Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-09-06
2004-03-09
Le, N. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200, C324S207210, C335S302000
Reexamination Certificate
active
06703829
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of magnetic position sensors, and more specifically relates to a non-contacting rotary magnetic position sensor for sensing rotational position of a structure over a predetermined range of rotation.
BACKGROUND OF THE INVENTION
Non-contacting position sensors are devices that generate change to an electronically interrogated physical parameter that is proportional to the movement of a structure, such as, for example, an actuator shaft operatively coupled to the sensor. This change is achieved without physical contact between the parameter and the interrogation device. In magnetic position sensing, the magnitude of magnetic field strength is generally measured by an appropriate measuring device, such as a Hall-effect element or magneto-resistive element. The value of the measured field intensity is translated through the measuring device to a voltage or current value that is uniquely representative of the specific rotational position of the actuator shaft.
Preferably, the magnetic field and voltage/current relationships have a substantially linear response. A linear response with minimum hysteresis is desired in almost all control algorithms that utilize sensor information. As virtually no magnetic material parameter has an exact linear relationship relative to position, it is often difficult to achieve a precise linear response from the sensing device relative to its position within the magnetic field. Additionally, magnetic hysteresis has the effect of causing an offset error signal to be generated whenever a magnetic element of the sensor (e.g., a magnetic pole piece or a magnetic rotor) is advanced from and returned to a predetermined reference position of the magnetic element. Annealing the magnetic element can minimize, but never totally eliminate, magnetic hysteresis.
For rotational magnetic position sensors, the actuator is typically a control shaft attached to some type of rotating object of interest. Normally, the shaft is attached directly to the sensor and rotation of the shaft correspondingly rotates the magnetic circuit of the sensor. Within the circuit's magnetic field, the sensing element is held in a fixed position, and the relative motion between the magnetic field and the sensing element generates a signal output that is directly proportional to the magnitude of the rotational movement.
To generate a magnetic field with a linear profile relative to the rotational movement, magnetic circuit designers often resort to complicated magnet shapes or field shaping pole pieces. Most circuit designs of these types suffer from performance or manufacturing limitations. Pole piece field shaping will generally suffer from hysteresis and assembly complexity. Complicated magnet shapes often lead to expensive magnet costs and package size limitations. Prior sensors also suffer from maximum physical and electrical rotation limitations. In some prior sensors, the control shaft passes through the center of the magnetic circuit. Many sensor applications can not utilize such a design due to the need to locate the working magnetic field within an area that is coaxial, with the axis of rotation of the control shaft.
Size and cost are always a priority in sensor design, particularly in the automotive and transportation industry. There are literally hundreds of applications for rotational position sensors in these industries. For these applications, a compact magnetic circuit design that can be applied to a wide variety of applications and physical configurations, as well as maintaining a degree of simplicity that will be reflected in a reduced sensor cost, is desired. Performance can not be compromised, and the ability to achieve the former with excellent linearity and hysteresis characteristics is highly desirable.
Thus, there is a general need in the industry to provide an improved magnetic position sensor. The present invention meets 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. 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.
In one form of the present invention, a magnetic position sensor is provided, comprising a magnet and a magnetic flux sensor. The magnet comprises a ring segment having a length. The magnet is polarized in a direction of magnetization extending generally along the length of the ring segment to generate a magnetic field. The magnetic flux sensor is disposed within the magnetic field and is operable to sense varying magnitudes of magnetic flux density during relative movement between the magnetic field and the magnetic flux sensor.
In another form of the present invention, a magnetic position sensor is provided, comprising an arc-shaped magnet and a magnetic flux sensor. The arc-shaped magnet defines an open inner region and is polarized in a direction of magnetization extending laterally across the open inner region to generate a magnetic field. The magnetic flux sensor is disposed within the magnetic field and is operable to sense varying magnitudes of magnetic flux density during relative movement between the magnetic field and the magnetic flux sensor.
In another form of the present invention, a magnetic position sensor is provided, comprising a magnet and a magnetic flux sensor. The magnet has a semi-annular ring configuration defining a diametric dimension and is polarized in a direction of magnetization extending generally along the diametric dimension to generate a magnetic field. The magnetic flux sensor is disposed within the magnetic field and is operable to sense varying magnitudes of magnetic flux density during relative rotational movement between the magnetic field and the magnetic flux sensor.
It is one object of the present invention to provide an improved magnetic position sensor.
It is another object of the present invention to provide an improved non-contacting rotary magnetic position sensor for sensing rotational position of a structure over a predetermined range of rotation.
Further objects, features, advantages, benefits, and aspects of the present invention will become apparent from the drawings and description contained herein.
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Kinder Darrell
Le N.
Woodard Emhardt Moriarty McNett & Henry LLP
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