Method and apparatus for sensing piston position
First Claim
1. A method of determining the position of a piston moveable within a cylinder housing, the cylinder housing enclosing a cavity filled with a fluid, comprising the steps of:
- generating real-time electromagnetic (EM) bursts;
launching the real-time EM bursts towards the piston through the fluid within the cavity in the cylinder housing;
detecting real-time reflections of the EM bursts from the piston;
generating an equivalent-time timing signal representative of the time between launching the EM bursts and detecting the reflections, the timing signal being of a slower time scale than that of the real-time EM bursts and reflections; and
converting at least the equivalent-time timing signal into a position signal representative of the position of the piston within the cylinder housing.
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Accused Products
Abstract
A system for determining the position of a piston moveable within a cylinder, or of an implement or joint, is disclosed herein. Electromagnetic (EM) bursts such as ultra-wideband or frequency pulses are generated and applied to a transmitter/receiver unit. The EM bursts are launched by the transmitter via a focusing antenna assembly from an end of the cylinder housing towards the piston. The fluid in the cylinder housing is in electrical communication with the piston such that a surface of the piston represents an electrical impedance discontinuity which causes the EM bursts to be reflected back to the receiver. The time for the EM bursts to travel from the transmitter to the piston and for the reflections to travel back to the receiver via the antenna assembly is determined and converted into a position signal representing the piston'"'"'s position. A compensation signal can be used to compensate the position signal for variations in a parameter of the fluid within the cylinder. The parameter may be the dielectric constant, and the variations may be caused by factors such as temperature, contamination and fluid type. The compensation circuit can include a pulse level analyzer, resonance circuit, mini-dipstick, or a capacitance circuit.
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Citations
26 Claims
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1. A method of determining the position of a piston moveable within a cylinder housing, the cylinder housing enclosing a cavity filled with a fluid, comprising the steps of:
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generating real-time electromagnetic (EM) bursts; launching the real-time EM bursts towards the piston through the fluid within the cavity in the cylinder housing; detecting real-time reflections of the EM bursts from the piston; generating an equivalent-time timing signal representative of the time between launching the EM bursts and detecting the reflections, the timing signal being of a slower time scale than that of the real-time EM bursts and reflections; and converting at least the equivalent-time timing signal into a position signal representative of the position of the piston within the cylinder housing. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for determining the position of a piston moveable within a cylinder housing, the cylinder housing enclosing a cavity filled with a fluid, comprising:
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a generator for generating real-time EM bursts; a transmitter coupled to the generator and to the cylinder housing, the transmitter configured to launch the real-time EM bursts towards the piston through the fluid within the cavity in the cylinder housing; a receiver coupled to the cylinder housing and configured to detect real-time reflections after the EM bursts are reflected by the piston towards the receiver; a timing circuit configured to generate an equivalent-time timing signal representative of the time for the EM bursts to travel from the transmitter to the piston and for the reflections to travel from the piston to the receiver, the timing signal being of a slower time scale than that of the EM bursts and reflections; and a conversion circuit configured to convert at least the equivalent-time timing signal into a position signal representative of the position of the piston within the cylinder housing. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. An electrohydraulic control system for controlling the position of an implement, the implement having at least one joint which is moved by extending or retracting at least one cylinder coupled to the joint, comprising:
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an input device configured to generate command signals representative of a commanded position of the implement; a source of pressurized hydraulic fluid; a valve assembly coupled between the cylinder and the source, the valve assembly configured to control the flow of hydraulic fluid between the cylinder and the source in response to control signals; a micropower impulse radar (MIR) sensor system coupled to the cylinder and configured to sense movement of the cylinder and to generate a position signal representative of the position of the implement, the MIR sensor system being configured to sense the movement using time domain reflectometry based on real-time signals traveling through the hydraulic fluid within a cavity of the cylinder; and a control circuit coupled to the input device, the valve assembly, and the MIR sensor system, the control circuit configured to generate the control signals based upon the command signals and the position signal and to apply the control signals to the valve assembly. - View Dependent Claims (24, 25, 26)
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Specification