Hydraulic cylinder piston position sensing with compensation for piston velocity

The process of establishing the piston position in a hydraulic cylinder piston position sensing system that employs resonance envelope signals as indicative of piston position comprising the steps:

• characterizing each cylinder by storing information in tabulated form correlated with piston travel, on at least one resonance width parameter value, for each piston position,
• introducing electromagnetic wave energy into the hydraulic fluid in said cylinder said electromagnetic wave energy varying in frequency through a range that includes all resonance frequencies of all positions of said piston,
• sensing resonance signals in said hydraulic fluid during travel of said piston;
• detecting the presence of at least one width parameter of at least one said resonance signal during travel of said piston;
• measuring at least said at least one width parameter of at least one resonance during said piston travel;
• compensating said measured resonance width parameter for piston velocity;
• and
• comparing at least one compensated measured resonance width parameter as the piston travels with at least one stored resonance width parameter and based on said comparison providing a piston position signal.

Apparatus for sensing the position of a piston in a hydraulic cylinder comprising in combination:

• storage means adapted for storing information on at least one resonance width parameter of a resonance in the hydraulic fluid in said cylinder;
• said storage means being further adapted to store said information in tabular form correlated with piston travel;
• transmitting means adapted for introducing electromagnetic wave energy at a first coupler into the hydraulic fluid in said cylinder between said piston and the end of said cylinder, said electromagnetic wave energy varying in frequency through a range that includes all resonance frequencies of all positions of said piston,
• receiving means adapted for sensing resonance signals delivered through a second coupler in said hydraulic fluid during travel of said piston;
• said receiving means being further adapted to detect the presence of at least one resonance width parameter related portion of at least one said resonance during travel of said piston;
• processing means adapted to measure at least one velocity compensated resonance width parameter at a reference level, of at least one resonance during
• said piston travel;
• and
• said processing means being further adapted to compare at least one measured resonance width parameter as the piston travels with at least one stored resonance width parameter and based on said comparison provide a piston position signal.