Optical temperature sensor

Abstract

To provide an optical temperature sensor capable of preventing damage to a protective window.SOLUTION: An optical temperature sensor provided herein comprises a cylindrical fiber probe having an optical fiber inserted therethrough, and a protective window made of sapphire and located on a tip end side of the fiber probe. The protective window has a surface on a side opposite the optical fiber in an axial direction of the fiber probe formed as a first surface and a surface on a side of the optical fiber formed as a second surface, where the first surface is an a-plane of sapphire.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to the technical field of optical temperature sensors using optical fibers. [Background technology]

[0002] Some optical temperature sensors measure temperature and other parameters by transmitting infrared light emitted from a measurement target to a detector through an optical fiber (see, for example, Patent Document 1). The optical temperature sensor described in Patent Document 1 is used in a molding machine that molds resin molded products, and measures the temperature and pressure of molten resin in a cavity or the like by connecting a fiber probe with an optical fiber inserted therein.

[0003] Some optical temperature sensors as described above have a protective window provided at the tip of the fiber probe to protect the fiber probe (optical fiber) (see, for example, Patent Document 2). In the optical temperature sensor described in Patent Document 2, the protective window is made of sapphire. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-232753 [Patent Document 2] Japanese Patent Application Publication No. 1-124725 Summary of the Invention [Problem to be solved by the invention]

[0005] However, optical temperature sensors such as those described above are sometimes used in high-temperature and high-pressure environments, such as the nozzle of an injection molding machine, etc. In such high-temperature environments, the pressure resistance of the protective window may be reduced compared to room-temperature environments, and there is a risk that the protective window may be damaged by pressure.

[0006] Therefore, an object of the present invention is to prevent damage to the protective window portion. [Means for solving the problem]

[0007] The optical temperature sensor according to the present invention comprises a cylindrical fiber probe through which an optical fiber is inserted, and a protective window portion formed of sapphire and positioned at the tip side of the fiber probe, wherein the surface of the protective window portion opposite the optical fiber in the axial direction of the fiber probe is formed as a first surface, and the surface on the optical fiber side is formed as a second surface, and the first surface is the a-plane of sapphire.

[0008] This makes it difficult for the maximum compressive stress of the protective window portion in a high-temperature environment to decrease compared to that in a normal-temperature environment. [Effects of the Invention]

[0009] According to the present invention, the maximum compressive stress of the protective window portion in a high-temperature environment is unlikely to decrease compared to that in a normal-temperature environment, so that damage to the protective window portion due to pressure during measurement can be prevented. [Brief explanation of the drawings]

[0010] [Figure 1] 2 and 4 show a first embodiment of the present invention, and this figure is a cross-sectional view of an optical temperature sensor. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a part of the optical temperature sensor. [Figure 3] FIG. 1 is a diagram for explaining crystal planes of sapphire. [Figure 4] FIG. 10 is a diagram showing test results regarding the pressure resistance of the protective window portion. [Figure 5] FIG. 10 is an enlarged cross-sectional view of an optical temperature sensor according to a second embodiment. [Figure 6] FIG. 10 is an enlarged cross-sectional view of an optical temperature sensor according to a third embodiment. [Figure 7] FIG. 10 is an enlarged cross-sectional view of an optical temperature sensor according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical temperature sensor according to an embodiment of the present invention will be described with reference to the accompanying drawings (see FIGS. 1 to 7).

[0012] The optical temperature sensor described below has a cylindrical fiber probe, and in the following description, the axial direction of the fiber probe is the up-down direction, and the tip side of the fiber probe is the downward direction, and the up-down, left-right directions are indicated. However, the up-down, left-right directions described below are for the convenience of explanation, and the implementation of the present invention is not limited to these directions.

[0013] Optical Temperature Sensor According to the First Embodiment First, an optical temperature sensor 1 according to a first embodiment will be described (see FIGS. 1 to 3).

[0014] The optical temperature sensor 1 is attached to, for example, an injection molding machine (not shown) and is used to measure the temperature of molten resin at the nozzle, for example. Note that the optical temperature sensor 1 may also be attached to various molding machines other than injection molding machines, such as extrusion molding machines and blow molding machines.

