阅读说明：本技术 螺栓轴力测量方法及该方法使用的螺栓
(Bolt axial force measuring method and bolt used by same
) 是由 津崎一浩
榊原利次 于 2019-07-30 设计创作，主要内容包括：本发明提供一种与以往相比能够更加可靠地高精度测量螺栓轴力的螺栓轴力测量方法及该方法使用的螺栓。本发明的螺栓轴力测量方法的特征在于,包括：探针插入工序,在该工序中,以与在螺栓(1)的头部(3)形成的阶梯凹部(5)对应的方式,将具有阶梯凸部(29)的探针(24)的所述阶梯凸部(29)插入所述头部(3)的所述阶梯凹部(5)；伸长量运算工序,在该工序中,基于从所述探针(24)朝向所述螺栓(1)的轴部的底面震荡的超声波脉冲的底面回波,运算紧固时的所述螺栓(1)的伸长量；以及轴力运算工序,在该工序中,基于所述螺栓(1)的伸长量运算所述螺栓(1)的轴力。(The invention provides a bolt axial force measuring method capable of more reliably and accurately measuring bolt axial force than the prior art and a bolt used by the method. The bolt axial force measuring method of the present invention is characterized by comprising: a probe insertion step in which a stepped convex portion (29) of a probe (24) having a stepped convex portion (29) is inserted into a stepped concave portion (5) of a head portion (3) of a bolt (1) so as to correspond to the stepped concave portion (5) formed in the head portion (3); an elongation calculation step of calculating the elongation of the bolt (1) during fastening, based on a bottom echo of an ultrasonic pulse oscillating from the probe (24) toward the bottom surface of the shaft portion of the bolt (1); and an axial force calculation step of calculating the axial force of the bolt (1) based on the elongation of the bolt (1).)
1. A bolt axial force measurement method, comprising:
a probe insertion step of inserting a stepped convex portion of a probe having a stepped convex portion into a stepped concave portion formed in a head portion of a bolt so as to correspond to the stepped concave portion;
an elongation calculation step of calculating an elongation of the bolt during fastening based on a bottom echo of an ultrasonic pulse oscillating from the probe toward a bottom surface of the shaft portion of the bolt; and
and an axial force calculation step of calculating an axial force of the bolt based on an elongation of the bolt.
2. The bolt axial force measurement method of claim 1,
the method further includes a gap forming step of forming a gap in which an ultrasonic wave propagation material is interposed between a surface of the bolt defined by a bottom surface of the stepped recess and a surface of the probe defined by a top surface of the stepped projection by bringing the stepped recess and the stepped portion of the stepped projection into contact with each other.
3. The bolt axial force measurement method of claim 2,
in the elongation calculation step, the elongation of the bolt during fastening is calculated based on a1 st order surface echo reflected by the surface of the bolt and a1 st order bottom echo reflected by the bottom surface of the shaft of the bolt when the ultrasonic pulse is oscillated from the probe toward the bottom surface of the shaft of the bolt.
4. A bolt used in the bolt axial force measuring method according to any one of claims 1 to 3,
the head of the bolt has a stepped recess into which the stepped projection of the probe is inserted.
Technical Field
The invention relates to a bolt axial force measuring method and a bolt used by the method.
Background
Conventionally, there is known a bolt axial force measurement method for measuring an axial force of a bolt by measuring an elongation of the bolt using a B echo (bottom echo) of an ultrasonic wave oscillating from a head of the bolt toward a bottom surface of a bolt shank. In such a bolt axial force measuring method, a propagation medium of ultrasonic waves is filled between an ultrasonic sensor that oscillates ultrasonic waves and a head of the bolt. However, if the thickness of the propagation medium interposed between the ultrasonic sensor and the head of the bolt changes, the elongation of the bolt cannot be measured with high accuracy.
Therefore, a bolt axial force measurement method is disclosed in which a protrusion protruding from the ultrasonic sensor side toward the head of the bolt maintains a constant distance between the ultrasonic sensor and the head of the bolt (see, for example, patent document 1).
According to the bolt axial force measuring method, the distance between the ultrasonic sensor and the head of the bolt is maintained constant, so that the elongation of the bolt can be measured with high accuracy.
Disclosure of Invention
However, in the conventional bolt axial force measuring method (see, for example, patent document 1), a gap is provided between the sensor holder and the housing so that the ultrasonic sensor can be urged to the head of the bolt. Therefore, when the ultrasonic sensor is biased toward the bolt side, the sensor holder may be inclined in the housing. Thus, in the conventional bolt axial force measuring method, there is a possibility that oscillation of ultrasonic waves and detection of B echo directed to the bottom surface of the bolt shank cannot be accurately performed, and the bolt axial force cannot be measured with high accuracy.
