Patent Publication Number: US-2022229020-A1

Title: Method and device for examining clinched portion of tubular body

Description:
TECHNICAL FIELD 
     The present invention relates to a method and device for examining a clinched portion of a tubular body. 
     BACKGROUND ART 
     A clinched body formed by clinching a metallic tubular body with another member (“clinch-target member”) is used in the parts of automobiles or other products. Patent Literature 1 discloses a method for clinching a tubular body with a clinch-target member by passing the tubular body through a hole formed in the clinch-target member and increasing the diameter of the tubular body to press the tubular body onto the clinch-target member. According to Patent Literature 1, the task of increasing the diameter of the tubular body is achieved by a method including the steps of inserting a coil into the tubular body so that the coil is located at the position of the hole in the clinch-target member, and instantaneously passing an extremely large amount of electric current through the coil. A magnetic field is thereby generated from the coil. The magnetic field induces eddy current in the tubular body. This generates a Lorentz force which acts between the coil and the tubular body, causing the increase in the diameter of the tubular body. This method can be suitably used for a tubular body made of a material having a high level of electric conductivity, such as aluminum. There are also mechanical techniques which are less productive than the previously described technique yet can produce a similar state of clinching. For example, an expansion-contraction mechanism may be inserted into the tubular body to increase its diameter. A rubber part or similar elastic body may be provided within the tubular body to increase its diameter by elastic deformation. An incompressible fluid may be introduced into the tubular body to apply high pressure. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2017-131959 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     After such a clinching process has been completed, whether or not the tubular body and the clinch-target member are sufficiently clinched should be examined. One method for such an examination is an X-ray computed tomographic (CT) examination. However, an X-ray CT examination which is performed with a sufficiently large field of view applicable to such an examination of the clinched body cannot detect a gap that is narrower than 1 μm. Even such a narrow gap can cause problems with the parts of automobiles or other products. 
     The problem to be solved by the present invention is to provide a method and device by which imperfect clinching due to a micro-sized gap between the tubular body and the clinch-target member can be assuredly detected. 
     Solution to Problem 
     A method for examining a clinched portion of a tubular body according to the present invention developed for solving the previously describe problem includes the steps of: giving an elastic vibration (which is hereinafter simply called the “vibration”) to a clinched body formed by clinching a tubular body with a clinch-target member; and acquiring, for each of a plurality of view areas which differ from each other in the position in the circumferential direction of the tubular body, a vibration distribution optically and simultaneously measured within the view area including a clinched portion of the tubular body and the clinch-target member, to determine whether or not the state of clinching is satisfactory over the entire clinched portion. 
     A device for examining a clinched portion of a tubular body according to the present invention includes: 
     a vibration source configured to give a vibration to a clinched body formed by clinching a tubular body with a clinch-target member; and 
     a vibration distribution acquirer configured to acquire, for each of a plurality of view areas which differ from each other in the position in the circumferential direction of the tubular body, a vibration distribution optically and simultaneously measured within the view area including a clinched portion of the tubular body and the clinch-target member. 
     Advantageous Effects of Invention 
     According to the present invention, imperfect clinching due to a micro-sized gap between a tubular body and a clinch-target member can be assuredly detected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram showing one embodiment of a device for examining a clinched portion of a tubular body according to the present invention. 
         FIG. 2  is a sectional view showing a method for producing a clinched body to be examined in the examination device and examination method according to the present embodiment. 
         FIG. 3  is a portion of the flowchart showing an operation of the examination device according to the present embodiment and the examination method according to the present embodiment, the portion showing the steps from the beginning of the entire operation through a vibration measurement for a plurality of view areas. 
         FIG. 4  is a portion of the flowchart showing an operation of the examination device according to the present embodiment and the examination method according to the present embodiment, the portion showing the steps from the completion of the vibration measurement to the completion of the entire operation. 
         FIG. 5  is a plan view showing a clinched body formed by clinching a tubular body with a clinch-target member as well as a view area, as viewed from a speckle-shearing interferometer. 
         FIG. 6  is a diagram for explaining a method for determining the state of vibration at each point within a view area during an operation of the examination device according to the present embodiment. 
         FIG. 7  is a portion of the flowchart showing a variation of the operation of the examination device and the examination method, the portion showing the steps from the beginning of the entire operation through a vibration measurement for a plurality of view areas. 
         FIG. 8  is a portion of the flowchart showing the variation of the operation of the examination device and the examination method, the portion showing the steps from the completion of the vibration measurement to the completion of the entire operation. 
         FIG. 9  is an image showing a result obtained by carrying out an examination method according to the variation using an examination device according to the present embodiment, the image showing the vibration distribution determined by observing the clinched body from the upper side. 
         FIG. 10  is an image showing a result obtained by carrying out an examination method according to the variation using an examination device according to the present embodiment, the image showing the vibration distribution determined by observing the clinched body from the left side. 
         FIG. 11  is an image showing a result obtained by carrying out an examination method according to the variation using an examination device according to the present embodiment, the image showing the vibration distribution determined by observing the clinched body from the bottom side. 
         FIG. 12  is an image showing a result obtained by carrying out an examination method according to the variation using an examination device according to the present embodiment, the image showing the vibration distribution determined by observing the clinched body from the right side. 
         FIG. 13  is a model diagram showing a result obtained by carrying out an examination method according to the variation using an examination device according to the present embodiment, the image showing a section perpendicular to the longitudinal direction of the tubular body. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the method and device for examining a clinched portion of a tubular body according to the present invention is hereinafter described using  FIGS. 1-13 . 
