Device for determining a length of linear movement or an angle o

Details Device for determining a length of linear movement or an angle o Device for determining a length of linear movement or an angle o

1989-07-26

1991-06-18

Snow, Walter E.

Electricity: measuring and testing

Magnetic

Displacement

32420715, 32420724, 32420725, 336 45, 336 79, G01B 714, H01F 2102, H01F 2104

Patent

active

050252135

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a device for determining the length or the angle of rotation and comprising a diaphragm connected with a machine part and arranged between two stationary bodies of which one has a coil on a surface thereof facing the diagram. A device this type, in which a coil is arranged on a stationary body and a diaphragm is moved between the latter and a second body, is already known. A layer of electrically conductive material is arranged on the side of the diaphragm facing the coil and on a semicircular region of the front side of the second body, which likewise faces the coil. When high-frequency alternating current flows through the coil, eddy currents are formed on the, layers. Due to the screening effect of the diaphragm, the magnitude of the measured-signal voltage is determined by the diaphragm position and the position of a machine part which is connected with the diaphragm is accordingly indicated. In so doing, axial displacements, e.g. due to bearing play or to wobbling movement of the diaphragm, can influence the magnitude of the eddy current formation and can accordingly influence the measured-signal voltage. This can result in a deviation from the characteristic line of the measurement voltage curve and can result in measurement errors.


SUMMARY OF THE INVENTION

The objection of the invention is to provide a measuring device which has the advantage that the measured signal is virtually free of measurement errors deriving from axial displacements or wobbling movements of the diaphragm. The object of the invention is achieved by arranging on the diaphragm alternating electrically conductive regions of non-ferromagnetic and ferromagnetic material in such a manner that eddy current and inductive current actions generated due to axial fluctuation of the diaphragm, cancel each other. The production of the device is simplified, since the bearing play and possible manufacturing errors influence the measured signal only to a negligibly slight degree. The device can be constructed inexpensively.
The present invention both as to its construction so to its mode of operation, together with additional objects and advantages thereof, will be best understood from the following description of the preferred embodiments with reference to the accompanying drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal cross-sectional view of the device according to the invention; FIG. 2 shows a cross-sectional view along line II; FIG. 3 shows a partially cross-sectional view along line III; FIGS. 4 and 5 show partial views a modification of the device according to the invention.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

A device for determining the length or the angle of rotation, particularly in a form of a disk or rotary potentiometer, is designated by 10 in FIG. 10. The device 10 comprises two disks 11, 12 which are arranged so as to be stationary at a constant distance "a" relative to one another. A shaft 14 projects through a central bore hole 13 formed in the disk 12. The shaft 14 leads to a machine part, not shown, whose rotational movement is to be determined. A semicircular diaphragm 15 is arranged at the end of the shaft 14 located between the two disks 11, 12. A coil 17, through which a high-frequency alternating current flows, is located on the inner front side 16, i.e. on the front side of the disk 12 facing the disk 11. A half side of the inner front face 18 of the disk 11 is covered with an electrically conductive layer 19.
On the front side 22 of the diaphragm 15 facing the coil 17, a plurality of strips 23 consisting of ferromagnetic material, and strips 24 consisting of material which is electrically conductive but not ferromagnetic, are arranged in a semicircular manner around the center of the diaphragm 15. The strips 23, 24 consisting of the two different materials are arranged in regular, alternating sequence from the edge of the diaphragm to the center point. In so doing, the diaphragm 15 can be made e.g., of Fe or a free-cutting ste

REFERENCES:
patent: 3742340 (1973-06-01), Kiedrowski
patent: 4507638 (1985-03-01), Brosh

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