Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-03-12
2001-10-23
Metjahic, Safet (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200, C324S165000
Reexamination Certificate
active
06307365
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the use of magnetic sensors for determining position and direction of a target having magnetic poles and, more particularly, to the use of an array of a plurality of magnetic sensors to determine position and/or direction.
Multiple magnetic sensors have been placed in proximity to a magnetic field from a multi-pole magnet to determine position and direction of a target. For example, a string of Hall effect devices may be used to provide signals that are summed to produce a sine wave that is representative of the average magnetic field over the multi-pole magnet. Summing the signals from the sensor elements in the first half of the Hall string and subtracting the sum of the signals from sensor elements in the second half of the Hall string produces a cosine wave, that is, a sine wave that is 90 degrees out of phase from the sine wave. The sine and cosine waves can then be used to determine the position and direction of a target equipped with the multi-pole magnet.
Such devices are useful in reducing errors in determining position of the target that are due to variations in the magnetic fields or the spacing of the magnetic poles. However, the known devices and methods require the string of sensor devices to have a length that is matched precisely to the pole spacing of the multi-pole magnet with which the magnetic sensors are to be used. In addition, an external magnetic field will bias the magnetic field, e.g., increasing the magnetic North poles and decreasing the magnetic South poles, causing the sine and cosine curves to shift such that the zero points will not be regularly spaced. In either case, the signal processing of the sine and cosine waves produces errors in the position measurement.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
SUMMARY OF THE INVENTION
In one aspect of the invention, this is accomplished by providing a method for determining position and/or position of a target, the target having a series of magnetic poles with a magnetic pole spacing d. The method comprises providing an array of an even number N of magnetic sensors with a sensor spacing x, the sensor array having an initial effective sensor array length (N+1)x, where the initial effective sensor array length is greater than the pole spacing d (or, alternatively greater than twice the pole spacing d); deactivating an equal number of magnetic sensors such that the magnetic sensors of the array remaining active are adjacent to each other and provide a new effective sensor array length that is closer to the pole spacing d than the initial effective sensor array length; dividing the magnetic sensors of the array remaining active into two equal groups A and B of at least one adjacent magnetic sensor for signal processing; summing the signals from group A and summing the signals from group B; adding the summation of signals from group B to the summation of signals from group A to obtain a sine wave; and subtracting the summation of signals from group B from the summation of signals from group A to obtain a cosine wave.
In a another aspect of the invention, this is accomplished by providing a method including a scaling means to balance the amplitude of a sine wave with respect to a cosine wave.
In a further aspect of the invention, this is accomplished by providing an ASIC chip comprising an array of an even number of magnetic sensors, selection means to selectively deactivate an even number of magnetic sensors such that the remaining magnetic sensors are adjacent to each other and signal processing means to process signals from the remaining magnetic sensors to generate a sine wave and a cosine wave.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.
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patent: 5430373 (1995-07-01), Ichkawa et al.
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patent: 5929631 (1999-07-01), Strker et al.
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Desbiolles Pascal
LaCroix Mark E.
Santos A. John
Bigler John C.
Metjahic Safet
The Torrington Company
Zaveri Subhash
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