     (1) Configuration of Device for Examining Clinched Portion of Tubular Body According to Present Embodiment 
       FIG. 1  shows the device  10  for examining a clinched portion of a tubular body according to the present embodiment (which is hereinafter simply called the “examination device”). The examination device  10  includes a vibration source  11 , vibration distribution acquirer  12  and clinching-state determiner  13 . 
     The examination device  10  is configured to examine a clinched body  90  formed by clinching a tubular body  91  with a clinch-target member  92 , to determine whether or not the tubular body  91  and the clinch-target member  92  are satisfactorily clinched together. Details of the clinched body  90  are hereinafter described using  FIGS. 1 and 2 . The clinched body  90  is created by the method shown in  FIG. 2 . The tubular body  911  before being clinched with the clinch-target member  92  is a metallic tube which is uniform in both inner and outer diameters. The clinch-target member  92  is a member having a hole  921  whose diameter is larger than the tubular body  911 . In order to produce the clinched body  90 , the tubular body  911  is initially inserted into the hole  921 . A coil  96  is subsequently arranged within the tubular body  911  at a position corresponding to the inside of the hole, with the axis of the coil  96  being parallel to that of the tubular body  911 . In this state, a large amount of pulse current is instantaneously passed through the coil  96 . A magnetic field is thereby generated from the coil  96 , and this magnetic field induces eddy current in the tubular body  911 . The eddy current generates a Lorentz force acting between the coil  96  and the tubular body  911 . This force increases the diameter of the tubular body  911 . The tubular body  911  having the increased diameter is pressed onto the clinch-target member  92 , whereby the two parts are clinched together ( FIG. 1 ). The method for increasing the diameter of the tubular body  911  is not limited to the one described in this paragraph. Other methods are also applicable, such as the previously mentioned techniques which use an expansion-contraction mechanism, elastic body, or incompressible fluid. 
     Referring once more to  FIG. 1 , details of each component of the examination device  10  will be hereinafter described. 
     The vibration source  11  includes a signal generator  111  and a vibrator  112 . The signal generator  111  is electrically connected to the vibrator  112  by a cable to generate an AC electric signal and send it to the vibrator  112 . When in use, the vibrator  112  is held in contact with the clinched body  90 , receives the AC electric signal from the signal generator  111 , converts the signal into mechanical vibrations, and gives the mechanical vibrations to the clinched body  90 . The contact position of the vibrator  112  may be located on either the tubular body  91  or the clinch-target member  92  of the clinched body  90 , provided that the contact position is outside the view area  95  (which will be described later). There is no specific limitation on the shape of the vibrator  112 , although it is preferable to provide the vibrator  112  with a pointing tip so that its contact area becomes small and allows for an easy contact with the curved surface of the tubular body  91 . 
     The vibration distribution acquirer  12  includes a laser light source  121 , illumination light lens  122 , speckle-shearing interferometer  123 , rotary mechanism  124  and vibration distribution determiner  125 . 
     The laser light source  121  is electrically connected to the signal generator  111  by a cable (which is different from the one that connects the signal generator  111  and the vibrator  112 ), and emits pulsed laser light at a timing when the AC electric signal is at a predetermined phase. The illumination light lens  122 , which is located between the laser light source  121  and the clinched body  90 , consists of a concave lens. The illumination light lens  122  has the function of increasing the diameter of the pulsed laser light from the laser light source  121  so as to cast the pulsed laser light onto an area including a section of the clinched portion  93  of the clinched body  90 . The entire area to be illuminated with the pulsed laser light, or a portion of that area including a section of the clinched portion  93 , is defined as the view area  95 . 
     The speckle-shearing interferometer  123  includes a beam splitter  1231 , first reflector  1232 , second reflector  1233 , phase shifter  1234 , converging lens  1235  and image sensor  1236 . The beam splitter  1231  is a half mirror located at an incident position of the pulsed laser light reflected on the surface of the clinched body  90  at each point within the view area  95 . The first reflector  1232  is located on the optical path of the pulsed laser light reflected by the beam splitter  1231 , while the second reflector  1233  is located on the optical path of the pulsed laser light passing through the beam splitter  1231 . The phase shifter  1234 , which is located between the beam splitter  1231  and the first reflector  1232 , is configured to change (shift) the phase of the pulsed laser light passing through the phase shifter  1234 . The image sensor  1236  is located on the optical path of the pulsed laser light passing through the beam splitter  1231  after being successively reflected by the beam splitter  1231  and the first reflector  1232 , as well as on the optical path of the pulsed laser light reflected by the beam splitter  1231  after being reflected by the second reflector  1233  after passing through the beam splitter  1231 . The converging lens  1235  is located between the beam splitter  1231  and the image sensor  1236 . 
     The first reflector  1232  is arranged so that its reflection surface is at an angle of 45 degrees to the reflection surface of the beam splitter  1231 . By comparison, the second reflector  1233  is arranged so that its reflection surface is at an angle slightly deviated from the angle of 45 degrees to the reflection surface of the beam splitter  1231 . The image sensor  1236  has a large number of detection elements. The components of light originating from a large number of points on the surface of the clinched body  90  within the view area  95  travel through the first reflector  1232  and the phase shifter  1234 , and fall onto the image sensor  1236 , to be respectively detected by different detection elements. Each detection element produces an electric signal corresponding to the intensity of the detected component of light. 