Therefore, an object of the present invention is to provide a bolt axial force measuring method capable of more reliably and accurately measuring a bolt axial force than in the related art, and a bolt used in the method.
The method for measuring the axial force of a bolt, which solves the above problems, is characterized by comprising: a probe insertion step of inserting a stepped convex portion of a probe having a stepped convex portion into a stepped concave portion formed in a head portion of a bolt so as to correspond to the stepped concave portion; an elongation calculation step of calculating an elongation of the bolt during fastening based on a bottom echo of an ultrasonic pulse oscillating from the probe toward a bottom surface of the shaft portion of the bolt; and an axial force calculation step of calculating the axial force of the bolt based on the elongation of the bolt.
The present invention for solving the above-described problems is a bolt used in the bolt axial force measuring method, wherein a head portion of the bolt has a stepped recess into which the stepped projection of the probe is inserted.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, it is possible to provide a bolt axial force measuring method capable of more reliably and accurately measuring a bolt axial force than in the related art, and a bolt used in the method.
Drawings
Fig. 1 is a block diagram of a bolt axial force measuring apparatus having a fastening device according to an embodiment of the present invention.
Fig. 2 is a partially enlarged sectional view of a fastening device constituting the bolt axial force measuring device of fig. 1.
Fig. 3 is an explanatory diagram of a bolt installation process in the bolt axial force measurement method according to the embodiment of the present invention.
Fig. 4 is a flowchart of a bolt axial force measuring process according to the bolt axial force measuring method of the embodiment of the present invention.
Fig. 5 is a flowchart of a bolt axial force measuring process according to the bolt axial force measuring method of the embodiment of the present invention.
Fig. 6 is a schematic diagram showing waveforms of a head echo and a bottom echo in the bolt shaft force measurement method according to the embodiment of the present invention.
Fig. 7 is an explanatory diagram of automatic tracking of the cycle of the head echo by the bolt axial force measurement method according to the embodiment of the present invention.
Fig. 8 is a graph showing an example in which the calculated axial force is plotted in time series.
Fig. 9 is an explanatory diagram of correction coefficients (increase widths) of the amplitudes of the head echo and the bottom echo.
Fig. 10 (a) and (b) are explanatory views of operations of a bolt fastening device constituting the bolt axial force measuring device.
Description of the reference numerals
1 bolt
2 shaft part
Bottom surface of 2c bolt
3 head part
10 bolt axial force measuring device
20 fastening device
31a nut power wrench stop command unit
31b axial force calculation unit
31c elongation calculation unit
31d echo detecting unit
31e bolt information processing part
31f ultrasonic wave transmission/reception control unit (amplitude correction unit)
31f1 first amplitude correction unit
31f2 second amplitude correction unit
34 display part
Detailed Description
The mode for carrying out the present invention (present embodiment) will be described in detail with reference to the accompanying drawings. The bolt axial force measuring device (and bolt axial force measuring program) having the fastening device, the bolt axial force measuring method, and the bolt according to the present embodiment will be described in detail below.
Bolt axial force measuring device
The bolt axial force measuring device in the present embodiment is configured to measure the axial force of a bolt while fastening the bolt. Further, the bolt axial force measuring device stops the fastening operation when the axial force of the bolt reaches a predetermined value.
Fig. 1 is a block diagram of a bolt axial force measuring device 10 according to the present embodiment.
As shown in fig. 1, the bolt axial force measuring device 10 of the present embodiment is mainly configured to include a bolt fastening device 20, a control unit 30, an input unit 33, and a display unit 34.
< fastening device >
The fastening device 20 is first explained.
Fig. 2 is a view illustrating the structure of the fastening device 20. In fig. 2, the bolt 1 fastened by the fastening device 20 is shown by an imaginary line (two-dot chain line).
As shown in fig. 2, the fastening device 20 includes a nut runner 21, a probe unit 23, an elastic coil spring 28 as a biasing mechanism, and a socket 22. The fastening device 20 further includes a nut runner control unit 21b (see fig. 1).
The nut power wrench 21 has a rotating shaft 21a, and the rotating shaft 21a is rotated at a predetermined torque and a predetermined rotational speed (rotational angular velocity) by a nut power wrench control unit 21b (see fig. 1) to be described later. The rotary shaft 21a is formed in a tubular shape.
