Alignment direction detection device
An alignment direction detection device includes an excitation coil to apply an AC magnetic field to a test object; one or more magnetic field sensors, each of which detects an inductive magnetic field caused by the AC magnetic field; a conveyance device; and processing circuitry. The processing circuitry performs band limitation on a distribution of the voltage outputted from each magnetic field sensor included in the one or more magnetic field sensors based on a radial direction space frequency corresponding to a size of the magnetic field sensor and a distance between the magnetic field sensor and the test object, transforms the band-limited voltage distribution into an output intensity waveform with respect to a space angle at the radial direction space frequency, and calculates a peak angle that is a peak position of the waveform as an alignment angle representing the alignment direction.
1 . An alignment direction detection device that detects an alignment direction of fibers in a test object including one or more sheets of electrically conductive composite materials each containing electrically conductive fibers, comprising:
an excitation coil to apply an AC magnetic field to the test object;
one or more magnetic field sensors arranged at positions maintaining a fixed positional relationship with the excitation coil, each of which detects an inductive magnetic field caused by the AC magnetic field and outputs voltage corresponding to the inductive magnetic field;
a conveyance device to move at least one of the test object and a sensor unit including the excitation coil and the one or more magnetic field sensors; and
processing circuitry to control the excitation coil, the one or more magnetic field sensors, and the conveyance device,
wherein the processing circuitry
calculates a radial direction space frequency as a function of (i) a size of the magnetic field sensor and (ii) a distance between the magnetic field sensor and the test object,
performs a band limitation on a distribution of the voltage outputted from each magnetic field sensor included in the one or more magnetic field sensors based on the calculated radial direction space frequency,
transforms the band-limited voltage distribution into an output intensity waveform with respect to a space angle at the radial direction space frequency, and
calculates a peak angle that is a peak position of the output intensity waveform as an alignment angle representing the alignment direction.
2 . The alignment direction detection device according to claim 1 , wherein the test object is a laminated body including a plurality of electrically conductive composite materials.
3 . The alignment direction detection device according to claim 1 , wherein
the one or more magnetic field sensors include a first magnetic field sensor and a second magnetic field sensor,
the excitation coil, the first magnetic field sensor, and the second magnetic field sensor are arranged coaxially, and
the first magnetic field sensor is arranged at a position closer to the test object compared to the second magnetic field sensor.
4 . The alignment direction detection device according to claim 3 , wherein
the first magnetic field sensor is arranged at a position closer to the test object compared to the excitation coil, and
the second magnetic field sensor is arranged at a position farther from the test object compared to the excitation coil.
5 . The alignment direction detection device according to claim 3 , wherein the first magnetic field sensor and the second magnetic field sensor are arranged inside the excitation coil.
6 . The alignment direction detection device according to claim 3 , wherein
the excitation coil includes a first excitation coil and a second excitation coil arranged at a position farther from the test object compared to the first excitation coil,
the first magnetic field sensor is arranged inside the first excitation coil, and
the second magnetic field sensor is arranged inside the second excitation coil.
7 . The alignment direction detection device according to claim 1 , further comprising:
a comparison object excitation coil that has a same structure as the excitation coil and applies an AC magnetic field to a comparison object having a same structure as the test object; and
a comparison object magnetic field sensor that has a same structure as the one or more magnetic field sensors and outputs voltage corresponding to an inductive magnetic field caused by the comparison object excitation coil,
wherein the processing circuitry transforms a difference between the band-limited voltage distribution and the voltage outputted from the comparison object magnetic field sensor into the output intensity waveform with respect to the space angle at the radial direction space frequency.
8 . The alignment direction detection device according to claim 1 , wherein
the one or more magnetic field sensors include first to fourth magnetic field sensors arrayed in two rows and two columns, and
distances from the test object to the first to fourth magnetic field sensors are equal to each other.
9 . The alignment direction detection device according to claim 1 , wherein the conveyance device includes:
a first conveyance unit to move the sensor unit in a first direction parallel to a surface of the test object; and
a second conveyance unit to move the sensor unit in a second direction parallel to the surface of the test object and crossing the first direction.
10 . The alignment direction detection device according to claim 1 , wherein the conveyance device includes:
a conveyance unit to linearly move the sensor unit in a direction parallel to a surface of the test object; and
a rotational conveyance unit to rotate the test object.
11 . The alignment direction detection device according to claim 1 , wherein
the one or more magnetic field sensors include:
a plurality of first magnetic field sensors arrayed in a predetermined array direction; and
a plurality of second magnetic field sensors arrayed in the array direction and including a same number of magnetic field sensors as the plurality of first magnetic field sensors, and
the plurality of first magnetic field sensors are arranged at a position closer to the test object compared to the plurality of second magnetic field sensors.
12 . The alignment direction detection device according to claim 1 , wherein
the one or more magnetic field sensors include:
a plurality of first magnetic field sensors arrayed in a predetermined array direction; and
a plurality of second magnetic field sensors arrayed in the array direction and including a same number of magnetic field sensors as the plurality of first magnetic field sensors, and
a distance from the test object to the plurality of first magnetic field sensors is equal to a distance from the test object to the plurality of second magnetic field sensors.
13 . The alignment direction detection device according to claim 11 , wherein the conveyance device includes a conveyance unit to linearly move the sensor unit in a direction parallel to a surface of the test object and orthogonal to the array direction.
14 . The alignment direction detection device according to claim 11 , wherein the conveyance device includes a rotational conveyance unit to rotate the test object.
15 . The alignment direction detection device according to claim 2 , wherein
the one or more magnetic field sensors include one or more detection coils, and
the processing circuitry sets a passband in the band limitation at a band of the radial direction space frequency that is proportional to a sum of (i) the size of each detection coil included in the one or more detection coils and (ii) the distance between the detection coil and the test object.
16 . The alignment direction detection device according to claim 15 , wherein the size of the detection coil is a diameter or a short side length.
17 . The alignment direction detection device according to claim 15 , wherein the detection coil includes a differential coil that outputs a difference between voltage outputs of two coils having a same structure.
18 . The alignment direction detection device according to claim 1 , wherein the processing circuitry uses the Radon transform as signal processing to transform the band-limited voltage distribution into the output intensity waveform.
19 . The alignment direction detection device according to claim 1 , wherein the magnetic field sensor includes at least one of a detection coil, a magnetoresistance element sensor, a magnetic impedance sensor, a Hall sensor, a flux gate sensor, a magnetooptic sensor, an optical pumping atomic magnetic sensor, or a superconducting quantum interference device.
20 . The alignment direction detection device according to claim 1 , wherein the fibers are carbon fibers, metallic thin lines, or silicon carbide fibers.