JP3019552B2 - Surface inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection apparatus for inspecting the surface of an inspection object such as a casting with a light beam.

[0002]

2. Description of the Related Art As a technique for sensing a surface defect of a casting, there is a technique described in Japanese Patent Application Laid-Open No. 2-124412. According to this technique, as shown in FIG. 7, a light beam emitted from a light source 10 is reflected by a polygon mirror 12, a light reflected by a surface 14 of the inspection object is received by a one-dimensional position detection unit 16, and a one-dimensional position is detected. Position detector 16
This is a technique for processing the output of the signal processing unit 18 to measure the length. The polygon mirror 12 is rotated by a motor 20, whereby the light beam scans the surface 14 of the inspection object, and the signal processing unit 18 performs the above-described processing according to the beam direction detected by the light direction detection unit 22. Execute.

[0003]

However, in this prior art, since mechanical scanning is involved, there is a limit to improvement in accuracy due to rattling or the like, and scanning requires a certain amount of time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to realize accuracy assurance and high speed by performing surface inspection without performing mechanical scanning. And

[0005]

In order to achieve the above object, the present invention illuminates a surface of a test object such as a casting with a light beam, performs a length measurement operation based on reflected light, and performs a length measurement operation. In a surface inspection apparatus for inspecting the surface condition of a light source, a plurality of light emitting units for irradiating a light beam modulated with pulses of mutually different frequencies toward the inspection object, and a light receiving unit for receiving reflected light from the inspection object and outputting current And the output current of the light receiving section
And the pulse of each modulation frequency, and further obtains its DC component.
A frequency separation unit that generates and outputs a DC component representing the condensing position of each light beam by extracting the light beam, and a processing unit that performs a length measurement operation for each modulation frequency based on the DC component. .

[0006]

According to the present invention, light beams modulated with pulses of different frequencies are emitted from a plurality of light emitting units toward the inspection object. The light reflected by the inspection object is received by the light receiving unit, and further separated by the frequency separation unit for each modulation frequency. The DC component output from the frequency separation unit indicates the condensing position of the light beam of each modulation frequency. Therefore, it is possible to perform a length measurement operation for each modulation frequency using the DC component. As a result, since the length is measured by the light beams emitted from the plurality of light emitting units, a certain area can be measured at the same time without scanning, ensuring accuracy by eliminating mechanical scanning and speeding up by simultaneous measurement. Is achieved. Further, the light beams are modulated by pulses of different frequencies, respectively, and there is no particular problem caused by simultaneous irradiation of a plurality of light beams.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the actual configuration of a surface inspection apparatus according to an embodiment of the present invention as a front view in (a) and a side view in (b). As shown in this figure,
In this embodiment, an optical fiber light emitter 24, a lens 26, and a one-dimensional position detecting element (PSD: Position Sensing Device) 2
8 is provided.

As shown in FIGS. 2A and 2B, a plurality of (ten in the figure) optical fiber light emitters 24 are provided.
The optical fibers 30 are arranged using a sleeve 32, and the SELFOC microlens (SM
L) 36. Laser light is incident on the optical fiber 30 from a laser diode (not shown),
This laser light is converted into a beam by the SML 36. This light beam is applied to the inspection object. Note that, as described later, the laser light is modulated by pulses having different frequencies.

The beam diameter is set to be 2.0 ^φ at an irradiation angle of 1.5 (deg) and a distance of 50 (mm), for example. The optical fiber 30 has a total of 10 optical fibers 30 each having a length of 5 and a width of 2.
They are arranged at a pitch of 2 (mm). With such an arrangement, ten light beams can be projected onto the surface of the inspection object at a high density.

The optical fiber light emitter 24, the lens 26 and the one-dimensional PSD 28 are arranged in a positional relationship as shown in FIG. That is, the light beam emitted from the optical fiber light emitter 24 is reflected by the surface 3 8 of the inspection object,
The light is condensed on a predetermined condensed spot on the one-dimensional PSD 28 by the lens 26.

The position X _j of the _focused spot of the light beam modulated at j [kHz] is determined as follows using the output currents i _1j and i _2j when the effective sensitivity band is given by 6. You.

X _j / 6 = (i _2j −i _1j ) / (i _2j + i _1j ) This operation is called normalization by the output current. Also,
D shown in FIG, W, if Sadamare is S _j, measuring the displacement d _{j is, d j = DS j / (} W-X j) and determined.

FIG. 4 shows a circuit configuration of the present embodiment. As shown in this figure, the present embodiment executes frequency separation by the synchronous detection method.

In this embodiment, the laser light is modulated at different pulse frequencies. That is, 5
A pulse oscillator 40 having a frequency of kHz, 6 kHz, 7 kHz,..., and a drive circuit 44 for driving a laser diode (LD) 42 by using these oscillation outputs. The laser light generated by driving the LD42, as described with reference to FIG. 1 to FIG. 3, is received by the P SD28.

When the reflected light is collected on the PSD 28, the PSD 28 outputs currents i _1j and i _2j . In this embodiment, the total current value of each frequency Σi ₁ = i ₁₅ + i ₁₆ + i
₁₇ +... + Harmonics, Δi ₂ = i ₂₅ + i ₂₆ + i ₂₇ +... + Harmonics, the modulation frequencies 5 kHz, 6 kHz, 7 kHz,
The components of ... are separated.

