Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-02-19
2003-07-01
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200, C324S207210, C324S207220
Reexamination Certificate
active
06586929
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 range of movement, and more specifically relates to a magnetic position sensor having shaped poles pieces for improved output linearity.
BACKGROUND OF THE INVENTION
Magnetic position sensors are devices that generate a change in electronic signal output that is proportional to the sensed movement of a mechanical component, such as, for example, a control shaft or rotor in the case of rotational position sensors or a carrier mechanism or linkage in the case of linear position sensors. Preferably, the change in electronic signal is achieved without physical contact between the mechanical component and the magnetic sensing element. In non-contacting magnetic position sensors, one or more magnets are used to provide a magnetic field having a magnetic field strength or flux density that varies as a function of position.
The magnitude of the magnetic flux density is measured by an appropriate sensing device, such as, for example, a Hall-effect element or magneto-resistive element. The magnitude of the magnetic flux density is translated through the sensing device to a voltage or current output signal that is uniquely representative of a specific position of a mechanical component relative to the magnetic field. Preferably, the magnetic position sensor provides a substantially linear relationship between electronic signal output and the position of the mechanical component. In addition to providing a linear relationship, minimizing hysteresis is also a desirable feature in most magnetic sensor applications. While annealing the magnets can reduce magnetic hysteresis, the annealing process can never eliminate magnetic hysteresis entirely.
To generate a magnetic field having a substantially linear profile, those skilled in the art sometimes resort to complicated magnet shapes. For example, U.S. Pat. No. 5,995,881 to White et al. discloses a magnetic circuit that utilizes tapered magnets to provide a magnet field having varying magnetic field strength. However, these types of magnetic circuits commonly suffer from performance and/or manufacturing limitations. For example, providing a magnet circuit having a linearly varying magnetic field strength is difficult to achieve via magnet shaping due to non-uniformity in material composition and the geometric configuration of the magnet. Typically, non-standard magnetic materials must be used to manufacture magnets having irregular shapes and configurations. Moreover, complicated magnet shapes often lead to increased manufacturing costs and package size limitations. Additionally, non-standard magnet compositions also increase manufacturing costs.
Magnetic position sensors may be used in a wide variety of applications. For example, magnetic position sensors are used extensively in the automotive industry to monitor the status of various automotive components. Position sensors that are used in automotive-related applications typically experience virtually constant movement and/or mechanical vibration while the automobile is in operation. To that end, such sensors must be constructed of mechanical and electrical components that are assembled in such a manner as to minimize the effects of misalignment and/or mispositioning to allow the sensor to operate in a sufficiently accurate and precise manner over the sensor's projected lifespan. Moreover, automotive position sensors are typically subjected to relatively harsh thermal environments, and therefore must be designed to withstand extreme temperatures and temperature gradients. Typically, automotive sensors must be able to function properly within a temperature range of −40 degrees Celsius to 160 degrees Celsius. Additionally, automotive position sensors must usually satisfy relatively high performance criteria, particularly with regard to sensor accuracy and repeatability.
Thus, there is a general need in the industry to provide a magnetic position sensor having improved output linearity. 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 improved output linearity. 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 sensor is provided which includes a magnet extending along an axis, and a pole piece positioned adjacent the magnet and being at least partially formed of a non-magnetic material. The magnet and the pole piece cooperate to generate a magnetic field having a magnetic flux density that linearly varies along the axis. The magnetic sensor also includes a magnetic flux sensor positioned within the magnetic field. The magnetic flux sensor is operable to sense varying magnitudes of magnetic flux density along the axis and to generate an output signal representative of a sensed magnitude of the magnetic flux density. In a further aspect of the invention, the pole piece is formed of a composite material comprising a non-magnetic material and a magnetizable material.
In another form of the present invention, a magnetic position sensor is provided which includes a first magnet spaced from a second magnet to define an air gap extending along an axis, and first and second pole pieces at least partially disposed within the air gap and positioned adjacent respective ones of the first and second magnets, with the first and second pole pieces being at least partially formed of a non-magnetic material. The magnets and the pole pieces cooperate to generate a magnetic field having a magnetic flux density that linearly varies along the axis. The magnetic sensor also includes a magnetic flux sensor positioned within the magnetic field. The magnetic flux sensor is operable to sense varying magnitudes of magnetic flux density along the axis and to generate an output signal representative of a sensed magnitude of the magnetic flux density. In a further aspect of the invention, the pole pieces are formed of a composite material comprising a non-magnetic material and a magnetizable material.
In yet another form of the present invention, a magnetic position sensor is provided which includes a magnet extending along an axis and a shaped pole piece positioned adjacent the magnet and cooperating with the magnet to generate a magnetic field having a magnetic flux density that linearly varies along the axis. The magnetic position sensor also includes a magnetic flux sensor positioned within the magnetic field. The magnetic flux sensor is operable to sense varying magnitudes of the magnetic flux density along the axis through a sensing plane oriented substantially perpendicular to the axis and to generate an output signal representative of a sensed magnitude of the magnetic flux density.
In still another form of the present invention, a magnetic position sensor is provided which includes a first magnet spaced from a second magnet to define an air gap extending along an axis, and first and second shaped pole pieces at least partially disposed within the air gap and positioned adjacent respective ones of the first and second magnets. The magnets and the shaped pole pieces cooperate to generate a magnetic field having a magnetic flux density that linearly varies along the axis. The magnetic sensor also includes a magnetic flux sensor positioned within the magnetic field. The magnetic flux sensor is operable to sense varying magnitudes of the magnetic flux density along the axis through a sensing plane oriented substantially perpendicular to the axis and to generate an output signal representative of a sensed magnit
Patidar Jay
Wabash Technologies, Inc.
Woodard Emhardt Moriarty McNett & Henry LLP
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