Thermal fatigue crack generator for large pipe

Abstract

The present invention discloses a thermal fatigue crack generator for a large pipe. According to the present invention, the thermal fatigue crack generator for a large pipe precisely manages and controls the heating and cooling conditions for the large size test pipes having a diameter of 250 to 610 mm to significantly improve the reliability of the accuracy and a reproducibility of the thermal fatigue cycle so that a useful advantage is expected to ensure the reliability and the effectiveness of the skill verification of the non-destructive testing.

Claims

1. A thermal fatigue crack generator for a large pipe, comprising: a frame unit which fixedly supports a pipe specimen having a semicircular shape cross-section obtained by cutting a cylindrical pipe having a diameter of 250 mm to 610 mm in a longitudinal direction; a heating unit which is disposed adjacent to an outer surface of a lower portion of the pipe specimen to locally heat the pipe specimen; a cooling unit which includes a cooling water pump which forcibly supplies cooling water into the pipe specimen; a discharge unit which is provided at one side of the pipe specimen to discharge the cooling water therein to the outside; and a cooling water ejection control unit which generates a thermal stress formed by a thermal fatigue cycle by repeatedly heating and cooling the pipe specimen by applying a control signal to the heating unit and the cooling unit and senses the presence of the heating operation of the heating unit to control the heating unit to perform a heating operation after discharging the cooling water in the pipe specimen by applying a control signal to the discharge unit before the heating operation.

2. The thermal fatigue crack generator of claim 1, wherein the frame unit includes: a fixed flange which is in close contact with any one of both surfaces of the pipe specimen in a longitudinal direction to be closed; a movable flange which is connected to the fixed flange by a plurality of guide posts to slide back and forth and is in close contact with the other surface of the pipe specimen to be closed and is connected with a cooling water supply line through which the cooling water is supplied from the outside at one side; an extension/contraction sensing unit which senses an extension/contraction rate by the heating and cooling operation acting on the pipe specimen fixedly supported between the fixed flange and the movable flange; and a thermal expansion compensating unit which is applied with a sensing signal from the extension/contraction sensing unit to displace the fixed flange and the movable flange in a longitudinal direction.

3. The thermal fatigue crack generator of claim 1, wherein the heating unit includes: a heater which is configured by any one of an induction heating coil which is applied with a high frequency current to form a magnetic field to induce the heating or a direct heating coil having a heating line which is supplied with a power to heat; a heating temperature sensor which measures a heating temperature of the heater; and a heating timer which measures a heating time of the heater.

4. The thermal fatigue crack generator of claim 1, wherein the cooling unit includes: a flow detector which detects a flow of the cooling water in the pipe specimen; a flow control valve which is installed on a cooling water line supplying the cooling water to the cooling water pump and the pipe specimen to control the flow; and a water temperature sensor which measures a temperature of the cooling water supplied to the pipe specimen.

5. The thermal fatigue crack generator of claim 1, wherein the discharge unit includes: a discharge pipe line which is connected into the pipe specimen through a lower side thereof; and a discharge valve which is installed on the discharge pipe line to selectively open/close a pipe line to discharge the cooling water in the pipe specimen to the outside.

6. The thermal fatigue crack generator of claim 1, wherein the cooling water ejection control unit includes: a discharge control unit which applies a control signal for a discharge operation to the discharge unit to eject all the cooling water in the pipe specimen before starting the heating operation of the heating unit in a state in which the cooling water is supplied in the pipe specimen; a heating control unit which is applied with a cooling water discharge completion signal from the discharge control unit to control a heating temperature and an on/off operation of the heating unit; and a heating position detecting unit which detects a position of the heating point of the pipe specimen which is locally heated by the heating unit.

7. The thermal fatigue crack generator of claim 2, wherein the extension/contraction sensing unit includes any one of an elastic displacement sensor which measures an elastic displacement in accordance with the extension/contraction of the pipe specimen by connecting the fixed flange and the movable flange and a pressurization sensor which is provided in one or both of the fixed flange and the movable flange in a portion in contact with the pipe specimen to measure a pressure; and the thermal expansion compensating unit includes: a pressurization control unit which is applied with sensing information from the extension/contraction sensing unit to calculate an extension/contraction rate of the pipe specimen and moves back and forth the movable flange with respect to the fixed flange based thereon to output a control signal to control the contact degree with the pipe specimen; and an actuator which is applied with a control signal from the pressurization control unit to be connected to any one of the movable flange and the fixed flange to generate a position displacement to a straight direction by a driving source.