The nut runner 21 drives and rotates the rotary shaft 21a in accordance with a command output from a nut runner control unit 21b (see fig. 1). The nut power wrench 21 is configured to stop in response to a command output from a nut power wrench stop command unit 31a (see fig. 1) to be described later.
The probe unit 23 includes a probe 24 (ultrasonic sensor), a probe supporting member 25, a mounting member 27 for the rotary shaft 21a, and a retaining member 26.
The probe 24 includes a piezoelectric element or the like (not shown) that oscillates an ultrasonic pulse and detects an echo of the oscillated ultrasonic pulse. The electric signal of the echo detected by the probe 24 is output to a control unit 30 (see fig. 1) described later.
The probe 24 is formed in a substantially cylindrical shape. A substantially cylindrical protrusion 24a protruding downward is formed at the center of the lower end surface of the probe 24. Thus, a stepped portion 29 having a stepped portion 24b is formed at the lower end of the probe 24.
As described later, the probe 24 is fitted into the recess 5 formed in the head 3 of the bolt 1.
The probe supporting member 25 includes a base portion 25a and a shaft portion 25b extending upward from a central portion of an upper surface of the base portion 25 a.
A locking portion 25a1 is formed at the lower portion of the base portion 25 a. The upper portion of the probe 24 is detachably attached to the locking portion 25a 1.
The shaft portion 25b can advance and retreat with respect to the hollow portion of the rotating shaft 21 a.
A substantially cylindrical structure is assumed as the mounting member 27.
The mounting member 27 is mounted on the lower outer periphery of the rotary shaft 21 a. As a method for attaching the attachment member 27 to the rotary shaft 21a, a known method such as fitting can be mentioned, but there is no particular limitation. The mounting member 27 may be formed integrally with the rotary shaft 21 a.
The mounting member 27 has a flange 27a extending radially inward at a lower end thereof. A retaining member 26 formed of a washer fitted into the distal end portion of the shaft portion 25b abuts on the upper surface of the flange 27 a.
The elastic coil spring 28 is disposed so as to surround the probe supporting member 25. The upper end of the elastic coil spring 28 is landed on the lower surface of the mounting member 27, and the lower end of the elastic coil spring 28 is landed on the outer peripheral step portion of the base portion 25 a.
In the probe supporting member 25, when the base portion 25a is displaced upward against the biasing force of the elastic coil spring 28, the shaft portion 25b can swing in the hollow portion of the rotary shaft 21 a.
The retaining member 26 abuts on the upper surface of the flange 27a, thereby preventing the shaft portion 25b from coming off the hollow portion of the rotating shaft 21 a.
The socket 22 is substantially cylindrical in shape. The lower portion of the rotating shaft 21a is detachably fitted to the inner peripheral side of the upper portion of the socket 22. Thereby, the circumferential displacement of the socket 22 with respect to the rotary shaft 21a is restricted. Incidentally, in the present embodiment, the rotation shaft 21a and the socket 22 are assumed to be spline-fitted, but the joining of the rotation shaft 21a and the socket 22 is not limited to this.
In the fastening device 20 described above, when the head 3 of the bolt 1 is engaged with the socket 22, the probe 24 having the recess 5 of the bolt 1 fitted with the recess is biased toward the head 3 by the elastic coil spring 28.
In addition, in such a fastening device 20, the socket 22 and the probe unit 23 are engaged with the rotation shaft 21a, respectively, independently of each other.
The probe 24 is supported by the rotary shaft 21a in a semi-floating manner by interposing an elastic coil spring 28 between the probe and the rotary shaft 21 a.
Next, the control unit 30 will be explained.
As shown in fig. 1, the control unit 30 mainly includes: an arithmetic Processing Unit 31 including a processor such as a Central Processing Unit (CPU); and a storage unit 32 including a ROM (Read Only Memory) in which a program is written, a RAM (Random Access Memory) for temporarily storing data, and the like.
The arithmetic processing unit 31 in the present embodiment includes a nut power wrench stop instruction unit 31a, an axial force arithmetic unit 31b, an elongation amount arithmetic unit 31c, an echo detection unit 31d, a bolt information processing unit 31e, and an ultrasonic wave transmission/reception control unit 31 f.
As described later, the nut power wrench stop instruction unit 31a outputs an instruction to stop the application of the axial force to the nut power wrench 21 when the axial force (F) of the bolt 1 reaches the target axial force value.
The axial force calculation unit 31b calculates the axial force based on equation 1 described later. The extension amount calculation unit 31c calculates the extension amount of the bolt 1 due to fastening of the bolt 1 (see fig. 2). The echo detection unit 31d calculates a zero cross point of the ultrasonic echo. The bolt information processing unit 31e outputs information of the bolt 1 to be measured to the storage unit 32. The ultrasonic transmission/reception control unit 31f oscillates an ultrasonic pulse to the probe 24 and amplifies the detected ultrasonic echo.