[0017] This operation will be described, the calculation of the focusing position X ₅ with the light beam modulated by 5kHz by extraction of the current i ₁₅ and i ₂₅ as an example. First, when the output of the 5 kHz pulse oscillator 40 is filtered by the band pass filter 46, a fundamental component of B · sin (2πft + φ) is obtained. Here, B is the gain of the band-pass filter 46, f is 5 kHz, and φ is the phase change by the band-pass filter 46. When this is multiplied by Σi ₁ by the multiplier 48, the DC component of the multiplication result is B · I ₁₅ · cosφ / 2. Here, I ₁₅ represents the amplitude of i ₁₅ (the same applies hereinafter). Since the minimum value of the difference between the modulation frequencies is 1 kHz,
The AC components are all components of 1 kHz or more. Therefore,
The output of the multiplier 48 is filtered by the low-pass filter 50, and only the DC component can be extracted. When this is amplified by the amplifier 52 having the gain G, the following DC signal is obtained.

Meanwhile _{K 1 = G · B · I} 15 · cosφ / 2, multiplied by the sum .SIGMA.i ₂ of the output current of the multiplier 54 PSD 28 to the output of the band pass filter 46, and瀘波low-pass filter 56, an amplifier When amplified by 58, the following DC signal is obtained. However, it is assumed that the characteristics of the low-pass filter 56 and the amplifier 58 match those of the low-pass filter 50 and the amplifier 52.

K ₂ = G · B · I ₂₅ · cos φ / 2 The two DC components thus obtained are I 2
It is proportional to ₁₅ or I ₂₅ . These are both 8-bit A
The signal is input to the / D converter 60 and is normalized. That is, (K ₁ −K ₂ ) / (K ₁ + K ₂ ) is calculated. Since GB · cos φ / 2 is a constant determined by the circuit setting, the calculation of this value is (I ₂₅ −I ₁₅ )
/ (I ₂₅ + I ₁₅ ). This is X _5/6, so that the focusing position X ₅ is determined. Also, 6
If the light beams modulated at kHz, 7 kHz,... are separated and normalized by the same configuration, the light condensing positions X ₆ , X ₇ ,.

In this embodiment, 5 kHz, 6 kHz
The laser was modulated at z, 7 kHz,.
If the modulation frequency is set in the range of at least 5 kHz to 9.5 kHz at a pitch of 0.5 kHz, a position is detected at a frequency which can be sufficiently handled by the slew rate of the PSD 28 and the harmonics are not included in the modulation frequency band and the error is small. It can be performed. Further, low-pass filters 50, 5
The cutoff of No. 6 may be relatively gentle.

FIGS. 5 and 6 show the results of experiments on the effects of the present invention. This experiment was performed at 7 kHz and 8 kHz.
This is an experiment using an apparatus that modulates a laser at three frequencies of z and 9 kHz and uses three light emitting elements. First, FIG. 5 shows a case where only 7 kHz is used among three frequencies.
And FIG. 6 shows the PSD normalized outputs at 7 kHz and 9 kHz when all three types of frequencies are used. The horizontal axis in these figures is
This is an irradiation position where a point 50 mm from the light emitting unit is set to 0.

From these figures, it is clear that a result almost coincident with the theory is obtained, and that even if a plurality of light beams are used, almost the same result as a single light beam can be obtained.

It should be noted that the apparatus according to the present embodiment has
It can be applied to the detection of sand bites, guilloches (steps), chips, cracks, nests, and others, and can be used to obtain minute surface information of an object.

[0024]

As described above, according to the present invention,
Since a plurality of light beams have different modulation frequencies, and the length of the signal related to the received reflected light is measured separately for each modulation frequency, mechanical scanning is not required, and a decrease in accuracy due to rattling or the like is prevented, Also, the speed can be increased by instantaneous simultaneous length measurement.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a surface inspection apparatus according to one embodiment of the present invention, wherein (a) is a front view and (b) is a side view.

FIG. 2 is a diagram showing a configuration of an optical fiber light emitting body;
(A) is a figure which shows a light emitting surface, (b) is a figure which shows a side surface, respectively.

FIG. 3 is a diagram showing a light receiving operation in this embodiment.

FIG. 4 is a diagram showing a circuit configuration of a main part of the embodiment.

FIG. 5 is a diagram showing the effect of the present invention by experimental results.

FIG. 6 is a diagram showing the effect of the present invention by experimental results.

FIG. 7 is a diagram showing a configuration of an apparatus according to a conventional example.

[Explanation of symbols]

 Reference Signs List 24 optical fiber light emitter 28 one-dimensional position detecting element (PSD) 46 band-pass filter 48 multiplier 50 low-pass filter 60 A / D converter

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Koji Imai 2-12-12 Kugata, Tenpaku-ku, Nagoya City, Aichi Prefecture Inside Toyota Institute of Technology (56) References JP-A-63-222202 (JP, A) JP-A-63-195774 (JP, A) JP-A-62-228902 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30

Claims (1)

(57) [Claims] 1. A surface inspection apparatus that irradiates a light beam onto a surface of an inspection object such as a casting and performs a length measurement operation based on reflected light to inspect the surface state of the inspection object. A plurality of light-emitting units for irradiating the inspected object with the irradiated light beam, a light-receiving unit for receiving reflected light from the inspection object and outputting a current, and multiplying an output current of the light-receiving unit by a pulse of each modulation frequency.
A frequency separation unit that generates and outputs a DC component representing a condensing position of each light beam by extracting the DC component, and a processing unit that performs a length measurement operation for each modulation frequency based on the DC component. Characteristic surface inspection equipment.