Description

DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a perspective view illustrating a state in which a pipe specimen is installed in a thermal fatigue crack generator for a large pipe according to the present invention.

[0030] FIG. 2 is a perspective view of a thermal fatigue crack generator for a large pipe illustrated in FIG. 1 as seen from a rear side.

[0031] FIG. 3 is a perspective view of a thermal fatigue crack generator for a large pipe illustrated in FIG. 2 as seen from a bottom.

[0032] FIGS. 4 and 5 are perspective views for explaining a configuration of a thermal fatigue crack generator for a large pipe according to the present invention.

[0033] FIG. 6 is a schematic view for explaining a configuration of an extension/contraction sensing unit and a thermal expansion compensating unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0034] FIG. 7 is a schematic view for explaining a configuration of a cooling unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0035] FIG. 8 is a block diagram for explaining a configuration of a cooling water ejection control unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0036] FIG. 9 is a block diagram for explaining a configuration of a guide unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0037] FIG. 10 is a block diagram for explaining a configuration of a cooling unit in a thermal fatigue crack generator for a large pipe according to the present invention. [Description of Main Reference Numerals of Drawings]

[0038]

TABLE-US-00002 1: Thermal fatigue crack generator for large pipe 10: Frame unit 11: Fixed flange 12: Guide post 13: Movable flange 15: Extension/contraction sensing unit 17a: Pressurization control unit 17b: Actuator 20: Guide unit 30: Cooling unit 31: Flow detector 32: Cooling water line 33: Flow control valve 34: Cooling water pump 36: Cooling water tank 40: Discharge unit 41: Discharge pipe line 43: Discharge valve 50: Ejection control unit

BEST MODE

[0039] Hereinafter, a configuration and an operation of the exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, it is not intended to limit the present invention to the specific embodiments, and it will be appreciated that the present invention includes all modifications, equivalences, or substitutions included in the spirit and the technical scope of the present invention. In the present application, it will be appreciated that terms “including” and “having” are intended to designate the existence of characteristics, numbers, steps, operations, constituent elements, and components described in the specification or a combination thereof, and do not exclude a possibility of the existence or addition of one or more other specific characteristics, numbers, steps, operations, constituent elements, and components, or a combination thereof in advance. That is, throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0040] If it is not contrarily defined, all terms used herein including technological or scientific terms have the same meaning as those generally understood by a person with ordinary skill in the art. Terms which are defined in a generally used dictionary should be interpreted to have the same meaning as the meaning in the context of the related art but are not interpreted as an ideally or excessively formal meaning if it is not clearly defined in the present invention.

[0041] Here, repeated description and detailed description for known functions and configurations which may unnecessarily obscure the gist of the present invention may be omitted to avoid the ambiguity of the gist of the present invention. Exemplary embodiments of the present invention are provided so that those skilled in the art may more completely understand the present invention. Accordingly, the shape, the size, etc., of elements in the figures may be exaggerated for explicit comprehension.

[0042] FIGS. 1 to 3 are perspective views of a thermal fatigue crack generator for a large pipe according to the present invention in which a pipe specimen is installed, seen from several directions.

[0043] In the drawings, a thermal fatigue crack generator 1 for a large pipe configured by a frame unit 10 which forms a frame and is a holding element to support both sides and an upper surface of a pipe specimen 100 having a semicircular arc cross-section obtained by cutting a cylindrical pipe in a longitudinal direction, a guide unit which is installed to be adjacent to a lower outer surface of the pipe specimen 100 to locally heat the pipe specimen 100, a discharge unit 40 which passes through a lower portion of the pipe specimen 100 to be connected therein in a position without interfering at one side of the guide unit 20 to discharge a cooling water in the pipe specimen 100 to the outside, a cooling unit 30 which is connected to one side of a movable flange 13 configuring the frame unit 10 to inject the cooling water supplied from the outside into the pipe specimen 100, and a cooling water ejection control unit which repeatedly controls operations of the guide unit 20 and the cooling unit 30 to set a thermal fatigue cycle to generate a thermal stress is illustrated.