The above components of the arithmetic processing unit 31 will be explained in detail together with the explanation of the bolt axial force measuring method described later.
The input unit 33 is assumed to be a keyboard or the like for inputting bolt information to the bolt information processing unit 31e, but may be a touch panel having the display unit 34 as well. Further, a request task for the arithmetic processing unit 31 can be input to the input unit 33.
The display unit 34 in the present embodiment is assumed to be a monitor, a speaker, or the like that visually or audibly displays information output from the arithmetic processing unit 31.
Bolt axial force measuring method
Next, a bolt axial force measurement method according to the present embodiment will be described.
The bolt axial force measuring method includes a bolt information input step (bolt information input step) for the bolt axial force measuring device 10, a bolt 1 (see fig. 2) setting step (bolt setting step) for the bolt axial force measuring device 10, and a bolt axial force measuring step.
< bolt information input Process >
In the bolt information input step, information of the bolt 1 (see fig. 2) to be measured is input to the control unit 30 (see fig. 1) via the input unit 33.
The bolt information in the present embodiment is the young's modulus (E), the effective diameter (a), and the fastened length (L) of the bolt 1 in the following formula 1, which calculates the axial force F.
F ═ (EA/L) δ · · · · · · · · · · · · · · · ·, formula 1, and
in equation 1, the amount of change in elongation (δ) of the bolt 1 is calculated by the elongation calculator 31c as described below.
The above-described bolt information is stored in the storage unit 32 via the bolt information processing unit 31e of the control unit 30.
< bolt setting Process >
Next, a bolt setting process will be described.
Fig. 3 is an explanatory view of a bolt setting process in the bolt axial force measurement method.
As shown in fig. 3, in the bolt installation step, a probe fitting step of fitting the probe 24 into the recess 5 of the bolt 1 and a gap forming step of forming a gap 41 between the bolt 1 and the probe 24 are performed in parallel.
In the probe fitting step, the probe 24 is fitted into the recess 5 (stepped recess) of the bolt 1 with a socket.
Specifically, in the probe fitting step, the outer peripheral surface of the distal end body portion 24c of the probe 24 abuts against the inner peripheral surface of the large diameter portion 14a of the recess 5.
The protruding portion 24a of the probe 24 is accommodated in the small diameter portion 14b of the recess 5.
In the gap forming process, a gap 41 is formed between the surface of the bolt 1 defined by the bottom surface 6 of the recess 5 and the surface of the probe 24 defined by the top surface 24d of the protrusion 24 a.
Specifically, the gap 41 is formed by the step 14c on the bolt 1 side and the step 24b on the probe 24 side abutting each other. The gap 41 is formed by facing the bottom surface 6 of the recess 5 in parallel with the top surface 24d of the protrusion 24 a.
Such a gap 41 is filled with a propagation material 42.
The propagation material 42 is not particularly limited, and examples thereof include known materials such as machine oil, water, aqueous polymers, liquid paraffin, castor oil, jelly-like materials, and elastomers, and jelly-like materials and elastomers are particularly preferable.
In fig. 3, reference numeral 22 denotes a socket into which the head 3 of the bolt 1 is fitted.
< measuring Process of axial force of bolt >
Next, a bolt axial force measuring process will be described.
Fig. 4 and 5 are flowcharts of the bolt axial force measuring process.
In this bolt axial force measuring step, a cycle of a head echo (S echo cycle) and a cycle of a bottom echo (B echo cycle) when the probe 24 (see fig. 3) oscillates an ultrasonic pulse to the bolt 1 (see fig. 3) are set.
The above setting is preset based on the gap 41 (see fig. 3) and the length of the bolt 1, wherein the gap 41 is acquired by the echo detection unit 31d (see fig. 1) with reference to the storage unit 32. The propagation time ranges for specifying the above cycle of the head echo (S echo cycle) and the cycle of the bottom echo (B echo cycle) are stored in the storage unit 32 by the echo detection unit 31 d.
Incidentally, the propagation time ranges of the S-echo period and the B-echo period are set to be wider than those of the S-echo period and the B-echo period for automatic tracking described later. The S-echo period and the B-echo period can be set to be about two cycle widths of the ultrasonic pulse, but are not limited thereto.
