Light irradiation device and light detector

Abstract

To provide a light irradiation device 100 that causes almost no loss of light amount, is simple in structure, and can detect the amount of light.SOLUTION: Provided is a light irradiation device 100 that includes an LED 1 for irradiating an object placed on a predetermined light path with light, and a light detector 3 for detecting the amount of light emitted from the LED 1, and in which the light detector 3 has a thermocouple 4 having a pair of metal element wires 41 whose tips are joined to form a contact point P, and outputs the electromotive force of the thermocouple 4 as a value corresponding to the amount of light, and a certain portion including the contact point P of the metal element wire 41 is exposed, and the exposed portion 41a is arranged on the light path.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light irradiation device that is suitably used for exposing, curing, bonding, etc., an object. [Background technology]

[0002] For example, in a conventional light irradiation device for exposure, in order to achieve exposure at a desired dose, as shown in Patent Document 1, a beam splitter is provided in the middle of the optical path to extract a portion of the emitted light, and this is introduced into a photodetector such as a photodiode so that the amount of light can be detected.

[0003] However, such a configuration requires at least an optical system including a beam splitter, and since a portion of the emitted light is split by the beam splitter, there is a problem in that a considerable amount of light is lost. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-142921 A Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above problems, the present invention aims to provide a light irradiation device that is capable of detecting the amount of light with a simple structure and with almost no loss of light, by using a new, previously unheard-of concept of using a thermocouple.

[0006] Here, we will explain why using a thermocouple to detect the amount of light is a new idea. As is well known, a thermocouple measures temperature by utilizing thermoelectromotive force, and therefore it is not possible to measure the amount of light directly. It has traditionally been thought that the only way to measure the amount of light is indirectly by irradiating light onto a specific indirect object and measuring the temperature of that indirect object with a thermocouple.

[0007] Therefore, in order to apply a thermocouple to the light amount detection of this type of light irradiation device, the indirect object is necessary, and an optical system that guides a part of the emitted light to the indirect object is also necessary, so in the end, there is no significant difference in configuration from the conventional light amount detection method using the above-mentioned photodiode, etc. Furthermore, compared to direct light amount detection using a photodiode, etc., since it is an indirect light amount detection that involves heat, it is inferior in accuracy and stability, and the response is also extremely slow, with a time constant of minutes. For the reasons above, in the technical field of the present invention, the idea of ​​using a thermocouple to detect the amount of light would never have been conceived in the first place.

[0008] As a result of extensive research into this existing technical common knowledge, the inventors have discovered for the first time that when ultraviolet light or visible light is directly irradiated onto a thermocouple, an electromotive force is generated with a rapid response which is unlikely to be due to temperature, and furthermore, that the output value corresponds precisely to the actual amount of light, although the reason for this is unclear, and thus the present invention has been completed. [Means for solving the problem]

[0009] That is, the light irradiation device according to the present invention includes a light source that irradiates light onto an object placed on a predetermined optical path, and a photodetector that detects the amount of light emitted from the light source.

[0010] The photodetector has a thermocouple consisting of a pair of metal wires whose tips are joined to form a junction, and outputs the electromotive force of the thermocouple as a value corresponding to the amount of light. A certain portion of the metal wires, including the junction, is exposed, and the exposed portion is positioned on the light path.

[0011] With such a device, only a thin metal wire needs to be placed on the optical path, and no optical system for extracting part of the emitted light is required, making it possible to realize an extremely simple configuration and suppressing light loss to almost 0. Furthermore, as mentioned above, the responsiveness, accuracy, and stability of light amount detection can be fully guaranteed.

[0012] A specific embodiment that can realize the present invention with a simpler structure includes a housing having a light-emitting window that emits light from the light source contained inside to the outside, and the exposed portion is bridged across the light-emitting window.

[0013] In order to make the contact points as small as possible, minimize light loss, and simplify manufacturing, it is preferable to form the contact points by spot welding. If the light source is an exposure light source that emits ultraviolet light, the effect of the present invention becomes more pronounced. Effect of the Invention

[0014] According to the present invention, as described above, almost no loss of light amount occurs and it is possible to detect the amount of light with a simple structure. [Brief description of the drawings]