[0044] FIGS. 4 and 5 are perspective views for explaining a configuration of a thermal fatigue crack generator for a large pipe according to the present invention in which the pipe specimen 100 is not mounted.

[0045] In the drawings, a thermal fatigue crack generator 1 for a large pipe configured by a frame unit 10 which forms a frame and includes a fixed flange 11 and a movable flange 13 disposed to be opposite to each other to be in close contact with both ends of the pipe specimen 100 having a semicircular arc shape to be closed, a plurality of guide posts 12 connecting the fixed flange 11 and the movable flange 13, and an extension/contraction sensing unit 15 which pressurizes and holds an upper edge of the pipe specimen 100, a cooling unit 30 which includes a cooling water line 32 and a flow control valve 33 connected to one side of the movable flange 13 to inject cooling water supplied from the outside into the pipe specimen 100, and a heating unit 20 which locally heats a lower one side of the pipe specimen 100 is illustrated.

[0046] FIG. 6 is a schematic view for explaining a configuration of an extension/contraction sensing unit and a thermal expansion compensating unit in a thermal fatigue crack generator for a large pipe according to the present invention which is a view of a thermal fatigue crack generator for a large pipe of FIG. 1 seen from the top.

[0047] In the drawing, the pipe specimen 100 in which both ends and an upper portion are held by the frame unit 10 is illustrated. At this time, in the pipe specimen 100, a cooling water discharge hole 100h is penetrated to be connected to a discharge pipe line 41 which configures a discharge unit 40 to be described below at one side of a lower surface to discharge the cooling water. Further, the movable flange 13 which configures the frame unit 10 is connected to the cooling water line 32 and the flow control valve 33 which configure the cooling unit 30 at one side. Further, the thermal fatigue crack generator 1 for a large pipe in which the extension/contraction sensing unit 15 is in close contact with an upper edge of the pipe specimen 100 not only to serve to hold the upper edge of the pipe specimen, but also to perform a function for sensing extension/contraction of the pipe specimen 100 held between the fixed flange 11 and the movable flange 13 generated in a longitudinal direction due to the repeated cooling and heating operations and the information sensed by the extension/contraction sensing unit 15 adjusts an interval between the fixed flange 11 and the movable flange 13 by a pressurization control unit 17a and an actuator 17b which configure the thermal expansion compensating unit is illustrated.

[0048] FIG. 7 is a schematic view for explaining a configuration of a cooling unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0049] In the drawing, the pipe specimen 100 having a semicircular arc shape cross-section is held by the frame unit 10 which forms a frame and the heating unit 20 and the discharge unit 40 are disposed at one side of the lower portion of the frame unit 10 so as not to interfere with each other. Further, a cooling water line 32 which configures the cooling unit 30 is connected to one side of the movable flange 13 among the elements which configure the frame unit 10 and the cooling water supplied through the cooling water line 32 is introduced into the pipe specimen 100 through a through hole formed in the movable flange 13. In the meantime, the cooling unit 30 configured by a cooling water tank 36 which preserves cooling water, a flow control valve 33 which is installed on the cooling water line 32 connecting the cooling water tank 36 and the movable flange 13 to control a flow of the cooling water supplied to the pipe specimen 100, and a cooling water pump 34 which supplies the cooling water preserved in the cooling water tank 36 into the pipe specimen is illustrated.

[0050] FIG. 8 is a block diagram for explaining a configuration of a cooling water ejection control unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0051] In the drawing, a cooling water ejection control unit 50 which reproduces a thermal fatigue cycle by regularly heating and cooling the pipe specimen 100 by controlling the heating unit 20 and the cooling unit 30 is illustrated. The cooling water ejection control unit 50 includes a discharge control unit 51 which controls a discharging operation for a discharge unit 40 for discharging the cooling water, a heating control unit 53 which controls a heating temperature and an on/off operation of the heating unit 20, and a heating position detecting unit 55 which detects a position of a heating point of the pipe specimen 100 which is locally heated by the heating unit 20.

