JP2018059874A - Heat source scanning type thermographic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means capable of simply detecting a defect existing inside a structure having a flat surface shape or a curved surface shape as a thermal image in a non-contact/nondestructive manner.SOLUTION: An active thermography system which flexibly handles structure samples each having different thermal diffusion by scanning the same while irradiating a solid sample 6 with a linearly converged light beam in a manner of electrical, mechanical or a combination thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermographic scanning device applied to nondestructive inspection.

  Thermography, which irradiates a substance with light and captures energy converted into heat as infrared radiation emitted therefrom, has been applied to nondestructive inspection inside a solid sample where the inside cannot be seen. In particular, in an active thermography apparatus that irradiates a measurement target sample with a light beam, a method of irradiating the entire surface of the sample [Non-Patent Document 1], a method of irradiating a sample with a point beam converged [Non-Patent Document 2], and Three methods [Non-Patent Document 3] are known in which a sample is focused and irradiated with a linear beam.

Regarding the method of converging the light beam into the third linear shape, a method proposed by the present applicant to switch on and turn on a plurality of light sources arranged electronically in different locations [Non-Patent Document 4] ] Is considered useful.

Tsutomu Hoshimiya: “Electronic scanning light source device and method”, Japanese Patent Application 2014-002421 (2014.1.9)

L.D.Fsavro, T.Ahmed, H.J.Jin, P.K.Kuo and R. L. Thomas: Photoacoustic and photothermal phenomena II, 490 (1990). C. Grass and D. Balageas: Proc., QIRT-92, 19 (1992). T. Hoshimiya, J. Hoshimiya and M. Tsuda: “Line-focus Beam-scan Time-domain Active Thermography with External Control”, Proc., QIRT-2012, 186 (2012). J. Hoshimiya and T. Hoshimiya: “Whole-electronic line-focus light-scanner for active thermography”, Proc., QIRT-2014, 222 (2014). ASTM D 4788-03 (2013), “Standard Test Method for Detecting Delaminations in Bridge Decks Using Infrared Thermography”, ASTM International, West Conshohocken, PA, 2013. Yoshinori Shimada: “Remote Sensing Technology of Internal Defects in Concrete Using Laser Ultrasound”, Inspection Technology, Vol. 14, p. 35 (2009).

  At present, aging of infrastructure structures such as bridges and tunnels throughout Japan has become a problem, and nondestructive inspection of concrete internal defects is an urgent issue. In conventional technology, non-destructive inspection using the temperature difference due to the difference in the amount of irradiation light between day and night [Non-Patent Document 5] has been performed in places with sunshine, but in the inspection inside the tunnel, hammering by hammering is performed. Method, contact ultrasonic method, etc. have been put into practical use, and laser ultrasonic method [Non-Patent Document 6] is a candidate for an automated device, but it is an expensive and large-sized device that can be used easily at the private level. A general-purpose inspection device that can be used has not yet been realized.

The inventor has attempted to develop an active thermography inspection apparatus using the electronic scanning technique disclosed in Patent Document 1. In the invention, by adopting a rod lens using a cylindrical transparent member, or a condensing optical system with a pipe structure hollowed out at the center thereof, and a light source that can change the light emission position and timing electronically or mechanically, An object of the present invention is to solve the above-described problems by a simple and large-sized apparatus using a method of scanning the position of a heat source generated by irradiation of a light sample.

In order to solve the above problems, the present invention provides the following means. The present invention uses a high-power lamp, high-intensity light-emitting diode (LED), or laser diode (LD) as a light source that can be driven by a personal computer (PC), and controls the DC power supply and power transistor drive circuit by the PC. Provided is a device that realizes a linear heat source that moves by sequentially driving an LED array to enable thermographic inspection capable of non-destructive inspection of industrial products, machines, and building structures.

With this method, a conventional non-destructive inspection device that previously required a heavy and expensive scanning device such as a mechanical slide stage has been realized by making electronic and information engineering control a lighter and cheaper product. It solves the problem.

The present invention has an effect of developing a safe and low-cost non-destructive inspection apparatus by using a large number of light emitting devices without using a large laser or an expensive scanning mechanism.

Due to its system configuration, this inspection device is safer and less expensive than other nondestructive inspection devices using X-rays, ultrasonic waves, magnetism, etc., and has accumulated technical knowledge and know-how. It is expected to spread widely because it is possible for even a small number of people to operate as easily as handling a personal computer.

FIG. 1 explains the claim 1 of the present invention and shows a basic configuration. FIG. 2 shows an example of a thermal image and a temperature waveform when a sample is irradiated with light from a plurality of high-intensity LED arrays using an analog output terminal having a plurality of channels.

 As shown in FIG. 1, an electrical signal generated by a signal generating personal computer 1 is output from an input / output device 2 having a plurality of output channels. The electric signals generated from the respective channels are input as time series having a delay time corresponding to each LED column to the power transistor column 3 for driving each LED, and drive the LED column 4 arranged in an array. The light emitted from the LED is imaged on the surface of the inspection sample 6 by the rod lens 5. The infrared signal generated by heating the sample is imaged in real time as an image by the thermo camera 7 and processed by the signal processing personal computer 8.

