JP2001108662A - Method for inspecting molten part and method for controlling energization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for inspecting molten part capable of accurately deciding whether a necessary thickness of the part having a sufficient strength to connect is formed or not in substantially overall area of the molten connected part while melting an EF joint and a PE tube. SOLUTION: The method for inspecting a molten part comprises the steps of previously detecting a time for reciprocating a ultrasonic wave at a distance from a molten boundary surface of a non-molten part and the molten part of a synthetic resin member and a surface of a synthetic resin member when the boundary surface is located at a predetermined position, checking whether an echo signal from the member is received within a predetermined time after the lapse of the reciprocating time after receiving the echo signal from the surface of the member each time of receiving the wave in a thickness direction of a synthetic resin joint or a synthetic resin tube, and deciding that the part is a predetermined thickness when signal received.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a fusion zone when a resin pipe and a resin joint are electrically fusion-bonded to each other, and a method for controlling electric current.

[0002]

2. Description of the Related Art Resin pipes such as polyethylene pipes (hereinafter abbreviated as PE pipes) are used for pipes of city gas buried underground. As a means for connecting the resin pipes, an electric fusion joint (hereinafter abbreviated as an EF joint) is frequently used. FIG. 2 shows the P connected via an EF joint.
The PE pipe 2A is fused to one end of the EF joint 1, and the PE pipe 2B is fused to the other end of the EF joint 1. The EF joint 1 includes a joint main body 101, a heating wire 12, and two connector pins 13A and 13B. The joint body 101 is made of polyethylene (hereinafter, referred to as PE) and is formed in a substantially cylindrical shape, and the heating wire 12 is embedded near the inner peripheral surface. Each of the two connector pins 13 </ b> A and 13 </ b> B has a lower portion fitted into both ends of the joint main body 101 and connected to each end of the heating wire 12. At both ends of the joint body 101, truncated conical protrusions 16 protruding from the middle part
A and 16B are formed and serve as a guide when the connector pins are inserted.

A method of connecting the PE pipes 2A and 2B to the EF joint 1 will be described. First, PE pipe 2A and PE
The pipe 2 </ b> B is inserted from each end of the EF joint 1 into the inner diameter part until it comes into contact with the projection 14. Next, connectors (not shown) are inserted into the connector pins 13 at both ends of the EF joint 1, respectively.
When the heating wire 12 is energized through this connector, the heating wire 12 is heated, and the inner diameter portion of the EF joint 1 and the outer diameter portion of the PE pipe 2 are fused and integrated. The part is cooled to complete the fusion.

The following method has been proposed as a method for inspecting the fused portion between the EF joint and the PE pipe fused as described above. For example, JP-A-1-301231
No. (Conventional Example 1), a concave portion for fitting a thermocouple is formed near the connector pin on the outer peripheral portion of the EF joint, and the thermocouple and the connector fitted to the connector pin are integrally held. Using a fusion plug, the connector is fitted to the connector pin, a thermocouple is fitted in the recess, and the temperature of the EF joint is continuously measured by the thermocouple while energizing, and the temperature reaches a preset temperature. A method is disclosed in which the energization is stopped when the temperature rises to a certain level, and when the temperature falls to a temperature at which the resin solidifies, it is determined that the fusion is completed. In this method, since the temperature inside the EF joint is directly measured, the energizing time is set in consideration of factors that affect the energizing time, such as the surrounding initial temperature, the temperature of the EF joint surface, and the electric resistance error of the heating wire. There is an advantage that there is no need.

Japanese Patent Application Laid-Open No. 10-132791 (Conventional Example 2) discloses that an EF joint and a portion near a heater of a PE pipe are fused to form a fusion portion, and an ultrasonic probe is connected to one end of the EF joint. While moving in a spiral form from the other end to the other end, ultrasonic waves are incident in the thickness direction of the EF joint or PE pipe,
Among the multiple echoes obtained, the fusion part and the EF joint or P
A gate that allows only the echo from the interface with the E-tube to pass is set, and for the echo that passes through the gate, the time from when the ultrasonic wave is incident until the echo is detected is determined. A method for calculating the depth of a part and inspecting a fusion part is disclosed.