     The rotary mechanism  124  is a device configured to rotate the tubular body  91  of the clinched body  90  about its axis. It includes a holding part which holds one end of the tubular body  91  and a motor (not shown) configured to rotate the holding part. The rotary mechanism  124  can be moved so that the clinched portion  93  of the clinched body  90  held with the holding part is located within the view area  95 . It is also possible to configure the device so that an operator can manually rotate the tubular body  91  without using the rotary mechanism  124 . 
     The vibration distribution determiner  125  is configured to determine the distribution of the vibration of (the tubular body  90  within) the view area  95 , as will be described later, based on the electric signals generated by the detection elements of the image sensor  1236 . 
     The clinching-state determiner  13  is configured to determine, as will be described later, whether or not the state of clinching at the clinched portion  93  is satisfactory based on a vibration distribution within the view area  95  determined by the vibration distribution determiner  125 , i.e. acquired by the vibration distribution acquirer  12 . 
     The vibration distribution determiner  125  and the clinching-state determiner  13  are embodied by a CPU and other hardware devices as well as a software system configured to determine the vibration distribution within the view area  95  and determine whether or not the state of clinching at the clinched portion  93  is satisfactory. 
     The examination device  10  according to the present embodiment additionally includes a display unit  14 , which is a display for showing the result of the determination by the clinching-state determiner  13  and other pieces of information, an input unit (not shown) for allowing an operator to enter information into the examination device  10 , as well as a control unit (not shown) configured to control the signal generator  111 , speckle-shearing interferometer  123  and rotary mechanism  124 . 
     (2) Operation of Examination Device According to Present Embodiment, and Method for Examining Clinched Portion of Tubular Body According to Present Embodiment 
     An operation of the examination device  10  according to the present embodiment is hereinafter described using  FIGS. 3-6 . The method for examining a clinched portion of a tubular body according to the present embodiment is carried out by operating this examination device  10 . The sequence of the operations of the examination device  10  is shown in the flowchart of  FIGS. 3 and 4 . The descriptions below will follow this flowchart. 
     Initially, one end of the clinched body  90  is held with the holding portion of the rotary mechanism  124 . This rotary mechanism  124  is subsequently moved so that the clinched portion  93  is located within the view area  95 . Thus, the clinched body  90  is set in the examination device  10  (Step  201 ). 
     The view area  95  is an area which appears to be a plane when viewed from the speckle-shearing interferometer  123  ( FIG. 5 ). On the other hand, the clinched portion  93  is a tubular portion surrounding the tubular body  91 . Therefore, one view area  95  includes only a portion of the clinched portion  93 . Therefore, in the examination device and examination method according to the present embodiment, the measurement for the entire clinched portion  93  is performed by repeating, a max  times (where a max  is an integer equal to or greater than two), the steps of performing the vibration measurement at one view area  95  and subsequently rotating the clinched body  90  with the rotary mechanism  124  by 360/a max  degrees to perform the measurement at another view area  95 . Serial numbers 1 to a max  are assigned to the a max  view areas  95  at each of which the vibration measurement should be performed (this serial number is hereinafter called the “view-area number a”). In the present embodiment, a max  is 4. The angle by which the clinched body  90  is rotated each time is 90 degrees in the present embodiment. 
     The view-area number a is given an initial value of “1” (Step  202 ), the measurement for the view area  95  having the view-area number 1 is performed by the following operations of Steps  203  through  208 . 
     In one view area, the measurement is performed m max  times at different phases of the vibration of the vibrator  112  (where m max  is an integer equal to or greater than three). The phase of the vibration of the vibrator  112  is the phase of the AC electric signal sent from the signal generator  111  to the vibrator  112 , which corresponds to the phase of the vibration induced in the clinched body  90  at the point of contact of the vibrator  112 . In the following description, each measurement is referred to as the “kth measurement” using a numerical value k (which is a natural number within a range from 1 to m max ). The following description deals with the case of m max =3 as one example. 
     First, the initial value of k is set at  1  (Step  203 ), and the AC electric signal is sent from the signal generator  111  to the vibrator  112  to initiate the operation of giving vibrations from the vibrator  112  to the clinched body  90  (Step  204 ). 
     Next, the signal generator  111  sends a pulsed signal to the laser light source  121  at every timing at which the phase of the vibration of the vibrator  112  is expressed by [ϕ 0 +2π(k−1)/m max ], where ϕ 0  is a predetermined initial value (e.g. ϕ 0 =0). Since k=1 at this stage, the phase of the vibration of the vibrator  112  is ϕ 0  when the pulsed signal is sent. The laser light source  121  repeatedly emits the pulsed laser light as the illumination light every time it receives the pulse signal. This illumination light is expanded by the illumination light lens  122  in the diametrical direction before being cast onto the surface of the clinched body  90  including the view area  95  (Step  205 ). 
     The illumination light is reflected on the surface of the clinched body  90  and falls onto the beam splitter  1231  in the speckle-shearing interferometer  123 . A portion of the illumination light is reflected by the beam splitter  1231  and passes through the phase shifter  1234 . After being reflected by the first reflector  1232 , the light once more passes through the phase shifter  1234 . A portion of this light passes through the beam splitter  1231  and falls onto the image sensor  1236  via the converging lens  1235 . Meanwhile, the remaining portion of the illumination light which has fallen onto the beam splitter  1231  passes through this beam splitter  1231 . After being reflected by the second reflector  1233 , a portion of this light is reflected by the beam splitter  1231  and falls onto the image sensor  1236  via the converging lens  1235 . In the image sensor  1236 , the components of the irradiation light reflected at a large number of points on the surface of the clinched body  90  are respectively detected by different detection elements. Each detection element receives not only a component of the irradiation light reflected at one point on the surface of the clinched body  90  but also another component of the irradiation light reflected at a point slightly displaced from that one point. 