Next, in the bolt axial force measuring step, the probe 24 (see fig. 3) oscillates an ultrasonic pulse to the bolt 1 (see fig. 3). The oscillation of the ultrasonic pulse is performed in accordance with an instruction from the ultrasonic transmission/reception control unit 31f (see fig. 1) of the control unit 30 (see fig. 1). The oscillation time of the ultrasonic pulse is stored in the storage unit 32 (see fig. 1) by the ultrasonic transmission/reception control unit 31 f. Incidentally, the oscillation of the ultrasonic pulse (specifically, the oscillation during the application of the axial force) in the present embodiment is assumed to oscillate at the repetition frequency, but is not limited thereto.
The ultrasonic pulse is reflected on the surface of the bolt 1 (see fig. 3) defined by the bottom surface 6 (see fig. 3) of the recess 5 (see fig. 3), and is reflected on the distal end surface of the shaft portion 2.
The probe 24 detects a 0 th head echo (S0 echo) reflected on the surface of the bolt 1 (see fig. 3), and detects a 0 th bottom echo (B0 echo) reflected on the bottom surface of the bolt 1. Here, the 0 th time represents measurement before the axial force is applied.
Then, the ultrasonic wave transmission/reception control unit 31f (see fig. 1) amplifies the S0 echo and the B0 echo detected by the probe 24, for example, independently of each other.
The echo detector 31d acquires the amplified S0 echo and B0 echo from the ultrasonic wave transmission/reception controller 31f, and acquires propagation time ranges of the S echo cycle and the B echo cycle with reference to the memory 32.
Next, the echo detector 31d sets the S echo period G based on the S0 echo and the B0 echoS0And B echo period GB0(refer to step S101)
Specifically, the echo detection unit 31d sets the S-echo period G based on the S0 echo in the propagation time rangeS0Starting point G ofS0SThe amplitude of the S0 echo is set to exceed a level L preset to be positive or negativeSThe peak position P of the first wave ofSThe position before 1/2 wavelength of the ultrasonic pulse (see fig. 6). The echo detector 31d sets the S echo period GS0End point G ofS0ESet at the starting point GS0SThe position after one wavelength of the ultrasonic pulse (see fig. 6).
In the present embodiment, the level LSSet to positive, the amplitude exceeds the level LSThat is, in a graph with propagation time as the horizontal axis, the amplitude is smaller than the level LSBecomes (a value whose absolute value is also small) toGreater than level LSValue (value with larger absolute value). Peak position P in this caseSA positive peak. In the level L, it should be noted thatSWhen the amplitude is set to be negative, the amplitude exceeds the level LSThat is, in a graph with propagation time on the horizontal axis, the amplitude is larger than the level LSIs changed to be smaller than the level L (a value having a smaller absolute value)SValue (value with larger absolute value). Peak position P in this caseSA negative peak.
Similarly, the echo detector 31d is based on B in the propagation time range0Echo, the B echo period GB0Starting point G ofB0SIs set at B0The amplitude of the echo exceeds a level L preset to be positive or negativeBThe peak position P of the first wavelength B1/2 (see fig. 6). The echo detector 31d also sets the B echo period GB0End point G ofB0ESet at the starting point GB0SThe position after one wavelength of the ultrasonic pulse (see fig. 6).
In the present embodiment, the level LBSetting positive, amplitude over level LBThat is, in a graph with propagation time on the horizontal axis, the amplitude is smaller than the level LBIs changed to be greater than the level LBThe value of (c). Peak position P in this caseBA positive peak. In the level L, it should be noted thatBWhen the amplitude is set to be negative, the amplitude exceeds the level LBThat is, in a graph with propagation time on the horizontal axis, the amplitude is larger than the level LBIs changed to be smaller than the level L (a value having a smaller absolute value)BValue (value with larger absolute value). Peak position P in this caseBA negative peak.
Next, the echo detection unit 31d acquires the S echo period GS0Propagation time of inner S0 echo and B echo period GB0The propagation time of the inner B0 echo (see step S102).
More specifically, the echo detection unit 31d detects the S echo period GS0Positive or negative peak pre-zero crossing point in the time domain, and obtaining the propagation time t of the zero crossing pointS0The propagation time of the echo of S0 (see fig. 6). In the present embodiment, the zero-cross point is a point at which the amplitude of the echo of the ultrasonic pulse is zero.
Similarly, the echo detector 31d detects the B echo period GS0Positive or negative peak pre-zero crossing point in the time domain, and obtaining the propagation time t of the zero crossing pointB0The propagation time of the B0 echo is shown (see fig. 6).
The echo detector 31d repeats step S102 until the acquisition of the propagation time of the echo of S0 and the propagation time of the echo of B0 is completed (no in step S103).
