JPH1151913A - Crack detecting method and crack detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack detecting method and a crack detector by which a crack is detected in a workpiece machining process in which direct observation from the device outside cannot be carried out. SOLUTION: This device, which detects generation of a crack in a crystal K manufactured in the inside of a vacuum furnace 11, is constructed of a supporting rod 15, which is arranged inside the vacuum surface 11 so as to support a crucible 13, and a vibration detection sensor 16 installed on the supporting rod 15. Because of vibration caused by cracking in the crystal K, the supporting rod 15 is vibrated, so that it is determined that a crack occurs in the crystal K when the vibration is detected and an alarm is outputted by means of a personal computer 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crack detecting method and a crack detecting apparatus used in a process of processing various objects which cannot be directly observed from outside the apparatus.

[0002]

2. Description of the Related Art Processing in the present invention means production such as crystal growth and processing such as thin film coating. Here, these two processes will be described. Therefore, an object to be processed is a crystal material in crystal growth, and is an optical material such as a crystal material or glass in thin film coating. As a crystal material, crystals such as calcium fluoride, magnesium fluoride, and barium fluoride are widely used for optical purposes. These crystals are often produced by the Bridgman-Stockberger method using a crystal growth apparatus in which the electric furnace is evacuated. According to the Bridgman-Stockberger method, a raw material is put into a crucible made of carbon (graphite), heated, melted, crystallized, and then gradually cooled so that the crystal is not broken, thereby producing a crystal. Is the way.

In the thin film coating, as an object to be processed (object to be coated), there are optical glass, various dielectric materials, metal materials and the like in addition to the above crystals. The coating of this thin film is often applied by vacuum evaporation. Such thin film coating by vacuum deposition,
The process is performed by heating an object to be processed to several hundred degrees Celsius in a vacuum evaporation apparatus to coat substances from various evaporation sources. Then, after the deposition is completed, the object to be processed is taken out from the vacuum deposition apparatus by gradually cooling.

[0004] When the treatment is performed in this manner, local microscopic changes (cracks) such as cracks, deformations, and transformations may occur in the object to be processed in the course of heating or cooling. An object to be processed having such a crack cannot be used as an optical element. However, it is difficult for the naked eye to directly observe the state of the middle part of the crystal growth apparatus or the vacuum evaporation apparatus, and it is particularly difficult to observe the crystal because it is manufactured in a crucible. For this reason, it was not possible to confirm whether or not cracks had occurred unless the crystal or optical glass was taken out of the vacuum device after the completion of crystal growth and thin film coating.

[0005]

As described above, when an object to be processed is processed using a crystal growth apparatus or a vacuum evaporation apparatus,
It is possible to determine whether or not cracks have occurred only after removing the processed object from each apparatus. That is, since it is known that cracks have occurred in the processed object after several weeks and months have been required for the processing step, it leads to a delay in the delivery date of the processed object and increases the cost. There was a problem.

[0006] As a detecting device for detecting the occurrence of cracks without directly observing the object when processing the object, there is an acoustic reflection crack monitor disclosed in Japanese Patent Publication No. 52-32266. There is a device. This monitoring device is configured to indirectly detect the occurrence of a crack by detecting an elastic wave (acoustic emission) which is a part of energy released when a crack occurs in a material. However, since this apparatus is configured to detect acoustic emission as an acoustic wave, it is not possible to detect cracks in an object to be processed which is processed by a crystal growth apparatus or a vacuum evaporation apparatus having a vacuum inside.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a wide and effective crack detection method and a crack detection apparatus for processing a workpiece which cannot be directly observed from outside the apparatus. It is intended to provide.

[0008]

In order to achieve the above object, a method for detecting a crack according to the present invention comprises supporting an object to be processed inside the apparatus with a support member provided inside the apparatus. By detecting the vibration of the support member,
The occurrence of cracks in the process of processing the workpiece is detected.
That is, when a crack occurs in the object to be processed, acoustic emission is generated from the object to be processed, and the acoustic emission causes the support member to vibrate.
Therefore, by detecting the vibration of the support member, it is possible to detect that a crack has occurred in the object to be processed.