     The phase shifter  1234  gradually changes (shifts) the phase of the irradiation light passing through the phase shifter  1234  while the illumination light, i.e. the pulsed laser light, is repeatedly generated. As a result, a gradual change in phase difference occurs between a component of the irradiation light falling onto one detection element of the image sensor  1236  after being reflected by one point on the surface of the clinched body  90  and another component of the irradiation light falling onto the same detection element after being reflected by another point slightly displaced from that one point. During such a change, each detection element of the image sensor  1236  continuously detects the intensity of the interference light resulting from the interference of the two components of the irradiation light (Step  206 ). 
     The upper drawing in  FIG. 6  graphically shows one example of the amount of phase shift by the phase shifter  1234  and the intensity of the interference light detected by a detection element of the image sensor  1236  when the phase of the vibration of the vibrator  112  is ϕ 0 . In  FIG. 6 , the relationship in which the detection intensity sinusoidally changes with the amount of phase shift is represented by a continuous curve. It should be noted that the data obtained by actual measurements are in a discrete form, and the continuous sinusoidal waveform is reproduced from those measured data by the least squares or other appropriate methods. To this end, it is necessary to detect the intensity at three or more different amounts of phase shift. 
     Subsequently, whether or not the value of k has reached m max  is determined (Step  207 ). Since k=1 and has not yet reached m max  (which is 3 in the present example) at this stage, the determination result of Step  207  is “NO”. When the result is “NO”, the operation proceeds to Step  208  to increase the value of k by 1, i.e. to “2” (the case where the determination result is “YES” in Step  208  will be described later). 
     Next, the operation returns to Step  205 . The signal generator  111  sends a pulse signal to the laser light source  121  at every timing at which the phase of the vibration of the vibrator  112  is expressed by [ϕ 0 +2π(k−1)/m max ] in which k=2, i.e. [ϕ 0 +2π/3]≡ϕ 1 . The laser light source  121  repeatedly casts the pulsed laser light as the illumination light onto the surface of the clinched body  90  every time it receives the pulse signal. Each detection element of the image sensor  1236  continuously detects the intensity of the interference light while the phase of the irradiation light reflected at each point within the view area is successively changed (shifted) to at least three values by the phase shifter  1234  (Step  206 ). 
     The middle drawing in  FIG. 6  graphically shows one example of the amount of phase shift by the phase shifter  1234  and the intensity of the interference light detected by a detection element of the image sensor  1236 , acquired when the phase of the vibration of the vibrator  112  is ϕ 1 . A comparison of the middle drawing and the upper drawing in  FIG. 6  demonstrates that the peak positions of the intensity of the interference light in the two drawings differ from each other by δϕ 1 −δϕ 0 . This difference indicates that the phase difference of the optical path between a component of the irradiation light reflected at one point on the surface of the clinched body  90  and another component of the irradiation light reflected at another point slightly displaced from that one point has changed due to the change in the phase of the vibration of the vibrator  112  at the point in time of the detection. This change in phase difference of the optical path indicates that the relative displacement between those two points in an out-of-plane direction has changed. 
     After the operation in Step  206  at the stage of k=2 has been completed in this manner, the value of k has not yet reached m max  (=3), so that the determination result in Step  207  is “NO” and the value of k is increased to “3” in Step  208 . Subsequently, the operation returns to Step  205 . The laser light source  121  repeatedly casts the pulsed laser light as the illumination light onto the surface of the clinched body  90  at every timing at which the phase of the AC electric signal is expressed by [ϕ 0 +2π(k−1)/m max ] in which k=3, i.e. [ϕ 0 +4π/3]≡ϕ 2 . Each detection element of the image sensor  1236  continuously detects the intensity of the interference light (Step  206 ). As a result, the relationship between the amount of phase shift by the phase shifter  1234  and the intensity of the interference light for the AC electric signal at the phase of ϕ 2  is obtained, as shown in the lower drawing in  FIG. 6 . 
     Subsequently, in Step  207 , since the value of k is 3 and has reached m max , the determination result is “YES”, and the operation proceeds to Step  209 . In Step  209 , the transmission of the AC electric signal from the signal generator  111  to the vibrator  112  is discontinued. Consequently, the vibrator  112  stops vibrating. 
     By the operations described to this point, the acquisition of the data in one view area  95  having the view-area number a=1 is completed. In Step  210 , whether or not the value of a has reached a max  is determined. In the example described to this point, since the value of a has not yet reached a max  (“NO” in Step  210 ), the operation proceeds to Step  211  (the case where the determination result is “YES” in Step  210  will be described later). 
     In Step  211 , the tubular body  91  of the clinched body  90  is rotated by the rotary mechanism  124  around the axis of the tubular body  91  by 360/a max  degrees to change the direction of the clinched body  90 . By this operation, the view area  95  is also changed. Subsequently, the value of the view-area number a is increased by 1 (Step  212 ). Thus, the new view area  95  has a view-area number of a=2. 