[0006]

However, in the conventional example 1, it is necessary to provide a thermocouple insertion hole in the EF joint.
Although the temperature inside the F-joint is measured, the state of fusion between the joint and the PE pipe is estimated based on the temperature only near the insertion hole. there were. Further, in Conventional Example 2, after heating the heater for a time such that the thickness of the fusion zone becomes a predetermined value,
It detects the echo from the interface and calculates the depth of the interface. However, ultrasonic waves have the property that the acoustic impedance changes and the echo is generated from the boundary surface when there is a density difference between the transmitting materials. Since there is no difference in density with the surrounding non-melted PE member, there is a problem that echo is hardly generated from the interface and highly reliable detection cannot be performed.
Furthermore, if the tip of the ultrasonic probe is displaced in the radial direction from a predetermined position by moving the scanning device, the displacement becomes an error in the echo detection time, and a correct interface depth cannot be obtained, and the displacement is large. In such a case, there occurs a problem that the target echo does not pass through the gate. In addition, in order to obtain a predetermined melted part thickness in consideration of errors in the surrounding initial temperature and electric resistance of the heating wire, it is necessary to set a longer energization time, which increases power consumption. .

SUMMARY OF THE INVENTION It is a first object of the present invention to provide an inspection method capable of judging the quality of a resin joint and a resin pipe over almost the entire area of a molten portion thereof with high accuracy. In addition, the present invention provides an inspection method capable of detecting whether or not a molten portion is well formed in a process of melting a resin joint and a resin pipe, and removing a defect related to melting at an early stage. This is the second purpose. Further, in the present invention, in the process of melting the resin joint and the resin pipe, while checking whether or not a fused portion is formed well, electricity is supplied until a sufficient fused portion is formed for fusion bonding. A third object is to provide a control method for performing the control.

[0008]

According to a first aspect of the present invention, there is provided a method of electrically heating a resin pipe and a resin joint and inspecting a molten portion of a resin member formed when the two are fused. When the melting boundary between the non-melted portion and the melting portion of the resin member is at a predetermined position, a reference reciprocating time for the ultrasonic wave to reciprocate the distance from the surface of the resin member to the melting boundary is set, and the surface of the resin member is set. Repeat the operation of injecting ultrasonic waves from inside toward the inside,
For each operation, it is checked whether or not an echo signal from the inside of the member is received within a predetermined time after the lapse of the reference reciprocating time from the time when the echo signal from the resin member surface is received. The thickness of the fusion zone is determined to be normal based on the reception. The predetermined position of the fusion boundary surface can be any position during the growth of the fusion zone, but is preferably a position where the resin pipe and the resin joint are fusion-bonded with sufficient strength.

According to a second aspect of the present invention, there is provided a method of electrically heating a resin pipe and a resin joint and inspecting a molten portion of the resin member formed when the two are fused. When the fusion boundary between the melting part and the fusion part is at a predetermined position determined by the elapsed time as the reference after the start of energization, the reference reciprocation time for the ultrasonic wave to reciprocate the distance from the surface of the resin member to the fusion boundary is set. The operation of injecting ultrasonic waves from the surface of the resin member toward the inside is repeated, and for each operation, the member is set within a predetermined time after a lapse of a reference reciprocating time from when an echo signal from the resin member surface is received. Check whether an echo signal from inside is received, compare the elapsed time from the start of energization to the reception of the echo signal with the reference elapsed time, and determine whether the difference between the two is within the allowable range To determine the quality of the fusion zone. . It is desirable to set the interval as short as possible after the time at which the melting boundary surface becomes substantially planar, as the reference elapsed time.

