Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2004-03-30
2004-11-02
LeDynh, Bot (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250
Reexamination Certificate
active
06812694
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic sensor adjusting method, a magnetic sensor adjusting device and the magnetic sensor itself.
BACKGROUND OF THE INVENTION
Some rotational sensors and length measuring sensors use magnetic sensors. Among various types of magnetic sensors, some magnetic sensors use a method in which a magnetic sensing target that rotates or moves along with a sensing object is disposed in a magnetic field, a variation of the magnetic field, according to the movement of the magnetic sensing target, is detected by a magnetic field detecting element such as a magnetoresistance effect element (MR element: JP-A-11-304,414 and JP-A-11-237,256) and a Hall element (JP-A-10-103,145) and, then, a rotation angle or a moving distance of the magnetic sensing target is calculated using the detected waveforms. Such a magnetic sensor is used because it has a relatively simple construction and high accuracy. For example, there is known a magnetic sensor for automobiles, that detects crank angles and the like by disposing a gear made of a soft magnetic material that has concave and convex portions formed on a outer circumferential surface so that it is opposed to a magnetic field generating magnet so as to create a magnetic gap therebetween, disposing a magnetic field detecting element (an MR element is often used because it is inexpensive and can be miniaturized easily) in the magnetic gap and, then, detecting a rotational position of the gear according to the output waveform of the magnetic field detecting element (JP-A-11-304,414 and JP-A-11-237,256). As the concave and convex portions form, with the magnetic field detecting element, respective sensing gap lengths that differ from each other, significant fluctuations occur in the magnetic field in the magnetic gap and, in particular, when the boundary regions between the concave and convex portions pass through the magnetic gap, which appear as variations in the waveform level detected by the magnetic detecting element. In actual sensors, this waveform is binarized (turned into a square wave) by a comparator and the like and the rotational position is determined based on the level transition edges.
Here, if the sensing gap lengths formed between the gear and the magnet are uneven between sensors due to factors such as errors in attachment or if the heights of the concave and convex portions in one gear are uneven due to the accuracy of finishing the gear and other factors, there may occur a problem that angle detection accuracy is degraded. Further, eccentricity of the rotation axis of the gear may also cause fluctuations in the sensing gap length according to the angular phase. More specifically, as the sensing gap becomes larger, the transition of the waveform level becomes less sharp when the boundary regions, between the concave and convex portions of the gear, pass through the sensing gap and, conversely, as the sensing gap becomes smaller, the transition of the waveform level becomes sharper. As a consequence, positions of the transition edges after binarization become irregular depending on the sensing gap length and, thus, the accuracy in detecting rotational positions is degraded. Such problem occurs not only in the rotational sensors but also in the length measuring sensors and, further, sensors using sensing targets other than the concave and convex portions (for example, when magnetic rotors or magnetic scales are used, regions having polarities opposite to each other that are disposed alternately substitute for the role of the concave and convex portions) in a similar manner.
JP-A-10-103,145 addresses this problem as follows. Even if the waveform before binarization fluctuates due to the unevenness of the sensing gap length, in terms of one pair of the concave and convex portions, the accuracy of the waveform cycle can be maintained so long as dimensional accuracy, in forming the concave and convex portions, is ensured. In this case, in the waveform after the binarization, the repetition period between a first level segment corresponding to the convex portion and a second level segment corresponding to the concave portion is constant in itself. Therefore, among the transition edges (binarized edges) between the first level segment and the second level segment, by adopting only one of either the rising edge and the falling edge as the sensing signal, the angle sensing accuracy can be assured by the dimensional accuracy in forming the concave and convex portions.
However, the above solution has the following problems:
(1) in the above solution, though the repetition period of the waveform is constant in itself, the phase of the binarized edge positions is irregular depending on the shape of the waveform and, therefore, does not uniquely correspond to the concavo-convex phase of the gear. It becomes a serious problem when the phase of attachment of the gear to the sensing object must be managed. For example, in the case of an angle sensor for detecting a crank angle of automobiles, if the gear is attached with respect to the concavo-convex phase, the irregularity of the phase of the binarized edge positions described above may adversely affect operations such as ignition timing control that is performed referentially; and
(2) because only one of the rising edge and the falling edge formed in the binarized waveform can be adopted, resolution of the angle sensing is reduced significantly in comparison with other solutions using both edges. Conversely, in order to implement the resolution comparable to the other solutions using both edges, the number of the concave and convex portions must be doubled but, as a result, the cost of machining the gear is increased and it becomes difficult to ensure the accuracy.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic sensor adjusting method that solves the above problems, a magnetic sensor adjusting device used for the method and the magnetic sensor.
It is another object of the present invention to provide a magnetic sensor adjusting method that can always be accurate in sensing a sensing target satisfactorily irrespective of fluctuations of a sensing gap length that may occur between different magnetic sensor products or in one magnetic sensor product, a magnetic sensor adjusting device used for the method and the magnetic sensor.
It is yet another object of the present invention to provide a magnetic sensor adjusting method that can prevent an irregularity of a phase of a binarized waveform edge, a magnetic sensor adjusting device used for the method and the magnetic sensor.
It is yet another object of the present invention to provide a magnetic sensor adjusting method that can always be accurate in sensing a sensing target satisfactorily irrespective of fluctuations of a sensing gap length that may occur between different magnetic sensor products or in one magnetic sensor product and that can prevent from occurring an irregularity of a phase of binarized waveform edges, a magnetic sensor adjusting device used for the method and the magnetic sensor.
According to the present invention, there is provided a method for adjusting a magnetic sensor including:
a magnet for generating a magnetic field;
a sensing target unit in which a first sensed portion and a second sensed portion are magnetically inequivalent to each other, are disposed along a moving path passing through a position opposed to the magnet through a magnetic gap, and can be moved integrally along the moving path;
a magnetic field detecting section for detecting magnetic field fluctuations in the magnetic gap based on the fact that the first sensed portions and the second sensed portions pass through the magnetic gap alternately;
a waveform processing section for binarizing detection waveform detected by the magnetic field detecting section based on a predetermined threshold; and
a threshold adjusting and setting section for setting the threshold so that it can be adjusted relatively with respect to the detection waveforms, the method comprising the steps
Denso Corporation
LeDynh Bot
Posz & Bethards, PLC
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