Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With voltage or current conversion
Reexamination Certificate
2000-08-31
2003-01-28
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With voltage or current conversion
C324S207170
Reexamination Certificate
active
06512360
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to stroke sensors suitable for detecting a stroke position of a fluid-pressure cylinder or a spool position of a spool value, and particularly to stroke sensors of a type which includes a coil section to be excited by an A.C. signal and a magnetic substance or electric, conductor movable relative to the coil section. More particularly, the present invention concerns a self-induction-type stroke sensor that uses only primary coils excitable by a single-phase A.C. signal to produce A.C. output signals presenting amplitude function characteristics of a plurality of phases in response to a stroke position to be detected.
Hitherto, there have been known various types of position detector apparatus which are designed to detect a stroke position in a fluid-pressure cylinder or the like. Of these position detector apparatus, induction-type cylinder position detector apparatus using electromagnetic coils are known, for example, from Japanese Utility Model Publication No. HEI-2-26003. In each of such conventional induction-type cylinder position detector apparatus, raised and recessed portions or a pattern of magnetic substance or electric conductor are first formed on the surface of the piston rod, and then a given protective coating is applied to the piston rod surface having the raised and recessed portions or pattern of magnetic substance or electric conductor formed thereon. Specifically, the known apparatus are based on a phase-shift-type position detection scheme, where a plurality of primary coils are exited by plural-phase A.C. signals (e.g., sin &ohgr;t and cos &ohgr;t) shifted from each other in electric phase and signals induced on secondary coils by the primary coils are synthesized together to produce a single secondary output signal such that an electric phase difference, from the exciting A.C. signals, of output signals from secondary coils indicates a position of the Piston to be detected.
With the conventional induction-type cylinder position detector apparatus having the piston rod surface formed to have raised and recessed portions or pattern of magnetic substance or electric conductor, however, manufacturing and processing of the piston rod is very cumbersome and time-consuming. Further, in this case, each piston rod must be manufactured and processed on a special order basis. For these reasons, a same position detector apparatus can not be applied to cylinders of various different types and sizes. Further, even with the processed piston rod having undergone the given coating process, the coating tends to peel off, after several years′ use, due to sliding wear caused by repeated reciprocative movement of the piston rod, which would lead to poor durability of the piston rod.
To avoid the disadvantages of the conventionally-known induction-type cylinder position detector apparatus, a more sophisticated cylinder stroke position detector apparatus has been proposed, for example, in Japanese Patent Laid-open Publication No. HEI 10-153203. The proposed cylinder stroke position detector apparatus is characterized in that the piston rod has an inner space for entry therein a sensor structure so that the need for applying particular processing to the peripheral surface of the piston rod can be eliminated and various components of the detector apparatus can be readily shared between cylinders of various different sizes. Also, the proposed cylinder stroke position detector apparatus thus arranged can have increased durability to reliably avoid the possibility of undesired sliding wear. The sensor structure provided in the inner space of the piston rod includes both primary coils and secondary coils, and the coil structure has much room yet to be improved.
Namely, because the coil structure of the inductive-type position sensor employed in the conventional cylinder stroke position detector apparatus requires both the primary and secondary coils, the necessary number of the component parts in the apparatus significantly increases so that significant limitations would be encountered in reducing the manufacturing cost and size of the detector apparatus. There is also known a position detector of a type that is designed to measure self-inductance of the exciting coils and can reduce the necessary number of the coils; however, a phase variation amount corresponding to displacement of an object to be detected in this position detector can be obtained only within a very narrow range, and thus the position detector presents the problems that the measurement of the phase variation amount is, in fact, difficult and the detecting resolution is very low, so that it can never be suitable for practical use.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a self-inductance-type stroke sensor which is compact in size and simple in structure, provides for a wider detectable stroke range and also achieves high-resolution detection even when displacement of an object to be detected is very minute.
In order to accomplish the above-mentioned object, the present invention provides an improved stroke sensor for detecting a stroke position of a movable member linearly movable relative to a main body within a space formed in the main body, which comprises: a sensor member having one end supported in a cantilever fashion adjacent a predetermined end of the main body and having another end extending into the space of the main body, the movable member having an inner space formed therein to permit entry of the sensor member into the movable member; a coil section having a plurality of coil segments excitable by a predetermined A.C. signal and sequentially arranged along a direction of linear movement of the movable member, the coil section being provided on one of the sensor member and an inner peripheral wall of the movable member defining the inner space; and a magnetism-responsive substance provided on other of the sensor member and the inner peripheral wall of the movable member defining the inner space in such a manner that the magnetism-responsive substance is movable relative to the coil section. Relative positions of the magnetism-responsive substance and the coil section vary in accordance with a stroke position of the movable member, in response to which respective inductance of the coil segments are caused to vary in such a manner that during movement of the magnetism-responsive substance from one end to the other of a particular one of the coil segments, a voltage across the particular coil segment is caused to progressively decrease or increase.
In the case where the present invention is applied as a stroke sensor for a fluid-pressure cylinder, the above-mentioned “body” corresponds to the cylinder body, and the above-mentioned “movable member” corresponds to the piston rod. In this case, the sensor member is supported at one end, in a cantilever fashion, adjacent a predetermined end of the cylinder body in such a way that its other end extends into the space of the cylinder body. Further, the piston and piston rod, i.e. the movable member, has an inner space formed therein to permit entry of the sensor member into the movable member. Such a structure is similar to what is disclosed in Japanese Patent Laid-open Publication No. HEI 10-153203 discussed above, which, as described therein, affords various benefits, such as simplification, enhanced durability, compactness and wider applications of the structure. Here, the stroke position detection is effected by detecting, in accordance with the induction principles, relative positions of the coil section and magnetism-responsive substance provided for relative displacement to the coil section, on the basis of output voltages corresponding to inductance variations of the individual coil segments that occur in response to changing relative positions of the coil section and magnetism-responsive substance. In the case where the present invention is applied as a spool valve position detector apparatus, on the other hand, the above-mentione
Goto Atsutoshi
Sakamoto Hiroshi
Sakamoto Kazuya
Tozawa Shoji
Amiteq Co., Ltd
Lefkowitz Edward
Morrison & Foerster / LLP
Zaveri Subhash
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