Then, when the acquisition of the propagation time of the echo of S0 and the propagation time of the echo of B0 is completed (yes in step S103), the echo detecting unit 31d acquires the start point GS0SAs the S-echo period GS0The reference position is tracked and held (see step S104) (see fig. 6).
Similarly, the echo detecting unit 31d acquires the start point GB0SAs the B echo period BS0The reference position is tracked and held (see step S104) (see fig. 6).
Next, in the bolt axial force measuring step, the nut runner control unit 31a (see fig. 1) outputs a drive command to the nut runner 21 (see fig. 1).
That is, an axial force is applied to the bolt 1 (see fig. 4) by the fastening device 20 (see fig. 1) of the bolt 1 (see step S107).
When the echo of the ultrasonic Pulse at the next (nth time; n is a natural number) transmission PRF (Pulse Repetition Frequency) is detected (yes in step S108), the echo detection unit 31d acquires the S-echo period GSn-1Propagation time of inner Sn echo and B echo period GBn-1The propagation time of the inner Bn echo (see step S109).
More specifically, the echo detection unit 31d detects the S echo period GSn-1The zero crossing point before the positive or negative peak in the interior is obtained, and the propagation time t of the zero crossing point is obtainedSnThe propagation time of the Sn echo is shown in fig. 7.
Although not shown, the echo detector 31d similarly detects the B echo cycleGBn-1The zero crossing point before the positive or negative peak in the interior is obtained, and the propagation time t of the zero crossing point is obtainedBnAs the propagation time of the Bn echo.
The echo detection unit 31d repeats step S109 until the acquisition of the Sn echo propagation time and the Bn echo propagation time is completed (no in step S110).
Then, when the acquisition of the propagation time of the Sn echo and the propagation time of the Bn echo is completed (yes in step S110), the axial force calculation unit 31b calculates the propagation time tSn、tBnAnd an initial propagation time T, and calculates an axial force F of the bolt 1 (see step S111).
The Sn echo and the Bn echo are suppressed from waveform disturbance by the probe 24 (see fig. 2) supported by a semi-floating structure.
Incidentally, the length of the bolt 1 can be based on the difference (t) between the propagation time of the zero-crossing point of the Sn echo and the propagation time of the zero-crossing point of the Bn echoBn-tSn) And (4) obtaining.
The elongation calculation unit 31c (see fig. 1) calculates the amount of elongation (δ) of the bolt 1 based on the difference in propagation time calculated by the echo detection unit 31d (see fig. 1).
The axial force calculation unit 31b (see fig. 1) acquires the amount of change (δ) in the extension of the bolt 1 calculated by the extension calculation unit 31c (see fig. 1), and acquires the parameter of expression 1 described above with reference to the storage unit 32 (see fig. 1). Then, the axial force calculation unit 31b (see fig. 1) calculates the axial force of the bolt 1 based on equation 1, and outputs the axial force to the display unit 34 (see fig. 1) (see step S108).
Next, the echo detecting unit 31d determines the S echo period GSnAnd B echo period GSnThe tracking processing is executed individually (refer to step S112).
Specifically, the echo detector 31d makes the previous (n-1 st) S-echo cycle GSn-1Starting point G ofSn-1SMoving time (t)Sn-tSn-1) Setting the current (nth) S echo period GSnStarting point G ofSnS(refer to fig. 7).
The echo detector 31d sets the S echo period GSnEnd point G ofSnEIs set from the starting pointGSnSStarting at one wavelength of the backward ultrasonic pulse (see fig. 7).
In the application of the axial force, the head 3 of the bolt 1 may be distorted by the applied axial force. The S echo period GSnThe tracking processing of (2) is processing for appropriately detecting Sn echo in response to the distortion of the head 3.
Although not shown, the echo detector 31d similarly makes the previous (n-1 st) B echo cycle GBn-1Starting point G ofBn-1S moving time (t)Bn-tBn-1) To set the B echo period G of this time (nth time)BnStarting point G ofBnS。
The echo detector 31d also sets the B echo period GBnEnd point G ofBnEIs set from the starting point GBnSStarting at one wavelength of the backward ultrasonic pulse.
In the application of the axial force, the shaft portion 2 of the bolt 1 is elongated by the applied axial force. The B echo period GBnAnd a process for appropriately detecting the Bn echo in response to the extension of the shaft 2.
Next, the axial force calculation unit 31b sets an axial force normal range based on the calculated axial force (F) (see step S113).
As shown in fig. 8, more specifically, the axial force calculation unit 31b calculates a straight line L that approximately represents the temporal change in the axial force (F) based on a graph in which the calculated axial force (F) is plotted in time series.