[0015] The optical temperature sensor 1 is configured by placing or supporting required parts in an outer casing 2 (see FIG. 1). The outer casing 2 has a housing 3 and a window support part 4. Each part of the outer casing 2 is formed, for example, from a metal material.

[0016] The housing 3 has a shaft portion 5 , a mounting portion 6 and a cover portion 7 .

[0017] The shaft portion 5 is formed into a cylindrical shape with its axial direction aligned vertically. Installation nuts 50 for attaching the optical temperature sensor 1 to the injection molding machine are attached to the shaft portion 5 except for the upper and lower ends. The lower end surface of the shaft portion 5 is formed as a pressing surface 5a (see Figures 1 and 2).

[0018] The mounting portion 6 has a flange portion 8 that projects outward from the upper end of the shaft portion 5, and a substantially cylindrical annular portion 9 that projects upward from the outer periphery of the flange portion 8. The mounting portion 6 is formed, for example, integrally with the shaft portion 5. The annular portion 9 has a notch 9a that opens upward and penetrates in the radial direction. The upper end of the annular portion 9 has a plurality of mounting holes 9b that open upward and are spaced apart in the circumferential direction.

[0019] The lid portion 7 is formed in an annular shape and has a screw hole 7a in the center. An adjustment screw 10 is threaded into the screw hole 7a. Screw insertion holes 7b that penetrate vertically are formed at intervals in the circumferential direction on the outer periphery of the lid portion 7. The lid portion 7 is attached to the placement portion 6 from above by inserting mounting screws 60 through the screw insertion holes 7b and threading them into the mounting holes 9b.

[0020] The window support part 4 is formed in a cylindrical shape with its axial direction aligned vertically, and has a fitting part 11, a holding part 12, and a receiving part 13. The window support part 4 has the fitting part 11, holding part 12, and receiving part 13 formed, for example, as a single unit. The fitting part 11 and the holding part 12 are both formed in a cylindrical shape, and the diameter of the fitting part 11 is larger than the diameter of the holding part 12. The holding part 12 is provided below the fitting part 11, continuing from the lower end part of the fitting part 11. The upper surface of the holding part 12 is formed as a pressed surface 12a, and the lower surface is formed as a tip surface 12b. The fitting part 11 of the window support part 4 is attached to the outside of the lower end part of the shaft part 5, and the pressing surface 5a of the shaft part 5 is pressed against the pressed surface 12a of the holding part 12.

[0021] The receiving portion 13 is provided in a state of projecting inward at the vertical intermediate portion of the holding portion 12 (see FIG. 2). The upper surface of the receiving portion 13 is formed as a first receiving surface 13a, and the lower surface is formed as a second receiving surface 13b. The space inside the receiving portion 13 is formed as a transmission hole 14. The diameter of the transmission hole 14 is set to be equal to or larger than the diameter of the optical fiber described below.

[0022] The space above the receiving portion 13 in the internal space of the holding portion 12 is formed as a first insertion space 15, and the space below the receiving portion 13 is formed as a second insertion space 16. Of the inner circumferential surface of the holding portion 12, the portion that forms the first insertion space 15 is formed as a first inner circumferential surface 12c, and the portion that forms the second insertion space 16 is formed as a second inner circumferential surface 12d. The first insertion space 15 and the second insertion space 16 are in communication via a through hole 14.

[0023] In the second insertion space 16, a sleeve material 17 and a protective window portion 18 are arranged.

[0024] The sleeve material 17 is formed in an annular shape with its axial direction in the up-down direction. The sleeve material 17 is made of a material, such as Kovar, whose thermal expansion coefficient is smaller than that of the window support part 4. It is desirable that the sleeve material 17 be made of a material whose thermal expansion coefficient is close to that of the protective window part 18.

[0025] The sleeve material 17 is inserted almost entirely into the second insertion space 16 with its upper surface in contact with the second receiving surface 13b, and its lower surface positioned flush with the tip surface 12b of the holder 12 or positioned slightly below the tip surface 12b. When inserted into the second insertion space 16, the sleeve material 17 has its outer peripheral surface 17a in contact with the second inner peripheral surface 12d of the holder 12. The sleeve material 17 is bonded to the holder 12 by, for example, welding. However, the sleeve material 17 and the holder 12 may also be bonded by brazing, a heat-resistant adhesive, or the like.