According to a third aspect of the present invention, there is provided an energization control method for electrically heating a resin pipe and a resin joint and fusing the two together, wherein a fusion boundary between a non-melted portion and a molten portion of the resin member is provided. When the surface is at a predetermined position determined according to the elapsed time after the start of energization, the reference reciprocating time for the ultrasonic wave to reciprocate the distance from the surface of the resin member to the melting boundary surface was set in accordance with the growth of the molten portion. Along with setting the elapsed reciprocating time for each of the plurality of reference elapsed times, when the fusion boundary surface between the non-melted portion and the molten portion of the resin member is at the fusion position where fusion bonding is good, from the surface of the resin member The reference reciprocating time during which the ultrasonic wave reciprocates the distance to the fusion boundary surface is set as the fusion reciprocating time, and the operation of irradiating the ultrasonic wave from the surface of the resin member toward the inside is repeated. From when the echo signal from the surface was received Within a predetermined time after the elapsed round-trip time, it is checked whether or not an echo signal from the inside of the member is received for each reference elapsed time, and the elapsed time from the start of energization to the reception of the echo signal is defined as the reference elapsed time. In comparison, the control for adjusting the energization state based on the difference between the two, and for each operation, within a predetermined time after the elapse of approximately the fusion reciprocating time from when the echo signal from the resin member surface is received, It is characterized in that whether or not an echo signal from the inside of the member is received is checked, and control is performed to stop the energization when the echo signal is received. The adjustment of the energization state may include determining whether the difference between the two is within an allowable range, continuing the energization when the difference is within the allowable range, and stopping the energization when the difference is outside the allowable range. Alternatively, the power may be adjusted and supplied according to the magnitude of the difference between the two.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an apparatus for carrying out the present invention, and the same parts as those in FIG. 2 are denoted by the same reference numerals. As shown in FIG. 1, the control device 21
A power source 11 for supplying electric power to the joint, a determination unit 10 for determining the quality of the fusion zone based on signals from probes (not shown) arranged in the probe holder 3, and a determination unit And a display unit 19 for displaying the molten state.

The probe holder 3 is a member having the same curvature as the outer peripheral surface of the EF joint 1 and extending along the axial direction of the EF joint 1 and having a length corresponding to the fusion zone. The EF joint 1 is mounted on the outer peripheral surface of the EF joint 1 so as to be rotatable in a direction indicated by an arrow in the figure by manual operation or mechanical means (not shown). In the probe holder 3, flood type, jet water type or contact type probes are attached in a line at a predetermined pitch along the longitudinal direction thereof, and each probe is instructed by the determination unit 10. Are sequentially scanned at a predetermined timing, and a predetermined frequency (for example, approximately 5M
Hz) is emitted almost vertically toward the center of the EF joint 1, and an echo of a reflected wave is received. By appropriately rotating the probe holder 3 in the circumferential direction, it is possible to know the molten state of the entire joint of the EF joint 1 and the PE pipes 2A and 2B. The judging unit 10 outputs a fusion end signal to the control unit 18 based on the fusion state when the fusion is abnormal or when the fusion is completed normally. The control unit 18 outputs a signal for stopping the power supply to the EF joint 1 to the power supply 11 and outputs a signal for displaying the melting state result on the display unit 19.

The method for inspecting the fusion zone with the above configuration is as follows. A connector (not shown) provided at the end of the connection conductor 20 connected to the power supply 11 is inserted into a connector pin of the EF joint 1, and ultrasonic waves are incident from the outer periphery of the EF joint 1 while energizing the heating wire. When the energization is continued, the EF joint near the heating wire and the PE member of the PE pipe are heated by Joule heat, and the melting starts when the temperature exceeds the melting point of PE (about 130 ° C.).

[0014] When energization of the heating wire is continued, the molten portion grows. FIG. 3 shows E after the heating wire (shown by a black circle) is energized.
It is an example which showed typically the result of having simulated the fusion | melting state of the F joint and the PE pipe (the fusion | melting part whose oblique line changed from solid phase to liquid phase). In the figure, the line when the scale on the vertical axis is 0 indicates the boundary surface between the inner peripheral surface of the EF joint and the outer peripheral surface of the PE pipe before energization, and the positive scale indicates the position from the boundary surface to the outer peripheral side of the EF joint. And the negative scale indicates the position from the boundary surface toward the center of the PE tube. In FIG. 3, (a),
(B), (c), (d) and (e) are 20 minutes after the start of energization.
Sec, 40 s, 60 s, 80 s, and 100 s after the lapse of 100 seconds.
It can be seen that it expands over the outer surface of the tube.

