Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1994-01-14
1995-09-05
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250237G, 356358, G01D 534
Patent
active
054480604
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a system for measuring relative displacements of a rotating shaft in a direction transverse to the axis of the shaft.
BACKGROUND OF THE INVENTION
Displacements of a shaft axis occur at frequencies comparable to or greater than the frequency of rotation of the shaft in many machines and apparatus. A shaft which supports a grinding wheel in a grinding machine is subject to such displacement both as a result of imbalance of the rotating masses and as a result of external forces applied to the grinding wheel when it engages a workpiece.
One known method of measuring displacement uses a probe to mechanically follow he shaft and a transducer to measure the displacement of the probe. For complete information two probes at right angles are required.
The present invention uses a known method of measuring angular displacement of a shaft. The method is applied at two or more angularly spaced locations and the resulting measurements are processed to produce a measurement of relative displacement of the shaft in the required transverse direction. Two locations are needed to measure displacement in a given direction. Three or more locations are necessary to provide full information about the displacement of the shaft.
SUMMARY OF THE INVENTION
According to the invention a displacement measuring system for indicating relative displacement of a shaft transverse to its axis, comprises: a first channel representative of angular displacement of the shaft as measured at the first station; station for producing electrical signals in a second channel representative of angular displacement of the shaft as measured at the second station; generate an indication of relative displacement between the detectors and the shaft in a direction transverse to the axis of the shaft.
It is an important advantage of the invention that the shaft displacement information is obtained from angular position detecting devices so that full information as to shaft angular motion and transverse displacement can be derived without using two separate measuring systems.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to specific embodiments shown in the accompanying drawings in which:
FIG. 1 shows a known form of optical shaft encoder;
FIG. 2 shows an embodiment of the invention having two measuring heads spaced at 180.degree. approximately and able to measure shaft displacement in a direction transverse to the diameter joining the measuring heads;
FIG. 3 shows a second embodiment in which three measuring heads spaced at angular intervals of approximately 60.degree. are used for measuring shaft displacements in any direction transverse to the axis of the shaft;
FIG. 4 shows how shaft displacement is derived from the measurements made in the embodiment of FIG. 2;
FIG. 5 shows how shaft displacement in a plane transverse to the axis of the shaft is derived from the measurements made in the three head embodiment of FIG. 3;
FIG. 6 is a block diagram of the circuit through which the output signals of the three measuring heads in the embodiment of FIG. 3 are processed to provide signal suitable for computer analysis; and
FIGS. 7 to 10 show applications of the shaft displacement measuring system of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The shaft displacement measuring system of the invention is an instrument for measuring the relative displacement of a rotating shaft in directions transverse to the axis of rotation of the shaft. In its simplest form (FIG. 2) the shaft displacement measuring system is capable only of measuring displacements in a single direction.
The shaft displacement measuring system uses optical shaft encoders of a known kind which produce as output an electrical signal comprising a train of pulses of frequency proportional to the angular velocity of the shaft. As shown in FIG. 1, an encoder of this kind comprises a transparent disc 10 arranged for rotation with the shaft 11 from which measurements are required to be tak
REFERENCES:
patent: 4547667 (1985-10-01), Sasaki et al.
patent: 5036192 (1991-07-01), Ishizuka et al.
patent: 5101102 (1992-03-01), Nishimura et al.
Le Que T.
Nelms David C.
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