[0052] FIG. 9 is a schematic view for explaining a configuration of a guide unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0053] In the drawing, a configuration of a heating unit 20 configured by a heater 21 configured by any one of an induction heating coil or a direct heating coil as an element of heating with a power supplied from the outside, a heating temperature sensor 23 which measures a heating temperature of the heater 21, and a heating timer 25 which measures a heating time of the heater 21 is illustrated.

[0054] FIG. 10 is a block diagram for explaining a configuration of a cooling unit in a thermal fatigue crack generator for a large pipe according to the present invention.

[0055] In the drawing, a cooling unit 30 configured by a flow detector 31 which detects a flow of a cooling water in the pipe specimen 100, a cooling water tank 36 which preserves the cooling water, a cooling water line 32 which supplies the cooling water to the pipe specimen 100, a cooling water pump 34 which is installed on the cooling water line 32 to pump the cooling water preserved in the cooling water tan 36 to forcibly convey the cooling water, a flow control valve 33 which controls the flow of the cooling water supplied to the pipe specimen 100, and a water temperature sensor 39 which measures a temperature of the cooling water supplied to the pipe specimen 100 is illustrated.

[0056] The configuration of the thermal fatigue crack generator for a large pipe according to the present invention will be described with reference to the above drawings.

[0057] The thermal fatigue crack generator for a large pipe according to the present invention does not control the flow of the cooling water supplied into the pipe specimen 100, but controls the heating unit 20 after completely discharging the cooling water filled in the pipe specimen 100 to the outside through the discharge unit 40 before the heating operation of the heating unit 20 which is installed at one side of the lower portion of the pipe specimen 100 to locally heat to locally heat the test piece 100. As a result, it is possible to precisely control while maximizing the internal temperature variation in a situation in which the shape of the external surface of the pipe specimen 100 does not change. Therefore, the reliability and the effectiveness of the actual crack reference test piece for skill verification of the non-destructive test for the pipe specimen 100 having a diameter of 250 to 610 mm which belongs to a large pipe may be increased.

[0058] To this end, the thermal fatigue crack generator for a large pipe according to the present invention is configured by a frame unit 10 which forms a frame, a heating unit 20 which is provided at one side of a lower portion of the pipe specimen 100 held and supported in the frame unit 10 to locally heat the pipe specimen, a cooling unit 3 which is connected to one side of the frame unit 10 to supply the cooling water into the pipe specimen 100, a discharge unit 40 which is connected to a cooling water discharge hole 100h penetrating to one side of the lower portion of the pipe specimen 100 to discharge the cooling water in the pipe specimen 100 to the outside with the received control signal, and a cooling water ejection control unit 50 which controls the operation of the discharge unit 40 to generate the thermal fatigue crack for the pipe specimen 100.

[0059] The frame unit 10 is an element for fixing and supporting the pipe specimen 100 having a semicircular arc shape cross-section obtained by cutting a cylindrical pipe having a dimeter of 250 to 610 nm in a longitudinal direction. The frame unit 10 with this configuration is configured by board type fixed flange 11 and movable flange 13 which are disposed to be opposite to each other to be in close contact with both ends of the pipe specimen 100 having a semicircular arc shape to close both ends, a guide post 12 which connects the fixed flange 11 and the movable flange 13 and supports the movable flange 12 to move back and forth with respect to the fixed flange 11, and an extension/contraction sensing unit 15 which pressurizes and supports the upper edge of the pipe specimen 100 to be in contact therewith to prevent the flowing.

[0060] Further, the cooling water line 32 which configures the cooling unit 30 is connected to one side of the movable flange 13 and a through hole is formed so as to introduce the cooling water supplied through the cooling water line 32 into the pipe specimen 100.

[0061] In the meantime, extension/contraction phenomenon is generated by the heating and the cooling applied to the pipe specimen 100 fixedly supported between the fixed flange 11 and the movable flange 13. The present invention proposes to additionally configure an extension/contraction sensing unit 15 and the thermal expansion compensating unit to maintain an appropriate interval between the fixed flange 11 and the movable flange 13 by sensing a ratio of expansion and contraction of the pipe specimen 100.