     Subsequently, the operation proceeds to Step  203  to perform the operations of Steps  203  through  209  for the new view area  95  and acquire the relationship between the amount of phase shift and the intensity of the interference light at each point within the view area  95 . Subsequently, if the determination result in Step  210  is “NO”, the operations of Steps  211  and  212  are performed, and the operations of Steps  203  through  209  are further performed. After the operations of Steps  203  through  209  for the view area  95  having the view-area number a max  have been completed, the determination result in Step  210  becomes “YES”, and the operation proceeds to Step  213 . Through the operations performed until the transition to Step  213 , the measurement of the vibration is completed. The task to be subsequently performed is the analysis of the acquired data. 
     The data analysis is individually performed for each of the a max  view areas  95 . First, the view-area number a is given an initial value of “1” (Step  213 ), and the distribution of the vibration state (amplitude and/or phase) at each point within the view area  95  having the view-area number a=1 (vibration distribution) is determined as follows: Initially, for each detection element of the image sensor, the maximum output phase shifts δϕ 0 , δϕ 1  and δϕ 2  at which the output of the detection element is maximized within the period in which the amount of phase shift was changed by the phase shifter  1234  are determined at each of the three vibration phases of ϕ 0 , ϕ 1  and ϕ 2 , respectively (see the upper, middle and lower graphs in  FIG. 6 ). Furthermore, the differences between the maximum output phase shifts at the different phases of vibration, i.e. (δϕ 1 −δϕ 0 ), (δϕ 2 −δϕ 1 ) and (δϕ 0 −δϕ 2 ), are determined. These three differences of the maximum output phase shifts are three sets of data which show, for each point within the view area  95 , a relative displacement in an out-of-plane direction between the point in question and another point slightly displaced from that point, where each set of data includes two values obtained at different phases of the vibration of the vibrator  112 , i.e. at different points in time (Step  214 ). Based on those three values of the relative displacement, the values of the following three parameters can be obtained for each point within the view area  95 : the amplitude of the vibration, phase of the vibration, and central value (DC component) of the vibration (Step  215 ). 
     The obtained values of the amplitude and phase of the vibration at each point contain information which shows whether or not the state of clinching at the clinched portion  93  is satisfactory. That is to say, if the tubular body  91  and the clinch-target member  92  are satisfactorily clinched, the amplitude of the vibration normally becomes small in the vicinity of the clinched portion  93 , since the tubular body  91  is bound by the clinch-target member  92 . By comparison, if the tubular body  91  and the clinch-target member  92  are not satisfactorily clinched due to the presence of a micro-sized gap between the two parts, the amplitude of the vibration becomes large at and around the clinched portion  93  since the tubular body  91  is not bound by the clinch-target member  92 . Accordingly, based on the obtained vibration distribution, it is possible to determine whether or not the state of clinching at the clinched portion  93 , and specifically, at the end of the clinch-target member  92  is satisfactory (Step  216 ). 
     After the determination on whether or not the state of clinching at the clinched portion  93  within the view area  95  having the view-area number a=1 is satisfactory has been completed in the previously described manner, whether or not the value of a has reached a max  is determined (Step  217 ). If the value has not yet reached a max  (if “NO” in Step  217 ), the value of a is increased by 1 (Step  218 ), and the operations of Steps  214  through  216  are performed to determine whether or not the state of clinching at the clinched portion  93  within the view area  95  having the next view-area number is satisfactory. If the value of a in Step  217  has reached a max , it means that the determination on whether or not the state of clinching is satisfactory has been completed for all view areas  95 , so that the entire sequence of operation is discontinued. 
     The example described so far has assumed that m max =3. Selecting a value of m which is greater than [2n+1] (where n is a natural number equal to or greater than two) enables the detection of the nth-order component (nth harmonic component) of the vibration induced in the clinched body  90 . Whether or not the state of clinching at the clinched portion  93  is satisfactory may also be determined based on the distribution of the vibration of those higher-order harmonic components in addition to the fundamental harmonic. 
     (3) Variation of Operation of Examination Device According to Present Embodiment, and Variation of Examination Method 
     An example is hereinafter described using the flowchart of  FIGS. 7 and 8  in which the operation and examination method of the examination device  10  according to the present embodiment are modified while there is no change in the configuration of the device. In the flowchart shown in  FIGS. 7 and 8 , the steps which are identical to those shown in the flowchart shown in  FIGS. 3 and 4  are denoted by the same reference signs, and the descriptions of those steps will be simplified. 
     In the present variation, as will be described later, the state of vibration within one view area is determined in b max  kinds of measurement modes (where b max  is an integer equal to or greater than two) which differ from each other in either the contact position of the vibrator  112  on the clinched body  90  (i.e. the position at which the vibration is given) or the vibration frequency of the vibrator  112 , or both. The larger the value of b max , the more reliable the determination on whether or not the clinching is satisfactory, although it means a corresponding increase in the period of time required for the measurement. The value should normally be within a range from 3 to 5. The combination of the position at which the vibration is given, and the frequency of the vibration, is hereinafter called the “vibration-giving condition”. The vibration-giving conditions are sequentially and individually denoted by the vibration-giving condition number b from 1 to b max . 
     Initially, as in the previous embodiment, the clinched body  90  is set in the examination device  10  (Step  201 ), and the view-area number a is given an initial value of “1” (Step  202 ). Next, the vibration-giving condition number b is given an initial value of “1” (Step  2021 ). Subsequently, the measurement according to Steps  203  through  209  is performed by the same method as in the previous embodiment for the view area  95  of a=1 under the vibration-giving condition of b=1. 
