Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2003-12-15
2004-11-16
LeDynh, Bot (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207230
Reexamination Certificate
active
06819100
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a displacement sensor which comprises a detector in which an AC magnetic field for detecting an object is generated by an oscillation circuit and detects a distance to a detection object, using a change in oscillation state of the oscillation circuit. More particularly, the present invention relates to technique for creating a conversion table for finding a detection distance from an oscillation state of an oscillation circuit in this kind of sensor (referred to as a displacement sensor or simply a sensor, hereinafter).
2. Description of the Prior Art
According to a proximity-type of displacement sensor intended for a metal body, in general, a high-frequency magnetic field from a detection coil acts on a detection object so that a distance to the detection object is detected (this detected distance is referred to as a detection distance, hereinafter), using a phenomenon in which an oscillation amplitude of the oscillation circuit changes according to a change in inductance due to the act of an eddy current magnetic field from the detection object.
The conventional displacement sensor incorporates a memory in which a conversion table showing the relation between the oscillation amplitude of the oscillation circuit and the detection distance is stored, and a controller such as a microcomputer. The controller finds the distance to the detection object by referring the conversion table to the measured value of the oscillation circuit and outputs it as a voltage signal proportional to the distance.
In the memory of the conventional displacement sensor, a table showing a standard relation between an oscillation amplitude and a detection distance is set every kind of the detection object (this table is referred to as a source table and a curving line of the source table is referred to as a standard curving line, hereinafter. Since the oscillation amplitude is detected as a voltage, it is referred to as an amplitude voltage or simply a voltage as needed.). However, since the relation between the amplitude voltage and the detection distance varies depending on a size of the detection object or variation of the detection coil, when it is necessary to perform high-precision measurement processing, the source table is corrected by teaching assisted by an actual detection object and creates the conversion table according to an installation condition.
Publicly known technique for creating the conversion table is disclosed in the following patent document 1. According to this patent document 1, sensor heads comprising coils are arranged at a point abutting on a detection object (a distance at this point is referred to as the minimum distance hereinafter), a point provided at the farthest distance as far as the detection object can be detected (distance at this point is referred to as the maximum distance, hereinafter), and a middle point between them, and measure amplitude voltages at the points. In addition, apart from these measurement, a voltage in a state which is not affected by the detection object (referred to as an open-state voltage in the patent document 1) is measured and the actually measured values at the three points are normalized by the open-state voltage. Then, the standard curving line corresponding to a range from the minimum distance to the maximum distance is corrected so that the voltages corresponding to the three points may be equal to the normalized actually measured values and its corrected result is stored in the memory as the conversion table.
Patent document 1 is Japanese Unexamined Patent Publication No. 2001-165603.
According to the method of the patent document 1, since each actually measured value is normalized by an open-state voltage so that an influence due to characteristics of the sensor head can be removed from each actually measured value, the high-precision conversion table can be created.
In addition, according to patent document 2 also, voltages are measured at three measurement points such as points corresponding to the minimum distance and the maximum distance and a middle point between them, and a correction value for correcting the amplitude voltage linearly is found, using these actually measured values. According to this document, the voltage at the measurement points of the minimum distance and the maximum distance are measured and shift correction and rotation correction are carried out so that these voltages may reach respective predetermined values. Then, the voltage at the middle point is measured and the shift correction and after the rotation correction are performed on the actually measured value, a correction value which is most suitable for the actually measured values at three points after the correction is called from a storage circuit and set.
Patent document 2 is Japanese Unexamined Patent Publication No. 7-131321.
According to the both patent documents 1 and 2, the voltages are measured while the detection object or the sensor head is moved so that the sensor head may be positioned at three points which were determined for the detection object.
According to this kind of sensor, since the oscillation state could be varied due to an influence of peripheral metal or an electromagnetic wave, it is preferable that the sensor is actually positioned in a usage environment and then the conversion table is created, in order to perform the high-precision measurement processing. However, when the measurement points are fixed like in the patent documents 1 and 2, the measurement at the position corresponding to the measurement point is sometimes difficult (for example, some kind of member is disposed at the position corresponding to the measurement point). In addition, when the open-state voltage is measured like in the patent document 1, it is preferable that the measurement is performed under a condition which is unaffected by the peripheral metal. However, it is considerably difficult to perform such measurement at a place where the sensor is installed.
Thus, when the measurement cannot be performed at the measurement point in the place where the sensor is installed, or in order to precisely measure the open-sate voltage, it is necessary to perform the measurement at another place before the sensor is installed or after the sensor is removed. Therefore, it is difficult to secure precision of the conversion table.
Furthermore, according to the method of the patent document 2, since the shift correction amount and the rotation correction amount are found by measuring the voltages at the measurement points of the minimum distance and the maximum distance and then the voltage is measured at the middle point is performed, the order of the measurement is fixed so that operationality is lowered.
SUMMARY OF THE INVENTION
The present invention was made in view of the above problems and it is an object of the present invention to be able to create a conversion table using measured values at any measurement points arbitrarily decided by a user under a condition where a sensor is installed in an actual usage environment, and to be able to create a conversion table suitable for an actual usage environment or usage condition.
A method according to the present invention is a method of creating a conversion table used in process for converting an oscillation state of an oscillation circuit, to a distance to a detection object, in a displacement sensor including a detector in which the oscillation circuit generates an AC magnetic field for detecting the object. The method of creating the conversion table according to the present invention comprises a step of arranging the detection object at each measurement point of any three measurement points whose distance from the displacement sensor is known, in any order and measuring the oscillation state of the oscillation circuit at the measurement point; a step of extracting a range which corresponds to a distance between the nearest measurement point and the farthest measurement point from the detector, in which a ratio be
Hosoda Toru
Iida Yusuke
Ohtsuki Hidetomo
Foley & Lardner LLP
LeDynh Bot
Omron Corporation
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