and microprocessor means for delivering a control signal to said counting means in response to receiving said fourth signal, receiving said count signal, determining the linear position of said piston and piston rod relative to said housing in response to the magnitude of said count signal.
Claim 16
Dependent Claim
17 words
An apparatus, as set forth in claim 9, wherein said first coupling means includes a loop antenna.
Claim 17
Dependent Claim
23 words
An apparatus, as set forth in claim 9, wherein said second coupling means includes a loop antenna and a radio frequency signal detector.
Claim 18
Dependent Claim
21 words
An apparatus, as set forth in claim 9, wherein the frequency of said second signal is within the radio frequency spectrum.
Claim 19
Independent Claim
290 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, said piston and piston rod being movable within said housing and defining a variable length coaxial resonant cavity, comprising: means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving said first control signal and delivering a second signal of a preselected frequency in response to the magnitude of said first control signal; first coupling means for receiving said second signal and delivering an electromagnetically radiated signal into said coaxial cavity; second coupling means for receiving electomagnetic wave signals within said coaxial cavity and delivering a third signal in response to receiving said electromagnetic wave signals; and detector means for receiving said third signal and delivering a fourth signal in response to the magnitude of said third signal exceeding a preselected setpoint; means for holding the magnitude of said first signal at a preselected value in response to receiving said fourth signal; means for resetting said first control signal to said minimum value a preselected duration of time after receiving said fourth signal; means for receiving at least a portion of said second signal and delivering a frequency divided signal; means for receiving said frequency divided signal, counting the number of cycles occurring within a preselected duration of time in response to receiving a control signal, and delivering a count signal having a magnitude responsive to the count; and microprocessor means for delivering a control signal to said counting means in response to receiving said fourth signal, receiving said count signal, and determining the position of said piston and piston rod relative to said housing in response to the magnitude of said count signal.
Claim 20
Independent Claim
290 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, said piston and piston rod being movable within said housing and defining a variable length coaxial resonant cavity, comprising: means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving said first control signal and delivering a second signal of a preselected frequency in response to the magnitude of said first control signal; first coupling means for receiving said second signal and delivering an electromagnetically radiated signal into said coaxial cavity; second coupling means for receiving electomagnetic wave signals within said coaxial cavity and delivering a third signal in response to receiving said electromagnetic wave signals; and detector means for receiving said third signal and delivering a fourth signal in response to the magnitude of said third signal exceeding a preselected setpoint; means for holding the magnitude of said first signal at a preselected value in response to receiving said fourth signal; means for resetting said first control signal to said minimum value a preselected duration of time after receiving said fourth signal; means for receiving at least a portion of said second signal and delivering a frequency divided signal; means for receiving said frequency divided signal, counting the number of cycles occurring within a preselected duration of time in response to receiving a control signal, and delivering a count signal having a magnitude responsive to the count; and microprocessor means for delivering a control signal to said counting means in response to receiving said fourth signal, receiving said count signal, and determining the position of said piston and piston rod relative to said housing in response to the magnitude of said count signal.
Claim 21
Independent Claim
96 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, the piston and piston rod being movable within the housing and defining a variable length coaxial resonant cavity, comprising: means for exciting a transverse electromagnetic wave within the coaxial cavity; means for detecting the transverse electromagnetic wave and delivering a signal responsive to the frequency of the transverse electromagnetic wave; and means for receiving the signal and determining the linear position of the piston and piston rod relative to the housing in response to the transverse electromagnetic wave frequency.
Claim 22
Independent Claim
96 words
An apparatus for detecting linear position of a piston and a piston rod relative to a housing, the piston and piston rod being movable within the housing and defining a variable length coaxial resonant cavity, comprising: means for exciting a transverse electromagnetic wave within the coaxial cavity; means for detecting the transverse electromagnetic wave and delivering a signal responsive to the frequency of the transverse electromagnetic wave; and means for receiving the signal and determining the linear position of the piston and piston rod relative to the housing in response to the transverse electromagnetic wave frequency.
Claim 23
Dependent Claim
78 words
An apparatus, as set forth in claim 18, wherein the means for exciting a transverse electromagnetic wave includes means for delivering a first signal having a preselected magnitude varying between preselected minimum and maximum values; means for receiving the first signal and delivering a second signal of a preselected frequency in response to the magnitude of the first signal; and first coupling means for receiving the second signal and delivering an electromagnetically radiated signal into the coaxial cavity.
Claim 24
Dependent Claim
74 words
An apparatus, as set forth in claim 19, wherein the means for detecting the transverse electromagnetic wave includes a second coupling means for receiving the transverse electromagnetic wave signals within the coaxial cavity and delivering a third signal having a magnitude responsive to the transverse electromagnetic wave energy; and detector means for receiving the third signal and delivering a fourth signal in response to the magnitude of the third signal exceeding a preselected setpoint.
Claim 25
Dependent Claim
58 words
An apparatus, as set forth in claim 19 wherein the first coupling means includes processing means for receiving at least a portion of said second signal, determining the frequency of said received second signal in response to receiving said fourth signal, and determining the linear position of said piston in response to the frequency of said second signal.
Claim 26
Dependent Claim
29 words
An apparatus, as set forth in claim 20, including means for holding the magnitude of said first signal at a preselected value in response to receiving said fourth signal.
Claim 27
Dependent Claim
28 words
An apparatus, as set forth in claim 20, including means for resetting the first signal delivering means to the minimum value in resposne to receiving the fourth signal.
Claim 28
Dependent Claim
25 words
An apparatus, as set forth in claim 23, wherein said fourth signal is delivered to said first signal delivering means after a preselected time delay.
Claim 29
Dependent Claim
114 words
An apparatus, as set forth in claim 21, wherein said processing means includes means for receiving at least a portion of said second signal and delivering a frequency divided signal; means for receiving said frequency divided signal, counting the number of cycles occurring within a preselected duration of time in response to receiving a control signal, and delivering a count signal having a magnitude responsive to the count; and microprocessor means for delivering a control signal to said counting means in response to receiving said fourth signal, receiving said count signal, determining the linear position of said piston and piston rod relative to said housing in response to the magnitude of said count signal.
Claim 30
Dependent Claim
17 words
An apparatus, as set forth in claim 19, wherein said first coupling means includes a loop antenna.
Claim 31
Dependent Claim
23 words
An apparatus, as set forth in claim 20, wherein said second coupling means includes a loop antenna and a radio frequency signal detector.
Claim 32
Dependent Claim
21 words
An apparatus, as set forth in claim 19, wherein the frequency of said second signal is within the radio frequency spectrum.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-04-12 | 1991-10-12 | 1992-04-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-04-12 | 1995-10-12 | 1996-04-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-04-12 | 1999-10-12 | 2000-04-12 | $7700.00 | Window Closed / Lapsed |