     Next, whether or not the value of b has reached b max  is determined (Step  2091 ). In the present case, since b=1 and has not yet reached b max  (“NO” in Step  2091 ), the operation proceeds to Step  2092  to change the vibration-giving condition, i.e. the position of the vibrator  112  and/or the vibration frequency of the vibrator  112 . Furthermore, the value of b is increased by 1 (Step  2092 ). Subsequently, the operation returns to Step  203 , and the measurement according to Steps  203  through  209  is performed for the view area  95  of a=1 under the vibration-giving condition of b=2. 
     As a result of the repetition of the measurement according to Steps  203  through  209  for the view area  95  of a=1, the value of b will eventually reach b max  (“YES” in Step  2091 ). Then, the measurement for the view area  95  of a=1 is completed, and the operation proceeds to Step  210  to determine whether or not the value of a has reached a max . If the value of a has not yet reached a amx  (“NO” in Step  210 ), the direction of the clinched body  90  is changed by the rotary mechanism  124  in the previously described manner (Step  211 ), the view-area number a is increased by 1 (Step  212 ), and the operation returns to Step  2021 . Subsequently, the operations of Steps  203  through  2093  are performed for the view area  95  having the new view-area number a. If the value of a has reached a max  (“YES” in Step  210 ), the operation proceeds to Step  213 . 
     In Step  213 , the view-area number a is given an initial value of “1”. Subsequently, in Step  2131 , the vibration-giving condition b is given an initial value of “1”. Subsequently, the distribution of the vibration state (amplitude and/or phase) at each point within the view area  95  having a view-area number of a=1 (vibration distribution) is determined in Steps  214  and  215  by the same method as in the previous embodiment. 
     Next, whether or not the value of b has reached b max  is determined (Step  2151 ). In the present case, since b=1 and has not yet reached b max  (“NO” in Step  2151 ), the value of b is increased by 1 (Step  2152 ), and the operations in Steps  214 ,  215  and  2151  are once more performed. When the value of b has reached b max  (i.e. the determination result is “YES”) in Step  2151 , the operation proceeds to Step  2161 , and whether or not the state of clinching within the view area  95  of a=1 is satisfactory is determined as will be hereinafter described. 
     If the state of clinching at the clinched portion  93  is satisfactory, the amplitude of the vibration at the clinched portion  93  normally becomes small in the vicinity of the clinched portion  93 , since the tubular body  91  is bound by the clinch-target member  92 . Accordingly, based on the obtained vibration distribution, whether or not the state of clinching at the clinched portion  93  is satisfactory can be determined by examining whether or not the amplitude of the vibration in the vicinity of the clinched portion  93  is small. However, if a standing wave is formed in the clinched body  95 , a node of the standing wave may accidentally be located at the position of the clinched portion  93 , causing the amplitude of the vibration to be smaller than the other portion. In such a situation, even when the actual state of clinching is imperfect, the state of clinching may be judged to be satisfactory if a single state of vibration is used as the basis for the judgment. To address this problem, in the present variation, a plurality of vibration-giving conditions are prepared for one view area  95 , and the measurement of the vibration state is performed under each condition. When a node of the vibration is formed at the clinched portion  93  under all vibration-giving conditions, it is determined that the state of clinching is satisfactory. 
     After the determination on the state of clinching within one view area  95  is satisfactory has been completed in Step  2161 , the operation proceeds to Step  217  to determine whether or not the value of a has reached a max . If the value has not yet reached a max  (“NO” in Step  217 ), the value of a is increased by 1 (Step  218 ), and the operations of Steps  214  through  2161  are performed to determine whether or not the state of clinching at the clinched portion  93  within the view area  95  having the next view-area number is satisfactory. If the value of a in Step  217  has reached a max , the entire sequence of operations is discontinued. 
     (4) Experimental Example of Examination of Clinched Portion by Examination Method According to Variation 
       FIGS. 9-13  show an experimental example of the examination of the clinched portion  93  of the clinched body  90  using the examination method according to the variation. In this example, the number of view areas  95 , i.e. a max , is four. The vibration state was measured from four directions at right angles, i.e. from the upper, left, lower and right sides, as shown in  FIG. 13  which is a sectional view at a plane perpendicular to the longitudinal direction of the tubular body  91 . Five vibration-giving conditions (b max =5) with different frequencies were used for each view area  95 . 
       FIGS. 9-12  each show the distribution of the amplitude within one of the view areas  95  calculated by measuring the distribution of the amplitude of the standing wave (vibration distribution) under each of the five different vibration-giving conditions and averaging the five measured amplitudes. In those figures, higher average values are represented by brighter points. Accordingly, a point at which a node (with an amplitude of zero) of the standing wave was formed under all of the five vibration-giving conditions is represented by the darkest, black color. By comparison, a point at which a node of the standing wave was formed under some of the five vibration-giving conditions but not under the other conditions is not represented by the black color in  FIGS. 9-12 . Thus, the present method can prevent the situation in which the state of clinching at a position where a node of the standing wave has been accidentally formed is incorrectly judged as satisfactory despite the actual state of clinching being imperfect. 
