Electrical generator or motor structure – Dynamoelectric – Linear
Patent
1998-03-02
1999-09-14
Ramirez, Nestor
Electrical generator or motor structure
Dynamoelectric
Linear
H02K 4100
Patent
active
059527439
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electric motor, for instance of the linear electromagnetic type, comprising an integral position measurement system for providing force or thrust in response to an electrical current.
The provision of an integral position measurement system greatly enhances the applications of such motors, allowing them to provide information on the output movement produced and to be servo position controlled. Applications for such motors include industrial automation, instrumentation, proportional valve control, vibration testing, pumping and metering.
FIG. 1 of the accompanying drawing shows a linear motor of the type particularly relevant to this invention, this being described in a prior GB Patent application 8801924. The main elements of the motor are a moving assembly comprising a permanent magnet 1, pole-pieces 2 and 3, split stationary windings W1 and W2, and a soft iron magnetic return circuit formed by an outer shell 4. Magnetic flux due to the permanent magnet 1 is forced to flow radially between the pole-pieces 2, 3 and the outer shell 4 and thus to traverse the windings W1, W2 substantially at right angles to the direction of current flow in the windings W1, W2. It can be appreciated that the direction of magnetic flux is opposite for the two pole-pieces 3, 4, these being arranged at the North and South polarity ends of the magnet 1. Thus in order for the current flow in the windings W1, W2 to produce a consistent or net force on the moving assembly it is necessary that the direction of current flow in the two windings WI, W2 surrounding the pole-pieces 3, 4 be mutually opposite. It is for this reason the winding in the motor of FIG. 1 is split or comprises two separate windings W1, W2 surrounding the pole-pieces 3, 4. Providing the correct direction of current flow is achieved, the windings W1, W2 may be series or parallel connected to provide a two terminal connection to the driving source.
To make efficient use of the permanent magnet 1 and winding material, the windings W1, W2 must be arranged substantially as shown in FIG. 1. Here the windings are arranged to fill a significant portion of the radial gap around each pole-piece 3, 4 and to overlap each pole-piece 3, 4 by a given amount in the axial direction. In this way the flux produced by the permanent magnet 1 is forced to flow across the windings W1, W2 and to contribute to the production of output thrust. The overlap of windings W1, W2 is used to encompass leakage or stray flux but is also necessary to allow movement of the magnet and pole-piece assembly without substantial change in the amount of flux linked by the windings W1, W2. For short stroke linear motors of this type it can be seen that the windings are very effectively used in linking the working permanent magnet flux of the machine and thus contributing to an overall high electrodynamic efficiency. Any reduction in the volume of the windings or the consistency of flux linking due to the introduction of additional windings or electrodes for the provision of position measurement of the moving assembly, will reduce the effective working volume of the windings and thus degrade the force output and efficiency of the machine.
These features of the motor make it difficult to use the simple split winding arrangement to perform the additional function of position measurement. In GB Patent application 8801924 the windings are shown series connected, this resulting in a centre connection node. The winding ends are driven, in addition to the thrust producing current, by an AC energising signal, this being applied as anti-phase EMFs impressed on the ends of the windings. Here the moving assembly is intended to function as a magnetically salient object, the movement of which produces differential changes in inductance of the two windings. This differential inductance change results in an imbalance of the impedance of the windings and a corresponding output at the centre tap of the windings of a fraction of the AC energising voltage.
With this arrangement there is a con
REFERENCES:
patent: 5345206 (1994-09-01), Morcos
Patent Abstracts of Japan, vol. 007, No. 170 (E-189), Jul. 27, 1983 & JP,A,58 075458 (Yoshiteru Takahashi), May 7, 1983 (Abstract Only).
Patent Abstracts of Japan, vol. 006, No. 021 (E-093), Feb. 6, 1982 & JP,A,56 141769 (Sato Ryoda), Nov. 5, 1981 (Abstract Only).
Jones Judson H.
Ramirez Nestor
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