Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-12-31
2004-03-16
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207170, C324S207250, C324S207240
Reexamination Certificate
active
06707291
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to self-induction-type position detector devices which include a coil to be excited by an A.C. signal and a magnetic or electrically-conductive member movable relative to the coil and which are suitable for detection of a linear or rotational position. More particularly, the present invention relates to an improved self-induction-type position detector device which, in response to a position of an object of detection (i.e., an object to be detected), can generate A.C. output signals presenting amplitude function characteristics of a plurality of phases using only a primary coil to be excited by a single-phase A.C. output signal.
There have ben known induction-type linear position detector devices which are commonly called “LVDTs”. In two-wire-type LDVTs including one primary coil and one secondary coil, an induction coupling between the primary coil and the secondary coils varies in accordance with an amount of entry, into a coil section, of a movable section made of a magnetic substance, so that an inductive output signal of a voltage level corresponding to the induction coupling variation is produced in the secondary coil. Further, three-wire-type LDVTs are constructed as a differential transformer including one primary coil and two secondary coils connected in series in opposite phases, where an induction coupling between the primary coil and the secondary coils varies in a balanced manner in accordance with an amount of entry, into one of the two coils of the opposite phases, of a movable section made of a magnetic substance having a predetermined length, so that inductive output signals of voltage levels corresponding to the induction coupling variation are produced in the secondary coils. In such three-wire-type LDVTs, output signals of sine and cosine characteristics corresponding to a position of the movable section are generated by performing analog addition or subtraction on the output signals from the secondary coils, and these output signals of sine and cosine characteristics are then processed via an R-D converter to thereby generate digital data indicative of a detected current position of the movable section. Other type of position detector device have also been known (e.g., from Japanese Patent Laid-open Publication No. SHO-53-102070 and U.S. Pat. No. 4,112,365 corresponding thereto), which include only an exciting coil and where a variation in the self-inductance of the exciting coil responding to a movement of a movable magnetic core is detected by measuring an amount of phase shift through an R-L circuit.
However, because the conventionally-known LVDTs require both of the primary and secondary coils, the necessary number of component parts would increase, which unavoidably results in significant limits to reduction in the manufacturing cost and size of the devices. In addition, an available phase angle range in the output signals of sine and cosine characteristics corresponding to a current position of the movable section is relatively narrow, such as about 45° in the two-wire-type LVDTs or about 90° in the three-wire-type LVDTs, so that the detectable phase angle range can not be expanded satisfactorily in the conventionally-known LVDTs. Further, because the conventional three-wire-type LVDTs can only detect such positions displaced leftward and rightward from a predetermined reference point where the movable section is located centrally along the length the coil section, they provide a very poor convenience of use.
With the conventionally-known position detector devices of the type which measures the self-inductance of the exciting coil, on the other hand, it is possible to reduce the necessary number of coils, but the phase shift amount responding to the displacement of the object to be detected can be detected only within an extremely narrow range, which, in effect, would make it very difficult to measure the phase shift amount. Also, these known position detector devices provide a very poor detecting resolution and thus are not suitable for practical use. In addition, because the phase shift amount varies as the impedance of the coil changes in response to a change in ambient temperature, the position detector devices could not properly compensate or adjust their temperature characteristics.
Induction-type rotational position detector devices of the type which produces two-phase outputs (i.e., outputs of sine and cosine phases) in response to a single-phase exciting input are commonly known as “resolvers”, and induction-type rotational position detector devices of the type which produces three-phase outputs (i.e., outputs of three phases shifted from each other by 120°) in response to a single-phase exciting input are commonly known as “synchros”. In the resolvers in the most traditional form, a stator includes two-pole (sine and cosine poles) secondary windings that intersect each other at a 90° mechanical angle, and a rotor includes a primary winding. The resolvers of this type are not satisfactory in that they need a brush to electrically contact the primary winding of the rotor. There have also been known brush-less resolvers that require no such brush; that is, these brush-less resolvers include, in the rotor, a rotary transformer in place of the brush. However, because of the provision of the rotary transformer in the rotor, it is difficult to reduce the overall size of the devices and thus there are limitations to the downsizing of the brush-less resolvers. Further, the provision of the rotary transformer increases the number of the component parts, which also leads to an unavoidable increase in the manufacturing cost.
Also known in the art are rotational position detector devices of the non-contact/variable-reluctance type (known in the past by the tradename “microsyn”), where a stator includes primary and secondary windings disposed on a plurality of projecting poles and a rotor is formed of a magnetic body having a predetermined shape (such as an eccentric circular shape, an oval shape or a shape having a projection). In these rotational position detector devices (rotary-type position detector devices), a reluctance variation responding to a rotational position of the object to be detected is produced on the basis of variations in gaps between the stator's projecting poles and the rotor's magnetic body that occur in response to a changing rotational position of the object to be detected, so that an output signal corresponding to the reluctance variation is provided. Further, similar reluctance-based rotational position detector devices are also disclosed, for example, in U.S. Pat. No. 4,754,220, Japanese Patent Laid-open Publication Nos. SHO-55-46862, SHO-55-70406 and SHO-59-28603. As position detection techniques based on the detector output signal, there have been known both a phase-based scheme in which position detecting data corresponds to an electrical phase angle of the output signal and a voltage-based scheme in which position detecting data corresponds to a voltage level of the output signal. In the case where the phase-based scheme is employed, the individual primary windings disposed at different mechanical angles are excited by phase-shifted inputs, such as two-phase or three-phase exciting inputs, so as to generate a single-phase output signal having a different electrical angle corresponding to a current rotational position. Further, in the case where the voltage-based scheme is employed, the relationship between the primary and secondary windings is reversed from that in the phase-based scheme, and plural-phase outputs are produced in response to a single-phase exciting input in the same manner as in the resolvers.
Typically, the rotational position detector devices, such as the resolvers, which produce plural-phase outputs in response to a single-phase, are arranged to produce two-phase outputs, namely, sine-phase and cosine-phase outputs. To this end, in the conventional resolver-style rotational position detector devices of the non-contact/variable-reluctanc
Goto Atsutoshi
Sakamoto Hiroshi
Sakamoto Kazuya
Goto Atsutoshi
Le N.
Morrison & Foerster / LLP
Zaveri Subhash
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