     In  FIGS. 9-12 , reference sign  97  denotes the section of the clinched portion  93  within which bright points are noticeably located. Specifically, the bright points are distributed over a significant portion as viewed from above ( FIG. 9 ), a small portion as viewed from the left ( FIG. 10 ), and the entirety as viewed from below of the clinched portion  93  ( FIG. 11 ), indicating that the state of clinching is imperfect at those portions. The points within the other sections of the clinched portion  93  are represented by the black color, which means that nodes of the standing wave are present at those points. This demonstrates that the state of clinching at those points are satisfactory. 
     The states of clinching obtained in  FIGS. 9-12  are shown in  FIG. 13 . Reference signs  97  in  FIG. 13  denote the sections at which the clinching is imperfect, while reference signs  98  denote the sections at which the clinching is satisfactory. 
     (5) Other Variations 
     The examination device and examination method according to the present embodiment, as well as one variation of the examination method have been described so far. The present invention is not limited to those examples. Two more variations will be hereinafter described. The present invention can be subjected to further modifications. 
     In the previously described variation, the measurement of the vibration state within one view area was individually performed under each of the plurality of vibration-giving conditions. Alternatively, the measurement of the vibration state may be performed only one time for each view area while giving a vibration containing a plurality of frequencies superposed on each other. The distribution of the vibration at each frequency can be determined at a later point in time by a frequency analysis. Although this method requires a more complex data analysis than the previously described variation, the period of time required for the measurement of the vibration state can be shortened. 
     In the examination device according to the previously described embodiment, a speckle interferometer may be used in place of the speckle-shearing interferometer  123  to measure the vibration distribution. In a speckle interferometer, a laser beam from a laser light source  121  is divided into illumination light and reference light. The illumination light is cast onto the view area  95  and is subsequently made to interfere with the reference light (which is not cast onto the view area  95 ). The intensity of the resulting interference light is acquired at each position within the view area  95 . Other commonly known vibration measurement methods may also be used, such as the grating projection, sampling moire, digital image correlation, or laser Doppler method. 
     (6) Various Modes of Invention 
     Various modes of the present invention are hereinafter described. 
     A method for examining a clinched portion of a tubular body according to the first mode of the present invention includes the steps of: giving an elastic vibration to a clinched body formed by clinching a tubular body with a clinch-target member; and acquiring, for each of a plurality of view areas which differ from each other in the position in the circumferential direction of the tubular body, a vibration distribution optically and simultaneously measured within the view area including a clinched portion of the tubular body and the clinch-target member, to determine whether or not the state of clinching is satisfactory over the entire clinched portion. 
     In the method for examining a clinched portion of a tubular body according to the first mode, whether or not the state of clinching at the clinched portion within the view area is satisfactory can be determined, as will be described later, by optically and simultaneously measuring the vibration distribution within the view area including the clinched portion. By acquiring the vibration distribution for a plurality of view areas which differ from each other in the position in the circumferential direction of the tubular body, whether or not the state of clinching is satisfactory over the entire clinched portion can be determined. 
     If the tubular body and the clinch-target member are satisfactorily clinched, the amplitude of the vibration becomes small at the clinched portion, since the tubular body is bound by the clinch-target member. By comparison, if the tubular body and the clinch-target member are not satisfactorily clinched due to the presence of a micro-sized gap between those two members, the amplitude of the vibration becomes large at and around the clinched portion since the tubular body is not bound by the clinch-target member. Accordingly, based on the obtained vibration distribution, whether or not the state of clinching at the clinched portion is satisfactory can be determined by examining whether or not the amplitude of the vibration at the clinched portion is small. By such a method, imperfect clinching can be detected even if the gap between the tubular body and the clinch-target member is a micro-sized one. Furthermore, whether or not the state of clinching is satisfactory can be examined over the entire clinched portion by acquiring data at a plurality of view areas which differ from each other in the position in the circumferential direction of the tubular body. Thus, by the method for examining a clinched portion of a tubular body according to the first mode, imperfect clinching due to a micro-sized gap between the tubular body and the clinch-target member can be assuredly detected. 
     Various methods are available for measuring the vibration distribution within the view area, such as a speckle method, speckle-shearing method, grating projection, sampling moire, digital image correlation or laser Doppler method. The speckle method is a method in which irradiation light cast from a light source onto each point within a view area and reflected by that point is made to interfere with reference light branched from the irradiation light at a position between the light source and the view area, and the vibration distribution within the view area is determined from the interference pattern. The speckle-shearing method is a method in which irradiation light cast from a light source onto each point within a view area and reflected by that point is made to interfere with reference light which is the irradiation light reflected at another point in the vicinity of that point, and the vibration distribution within the view area is determined from the interference pattern. The speckle-shearing method may be modified so that the irradiation light cast from a light source onto each point within a view area and reflected by that point is made to interfere with reference light which is the irradiation light reflected by a number of points within an area in the vicinity of that point, and the vibration distribution within the view area is determined from the interference pattern. 
     A method for examining a clinched portion of a tubular body according to the second mode of the present invention is a specific form of the method for examining a clinched portion of a tubular body according to the first mode. In the second mode, in each of the plurality of view areas, a measurement of the vibration distribution is performed while each of a plurality of the elastic vibrations which differ from each other in either the position on the clinched body at which the vibration is given, or the frequency of the vibration, or both, is given to the clinched body, and it is determined that the state of clinching at the clinched portion within the view area is satisfactory if all of the plurality of kinds of measured vibration distributions have a node of the vibration at the clinched portion. 
