Caterpillar Inc.

Ali A Bitar

Denny E Morgan

Charles W Bowman

Kenneth Lee Stratton

Adam J Gudat

William E Allen

John F Szentes

James A Garman

Robert A Herold

Wesley E Jacobson

Brian D Huggins

An apparatus (102) is adapted to detect the linear extension (position), velocity and acceleration of a hydraulic cylinder (108). The hydraulic cylinder (108) defines a variable length coaxial resonant cavity (112). Under the control of a controller (228), an RF transmitting section (114) and an RF receiving section (116) are used to determine the resonant frequency of the cavity. The resonant frequency of the cavity (112) is determined by comparing a received signal with a threshold and detecting slope intercept conditions.

Linear position sensor using a coaxial resonant cavity

An apparatus (102) is for detecting the linear extension (position), velocity and acceleration of a hydraulic cylinder (108). The hydraulic cylinder (108) defines a variable length coaxial resonant cavity (112). Under the control of a controller (228), an RF transmitting section (114) and an RF receiving section (116) are used to determine the resonant frequency of the cavity. The resonant frequency of the cavity (112) is determined by comparing a received signal with a threshold and detecting slope intercept conditions.

Apparatus and method for determining the linear position of a hydraulic

An apparatus is adapted to detect the linear extension of a hydraulic cylinder. The hydraulic cylinder defines a variable length coaxial resonant cavity. Under the control of a controller, a transmitting section and a receiving section are used to determine the linear extension of the hydraulic cylinder. The controller detects two subsequent harmonics of the resonant frequency and responsively determines the resonant frequency. The linear extension is determined as a function of the resonant frequency.

Radio frequency linear position sensor using two subsequent harmonics

The fluid seals on the currently available piston assemblies are ineffective for blocking the leakage of electrical signals between the piston and the cylinder. The present invention utilizes an electrically conductive split ring seated in an annular groove in a piston and an electrically conductive annular spring disposed between the split ring and the piston to resiliently urge the split ring into conductive engagement with the hydraulic cylinder while providing continuous electrical contact between the split ring and the piston to block the leakage of electrical signals.

Piston assembly for a hydraulic cylinder

An apparatus is adapted to detect the linear extensions of a plurality of hydraulic cylinders. Each hydraulic cylinder defines a variable length coaxial resonant cavity. Under the control of a controller, a transmitting section, a receiving section and multiplexers are used to multiplex RF signals to and from the cavity of each cylinder and to determine the resonant frequency of the cavity. The controller determines the linear extension of each cylinder as a function of its resonant frequency.

Multiplexed radio frequency linear position sensor system

A velocity reference system uses a Doppler shift between transmitted and received wave energy to determine the relative speed between the system and a surface or element. Other systems employing Doppler shifts for detecting velocity suffer from poor measurement accuracy. Cross talk between channels of systems having multiple transmitters and receivers produces measurement errors. Additionally, errant movement generates measurement errors since the sensors cannot distinguish such errant movement from forward velocity. Two sensing units directed towards one another, and preferably towards the same location on the surface, effectively eliminates random vehicle movement. Furthermore, transmitting different frequencies from the two sensing units reduces cross talk between the two channels. Vehicle applications require a system capable of minimizing errant movement and environmental noise.

Velocity reference system

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.

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Peoria, IL, United States of America

Ali A Bitar