Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
2001-12-05
2004-08-31
Le, N. (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S207210, C324S207250
Reexamination Certificate
active
06784659
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for sensing and a magnetic sensor for moving objects. More particularly, the present invention relates to a sensor for determining speed and direction of moving or rotating targets, such as, for example, gears, shafts, joints, wheels, fans, turbines, tires, conveyors or like moveable objects.
BACKGROUND OF THE INVENTION
The demand for higher performance vehicles and for lightweight devices providing accurate speed and direction of rotation measurements for shafts, wheels, and gears continues to increase rapidly. As a result, improvements in electronics-based products for use in sensing applications are needed. For example, in the automotive industry, it is desirable to use sensors to accurately measure the speed and direction of rotation of wheels, transmissions, shafts, gears and other rotatable objects. This measurement information can be processed by on board computers in communication with the sensors to improve the fuel efficiency and power in automatic transmissions, to monitor the performance of the transmission or to control the automobile's braking systems (e.g. an Anti-lock Braking System). For example, in an automobile equipped with anti-lock brakes, a computer in communication with the automobile braking sensors may receive information relating to the tire's rotational velocity and rotational direction, process such information and thereafter control the automobile's brakes to lessen the severity of any perceived skid or braking malfunction.
A large number of speed and direction sensing devices exist. Such devices are discussed, for example, in U.S. Pat. Nos. 5,880,585, 5,523,679, 5,264,789 and 4,789,826. Furthermore, ring magnets or linear magnets are well known in the sensing arts. A conventional ring magnet
110
is illustrated in
FIGS. 1A and 1B
, while a conventional linear magnet
109
is illustrated in
FIGS. 1C and 1D
. Ring magnet
110
is typically formed in a circular pattern, having a plurality of alternating north and south pole permanent magnet segments. This ‘chain’ of magnets forms a circle or ring of magnets which, for example, can be placed or disposed circumferentially around an object. Similarly, linear magnet
109
is typically formed in an approximately linear pattern, having a plurality of alternating north and south pole permanent magnet segments. For purposes of this discussion, the north polarity of each magnet is referred to in the drawings as item
113
while the south polarity is referred to in the drawings as item
112
.
As seen in
FIGS. 1A through 1D
, a plurality of flux lines
102
are illustrated which represent an exemplary magnetic field generated by each magnet. As is known in the art, a magnetic field (represented by magnetic flux lines) exists such that the magnetic field flows from the north polarity to the south polarity regardless of the coordinate dimension used. For example, the flux lines illustrated in
FIGS. 1A and 1B
may depict a magnetic field which is external to the ring magnet
110
, internal to the ring magnet
110
, or may depict a magnetic field in any orientation (e.g., three dimensional) flowing from the magnet's north polarity to the magnet's south polarity. Similarly, the flux lines exemplified in
FIGS. 1C and 1D
may depict a magnetic field adjacent to the linear magnet
110
or may depict a magnetic field in any orientation (e.g., three dimensional) flowing from the magnet's north polarity to the magnet's south polarity. In each case, the flux lines flow away perpendicular (e.g.,
103
) from the magnet's north polarity (e.g.,
113
) and magnetically curve or bend towards the magnet's south polarity (e.g.,
112
) where they flow back perpendicular (e.g.,
105
) to the magnet's south polarity. The area where the flux lines magnetically curve or bend can be represented by a portion of the flux line (e.g.,
104
) which is approximately horizontal or parallel to the magnet's surface in any given coordinate location. Thus, for example, as seen in
FIG. 1B
, flux line
106
may represent a portion of a magnetic field which can be generated between any north polarity of a magnet and a south polarity of a magnet in any coordinate axis.
A Wheatstone bridge, such as the representative circuit illustrated in
FIG. 2
, may be helpful in determining resistance of a variable resistor, and thus, it may be useful as a sensing means in some applications. A typical Wheatstone bridge includes resistive elements R
A
(
231
), R
B
(
232
), R
C
(
233
) and R
D
(
234
), all in electrical communication with voltage source
210
and ground
240
. A differential voltage V
B
may be measured to obtain a voltage signal that changes with changes in the resistance of each of the four resistive elements R
A
(
231
), R
B
(
232
), R
C
(
233
) and R
D
(
234
). A Wheatstone bridge such as the one illustrated in
FIG. 2
has the advantage of being able to self-compensate for temperature variations in the range of, for example, −40° to 200° Centigrade. Thus, for example, a Wheatstone bridge could be used in thermocouple applications.
When a sensor is placed within a magnetic field, the sensor's resistors may be influenced by the magnetic field. As illustrated in
FIG. 3A
, a magnetic field (e.g., flux lines
102
) which runs substantially parallel to a resistive device
301
tends to have little or no electrical effect on the resistive device. In contrast, as illustrated in
FIG. 3B
, a magnetic field
102
which runs perpendicular to the resistive device
301
appears to electrically influence the resistive device and appears to change the resistivity of the device.
Prior art magnetic sensing devices suffer from many disadvantages. For example, prior art magnetic sensing devices (such as silicon Hall integrated sensors) have a limitation of around 20 gauss minimum signal due to inherent stress-induced offsets. This reduces the range of available signal which in turn reduces the available mechanical tolerance. Using two independent sensors would produce placement errors which may be very difficult to tolerate in a manufacturing environment.
SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can only be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The method and device according to the present invention addresses many of the shortcomings of the prior art and further provides the advantage of, among other items, generating the rotational velocity and rotational direction of a rotating object. In accordance with one exemplary embodiment of the present invention, at least two bridges are provided, each having resistors. The resistors are configured to be electrically influenced by a magnetic field from an adjacent array of magnetic elements. In another embodiment, the bridges are in electrical communication with a computing means, such as a microprocessor or a microcontroller. Thus, for example, each bridge may comprise a Wheatstone bridge in communication with a microprocessor. In another embodiment, at least two bridges in communication with a computing means may be provided adjacent to a magnetic array, each bridge having resistors which are electrically influenced by a magnetic field. In another embodiment, the present invention includes at least two bridges with each bridge having a first set of resistors and a second set of resistors configured in a bridge, the first set of resistors being oriented approximately perpendicular to the second set of resistors. In another embodiment, the present invention includes at least two bridges fabricated as an integrated circuit, the bridges each comprising resistors which are electrically influenced by a magnetic field. In another embodiment, the present invention comprises at least two bridges, f
Haji-Sheikh Michael J.
Kryzanowski Robert
Plagens Mark
Aurora Reena
Fredrick Kris T.
Honeywell International , Inc.
Le N.
Lopez Kermit D.
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