[0026] The protective window 18 is cylindrical with its axial direction aligned vertically, with the lower surface formed as a first surface 18a and the upper surface formed as a second surface 18b. The first surface 18a and the second surface 18b are substantially parallel. The protective window 18 is made of, for example, sapphire. As shown in FIG. 3, sapphire has crystal planes such as the c-plane, m-plane, a-plane, and r-plane with the c-axis as its growth axis, and the first surface 18a and the second surface 18b are the a-planes of the sapphire crystal planes. Note that the protective window 18 may be chamfered at the connecting portion between the outer peripheral surface 18c and the first surface 18a.

[0027] The outer diameter of the protective window portion 18 is larger than the diameter of the transmission hole 14 and is approximately the same as or slightly smaller than the inner diameter of the sleeve material 17 (see FIG. 2). The protective window portion 18 is inserted into the sleeve material 17 and attached to the window support portion 4 with the outer periphery of the second surface 18b in contact with the second receiving surface 13b. The outer periphery 18c of the protective window portion 18 is bonded to the inner periphery 17b of the sleeve material 17 by brazing with silver solder, for example. However, the sleeve material 17 and the protective window portion 18 may also be bonded by low-melting-point glass, a heat-resistant adhesive, or the like.

[0028] When the protective window portion 18 is attached to the window support portion 4, the lower end portion protrudes downward from the sleeve material 17. This makes it difficult for molten resin to remain at the tip portion when the optical temperature sensor 1 is attached to a molding machine such as an injection molding machine and used to measure the temperature of molten resin.

[0029] The thermal expansion coefficient of the protective window portion 18 is set to be smaller than that of the window support portion 4 and larger than that of the sleeve material 17 .

[0030] A fiber probe 19 is disposed inside the outer casing 2 (see FIG. 1). The fiber probe 19 is formed, for example, from a metal material and has a cylindrical portion 20 whose axial direction is in the up-down direction and a flange portion 21 that is continuous with the upper end of the cylindrical portion 20. The outer diameter of the flange portion 21 is larger than the outer diameter of the cylindrical portion 20. The upper surface of the flange portion 21 is formed as a pressed surface 21a.

[0031] An optical fiber 23 is inserted and held in the fiber probe 19. One end 23a of the optical fiber 23 is inserted into the cylindrical portion 20, and a bent portion 23b connected to the one end 23a is bent, for example, at a substantially right angle inside the flange portion 21. In the optical fiber 23, a portion between the bent portion 23b and the other end is provided as an intermediate portion 23c, and the intermediate portion 23c passes through the notch 9a and is positioned outward from the outer circumferential surface of the flange portion 21 to the fiber probe 19. A detector or the like (not shown) is connected to the other end of the optical fiber 23. An end face (lower end face) of the one end 23a of the optical fiber 23 is formed as an incident surface 23d onto which infrared light is incident (see FIG. 2).

[0032] The fiber probe 19 is supported by having its cylindrical portion 20 inserted into the shaft portion 5 and its tip inserted into the first insertion space 15 in the holder 12. The outer peripheral surface of the cylindrical portion 20 is in contact with the first inner peripheral surface 12c of the holder 12, and the tip surface (lower surface) 19a of the fiber probe is in contact with the first receiving surface 13a of the receiving portion 13. At this time, the center of the optical fiber 23 (incident surface 23d) is approximately aligned with the center of the transmission hole 14. In this way, the fiber probe 19 is arranged inside the window support 4 with the outer peripheral surface of the cylindrical portion 20 in contact with the first inner peripheral surface 12c of the holder 12, ensuring a stable arrangement without rattle relative to the window support 4.

[0033] The flange 21 is positioned in the placement portion 6, and when the cover portion 7 is attached to the placement portion 6, an elastic member 22 is positioned between the lower surface of the adjustment screw 10 and the pressed surface 21a of the flange 21 (see Figure 1).

[0034] For example, a compression coil spring is used as the elastic member 22. The fiber probe 19 is urged downward by the urging force of the elastic member 22. Therefore, the tip surface 19a of the fiber probe 19 is pressed against the first receiving surface 13a of the receiving portion 13 by the urging force of the elastic member 22. Note that a disc spring, a leaf spring, or the like may also be used as the elastic member 22, and the elastic member 22 may also be made of a rubber material or the like.