The axial force calculation unit 31b sets the normal range Rn of the axial force by using a preset value (for example, 10% above or below) for the straight line L.
Next, when the axial force (F) is outside the normal range of axial force Rn and continues at or above the preset amount of change in elongation (δ) (yes in step S114), the axial force calculation unit 31b determines that an abnormality has occurred in the measurement.
In this case, the nut power wrench stop command unit 31a (see fig. 1) outputs a stop command for applying an axial force to the nut power wrench 21 (see fig. 1). That is, the application of the axial force to the bolt 1 is stopped. Further, although not shown, the nut runner 21 is stopped, and the automatic tracking is also stopped, and the series of bolt axial force measurement steps are ended (abnormal end).
On the other hand, when the axial force (F) is within the normal range of axial force Rn and continuously falls within the preset amount of change in elongation (δ) (no in step S114), the axial force calculation unit 31b determines that the measurement is normally performed.
The nut power wrench stop command unit 31a (see fig. 1) acquires the axial force (F) of the bolt 1 calculated by the axial force calculation unit 31b (see fig. 1). Then, the nut power wrench stop command section 31a determines whether or not the axial force (F) of the bolt 1 reaches the target axial force value (refer to step S115).
When the axial force (F) does not reach the target axial force value (no in step S115), the nut power wrench stop command unit 31a (see fig. 1) outputs a subsequent command for applying the axial force to the nut power wrench 21 (see fig. 1). That is, returning to step S108, the axial force against the bolt 1 is continued to be applied.
When the axial force (F) reaches the target axial force value (yes in step S115), the nut power wrench stop command unit 31a (see fig. 1) outputs a command to stop the application of the axial force to the nut power wrench 21 (see fig. 1). That is, the application of the axial force to the bolt 1 is stopped. Further, although not shown, the nut runner 21 is stopped, and the automatic tracking is also stopped, and the series of bolt axial force measuring steps is ended (normally ended).
The present flow may be configured to perform abnormality determination based on the amount of change in elongation (δ) of the bolt 1 and the normal range thereof, instead of the axial force (F), or may be configured to end the bolt axial force measurement step when the amount of change in elongation (δ) of the bolt 1 reaches a target value.
< method for amplifying echo >
In the present embodiment, the ultrasonic wave transmission/reception control unit 31f includes a first amplitude correction unit 31f1, a second amplitude correction unit 31f2, and a third amplitude correction unit 31f 3.
The first amplitude correction unit 31f1 sets the amplitude increase width for the entire time axis, and corrects the amplitude of both the head echo period and the bottom echo period by the same amount based on the amplitude increase width.
In the present embodiment, the correction coefficient C1 (fig. 9) that is the amplitude increase is set in advance by a preliminary experiment or the like.
The second amplitude correction unit 31f2 corrects the amplitude of one of the head echo period and the floor echo period so as to be close to the amplitude of the other of the head echo period and the floor echo period, with reference to the one of the head echo period and the floor echo period.
In the present embodiment, the correction coefficient C2 (fig. 9), which is an amplitude increase, is corrected so that the amplitude of the Bn echo is close to the amplitude of the Sn echo, and is set in advance by a preliminary experiment or the like. The second amplitude correction unit 31f2 multiplies the Bn echo by the correction coefficient C2 in the propagation time of the echo cycle in which the Bn echo is detected. Thus, the second amplitude correction unit 31f2 can make the amplitudes in the echo periods of the Sn echo and the Bn echo substantially the same and display them on the display unit 34.
The third amplitude correction unit 31f3 corrects the amplitude of one of the head echo period and the bottom echo period. In the present embodiment, the correction coefficient C3 (see fig. 9), which is an amplitude increase, is corrected so that the amplitude of the Bn echo is close to the amplitude of the Sn echo, and is set in advance by a preliminary experiment or the like. Thus, the third amplitude correction unit 31f3 can make the amplitudes in the respective echo periods of the Sn echo and the Bn echo substantially the same and display them on the display unit 34.
The bolt axial force measuring apparatus 10 may perform amplitude correction on any one of the first amplitude correction unit 31f1, the second amplitude correction unit 31f2, and the third amplitude correction unit 31f3 alone, or may perform substantially the same correction on the amplitude in each echo period using both the second amplitude correction unit 31f2 and the third amplitude correction unit 31f 3.
When both the second amplitude correction unit 31f2 and the third amplitude correction unit 31f3 are used, the amplitude of both the Sn echo and the Bn echo may be corrected by the second amplitude correction unit 31f2, and then the amplitude of the Bn echo may be corrected by the third amplitude correction unit 31f 3. According to this correction method, the amplitudes of the Sn echo and the Bn echo in the respective echo periods can be made closer to each other more accurately.