[0015] [Figure 1] 1 is an overall perspective view showing a light irradiation device according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a front view of the light irradiation device according to the embodiment. [Diagram 3] FIG. 2 is a plan view of the light irradiation device in the embodiment. [Figure 4] 4 is a cross-sectional view taken along line AA in FIG. [Diagram 5] 5 is a partially enlarged view of a portion B in FIG. 4. [Figure 6] 4 is a graph showing the light amount detection characteristics of a photodetector using a thermocouple in the embodiment. [Figure 7] 13 is a graph showing the response of a photodetector using a thermocouple in the embodiment. [Figure 8] FIG. 11 is an overall perspective view showing a light irradiation device according to another embodiment of the present invention. [Figure 9] 9 is a partial cross-sectional view taken along the line CC in FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] As shown in FIG. 1 etc., the light irradiation device 100 of this embodiment emits ultraviolet light to expose an object, and includes a plurality of ultraviolet LEDs 1, a housing 2 that holds the LEDs 1, and a photodetector 3 that detects the amount of light (brightness) of the LEDs 1. As shown in FIGS. 1 and 2, the LEDs 1 are, for example, surface mount type, and a plurality of LEDs 1 are arranged in a matrix on a rectangular wiring board 1a.

[0018] As shown in Figs. 1 to 4, the housing 2 is a rectangular parallelepiped having a front plate, a back plate, a flat plate, a bottom plate, and left and right side plates. The front plate is provided with a light-emitting window 2a for emitting ultraviolet light from the LED 1 to the outside. The light-emitting window 2a is formed of a rectangular window frame 21 having a certain depth. The LED 1 mounted on the wiring board 1a is disposed at the back of the window frame 21 so as to emit ultraviolet light toward the front side. The inner peripheral surface 21a of the window frame 21 is a mirror surface, so that the ultraviolet light emitted from the LED 1 is reflected by the inner peripheral surface 21a.

[0019] The photodetector 3 has a thermocouple 4 made of a pair of metal wires 41 whose tips are joined together to form a junction P. As shown in Figure 4, the tip side of each of these metal wires 41 is an uncoated exposed portion 41a, and the base end side is a coated portion 41b coated with a sheath S (shown in Figure 5). The exposed portions 41a of the metal wires 41 are disposed in the air, spanning the light emitting window 2a.

[0020] 4, 5, etc., a through hole is provided in each of the opposing inner peripheral surfaces 21a of the window frame 21, and only the exposed portion 41a of each metal wire 41 extends from each through hole into the light emitting window 2a. In this embodiment, the extending direction of the exposed portion 41a is parallel to the short side of the light emitting window 2a, and the contact point P is set to be in the center of the left and right and the top and bottom of the light emitting window 2a when viewed from the front.

[0021] The coated portion 41b of each of the metal wires 41 does not protrude into the light emitting window 2a, but passes through the through hole inside the housing 2, penetrates the back plate of the housing, and extends to the outside. The base end portion to which the wires extend is connected to a measuring device (not shown) that measures the thermoelectromotive force that appears as a voltage between the metal wires 41 and converts this voltage (a light quantity corresponding value as referred to in the claims) into a light quantity.

[0022] This measuring instrument is composed of an electric circuit consisting of an analog circuit and a digital circuit, and this electric circuit functions as a voltage measuring section that measures the voltage between the metal wires 41 and a conversion section that converts the measured voltage into the amount of light. For the conversion in this conversion section, a correlation between the measured voltage and the amount of light is required, and here this correlation is obtained in advance by experiment.

[0023] The experimental results are shown in Figure 6. It can be seen that the amount of light (sensor measurement value) measured separately by a UV sensor using a photodiode is stably proportional with high accuracy to the measured voltage between the metal wires 41 (thermocouple output value). This proportional equation is the correlation relationship mentioned above. Note that in the figure, "ambient temperature" refers to the temperature around the thermocouple 4, and is the value measured by a separately installed temperature sensor. The ambient temperature around the thermocouple 4 hardly changes, indicating that the measured voltage between the metal wires 41 (thermocouple 4 output value) is not due to the influence of the ambient temperature, but is due to the irradiation of UV light. Incidentally, Fig. 7 shows the responsiveness of light quantity measurement using the thermocouple 4. It can be seen from Fig. 7 that the response time constant of light quantity measurement using the thermocouple 4 is about 10 to 30 seconds, which is a sufficiently fast response.

[0024] Figure 7 also shows data for a thin thermocouple wire (thin thermocouple output). This result is surprising. If the output of thermocouple 4 is caused by a rise in temperature due to UV irradiation, then a thinner thermocouple would have a smaller thermal capacity, improving responsiveness and yielding better results. However, as is clear from the thin thermocouple output graph, the output value oscillates. This suggests that thermocouple 4 is not sensing temperature changes, but rather that its output value fluctuates due to the direct effect of light. This is a completely new finding. It also shows that a smaller thermocouple diameter is not necessarily better, and that there is an optimal diameter.