When the energization is continued as described above, the PE temperature of the molten portion becomes about 200 ° C., and the density at this time becomes 0.7%.
5 g / mm ³ and a density at 20 ° C. of 0.95 g / mm 3
^It has dropped significantly from ³ . As described above, when the density of the medium through which the ultrasonic wave propagates changes, the acoustic impedance that propagates greatly changes. That is, the ultrasonic wave is largely reflected at the boundary surface between the melted portion and the non-melted portion and an echo is generated, so that the boundary surface can be easily detected. As the above-mentioned echoes, as shown in FIG. 4, echoes A and PE pipes 2 from the fusion boundary 5a between the EF joint 1 and the fusion zone 5 are formed.
Besides the echo D from the fusion interface 5b between
An echo S from the surface of the EF joint 1, an echo C from the heating wire 12, an echo B from a joint surface between the inner surface of the EF joint 1 and the outer surface of the PE tube 2, and an echo E from the inner surface of the PE tube are obtained.

Incidentally, the thickness of the fusion zone 5 when the EF joint 1 and the PE pipe 2 are fused well is known. For example, as shown in FIG.
After 0 seconds, the case where the melting boundary 5a exceeds the line of about 4 on the scale of the vertical axis and the melting boundary 5b exceeds the line of about -2. The melting portion 5 has a thickness of approximately the same size in the vertical direction with the heating wire 12 as a center.
For example, it can also be determined from the distance from the EF joint surface to the fusion boundary 5a and the distance to the fusion boundary 5b. Further, since there is almost no variation in the dimensions and quality of the EF joint and the PE pipe, the thickness of the fusion zone is replaced with the fusion boundary surface 5a.
Or the position of the fusion boundary 5b can be used as a reference for evaluation.

Next, in order to check whether or not the thickness of the melted portion has been sufficiently fused, whether or not the distance from the surface of the EF joint to the melt boundary 5a has reached a predetermined reference value is determined. The method will be described with reference to FIG. The thickness of the EF joint is determined for each product, and the distance from the EF joint surface when the molten boundary surface 5a is at a predetermined position can be obtained. Further, the ultrasonic wave propagation speed of the PE material in the solid state is also constant. Therefore, the time for the ultrasonic wave to reciprocate between the surface of the EF joint and the fusion boundary surface 5a is a constant value. When the probe is in close contact with the surface of the EF joint, the ultrasonic wave is emitted and the signal of the echo A is received. It can be obtained as the reference round trip time up to. Therefore, a gate having a predetermined width is provided so as to be opened approximately after the reference reciprocating time after the ultrasonic wave is emitted to the determination unit 10 in FIG. 2, and it is monitored that a signal passes through this gate. It can be determined that the distance from the EF joint surface to the fusion boundary 5a has reached the reference value.

However, if the probe position is shifted in the radial direction, the time from injection to reception is also shifted. Even if the melting boundary 5a is located at a predetermined position in the gate set as described above, the time is not changed. It cannot be determined. Therefore, paying attention to the echo S always obtained from the surface regardless of the probe position, the echo S
A gate is set based on the time of reception of. That is, the gate receives the surface echo S for a predetermined time t after T seconds.
Set to open for seconds. T is the time when the ultrasonic wave reciprocates between the surface and the molten boundary surface 5a when the distance between the surface of the EF joint and the molten boundary surface 5a reaches the reference value L, and the ultrasonic wave propagation velocity of PE in the solid state. Is V, it can be represented by the following equation. Note that t is determined from the allowable range of the position of the fusion boundary surface 5a and the like. T = 2L / V

FIG. 5 schematically shows the relationship between the energization time, the state of echo generation in the molten state, and the gate shown in FIG. 3, and the horizontal axis represents the time from ultrasonic emission to reception of the echo. Is represented. FIG. 5A shows the relationship between each echo and the gate of the ultrasonic wave emitted 60 seconds after the start of energization. The melted portion has not yet grown sufficiently, and the echo A is not reflected after the gate is closed. It is the timing as received. FIG. 5B shows a state 80 seconds after the start of energization. The melted portion has grown considerably, and the echo A is shown in FIG.
It occurs earlier than at the time, but has not yet passed the gate. FIG. 5C shows the state 100 seconds after the start of energization. The melted portion grows to a predetermined size, and the signal of echo A passes through the gate. Echo A is Echo S
And the signal that first passes through the gate and can be reliably detected. The time required for the signal to pass through the gate in this case depends on the growth rate of the melted portion. It becomes longer when the ambient temperature or the member temperature is low, and becomes shorter when the temperature is high, but it can be reliably detected when the molten portion has a predetermined size. In addition, the required amount of electric energy according to the target condition is supplied, and no extra electric energy is supplied.