[0062] The extension/contraction sensing unit 15 not only serves to hold the pipe specimen 100 by being in close contact with the upper edge of the pipe specimen 100 having a semicircular arc shape cross-section to prevent the flowing, but also performs a function of sensing the extension/contraction phenomenon of the pipe specimen 100 held between the fixed flange 11 and the movable flange 13 generated in the longitudinal direction by the repeated heating and cooling operations. The information sensed by the extension/contraction sensing unit 15 is configured to adjust the interval between the fixed flange 11 and the movable flange 13 by a pressurization control unit 17a and an actuator 17b which configure the thermal expansion compensating unit.

[0063] For example, when the pipe specimen 100 extends by 5 mm in a longitudinal direction due to a thermal fatigue stress, the extension/contraction sensing unit 15 senses the force or the distance extending in the longitudinal direction to apply a signal to the pressurization control unit 17a which configures the thermal expansion compensating unit. Next, the pressurization control unit 17a applies a control signal to the actuator 17b which pressurizes and supports the movable flange 13 toward the fixed flange 11 based on the sensed information to control the movable flange 13 and the fixed flange 11 to maintain a predetermined interval.

[0064] In the meantime, the extension/contraction sensing unit 15 may apply a known elastic displacement sensor which generates an elastic displacement in accordance with the extension/contraction of the pipe specimen 100 and measures the elastic displacement or use a pressurization sensor which is provided in one or both of the fixed flange 11 and the movable flange 13 in a portion in contact with the pipe specimen 100 to measure a pressure in accordance with the extension/contraction of the pipe specimen 100. Various known techniques may be used to sense the extension/contraction of the pipe specimen 100.

[0065] The heating unit 20 is an element which is disposed adjacent to a lower outer surface of the pipe specimen to perform a local heating operation. The heating unit 20 is disposed adjacent to one outer surface of the lower portion of the pipe specimen 100 to locally heat and is configured by a heater 21 which is formed by any one of an induction heating coil which is applied with a high frequency current to form a magnetic field to induce the heating or a direct heating coil having a heating line which is supplied with a power to heat, a heating temperature sensor 23 which measures a heating temperature of the heater 21, and a heating timer 25 which measures a heating time of the heater 21. Here, as the heater 21, the high frequency induction heating coil has been proposed, but the present invention is not limited thereto and the direct heating coil which includes a heating line which is supplied with the power to heat may be used.

[0066] The cooling unit 30 is an element which forcibly supplies the cooling water into the pipe specimen 100 to cool. The cooling unit forcibly supplies the cooling water into the pipe specimen 100 to cool and is configured by a flow detector 31 which detects a flow of the cooling water in the pipe specimen 100 held by the frame unit 10, a cooling water tank 36 which preserves a predetermined amount of cooling water, a cooling water pump 34 which is installed on the cooling water line 32 for supplying the cooling water to the pipe specimen 100 to pump the cooling water preserved in the cooling water tank 36 to forcibly convey, a flow control valve 33 which controls a flow of the cooling water supplied to the pipe specimen 100, and a water temperature sensor 39 which measures a temperature of the cooling water supplied to the pipe specimen 100.

[0067] Referring to the drawing, one end of the cooling water line 32 is connected to one side of the movable flange 13 to be piped to supply the cooling water. At this time, the movable flange 13 is a configuration in which a through hole (no reference numeral) through which the cooling water supplied through the cooling water line 32 is supplied into the pipe specimen 100 located therein is formed.

[0068] Further, the flow control valve 33 which is installed on the cooling water line 32 to control the flow of the cooling water supplied to the pipe specimen may include a manual valve which opens/closes a pipe line by means of the manual operation or a solenoid valve which opens/closes the pipe line with a control signal of a cooling water ejection control unit 50 to be described above. However, this may be performed by the known technology so that a detailed description thereof will be omitted.

[0069] The discharge unit 40 is an element which is provided at one side of the pipe specimen 100 to discharge the cooling water therein to the outside. The discharge unit 40 is configured by a discharge pipe line 41 whose one end is connected to a cooling water discharge hole 100h penetrating at a lower side of the pipe specimen 100 and a discharge valve 43 which is installed on the discharge pipe line 41 to selectively open/close the pipe line to discharge the cooling water in the pipe specimen 100 to the outside. Here, the cooling water discharge hole 100h preferably penetrates a center portion of the lower surface to naturally discharge the cooling water filled in the pipe specimen 100 and as the discharge valve 43, it is proposed to use a known solenoid valve to be supplied with the control signal of the cooling water ejection control unit 50 to be described below to open/close the pipe line.