In the above crack detection method, it is preferable to detect the vibration acceleration of the support member using an acceleration converter. Thus, the vibration of the support member can be detected with higher accuracy than when the vibration is detected based on the displacement amount.

In order to achieve the above object, a crack detecting apparatus according to the present invention detects the occurrence of cracks in the course of processing an object to be processed inside a processing apparatus. A support member disposed in the processing apparatus to support the object to be processed, and a vibration detector attached to the support member to detect vibration of the object to be processed.

According to the crack detecting device having the above-described structure, when a crack occurs in the workpiece, the support member supporting the workpiece vibrates due to acoustic emission caused by the crack. Then, by detecting this vibration with a vibration detector, it is possible to detect the occurrence of cracks in the processing target being processed in the processing apparatus.

The crack detecting device is preferably used when the processing device is a vacuum device that performs processing of an object to be processed in a vacuum state. That is, in this crack detection device, since the acoustic emission is detected not as an acoustic wave but as a vibration, the acoustic emission can be reliably detected even when the processing of the processing target is performed in a vacuum state.

Further, in the above-described crack detecting device, a part of the support member may be projected outside the processing device, and the vibration detector may be attached to the portion of the support member projecting outside the processing device. preferable. With such a configuration, it is not necessary to dispose the vibration detector inside the processing apparatus, so that the vibration detector can be kept at room temperature even when the processing apparatus is an electric furnace.

In the above crack detecting device, it is preferable to use an acceleration converter for detecting an acceleration of the support member when the support member vibrates, as a vibration detector.
Preferably, a piezoelectric acceleration transducer is used. With such a configuration, even a minute vibration at the time of occurrence of a crack can be accurately detected.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a crack detecting apparatus for detecting a crack in an object to be processed using the crack detecting method of the present invention will be described below with reference to FIG. First, the crystal growth apparatus 1 will be described. This crystal growth apparatus 1 is for producing a crystal by the Bridgman-Stockberger method.

The crystal growing apparatus 1 includes a vacuum furnace (manufacturing apparatus) 11 also called a vacuum bell jar, an electric heater 12 made of carbon disposed in the vacuum furnace 11, and a position inside the electric heater 12. And a crucible 13 made of carbon supported at the upper end of the support rod 15.
The support rod 15 is formed of a metal rod such as stainless steel, and its lower end penetrates the bottom surface of the vacuum furnace 11 to form the vacuum furnace 1.
1 and can be lowered (pulled down) with the growth of the optical crystal (product) K.
In the crystal growth apparatus 1 described above, the crucible 13 and the support rod 15 constitute a support member described in claims.

A vibration detection sensor (vibration detection means) 16 is attached to a portion of the support rod 15 protruding outside the vacuum furnace 11. The vibration detection sensor 16 includes a signal conditioner 17 for adjusting (amplifying) the detected vibration signal so as to be easily processed and transmitting the same, and a data processing analyzer for transmitting the detected vibration signal to the personal computer 19. 18 are connected. The personal computer 19 receives a signal from the data processing analysis device 18 and outputs a detection result detected by the vibration detection sensor 16.

The vibration detection sensor 16 is a so-called piezoelectric acceleration converter, which measures vibration by measuring the vibration acceleration of a vibrating object (here, the support rod 15). The piezoelectric acceleration transducer is a transducer using a piezoelectric effect element, and a detailed description thereof is omitted here because various products are known, but in brief, it is proportional to the acceleration. A force is applied to the piezoelectric element to generate a charge on a terminal of the element. In addition,
As the vibration detection sensor 16, it is not always necessary to use the piezoelectric acceleration transducer as described above, and a vibration detection unit having another configuration such as a strain gauge acceleration transducer may be used. A sensor commercially available under the name of "AE sensor" has the same principle and can be used for this purpose.

According to the crystal growth apparatus 1 configured as described above, calcium fluoride, magnesium fluoride, barium fluoride, etc., which are often used as optical crystals, are internally formed based on the Bridgman-Stockberger method. Heated by a heater 12 in a vacuum furnace 11 which is evacuated,
After being melted, it is manufactured by growing crystals. At this time, since the raw materials are put in the crucible 13, the inside of the crucible 13 cannot be directly observed.