     In the method for examining a clinched portion of a tubular body according to the second mode, if the clinched portion is satisfactory clinched, it is normally the case that the vibration given to the clinched body produces a standing wave having a node located at the clinched portion independently of the position or frequency of the vibration. Therefore, if all of the plurality of kinds of vibration distributions have a node of the vibration at the clinched portion, it is possible to conclude that the state of clinching is satisfactory. Since the presence of a node of a vibration is easier to recognize than the presence of the continuity of the vibration, the state of clinching can be more easily determined by the method according to the second mode. However, if the vibration distribution is determined from only one kind of vibration, a node of a standing wave may accidentally be located at the clinched portion regardless of whether or not the state of clinching is satisfactory. To address this problem, a vibration distribution is determined from each of the plurality of kinds of vibrations in the second mode. 
     In the case giving a plurality of different frequencies of vibrations to the clinched body in the second mode, the vibration distribution can be measured while giving the vibration to the clinched body at a different timing for each frequency. Alternatively, a vibration containing the plurality of frequencies superposed on each other may be simultaneously given, and the vibration distribution at each frequency may subsequently be determined by a frequency analysis. The former method is preferable in that the data analysis is easier than in the latter method, while the latter method is preferable in that the period of time required for the measurement can be shorter than in the former method. 
     A method for examining a clinched portion of a tubular body according to the third mode of the present invention is a specific form of the method for examining a clinched portion of a tubular body according to the first or second mode. In the third mode, the measurement of the vibration distribution is carried out by performing stroboscopic illumination of the view area and measuring the displacement in an out-of-plane direction of each point within the view area at three or more different phases of the vibration by controlling the timing of the elastic vibration and the stroboscopic illumination. 
     In the method for examining a clinched portion of a tubular body according to the third mode, the vibration distribution within the view area can be easily obtained by measuring the displacement in an out-of-plane direction of each point within the view area at three or more different phases of the vibration. 
     A device for examining a clinched portion of a tubular body according to the fourth mode of the present invention includes: 
     a vibration source configured to give an elastic vibration to a clinched body formed by clinching a tubular body with a clinch-target member; and 
     a vibration distribution acquirer configured to acquire, for each of a plurality of view areas which differ from each other in the position in the circumferential direction of the tubular body, a vibration distribution optically and simultaneously measured within the view area including a clinched portion of the tubular body and the clinch-target member. 
     By the device for examining a clinched portion of a tubular body according to the fourth mode, as with the method for examining a clinched portion of a tubular body according to the first mode, imperfect clinching due to a micro-sized gap between the tubular body and the clinch-target member can be assuredly detected. The task of determining whether or not the state of clinching is satisfactory based on the vibration distribution acquired by the vibration distribution acquirer may be performed by an operator (person), or alternatively, by the configuration of the device for examining a clinched portion of a tubular body according to the fifth mode (which will be described below). 
     The device for examining a clinched portion of a tubular body according to the fifth mode of the present invention is a specific form of the device for examining a clinched portion of a tubular body according to the fourth mode. The device further includes: 
     a clinching-state determiner configured to determine, at each of the plurality of view areas, whether or not the state of clinching at the clinched portion within the view area is satisfactory based on the vibration distribution acquired by the vibration distribution acquirer. 
     By the device for examining a clinched portion of a tubular body according to the fifth mode, the task of determining whether or not the state of clinching is satisfactory is performed by the clinching-state determiner in place of an operator. Therefore, the operator can easily operate the device. The determination by the clinching-state determiner can be performed by a method similar to the method for examining a clinched portion of a tubular body according to any of the first through third modes. 
     The device for examining a clinched portion of a tubular body according to the sixth mode of the present invention is a specific form of the device for examining a clinched portion of a tubular body according to the fourth or fifth mode. The device further includes: an illuminator configured to perform stroboscopic illumination of the view area; and a displacement measurement section configured to measure the displacement in an out-of-plane direction of each point within the view area at three or more different phases of the vibration by controlling the timing of the elastic vibration and the stroboscopic illumination. 
     In the device for examining a clinched portion of a tubular body according to the sixth mode, the vibration distribution within the view area can be easily obtained by measuring the displacement in an out-of-plane direction of each point within the view area at three or more different phases of the vibration. 
     REFERENCE SIGNS LIST 
     
         
           10  . . . Examination Device (for Clinched Portion of Tubular Body) 
           11  . . . Vibration Source 
           111  . . . Signal Generator 
           112  . . . Vibrator 
           12  . . . Vibration Distribution Acquirer 
           121  . . . Laser Light Source 
           122  . . . Illumination Light Lens 
           123  . . . Speckle-Shearing Interferometer 
           1231  . . . Beam Splitter 
           1232  . . . First Reflector 
           1233  . . . Second Reflector 
           1234  . . . Phase Shifter 
           1235  . . . Converging Lens 
           1236  . . . Image Sensor 
           124  . . . Rotary Mechanism 
           125  . . . Vibration Distribution Determiner 
           13  . . . Clinching-State Determiner 
           14  . . . Display Unit 
           90  . . . Clinched body 
           91  . . . Tubular Body 
           911  . . . Tubular Body before Being Clinched with Clinch-Target Member 
           92  . . . Clinch-Target Member 
           921  . . . Hole in Clinch-target Member 
           93  . . . Clinched Portion 
           95  . . . View Area 
           96  . . . Coil 
           97  . . . Section with Imperfect Clinching 
           98  . . . Section with Satisfactory Clinching