Measuring and testing – Vibration – By mechanical waves
Patent
1983-11-30
1985-09-24
Birmiel, Howard A.
Measuring and testing
Vibration
By mechanical waves
73119R, 73627, G01N 2900
Patent
active
045426520
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention comprises a method for determining the relative distance between a piston and cylinder in a piston and cylinder assembly which is provided with a chamber that is filled with a flowable medium, the walls of the cylinder and the piston forming the chamber. The invention further comprises the apparatus for accomplishing a method of this type.
BACKGROUND OF THE INVENTION
Methods and apparatuses of the above-referenced type are well known. For example, a measuring rod extending through the cylinder head wall is moved with the piston, and the position of the rod is detected capacitively or resistively. It is also possible to drive an electro-optical sensing device from the piston rod through a transmission device. Such a method requires large free space and substantially structural expense. Other well known distance measuring methods are unsuited for the determination of the relative distance between the piston and cylinder head of the assembly because the necessary measuring devices are too sensitive. Excluded equipment, for example, includes forklifts with hydraulically operated lifting forks, earth-moving equipment with hydraulically adjustable shovels, hydraulically operated extrusion presses, and many other applications of piston and cylinder assemblies for which there is no satisfactory device to exactly determine the relative positioning.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to provide a method which constitutes an improvement over the prior art mentioned above, which can be accomplished at minimum expense and which delivers precise measuring results. It is a further object to provide a corresponding apparatus that is built with a minimum size at minimum expense and which operates precisely and reliably.
These objects are achieved according to the present invention in a method of the type described above in which a group of sequential ultrasonic oscillations are transmitted from a first end wall of the cylinder chamber and after reflection in the region of the oppositely disposed second end wall, the group received as a group of measurement oscillations. The elapsed time of the measurement oscillations between the transmission of the group of ultrasonic oscillations and the receipt of the group of measurement oscillations is utilized as a measure of the relative distance. A fluid medium extends along a reference path of a prescribed length and at the first end of the path, the group of ultrasonic oscillations are transmitted and after reflection at a reflecting reference surface forming the second end of the reference path, the group of oscillations are received again as reference oscillations. Through the measurement of the actual elapsed travel time between the transmission of the group of ultrasonic oscillations from the first end and the receipt of the reference oscillations, a proportional reference signal is produced, and the measurement signal obtained on the basis of the elapsed time measurement of the group of measurement oscillations is modified in response to the reference signal in the sense of a compensation for the influence of changes in the ultrasonic propagation conditions affecting the measuring signal.
Another object of the invention is to provide an apparatus for accomplishing the method. Embodiments of the method and correspondingly the apparatus are given in the following specification and claims.
According to the method and the apparatus of the present invention, a group or packet of sequential ultrasonic oscillations are transmitted from one end of a cylinder chamber, are reflected at the oppositely disposed end, and then are captured again at the first end. The travel time is a relatively accurate measure of the distance between the oppositely disposed ends, and accordingly, the distance between a piston and cylinder. Since the travel time for the ultrasonic oscillations in the cylinder chamber is always dependent upon the propagation speed of the ultrasonic waves in the fluid medium filling the cyli
REFERENCES:
patent: 3184969 (1965-05-01), Bolton
patent: 4210969 (1980-07-01), Massa
patent: 4254660 (1981-03-01), Prause
patent: 4345657 (1982-08-01), Howard
Konig Johannes
Reuter Martin
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