However, the support rod 15 supporting the crucible 13 extends out of the vacuum furnace 11, and when a crack occurs in the crystal K in the crucible 13, the crack is transmitted to the support rod 15 as vibration. Therefore, this vibration is detected by the vibration detection sensor 1.
6, it can be determined that a crack has occurred in the crystal K.

The frequency of vibration caused by the occurrence of cracks varies depending on various states of the product (shape, internal stress state, holding state, etc.). In addition, various types of vibrations are detected by the vibration detection sensor 16, such as vibrations that are applied to an actual device on a daily basis, vibrations caused by a car traveling outside, and vibrations caused by a person walking nearby. Therefore, it is necessary to determine whether or not the vibration detected by the vibration detection sensor 16 is the vibration caused by the occurrence of the crack.

In order to make this determination, a crack is generated in an object to be processed in an actual processing step, its frequency is specified, and the specified frequency is stored in the personal computer 19. Further, this vibration does not last for a long time, and a short-time vibration and a subsequent damped vibration are observed. Therefore, this damped vibration is also stored in the personal computer 19 as valuable information for identifying a crack. In this way, the frequency that occurs when a crack actually occurs is investigated and stored in advance, and the frequency detected by the vibration detection sensor 16 is compared with the stored frequency to determine the vibration caused by the crack. Is determined.

Next, with reference to FIG. 2, a description will be given of a case in which a crack generated in vacuum deposition which is a step of coating a thin film is detected. When vacuum-depositing fluoride crystals or optical glass (lens) containing fluoride as a main component, a vacuum deposition apparatus 2 is used. The vacuum deposition apparatus 2 includes a vacuum furnace 21, an electric heater 22 disposed in the vacuum furnace 21, and a lens positioned below the electric heater 22 and supported at a lower end of a rotating shaft 25. It comprises a holder 23 and an evaporation source holding member 24 disposed below the vacuum furnace 21 and holding the evaporation source J. The rotating shaft 25 is configured to be rotatable with respect to the vacuum furnace 21.

In the vacuum vapor deposition apparatus 2 configured as described above, even when the lens L is vapor-deposited, cracks may be generated in the lens L during the heating / film formation process or the cooling process. Therefore, also in the vacuum evaporation apparatus 2, since the upper end of the rotating shaft 25 penetrates the upper surface of the vacuum furnace 21 and protrudes out of the vacuum furnace 21, the vibration detecting sensor 16 is attached to the rotating shaft 25 and the rotating shaft 25 is rotated. If the vibration of 25 is detected, the occurrence of a crack in the lens L can be detected in the same manner as described above.

The vacuum deposition apparatus 2 is also provided with a vibration detection sensor 16, a signal conditioner 17, a data processing analyzer 18, and a personal computer 19; Since the configuration is the same as that of the sensor 16 and the like, the same reference numerals are given and the detailed description is omitted here.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a crack detecting apparatus according to the present invention for detecting a crack in a crystal growing apparatus 1 will be described below. As the vibration detection sensor 16 for detecting the vibration of the support rod 15, a piezoelectric acceleration sensor made by NEC Corporation, which is a piezoelectric acceleration sensor having higher sensitivity than a strain gauge acceleration sensor, was used. The charge conditioner 17G is used as the signal conditioner 17 and the signal processor DP600 is used as the data processing / analyzing device 18.
0 series was used.

Before the production of the optical crystal K by the crystal growing apparatus 1 was started, various vibrations transmitted to the vibration detection sensor 16 via the support rod 15 were detected. As the vibration, vibration of a rotary pump for evacuating the vacuum furnace 11, vibration of an electric heater 12 and a 200 V AC power supply for driving the rotary pump, and the like were constantly detected. In addition, vibrations caused by a person walking around the crystal growth apparatus 1 and vibrations caused by a car running outside were also detected.
The detected frequencies of these vibrations are used as the frequencies of the miscellaneous vibrations other than the crack generation vibrations.
9 is stored.

