Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-07-12
2004-05-04
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240
Reexamination Certificate
active
06731109
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of magnetic sensors for sensing the position of a structure over a predetermined sensing range, and more specifically relates to a non-contacting magnetic position sensor having a stepped magnet interface that provides a magnetic field having improved linear characteristics over an extended sensing range.
BACKGROUND OF THE INVENTION
Magnetic position sensors are devices that generate an electronic signal output that is indicative of the relative position of a mechanical component, such as, for example, a control shaft or rotor in the case of a rotational position sensor or a carrier mechanism or linkage in the case of a linear position sensor. Certain types of magnetic position sensors generate an electronic signal output representative of the relative position of the mechanical component without actual physical contact with the mechanical component. These types of non-contacting magnetic position sensors include a magnetic circuit that is operably coupled to the mechanical component and which is configured to produce a magnetic field having a magnetic field strength that varies along an air gap. A magnetic sensing element is positioned within the air gap and is operable to sense variations in the magnitude of the magnetic field strength in response to relative displacement between the magnetic field and the sensing element. The magnitude of the magnetic field strength is translated through the sensing element and is converted to a voltage or current output signal that is uniquely representative of the relative position of the mechanical component.
Referring to
FIG. 1
, shown therein is one example of a prior art magnetic position sensor
10
. The magnetic position sensor
10
includes a pair of permanent magnets
12
a
,
12
b
and a pair of magnetically permeable plates
14
a
,
14
b
extending between the magnets
12
a
,
12
b
and spaced apart to define an air gap
16
therebetween. The magnets
12
a
,
12
b
and the plates
14
a
,
14
b
cooperate to form a closed magnetic circuit that produces a magnetic field having a magnetic field strength that varies along the length of the air gap
16
. A magnetic sensing element
18
is positioned within the air gap
16
and is operable to sense variations in magnetic field strength as the sensing element
18
is relatively displaced along the air gap
16
. Notably, the magnetically permeable plates
14
a
,
14
b
are rectangular-shaped, each defining a flat, uninterrupted inner surface
20
that is operably attached to a corresponding flat magnetic pole surface
22
defined by each of the magnets
12
a
,
12
b
. As a result, the width w of the air gap
16
is equal to the distance d between the pole surfaces
22
of the magnets
12
a
,
12
b.
The sensing element
18
is physically capable of being displaced along virtually the entire length of the air gap
16
. When positioned at the approximate midpoint
24
of the air gap
16
, the magnitude of the magnetic flux density passing through the sensing element
18
is at or near zero. As the sensing element
18
is relatively displaced on either side of the midpoint
24
, the absolute value of the magnetic flux density increases in a manner proportional to the distance from the midpoint
24
. However, since the magnetic field flows in opposite directions on either side of the midpoint
24
, the actual value of the magnetic flux density on one side of the midpoint
24
is interpreted as being positive while the actual value of the magnetic flux density on the other side of the midpoint
24
is interpreted as being negative.
As shown in
FIG. 2
, the magnitude of the magnetic flux density varies in a substantially linear manner along the mid-portion
28
of the air gap
16
on either side of the midpoint
24
. However, as the relative position of the sensing element
18
approaches the end portion
30
a
of the air gap
16
adjacent the magnet
12
a
and the end portion
30
b
of the air gap
16
adjacent the magnet
12
b
, the change in magnitude of the magnetic flux density significantly deviates from that experienced along the mid-portion
28
of the air gap
16
. This phenomenon at least partially results from the tendency of the magnetic flux to leak from the interfaces between the inner plate surface
20
and the magnetic pole surface
22
, thereby resulting in an increased concentration of the magnetic flux density field strength in the areas adjacent the magnets
12
a
,
12
b
. This non-linearity in the magnitude of the magnetic flux density field strength adjacent the magnets
12
a
,
12
b
reduces the overall sensing range of the magnetic position sensor
10
. Although an auxiliary electronic circuit may be used to compensate for these non-linear characteristics, post processing of the sensor output signal typically results in increased sensor costs and a possible decrease in sensor accuracy and reliability.
Thus, there is a general need in the industry to provide a magnetic position sensor having improved linear characteristics over an extended sensing range. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.
SUMMARY OF THE INVENTION
The present invention is directed to a magnetic position sensor having a stepped magnet interface that provides a magnetic field having improved linear characteristics over an extended sensing range. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the preferred embodiments disclosed herein are described briefly as follows. However, it should be understood that other embodiments are also contemplated as falling within the scope of the present invention.
In one form of the present invention, a magnetic position sensor is provided which includes a magnet, a pair of pole piece segments spaced apart to define an air gap, and a magnetic flux sensor. The pole piece segments form a stepped interface with the magnet to provide a magnetic field within the air gap having a varying magnetic flux density. The magnetic flux sensor is positioned within the magnetic field and is operable to sense a magnitude of the varying magnetic flux density along the air gap and to provide an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In another form of the present invention, a magnetic position sensor is provided which includes first and second magnets, first and second pole pieces extending between the magnets and spaced apart to define an air gap, and a magnetic flux sensor. The first and second pole pieces form a stepped interface with the magnets to form a closed magnetic circuit that provides a magnetic field within the air gap having a varying magnetic flux density. The magnetic flux sensor is positioned within the magnetic field and is operable to sense a magnitude of the varying magnetic flux density along the air gap and to provide an output signal representative of a position of the magnetic flux sensor relative to the magnetic field.
In yet another form of the present invention, a magnetic position sensor is provided which includes a magnet, a pair of pole piece segments spaced apart to define an air gap, and a magnetic flux sensor. The magnet has a first pole surface, a second pole surface, and side surfaces extending between the first and second pole surfaces. The pole piece segments each include a first portion positioned adjacent a respective one of the first and second pole surfaces of the magnet, and a second portion positioned adjacent one of the side surfaces of the magnet. The magnet and the pole piece segments cooperate to provide a magnetic field within the air gap having a varying magnetic flux density. The magnetic flux sensor is positioned within the magnetic field and is operable to sense a magnitude of the varying magnetic flux density along the air gap and to provide an output signal representative of a positio
Domanski Stanley J.
Johnson Gary W.
Strecker Gerard R.
Wabash Technologies, Inc.
Woodard Emhardt Moriarty McNett & Henry LLP
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