GB2279148A

GB2279148A - Magnetic position transducer

Info

Publication number: GB2279148A
Application number: GB9312518A
Authority: GB
Inventors: Turgut Meydan
Original assignee: University College Cardiff Consultants Ltd; Cardiff University
Current assignee: University College Cardiff Consultants Ltd; Cardiff University
Priority date: 1993-06-17
Filing date: 1993-06-17
Publication date: 1994-12-21
Also published as: GB9312518D0

Abstract

A position-sensing transducer comprises a magnetically permeable core 10 of varying cross-section and two coils 12, 14 disposed around the core, one coil 12 being fixed and other coil 14 being slidable relative to the core. The transducer may be a rotary position transducer comprising a circular or tubular core 10 which tapers around at least part of its circumference. Alternatively, the transducer may be a linear position transducer having a linear core forming an open magnetic circuit. Preferably the core 10 comprises a ferromagnetic amorphous alloy in the form of a wound ribbon. <IMAGE>

Description

POSITION TRANSDUCER This invention relates to a transducer for determining the position of an element relative to the transducer and particularly, but not solely, relates to a transducer for determining the angular position of an element which is rotatable relative to the transducer.

There is a need for an electrical transducer of simple construction and low cost, for use in a variety of applications in automobiles. We have now devised such a transducer.

In accordance with this invention, there is provided a position transducer which comprises a core of magnetically permeable material and varying cross-section, a coil disposed around the core at a fixed position thereof, and a coil disposed around the core and slidable relative to the core.

The magnetic coupling, which is provided between the two coils by the common core, varies according to the position of the movable coil, because of the varying cross-section of the core. Therefore if a constant current is fed through one coil, the voltage across the other coil will vary according to the position of the movable coil. In addition to the coupling via the core, there may be some mutual coupling between the two coils, which increases as the coils approach each other: the core may be shaped to take account of this so that the transducer provides an output voltage linearly related to the position of the movable coil.

Preferably the transducer is a rotary position transducer comprising a circular, annular or tubular core, forming a closed magnetic circuit, the core tapering around at least part of its circumference.

The transducer may instead comprise a linear position transducer, comprising a linear core forming an open magnetic circuit.

The core may comprise any ferromagnetic material. A preferred material is ferromagnetic amorphous alloy in the form of a ribbon, which is therefore easy to form to the required shape. Typical such alloys follow the atomic composition formula TXMlsx where T represents one or more of the transition elements iron (Fe), nickel (Ni) or cobalt (Co) and M represents one or more of the metalloid or glass-formed elements phosphorus (P), boron (B), carbon (C) or silicon (Si). The transition metal content x is usually in the range 75 to 86%.

Such ferromagnetic amorphous alloys exhibit particularly high magnetic permeability.

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawing, the single figure of which is a schematic view of a rotary position transducer in accordance with the invention.

Referring to the drawing, there is shown a rotary position transducer which comprises a magnetically permeable core 10 in the form of a tube. This core may be made by wrapping a ribbon of ferromagnetic amorphous alloy into tubular shape. The core shown tapers in the axial dimension over at least a portion of its circumference.

A coil 12 is disposed around the core 10 at a fixed position, and a coil 14 is disposed around the core 10 but is able to slide circumferentially around the core. The coils 10,12 are preferably wound on bobbins, through which the ribbon forming the core is threaded before the ends of the ribbon are joined together. The bobbin of the movable coil 14 is mounted to an element which moves angularly relative to the axis of the tubular core: the rotary or angular position of this element is to be determined by the transducer.

In use, a constant current is fed through one of the coils, as primary, e.g. the fixed coil 12. The voltage developed across the other or secondary coil varies according to the position of the movable coil 14, because the coupling between the coils via the core varies with the cross-section of the core at the position of the movable coil. There may also be some mutual coupling between the two coils, which increases as the coils approach each other. Preferably the taper of the core takes account of any such mutual coupling, so that the output from the secondary coil varies linearly with angular position of the movable coil.

It will be seen that the transducer which has been described is of simple construction and involves a minimum of components and is therefore of low cost. Furthermore, the coils 12,14 are easy to wind onto bobbins and then thread onto the core before the ends of the latter are joined together: the transducer is therefore simple to make. However, the transducer is reliable and effective in performance.

Claims

1) A position transducer, comprising a core of magnetically permeable material and varying cross-section, a coil disposed around the core at a fixed position thereof, and a coil disposed around the core and slidable relative to the core.

2) A position transducer according to claim 1, wherein said core is shaped such that said transducer provides an output voltage which is linearly related to the position of said slidable coil.

3) A position transducer according to claims 1 or 2 wherein said transducer is a rotary position transducer.

4) A position transducer according to claims 1, 2 or 3 wherein said core forms a closed magnetic circuit.

5) A position transducer according to claim 4, wherein said core is circular.

6) A position transducer according to claim 4, wherein said core is annular.

7) A position transducer according to claim 4, wherein said core is tubular.

8) A position transducer according to any of claims 3 to 7, wherein said core tapers around at least part of its circumference.

9) A position transducer according to claims 1 or 2, wherein said transducer is a linear position transducer.

10) A position transducer according to claim 9, wherein said core is a linear core which forms an open magnetic circuit.

10) A position transducer according to any preceding claim, wherein said core comprises a ferromagnetic material.

11) A position transducer according to claim 10, wherein said ferromagnetic material is ferromagnetic amorphous alloy in the form of a ribbon.

12) A position transducer according to claim 11, wherein said ferromagnetic amorphous alloy follows the atomic composition formula TxMx, where T represents one or more of the transition elements iron (Fe), nickel (Ni) or cobalt (Co), M represents one or more of the metalloid or glass-formed elements phosphorous (P), boron (B), carbon (C) or silicon (Si) and where X represents the transition metal content.

13) A position transducer according to claim 12, wherein X is in the range 75 to 86%.

14) A position transducer as hereinbefore described with reference to the accompanying drawing.