[0035] In the optical temperature sensor 1, the biasing force of the elastic member 22 against the fiber probe 19 can be adjusted by rotating the adjustment screw 10 to change the screwing position relative to the screw hole 7a. Note that the optical temperature sensor 1 may also be configured without the elastic member 22.

[0036] When the optical temperature sensor 1 configured as described above is attached to a molding machine such as an injection molding machine and used to measure the temperature of molten resin, infrared light emitted from the object to be measured enters the protective window 18 from the first surface 18a, is guided inside the protective window 18, and exits from the second surface 18b. The infrared light exiting from the second surface 18b passes through the transmission hole 14, enters the optical fiber 23 from the incident surface 23d, and is transmitted via the optical fiber 23 to the detector.

[0037] In an optical temperature sensor in which infrared light passes through a protective window and enters an optical fiber, if there is an air layer between the protective window and the incident surface, the light may be reflected at the interface between the protective window and the air layer or at the interface between the air layer and the incident surface, depending on the conditions of the air layer, resulting in optical interference. Such optical interference occurs when the thickness of the air layer is extremely small, on the order of nanometers to micrometers. For example, if the thickness of the air layer changes due to thermal expansion of the protective window, the degree of optical interference also changes, which may affect the measurement results of the optical temperature sensor.

[0038] In the optical temperature sensor 1 described above, by providing the receiving portion 13 on the window support portion 4, a certain distance is maintained between the upper surface of the protective window portion 18 and the incident surface 23d of the optical fiber 23 via an air layer (transmission hole 14). Because the receiving portion 13 is a structure, the thickness of this air layer is not on the order of nanometers or micrometers, but on the order of millimeters or more. Therefore, the receiving portion 13 maintains a certain distance or more between the optical fiber 23 and the protective window portion 18, which suppresses the occurrence of optical interference and ensures stable measurement conditions.

[0039] Furthermore, the first receiving surface 13a of the receiving portion 13 contacts the fiber probe 19, and the second receiving surface 13b contacts the protective window portion 18. This makes it difficult for the urging force of the elastic member 22 applied to the fiber probe 19 to be transmitted to the protective window portion 18, and when the pressure of the molten resin is applied to the protective window portion 18, the pressure of the molten resin is transmitted from the protective window portion 18 to the outer casing 2 via the receiving portion 13, thereby reducing the load on the protective window portion 18 due to the pressure of the molten resin.

[0040] Furthermore, in the optical temperature sensor 1, a sleeve material 17 is provided between the protective window portion 18 and the window support portion 4. This prevents molten resin from entering between the protective window portion 18 and the window support portion 4, making it difficult for excessive radial force to be applied to the protective window portion 18.

[0041] Furthermore, because the protective window 18 is made of sapphire glass and the sleeve material 17 is made of Kovar, the thermal expansion coefficient of the sleeve material 17 is smaller than but close to that of the protective window 18, and the degree of expansion of the protective window 18 and the sleeve material 17 is similar. Therefore, when the protective window 18 expands, it is slightly constricted by the sleeve material 17, further preventing the intrusion of molten resin between the protective window 18 and the sleeve material 17.

[0042] <Test results for pressure resistance> The test results regarding the pressure resistance of the protective window are explained below (see Figure 4).

[0043] The pressure resistance test measured the maximum compressive stress in the axial direction of a cylindrical protective window made of sapphire. Two types of protective window were used in the test: protective window A, with both axial surfaces (first and second surfaces) made of a-plane, and protective window C, with both axial surfaces made of a-plane. Measurements were taken after 10 minutes of compression in both room temperature (21.9°C) and high temperature (450°C) atmospheres.

[0044] As shown in Figure 4, the maximum compressive stress of protective window C was significantly reduced in a high-temperature atmosphere compared to a room-temperature atmosphere. On the other hand, the decrease in maximum compressive stress of protective window A in a high-temperature atmosphere compared to a room-temperature atmosphere was smaller than that of protective window C.