The reference value L of the distance between the surface of the EF joint and the fusion boundary surface 5a is a value corresponding to the size of the final fusion portion necessary for fusion, and determines whether the fusion portion has a predetermined size. Can be set to a value corresponding to the size of the melted portion during energization, and the quality of the melted state during energization can also be checked. In this case, the EF at the reference elapsed time Ji (for example, 40, 60, and 80 seconds) set for the halfway check after the energization is started.
A gate Ti for the check time Ji is set for the distance Li between the joint surface and the fusion boundary 5a in the same manner as described above. The time when the signal passes through the gate Ti from the start of energization is monitored, and the determination can be made based on the relationship between the actual time j up to this passage and the reference elapsed time Ji. For example, the time when the echo of the gate T ₆₀ that is configured for checking the time 60 seconds has passed is 61 seconds from the energization, if it is implemented in the allowable time, for example 58 seconds to 62 seconds, melting normally line You can judge that it has been done. On the other hand, the transit time of the echo is 56
If it is seconds, it is shorter than the allowable time, and it is considered that an overcurrent is flowing. Conversely, if the echo transit time is longer than 62 seconds, the supply current is small, and the cause is that the current is supplied. It is conceivable that the connection conductor is about to be cut, and the welding operation may be interrupted immediately and the conductor may be replaced. The permissible time may be set in consideration of factors such as a change in environmental conditions such as an external temperature and a resin material, and an appropriate value may be selected for each reference elapsed time.

Although the method for inspecting the melted portion has been described above, the present invention can also be applied to an energization control method for melting the resin. Normally, a constant power predetermined for each product is supplied from the start to the stop of energization. However, if there is a defect in the control device or the object to be melted, a normal molten state cannot be maintained during energization. In such a case, it is important to stop the work promptly, and therefore, for the plurality of reference elapsed times appropriately determined with the lapse of time described above, the actual position of the fusion boundary surface expected at this time is actually determined. It is effective to detect and compare the required energization time, determine whether or not energization is to be continued based on the difference between the two, and use control to display that fact on the display unit. In this case, the power amount may be adjusted according to the magnitude of the difference, instead of simply determining whether the energization is ON or OFF. Since the fact that the fusion zone has reached the target size can be determined by the method described above, the energization may be stopped based on this information. In addition, the reference elapsed time when the fusion zone becomes the target size can be set,
When the target size is reached within the allowable time, a signal indicating normal melting can be output to the display unit to be displayed, and the reliability of the melting can be improved.

In the above embodiment, the case where attention is paid to echo A has been described.
And may be performed using both echo A and echo D. Alternatively, the measurement may be performed using the echo E obtained through the fusion part. In this case, by adding the EF joint thickness, the PE pipe thickness, and the ultrasonic transmission speed data of the fusion zone, a gate when the fusion zone thickness reaches a predetermined dimension can be calculated. Since the reflection part of the echo D is on the opposite side of the transmission / reception position of the ultrasonic wave from the heating wire and in the vicinity of the heating wire, the ultrasonic wave is scattered and attenuated by the heating wire, and the level of the echo D is low. When setting a gate that can pass only the echo D, it is preferable to set a larger gain than when setting a gate that can pass only the echo A. Also, the probe holder 3
Are inserted into the PE tubes 2A and 2B, and the PE tubes 2A and 2B
The welded portion can be inspected from the inner peripheral side of the above. Echo D
This is more preferable when using. Also, PE
It goes without saying that the present invention is not limited to the case where a pipe and a joint member made of PE are used, but is also applicable to a case where another synthetic resin tube and a joint member are fusion-spliced.

[0023]

According to the present invention, it is possible to determine whether or not the thickness of the melted portion is the predetermined thickness based on the presence or absence of a signal passing through a gate which is set in advance according to the product to be inspected. . For this reason, even when inspecting a wide range by electrically scanning or mechanically moving a plurality of probes, it is possible to make almost instantaneous judgments, and to inspect the entire fused area with high reliability. Can be. In addition, since it is possible to know the state of the molten portion growing stage during energization, it is possible to detect a defect relating to melting at an early stage. further,
Since a fused portion capable of guaranteeing the fusion strength is reliably formed in accordance with a change in the environment (ambient temperature), it is not necessary to supply an excessive amount of electric power, thereby saving energy. Furthermore, when the environment (ambient temperature) changes greatly,
In the case where there is an abnormality in the control device, the power is cut off and control is performed so as to display this fact.
It is efficient because it can take countermeasures at an early stage.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus for carrying out the present invention.