[0025] In this embodiment, the proportional formula is stored in a memory included in the measuring device, and a CPU is caused to perform a calculation based on the proportional formula to calculate the light quantity from the measured voltage.

[0026] With this configuration, since only the thin metal wires 41 are arranged on the light path, i.e., on the light emitting window 2a, the loss of light quantity can be suppressed to almost zero. Also, since no optical system for measuring the light quantity is required, the structure can be extremely simple. Moreover, as described above, the responsiveness, accuracy, and stability of the light quantity detection can be fully guaranteed.

[0027] Furthermore, in this embodiment, the metal wire 41 is suspended across the light path, i.e., across the light emitting window 2a, and the suspension direction is parallel to the short side direction of the light emitting window 2a to minimize the length, i.e., the area, of the metal wire 41 that blocks light. This also reduces the amount of light loss as much as possible.

[0028] The present invention is not limited to the above-described embodiment. For example, the shape of the housing, the type and arrangement of the LEDs, the shape of the light-emitting window, etc. can be appropriately changed, and the present invention can be applied not only to light irradiation devices for exposure but also to light irradiation devices for inspection. For example, an example in which the present invention is applied to a ring-shaped inspection light irradiation device 100 is shown in Figs. 8 and 9. In this example, as shown in Fig. 9, light is emitted from an LED 1 housed inside a housing 2 to the outside through a transparent ring-shaped cover body 9, and a metal wire 41a extending in the radial direction in a plan view is arranged to bridge the light path between the LED 1 and the cover body 9, with its contact point P located at the center. The light is not limited to ultraviolet light, and may be visible light.

[0029] A plurality of thermocouples may be used, for example, a plurality of pairs of metal wires may be arranged at different positions on the optical path. The metal wire does not have to be bridged across the optical path (light emitting window 2a) as in the above embodiment. For example, a pair of metal wires may form a V shape, with the contact point at the apex, and protrude onto the optical path. However, in such a configuration, the contact point cannot be reliably fixed, and there is a risk that its position may change due to vibration or the like. In contrast, if the metal wire is bridged with a certain degree of tension as in the above embodiment, it is possible to stably hold the metal wire and the contact point with a simple structure.

[0030] In addition, if only the exposed parts of the metal wire are placed on the light path, the area that blocks light can be minimized, but it does not matter if some of the covered parts are on the light path as long as a sufficient amount of light is obtained or uneven illuminance due to light blocking is not a problem.

[0031] In the above embodiment, the exposed portion of the wire including the contact is disposed inside the light emitting window 2a, but it may protrude outside the housing as long as it is on the optical path. Also, the exposed portion may be disposed not on the optical path but in a portion irradiated with light that is correlated with the emitted light amount, such as leakage light.

[0032] Furthermore, the present invention is not limited to the above-described embodiment and modified examples, and various modifications are possible without departing from the spirit of the invention, such as by appropriately combining the respective configurations. [Explanation of symbols]

[0033] 100...Light irradiation device 1 LED 2. Housing 2a Light emitting window 3. Photodetector 4. Thermocouple 41 Metal wire 41a...Exposed area P...Contact

Claims

1. A light irradiation device including a light source that irradiates light onto an object placed on a predetermined optical path, and a light detector that detects the amount of light emitted from the light source, the photodetector has a thermocouple made of a pair of metal wires whose tips are joined together to form a junction, and outputs an electromotive force of the thermocouple as a value corresponding to the amount of light; A light irradiation device, characterized in that a certain portion including a contact point of the metal wire is exposed, and the exposed portion is disposed on the light path.

2. 2. The light irradiation device according to claim 1, wherein the exposed portion is held in a floating state in midair.

3. 3. The light irradiation device according to claim 2, further comprising a housing having a light emitting window formed therein for emitting light from the light source housed therein to the outside, the exposed portion being bridged across the light emitting window.

4. 4. The light irradiation device according to claim 1, wherein the contact points are formed by spot welding.

5. 5. The light irradiation device according to claim 1, wherein the light source emits ultraviolet light.

6. A photodetector used in a light irradiation device having a light source that irradiates light onto an object placed on a predetermined light path, An optical detector comprising a thermocouple consisting of a pair of metal wires whose tips are joined together to form a junction, the optical detector outputs the electromotive force of the thermocouple as a value corresponding to the amount of light, and a certain portion of the metal wires including the junction is exposed, the exposed portion being positioned on the optical path.

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