The vibration of the crystal K in the crucible 13 due to the crack due to the thermal shock was examined.
When the raw material of the optical crystal was calcium fluoride, it was found that the frequency had a component of 400 to 1000 Hz.
For this reason, the personal computer 19 connected to the data analyzer 18 constantly monitors the frequency in this range during the operation of the crystal growth apparatus 1, and the frequency of 400 to 1000 Hz caused by the occurrence of the cracks of calcium fluoride. When the frequency is detected, an alarm is provided to the operator. Here, the observed frequency is established only in the present embodiment, and is different in other device configurations, so the numerical value here does not limit the present invention.

[0029]

As described above in detail, the crack detecting method and the crack detecting apparatus according to the present invention detect the vibration of the supporting member for supporting the processing object in the apparatus by detecting the vibration of the supporting member by the vibration detecting means. The occurrence of cracks is detected. For this reason, even when it is not possible to directly view the object to be processed, or when it is difficult to find the crack because the crack is fine even if the object can be directly viewed, the crack in the processing step of the object to be processed is The time of occurrence of the can be known.

As a result, since the process can be appropriately improved, the cost can be significantly reduced. Further, at the time of occurrence of a crack, the processing step can be interrupted and a new processing can be started, so that a delay in delivery of the workpiece can be minimized. Furthermore, by improving the process based on the known crack generation timing, a process that minimizes the crack generation rate can be created, and the yield can be improved.

The crack detecting device described above is preferably used when the processing device is a vacuum device that performs processing of an object to be processed in a vacuum state in order to detect the acoustic emission not as an acoustic wave but as a vibration. In addition, even if the processing apparatus is a vacuum furnace, it is possible to reliably detect the occurrence of cracks in the processing object inside.

Further, in the above-described crack detecting device, a part of the support member may be projected outside the processing device, and the vibration detector may be attached to the portion of the support member projecting outside the processing device. preferable. With such a configuration, it is not necessary to dispose the vibration detector inside the processing apparatus, and therefore, even when the processing apparatus is an electric furnace, the vibration detector can be kept at room temperature. In addition, a ready-made vibration detecting means can be used, and the detecting device can be manufactured at low cost.

Further, in the above crack detecting device, it is preferable to use an acceleration converter for detecting the acceleration of the support member when the support member vibrates, and it is more preferable to use a piezoelectric acceleration converter as the vibration detecting means. . With such a configuration, even a minute vibration at the time of occurrence of a crack can be detected with high accuracy, so that it is possible to further reduce the cost and to improve the yield.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a state in which a crack detection device according to the present invention is used in a crystal growth device using the Bridgman-Stockberger method.

FIG. 2 is a conceptual diagram showing a state in which the crack detection device is used in a vacuum heating vapor deposition device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crystal growth apparatus 2 Vacuum evaporation apparatus 11, 21 Vacuum furnace 12, 22 Electric heater 13 Crucible 15 Support axis 16 Vibration detection sensor 17 Signal conditioner 18 Data analysis processing apparatus 19 Personal computer 23 Lens holder 24 Evaporation source holding member 25 Rotation axis K crystal J evaporation source L lens

Claims (7)

[Claims] An object to be processed inside an apparatus is supported by a supporting member disposed inside the apparatus, and cracks in the process of processing the object are detected by detecting vibration of the supporting member. A crack detection method that detects the occurrence of cracks. 2. The crack detecting method according to claim 1, wherein the vibration of the supporting member is detected by using an acceleration converter. 3. A crack detection device for detecting occurrence of cracks in a process of processing an object to be processed inside a processing device, wherein the device is disposed in the processing device and supports the object to be processed. And a vibration detector attached to the support member for detecting vibration of the workpiece. 4. The crack detection device according to claim 3, wherein the processing device is a vacuum device that performs processing of the workpiece in a vacuum state. 5. The apparatus according to claim 1, wherein a part of the support member protrudes outside the processing apparatus, and the vibration detector is attached to a part of the support member protruding outside the processing apparatus. The crack detection device according to claim 3 or 4. 6. The crack detecting device according to claim 3, wherein the vibration detector is an acceleration converter. 7. The crack detecting device according to claim 6, wherein the acceleration converter is a piezoelectric acceleration converter.