FIG. 2 is a sectional view showing a connection portion between an EF joint and a PE pipe.

FIG. 3 is a diagram schematically showing a state of formation of a molten portion after a predetermined time has elapsed from the start of energization.
(B) after 40 seconds, (c) after 60 seconds, (d) after 80 seconds,
(E) After 100 seconds

FIG. 4 is a view showing echoes from a fusion part of an EF joint and a PE pipe.

FIGS. 5A and 5B are diagrams showing changes in echoes with the passage of energization time. FIG. 5A shows a state after 60 seconds, FIG. 5B shows a state after 80 seconds, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 EF joint 2 PE pipe 3 Probe holder 10 Judgment part 11 Power supply 13 Connector 18 Control part 19 Display part 20 Connection lead 21 Control device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Kawai 2nd Daifuku, Kuwana-shi, Mie F-term in Kuwana Plant of Hitachi Metals Co., Ltd. 2G047 AA08 AB01 BC02 EA10 GG30 GG33 3H019 GA03 4F211 AD05 AD12 AG08 AK09 AP20 AQ02 AR16 TA01 TC11 TD07 TJ30 TN08 TN31 TW39

Claims (3)

[Claims] 1. A method of electrically heating a resin pipe and a resin joint and inspecting a molten portion of a resin member formed when the two are fused together, the method comprising the steps of: When the molten boundary surface is at a predetermined position, a reference reciprocating time for the ultrasonic wave to reciprocate the distance from the surface of the resin member to the molten boundary surface is set, and the ultrasonic wave is incident from the surface of the resin member toward the inside. The operation is repeated, and for each operation, it is checked whether or not an echo signal from the inside of the member is received within a predetermined time after a lapse of the reference reciprocating time from the time when the echo signal from the resin member surface is received. And determining that the thickness of the fusion zone is normal based on the reception of the echo signal. 2. A method of electrically heating a resin pipe and a resin joint and inspecting a molten portion of a resin member formed when the two are fused together, the method comprising the steps of: When the molten boundary surface is at a predetermined position determined by the elapsed time as a reference after the start of energization,
Set the reference reciprocating time for the ultrasonic wave to reciprocate the distance from the surface of the resin member to the melting boundary surface, repeat the operation of injecting the ultrasonic wave from the surface of the resin member toward the inside, and repeat the operation for each operation. Within a predetermined time after the lapse of the reference reciprocating time from the time when the echo signal is received from the member, it is checked whether or not the echo signal from the inside of the member is received. A method for inspecting a fusion zone, comprising: comparing an elapsed time with a reference elapsed time to determine whether a difference between the two is within an allowable range and determining a quality of the fusion zone. 3. An energization control method for electrically heating a resin pipe and a resin joint and fusing the resin tube and the resin joint together, the method comprising the steps of: When the ultrasonic wave reciprocates the distance from the surface of the resin member to the melting boundary surface at a predetermined position determined according to the elapsed time, the reference reciprocating time is set for each of a plurality of reference elapsed times set in accordance with the growth of the molten portion. And the distance from the surface of the resin member to the fusion boundary when the fusion boundary between the non-molten portion and the fusion portion of the resin member is at the fusion position where fusion bonding is good. Is set as the fusion reciprocating time, and the operation of applying ultrasonic waves from the surface of the resin member toward the inside is repeated, and for each operation, an echo signal from the resin member surface is generated. After a lapsed round trip time from the time of reception Within a predetermined time, whether or not an echo signal from the inside of the member is received is checked for each reference elapsed time, and the elapsed time from the start of energization until the echo signal is received is compared with the reference elapsed time. Control for adjusting the energization state based on the difference between the signals, and for each operation, within a predetermined time after the reciprocation time of the fusion welding has elapsed since the reception of the echo signal from the surface of the resin member, Controlling whether a signal is received or not and stopping the power supply when the echo signal is received.