[0045] From the above measurement results, it was confirmed that by using sapphire a-plane for the first and second surfaces of the protective window, high pressure resistance against axial pressure in a high-temperature environment is ensured.

[0046] Optical Temperature Sensor According to Second Embodiment Next, an optical temperature sensor 1A according to a second embodiment will be described (see FIG. 5).

[0047] In each of the following embodiments, only the parts that differ from the previously described embodiments will be described in detail, and other parts will be given the same symbols as those used for similar parts in the previously described embodiments, and descriptions thereof will be omitted.

[0048] In place of the window support portion 4, the optical temperature sensor 1A is provided with a window support portion 4A.

[0049] The window support portion 4A has a calibration insertion hole 24 formed therein, which penetrates the holding portion 12 from top to bottom. An optical temperature sensor for calibration, such as a thermocouple 25, is inserted into the calibration insertion hole 24. For example, a sheath-type thermocouple is used as the thermocouple 25, and the thermocouple 25 is attached by welding to the window support portion 4A with one end inserted into the calibration insertion hole 24. The other end of the thermocouple 25 is extended out of the outer casing 2 through the notch 9a, for example, and is connected to a measuring instrument or the like (not shown).

[0050] In this way, in the optical temperature sensor 1A, the calibration insertion hole 24 is formed in the window support part 4A, and the thermocouple 25 is attached to the calibration insertion hole 24. As a result, temperature is measured using both the optical fiber 23 and the thermocouple 25, making it possible to calibrate the measurement results and improving the measurement accuracy of the optical temperature sensor 1A.

[0051] Optical Temperature Sensor According to Third Embodiment Next, an optical temperature sensor 1B according to a third embodiment will be described (see FIG. 6).

[0052] In the optical temperature sensor 1B, a window support 4B and a spacer 26 are provided instead of the window support 4.

[0053] The window support part 4B has a fitting part 27, a connecting part 28, and a holding part 29. The fitting part 27, the connecting part 28, and the holding part 29 are all formed in a cylindrical shape, with the connecting part 28 being provided continuous with the lower end of the fitting part 27, and the holding part 29 being provided continuous with the lower end of the connecting part 28. The sleeve material 17 and the protective window part 18 are inserted into and supported by the holding part 29.

[0054] A spacer 26 is also supported by the window support portion 4B. The spacer 26 is formed, for example, from a metal material and has a cylindrical tubular portion 30 with its axial direction aligned vertically and a receiving portion 31 that protrudes inward from the lower end of the tubular portion 30. The upper surface of the receiving portion 31 is formed as a first receiving surface 31a, and the lower surface is formed as a second receiving surface 31b. The space inside the receiving portion 31 is formed as a transmission hole 32. The tubular portion 30 and the receiving portion 31 are formed, for example, as a single unit.

[0055] The tip of the fiber probe 19 is inserted into the cylindrical portion 30, the outer peripheral surface of the cylindrical portion 20 is in contact with the inner peripheral surface of the cylindrical portion 30, and the tip surface 19a of the fiber probe is in contact with the first receiving surface 31a of the receiving portion 31. The upper surfaces of the sleeve material 17 and the protective window portion 18 are in contact with the second receiving surface 31b of the receiving portion 31.

[0056] As described above, the optical temperature sensor 1B is provided with the spacer 26. This makes it difficult for the biasing force of the elastic member 22 applied to the fiber probe 19 by the receiving portion 31 to be transmitted to the protective window portion 18, and also transmits the pressure of the molten resin from the protective window portion 18 to the outer casing 2 via the spacer 26.

[0057] Furthermore, by providing the receiving portion 31 as a separate body from the window support portion 4B, it becomes possible to form the receiving portion 31 from a material different from that of the window support portion 4B. For example, by forming the spacer 26 from a material that is stronger than the window support portion 4B, the high strength of the receiving portion 31 can be ensured.

[0058] Optical Temperature Sensor According to Fourth Embodiment Next, an optical temperature sensor 1C according to a fourth embodiment will be described (see FIG. 7).

[0059] In the optical temperature sensor 1C, a sleeve material 17A and a protective window portion 18 are arranged in the second insertion space 16 in the window support portion 4.

