Displacement/angular position sensor

Details Displacement/angular position sensor Displacement/angular position sensor

1999-10-29

2001-11-13

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

C324S723000, C324S688000

Reexamination Certificate

active

06316947

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a capacitance-coupled contactless displacement/angular position sensor comprising a potentiometer path, which is arranged on a carrier and to which an alternating voltage can be applied, a collector path arranged on the carrier, a first probe guided for displacement above the potentiometer path, and a second probe electrically coupled with the latter and guided for displacement above the collector path.
DESCRIPTION OF RELATED ART
A capacitance-coupled contactless displacement/angular position sensor of that kind has been disclosed, for example, by U.S. Pat. No. 5,525,955.
Displacement/angular position sensors of that kind are used, for example, in hydraulic cylinders for detecting the cylinder position.
In the case of a known displacement sensor, illustrated in
FIG. 3
, both the potentiometer path
82
and the collector path
84
are arranged on both sides of a carrier
80
of substantially I-shaped configuration.
In most of the cases the carrier
80
is surrounded by a metallic tube that screens off any electromagnetic inferences from the outside. However, such screening is not capable of avoiding overcoupling effects between the potentiometer path
82
and the collector path
84
that are produced by a substantially dipolar electric field E forming around the potentiometer path
82
and the collector path
84
(compare FIG.
3
).
But even with the potentiometer path
82
and the collector path
84
provided in any other arrangement, for example in the parallel arrangement of the potentiometer path and the collector path described in U.S. Pat. No. 5,525,955, electric interference fields E may occur that have a negative influence on the operation of the displacement/angular position sensor.
In addition, numerous parasitic capacitances and loss resistances are encountered with such displacement/angular position sensors. A diagrammatic representation of such parasitic impedances is provided in FIG.
4
.
As can be seen in
FIG. 4
, parasitic capacitances Cpm′ and loss resistances Rpm′ are encountered between the potentiometer path and frame, for example a housing.
Parasitic capacitances Ckm′ and loss resistances Rkm′ are also encountered between the collector path and frame.
In addition, parasitic capacitances Csm and loss resistances Rsm occur between the electric coupling line of the two measuring probes and frame.
Finally, other parasitic capacitances and loss resistances result from the connection lines and the evaluation electronics.
SUMMARY OF THE INVENTION
Now, it is the object of the present invention to improve a displacement/angular position sensor of the generic kind in such a way that interference influences provoked by both electromagnetic fields and parasitic capacitances and loss resistances are minimized, whereby the measuring precision of the displacement/angular position sensor is improved.
The invention achieves this object with a displacement/angular position sensor of the before-mentioned kind by the fact that screening surfaces, connected to frame potential, are provided that surround the potentiometer path and the collector path and the probes guided above them so that both the potentiometer path with the first probe associated to it and the collector path with the second probe associated to it are each arranged in a spatially separate, screened space.
Arranging the potentiometer path with the first probe associated to it, and the collector path with the second probe associated to it in spatially separate, screened spaces provides the substantial advantage that any generation of electromagnetic fields between the potentiometer path and the collector path, and interfering influences resulting therefrom, can be largely avoided. Electromagnetic fields will only arise inside the two spatially separate, screened spaces and any field lines will be sort of “drawn off” in an especially favorable way by the screening surfaces connected to frame potential.
In principle, the screening surfaces may be configured and arranged in the most different kinds and ways. For example, they may be fixed to the carrier.
A particularly favorable embodiment, that has proved to be very favorable especially with respect to the production of the carrier and of the screening surfaces, provides that the screening surfaces are integrally formed with the carrier. In this way, both the carrier and the screening surfaces can be manufactured by a simple processing operation, for example by extrusion molding. In addition, it is further ensured in this way that the carrier and the screening surfaces are connected to the same potential, i.e. to frame potential.
With a view to minimizing any parasitic capacitances and loss resistances forming between the potentiometer path and the collector path and the carrier connected to frame potential, but also in order to simplify the assembly operations, an advantageous embodiment of the invention provides that projections for fixing both the potentiometer path and the collector path in their respective positions are provided on the carrier in each of the screened spaces, adjacent to the screening surfaces.
These projections permit on the one hand easy assembly of the potentiometer path and the collector path, and ensure on the other hand a very precise fixed position of the potentiometer path and the collector path so that a precise distance is obtained between the probes guided above the potentiometer path/collector path on the one hand, and the potentiometer path/connector path on the other hand.
In principle, the potentiometer path and the collector path may be fastened on the projections in the most different ways. For example, bonding them to the projections would be imaginable.
A very advantageous embodiment of the invention, which permits not only the assembly to be effected in a simple way, but also any irregularities of the projections or of the potentiometer path or collector path to be compensated for, provides that the potentiometer path and the collector path are urged against the projections by some elastic pull-back means, preferably a rubber cord.
In order to exclude any parasitic capacitances between the two separate areas of a potentiometer path, that has been linearized in the known way by milling off part of the resistance path in a controlled way, it is preferably provided that the projection arranged above the linearization area of the potentiometer path covers the linearization area of the potentiometer path. In this case, the carrier is of course connected to a defined voltage potential.
With respect to the configuration of the screening surfaces, no exact details have been provided so far. In principle, the screening surfaces may exhibit any shape, for example a plane, bent-off or any curved shape.
An especially advantageous embodiment of the invention, also with respect to the stability of the displacement/angular position sensor, provides that the screening surfaces are circularly bent toward the potentiometer path and the collector path, respectively, and that at least one opening, through which the probes can be introduced and establish electric contact, is provided between any two immediately opposite screening surfaces.
Further features and advantages of the invention will become apparent from the following description and from the illustrations of certain embodiments.


REFERENCES:
patent: 5049827 (1991-09-01), Tasma
patent: 5479057 (1995-12-01), Rossi et al.
patent: 5525955 (1996-06-01), Tonogai et al.
patent: 35 11 190 A (1985-10-01), None
patent: 38 22 314 A (1989-01-01), None
Patent Abstracts of Japan, vol. 096, No. 009, Sep. 30, 1996 & JP 08 114410 A (Fuji Photo Optical Co. Ltd.), May 7, 1996.
Patent Abstracts of Japan, vol. 096, No. 009, Sep. 30, 1996 & JP 08 114409 A (Fuji Photo Optical Co. Ltd.), May 7, 1996.

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