  FIG. 2 is an explanatory diagram of an imaging system using a rod lens. When the diameter of the cylindrical rod lens shown in Fig. 2 (a) is D and the refractive index of the material is n, the focal length is the formula.

Formula 1

（１）
で与えられ、光源からレンズの中心までの距離をaとすると、レンズの中心から像までの距離bは、レンズの結像公式

(1)
Given that the distance from the light source to the center of the lens is a, the distance b from the center of the lens to the image is the lens imaging formula

Formula 2

（２）
により与えられる。ここに焦点距離fは数式１で表されるものとする。

(2)
Given by. Here, the focal length f is expressed by Equation 1.

  Therefore, in the active thermography apparatus using the rod lens as shown in FIG. 1, when the shape of the surface of the object to be measured is known in advance, such as a flat surface or a curved surface inside the tunnel, a lens for arranging an LED array. If the distance a from the center of the LED to the LED light emitting surface is appropriately arranged for each column, correct imaging can be provided.

  If a high-brightness LED and a lens integrated with each other are rotated about the center of the rod lens so as to change the angle θ shown in FIG. 2A, mechanical scanning of the irradiated linear light beam is performed. Can also be performed.

  In the case of the concentric cylindrical rod lens shown in FIG. 2 (b), the refractive index of the internal medium is equivalently lowered, so that the focal length is slightly longer than the rod lens formula (1). In that case, it can be calculated based on an appropriate formula derived from the law of refraction of light.

  FIG. 3 is a drawing showing a combination of electronic scanning of a light source and mechanical scanning of a slit according to claim 3 of the present invention. In the electronic scanning according to the first aspect, since the size of the single light source is inevitably large, the position of the clearly imaged image becomes discrete, and it is difficult to generate a heat source at an intermediate position. In this figure, a light source with a relatively wide orientation is gently imaged by a condensing system, and a light beam is imaged only in the direction selected by a slit with 12 rotation mechanisms from the wide linear image. Therefore, the performance can be improved by further continuously scanning the discrete imaging. Since only the slit is rotated, the light source and the entire light collecting system described in claim 2 can be moved much more easily than rotating and scanning.

FIG. 4 shows, as data, a thermal image in which a linear heat source that moves to a sample coated with black paint is generated by the experimental apparatus of FIG. A thermal image of the same spot of the sample was shown every 5 seconds from the top. Although the intensity of the heat source varies somewhat depending on the characteristics of the LED, it is shown that the linear heat source moves at a substantially constant speed of 0.9 mm / sec.

Radiation inspection is dangerous and requires qualification, and ultrasonic inspection cannot perform non-contact measurement. On the other hand, the device of the present invention is simple and inexpensive, and can be easily judged as an image by operating a PC. High expectations are placed on consumer testing equipment.

DESCRIPTION OF SYMBOLS 1 Personal computer for signal generation 2 Control input / output device 3 Drive power transistor array 4 LED (or LD) light source array 5 Rod lens (columnar shape or concentric cylindrical shape)
6 Inspection sample 7 Thermo camera 8 Personal computer for thermal image / temperature waveform processing

9 Sample surface 10 Condensing lens 11 Light source 12 Slit with rotation mechanism

FIG. 1 explains the claim 1 of the present invention and shows a basic configuration. FIG. 2 shows an example of a thermal image and a temperature waveform when a sample is irradiated with light from a plurality of high-intensity LED arrays using an analog output terminal having a plurality of channels. FIG. 3 explains the third aspect of the present invention and shows a basic configuration. It is. FIG. 4 shows black light from five rows of high-intensity LED arrays by the experimental apparatus of FIG. A thermal image generated by generating a moving linear heat source by irradiating a paint-coated sample. It is shown as. From the top, the same point of the sample every 5 seconds from time 0 to 20 seconds The thermal image of was shown. Depending on the characteristics of the LED, there is some variation in the intensity of the heat source, It is shown that the heat source is moving at a substantially constant speed of 0.9 mm / sec.

Claims (4)

This is an active thermography device that scans the light beam as a heat source by switching the light emission of a high-output light source arranged in an array for each column and forming an image on a sample by an optical condensing system. Thermography device. A single or multiple high-output light source is combined with an optical condensing system having a cylindrical or cylindrical shape, and the entire sample irradiation optical system is mechanically rotated around the center of the rod lens to make the light beam into the sample. Thermographic device based on the principle of scanning against. A thermographic apparatus that scans a light beam serving as a heat source by combining the mechanical scanning mechanism according to claim 2 and the electronic scanning mechanism according to claim 1. An apparatus applying the principle of claims 1 to 3, wherein the sharpness of the image to be imaged is optimized in accordance with the measurement purpose in accordance with the surface shape of the sample to be irradiated with light (shape such as a plane or a curved surface). A thermography device including a function of adjusting the positional relationship between the light source and the lens.

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