[0060] A recess 33 that is open downward and inward is formed, for example, around the entire circumference at the lower end of the sleeve material 17A. With the protective window 18 inserted into the sleeve material 17A, a sealant 34 is filled into the recess 33, and the sealant 34 is baked to fix the protective window 18 to the sleeve material 17A.

[0061] For example, frit glass (bismuth-based glass, alumina-based glass, borosilicate glass, etc.) is used as the sealing material 34. It is necessary to select a sealing material 34 that will not deform at the temperature of the environment in which the optical temperature sensor 1C is used, and for example, a material with a softening point higher than the temperature of the environment in which the optical temperature sensor 1C is used is desirable.

[0062] However, if a recess is not formed in the sleeve material, or if the protective window is attached to the window support without a sleeve material, as in the optical temperature sensor described in Patent Document 2, and a sealant is applied to the boundary between the protective window and the window support or the sleeve material and then baked, the sealant may spread to an unintended area during baking, resulting in an insufficient seal between the protective window and the window support or the sleeve material, and molten resin may enter the inside of the optical temperature sensor. Furthermore, if the sealant is baked in a state where it has spread to the first surface of the protective window, there is a risk of a decrease in measurement accuracy.

[0063] As described above, in the optical temperature sensor 1C, the sleeve material 17A is formed with a recess 33 for filling with the sealant 34. This prevents the sealant 34 from spreading to unintended areas and allows it to be baked within the desired range, ensuring a good seal between the sleeve material 17A and the protective window 18 and preventing molten resin from entering the interior of the optical temperature sensor. In addition, the sealant 34 is unlikely to reach the first surface 18a of the protective window 18, ensuring a good measurement state of the optical temperature sensor 1C.

[0064] The above-described structure for fixing the protective window to the sleeve material is also effective for a protective window whose first surface is a crystal plane other than the a-plane of sapphire.

[0065] <Summary> As described above, in the optical temperature sensors 1, 1A, 1B, and 1C, the protective window 18 is made of sapphire, and the first surface 18a of the protective window 18 is the a-plane of the sapphire. This makes it difficult for the maximum compressive stress of the protective window 18 in a high-temperature environment to decrease compared to that in a normal-temperature environment, ensuring high pressure resistance of the protective window 18 in a high-temperature environment and preventing damage to the protective window 18 due to pressure during measurement.

[0066] The second surface 18b is also an a-plane of sapphire.

[0067] Sapphire is a uniaxial crystal with the c-axis as its optical axis, and has the optical property of producing birefringence in light incident from a direction at an angle to the c-axis. By making both the first surface 18a and the second surface 18b sapphire a-plane as described above, the effect of birefringence on the infrared light guided by the protective window 18 toward the optical fiber 23 (incident surface 23d) is suppressed, thereby ensuring high pressure resistance of the protective window 18 without causing a decrease in the measurement accuracy of the optical temperature sensor 1.

[0068] As described above, the optical temperature sensor 1 can ensure good measurement conditions even in high-temperature and high-pressure environments, and is therefore suitable for use in molding machines where the measurement environment is likely to be high-temperature and high-pressure. [Explanation of symbols]

[0069] 1 Optical temperature sensor 4 Window support 18 Protective window 18a First Side 18b Second Side 19 Fiber Probe 23 Optical Fiber 1A Optical Temperature Sensor 4A Window support 24 Calibration insertion hole 25 Thermocouple 1B Optical Temperature Sensor 4B Window support 26 spacer 1C Optical Temperature Sensor 33 Recess 34 Sealing material

Claims

1. a cylindrical fiber probe through which an optical fiber is inserted; a protective window portion formed of sapphire and positioned on the tip side of the fiber probe, a surface of the protective window portion opposite to the optical fiber in the axial direction of the fiber probe is formed as a first surface, and a surface of the protective window portion facing the optical fiber is formed as a second surface; The first surface is an a-plane of sapphire. Optical temperature sensor.

2. The second surface is an a-plane of sapphire. The optical temperature sensor according to claim 1 .

3. Used in molding machines 3. The optical temperature sensor according to claim 1.

4. a cylindrical window support portion into which at least a portion of the protective window portion is inserted; a calibration insertion hole is formed in the window support portion; A thermocouple is inserted into the calibration insertion hole.

3. The optical temperature sensor according to claim 1.

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