[0070] The cooling water ejection control unit 50 is an element which applies a control signal to the heating unit 20 and the cooling unit 30 to repeatedly heat and cool the pipe specimen 100 to form a thermal fatigue cycle to generate a local thermal stress. The cooling water ejection control unit senses a heating operation of the heating unit 20 to control the heating unit 20 to perform the heating operation after discharging all the cooling water filled in the pipe specimen 100 by applying a control signal to the discharge unit 40 before the heating operation. The cooling water ejection control unit 50 is mainly configured by a discharge control unit 51, a heating control unit 53, and a heating position detecting unit.

[0071] The discharge control unit 51 is an element which applies a control signal for a discharge operation to the discharge unit 40 to eject all the cooling water in the pipe specimen 100 before starting the heating operation of the heating unit 20 in a state in which the cooling water is supplied in the pipe specimen 100.

[0072] The heating control unit 53 is an element which is applied with a cooling water discharge completion signal from the discharge control unit 51 to control a heating temperature and an on/off operation of the heating unit 20. That is, the technical feature of the present invention is to control the heating unit 20 to locally heat the pipe specimen 100 in a state in which the cooling water in the pipe specimen 100 is completely discharged and this controls is repeated to maximize the internal temperature variation in a state in which the shape of the external surface of the pipe specimen 100 is not changed. That is, the heating unit 20 is located below the pipe specimen 100 so that the difference between the heating temperature in accordance with a setting temperature and the internal surface temperature of the pipe specimen 100 at the time of cooling by the cooling water ejection control unit 50 which is configured in the pipe specimen 100 may be most significantly and precisely controlled and managed so that the reliability for the thermal stress reproducibility formed by the thermal fatigue cycle which repeats the heating and the cooling may be significantly improved. As a result, the reliability and the effectiveness of the actual crack reference test piece for skill verification of the non-destructive test with respect to a large pipe having a comparative large thickness of a diameter of 250 mm to 610 mm may be ensured.

[0073] The heating position detecting unit is an element which detects a position of a heating point of the pipe specimen which is locally heated by the heating unit.

[0074] The thermal fatigue crack generator for a large pipe according to the present invention configured as described above regularly and uniformly reproduces the heating and cooling operation with respect to the pipe specimen 100 so that as a result, the reliability for reproducing the thermal fatigue cycle may be increased. Further, when the extension/contraction is generated in the pipe specimen 100 due to the thermal fatigue, the interval between the movable flange 13 and the fixed flange 11 which configure the frame unit 10 is appropriately adjusted by the extension/contraction sensing unit 15 and the pressurization control unit 17a so that the physical damage or deformation of the pipe specimen 100 or the frame unit 10 in accordance with the extension/contraction may be prevented in advance.

[0075] In the meantime, according to the present invention, the cooling water filled in the pipe specimen 100 is completely discharged to the outside before performing the heating operation of the heating unit 20 on the pipe specimen 100 and thereafter when the heating unit 20 heats, the cooling water does not remain in the pipe specimen 100 so that the internal temperature variation may be maximized in a situation in which the shape of the external surface of the large pipe does not change.

[0076] That is, the heating unit 20 is located below the pipe specimen 100 so that the difference between the heating temperature in accordance with the setting temperature and the internal surface temperature of the pipe specimen 100 by the cooling of the pipe specimen 100 may be most significantly and precisely controlled and managed, so that the reliability for the thermal stress reproducibility formed by the thermal fatigue cycle which repeats the heating and the cooling may be significantly improved. Specifically, the reliability and the effectiveness of the actual crack reference test piece for skill verification of the non-destructive test with respect to a large pipe having a large thickness of a diameter of 250 mm to 610 mm may be ensured.

[0077] The present invention is not limited to the exemplary embodiments described herein, and may be employed by changing a part to which the exemplary embodiment is applied, and it would be appreciated by those skilled in the art that various changes and modifications might be made to these embodiments without departing from the spirit and the scope of the invention. Therefore, such changes and modifications may be considered to belong to the claims of the present invention.