Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1997-05-06
2001-02-27
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C073S29000R
Reexamination Certificate
active
06194891
ABSTRACT:
RELATED APPLICATION
This application is related to copending applications “Magnetostrictive Position Measurement Apparatus with Anti-Reflection Waveguide Terminals,” Attorney's Docket No. PTR-051 and “Magnetostrictive Position Measurement Apparatus and Method of Using Same,” Attorney's Docket No. PTR-052, both filed simultaneously herewith by John D. Begin and assigned to Patriot Sensors and Controls, Inc.
FIELD OF THE INVENTION
This invention relates to position measurement apparatus of the type utilizing a magnetostrictive wire waveguide which extends through a measurement field and in which the position of a movable element within the field is determined as a function of the propagation times of sonic disturbances along the waveguide. The inventive apparatus features a resilient suspension system for the waveguide which reduces the effects of external shock and vibration inputs on the accuracy of the measurement function.
BACKGROUND OF THE INVENTION
The use of a magnetostrictive wire waveguide to measure the position of a moveable element such as a machine tool component or a float is described in the prior art including, by way of example, U.S. Pat. No. 4,839,590 issued Jun. 13, 1989 to Richard Koski, William Kosco, and Arthur Dumais and assigned by mesne assignments to Patriot Sensors, Inc. of Clawson, Mich. In general, the magnetostrictive wire waveguide extends through the measurement field and cooperates with a toroidal “user” magnet which is moveable along and in surrounding relationship to the waveguide, the position of the user magnet being related to the position of a quantity or component being monitored. Although the specific manner of using a magnetostrictive waveguide as a position transducer may vary, the measurement function in all cases involves a determination of the time required for a sonic disturbance to propagate along the waveguide from a fixed position at or near one end of the waveguide to the user magnet or vice versa. Since the propagation speed is known, distance can be determined as a function of time.
In such devices, the accuracy of the position measurement can be seriously degraded by high frequency shocks which are transmitted to the waveguide from the outside world through the waveguide housing and support components. Such shocks and reflections thereof can be erroneously interpreted by the pickup as sonic disturbances.
SUMMARY OF THE INVENTION
In accordance with the invention described herein, the effects of environmental shock and vibration on the accuracy of position measurement using a magnetostrictive wire waveguide are substantially reduced. In general, this is achieved by way of (a) a resilient, shock-dampening suspension system which effectively permits the wire waveguide to float relative to mechanical ground; i.e., (a) the position measurement reference, and (b) a signal generating apparatus consisting of a reference magnet disposed in operative association with the wire waveguide but fixed mechanically relative to the reference, and at least one user magnet which is moveable along and over the waveguide in proportion to the movement and/or position of the element or quantity being monitored. Both magnets create sonic disturbances which propagate toward a pickup located near one end of the waveguide and the signals resulting from both such disturbances are used in determining the absolute position of the user magnet or magnets. Because both reference and user magnets are tied to the same reference frame, shifts in the waveguide permitted by the resilient suspension are of no effect on measurement accuracy.
These and other features and advantages of the present system will be apparent from a reading of the following specification which describes an illustrative embodiment in detail.
REFERENCES:
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patent: 5680041 (1997-10-01), Begin
Patriot Sensors and Controls Corp.
Snow Walter E.
Young & Basile P.C.
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