Bolt (screw bolt)
The bolt 1 (see fig. 3) used in the above bolt axial force measuring method includes the shaft portion 2 (see fig. 3) and the head portion 3 (see fig. 3) as described above. The bottom surface 2c is defined at the distal end of the shaft portion 2 (see fig. 3).
An engagement portion (not shown) that engages with a fastening member (e.g., a torque wrench) of the bolt 1 is formed on an outer peripheral portion of the head portion 3.
In addition, the head 3 is formed with a recess 5 as shown in fig. 3. The recess 5 includes a bottom surface 6 and a peripheral wall 11 formed around the bottom surface 6. The bottom surface 6 is formed to include a plane having a bolt axis as a normal line.
Such a recess 5 is composed of a large diameter portion 14a formed on the opening side of the recess 5 and a small diameter portion 14b formed with a peripheral wall 11 having an inner diameter smaller than the inner diameter of the large diameter portion 14 a. The small diameter portion 14b is connected to the large diameter portion 14a via a stepped portion 14c for absorbing the difference in inner diameter.
The large diameter portion 14a, the step portion 14c, and the small diameter portion 14b form a stepped recess 5 (stepped recess) coaxial with the bolt axis in the head portion 3 of the bolt 1.
The stepped recess 5 is fitted into the stepped projection 29 of the probe 24 having the step 24b as described above.
The peripheral wall 11 constituting the small diameter portion 14b extends linearly from the bottom surface 6 side toward the opening side of the recess 5 when viewed from the side of the bolt 1 shown in fig. 3. However, the peripheral wall 11 may be formed so as to partially bulge outward in the radial direction of the head 3 without being limited to extending linearly as long as it fits in the probe 24.
Action and Effect
Next, the operation and effect of the present embodiment will be described.
< effect of the fastening device >
In the conventional fastening device, since the socket and the ultrasonic sensor are integrated, there is a problem that the socket falls down or shakes during fastening of the bolt and vibration is transmitted to the probe. As a result, the conventional fastening device has a problem that the accuracy of the bolt axial force measured while fastening the bolt is insufficient.
In contrast, in the fastening device 20 of the present embodiment, the socket 22 and the probe 24 are provided independently of each other.
Fig. 10 (a) and (b) are diagrams illustrating the operation of the fastening device 20 of the bolt 1 constituting the bolt axial force measuring device 10.
As shown in fig. 10 (a), the fastening device 20 of the present embodiment has the socket 22 and the probe 24 arranged independently of each other.
When the bolt 1 is fastened by the fastening device 20, the probe 24 is fitted in the recess 5 of the bolt 1 and the socket 22 is fitted in the bolt 1 as described above. Then, the socket 22 is rotated to tighten the bolt 1, and the elongation of the bolt 1 is detected by the probe 24.
As shown in fig. 10 (b), even when the socket 22 is shaken at the time of fastening the bolt 1, the fastening device 20 does not change the pressing angle of the probe 24 against the bolt 1 because the probe 24 and the socket 22 are independently arranged. This allows the fastening device 20 to accurately measure the elongation of the bolt 1 without being affected by the backlash of the socket 22.
As described above, the probe 24 is supported by the lower end of the rotary shaft 21a (see fig. 2) in a semi-floating manner by the elastic coil spring 28.
As a result, as shown in fig. 10 (b), even if the socket 22 is inclined with respect to the axis of the bolt 1, the probe 24 is not inclined with respect to the axis of the bolt 1.
Therefore, the fastening device 20 can measure the axial force with high accuracy.
The fastening device 20 in the present embodiment fits the probe 24 into the recess 5 in a socket manner as described above. Thereby, in the fastening device 20, the probe 24 is firmly fixed to the recess 5. Therefore, the fastening device 20 can measure the axial force with high accuracy.
The fastening device 20 in the present embodiment forms a gap 41 between the surface of the bolt 1 defined by the bottom surface 6 of the recess 5 and the surface of the probe 24 defined by the top surface 24d of the protrusion 24 a. The gap 41 is filled with a propagation material 42 of ultrasonic waves.
According to such a fastening device 20, a measurement error caused by a waveform change or the like in the gap 41 can be prevented. Therefore, the fastening device 20 can measure the axial force with high accuracy.
< effect of measuring bolt axial force >
In general, in an ultrasonic measuring bolt in which a probe is disposed in a recess formed in a head portion, there is fluctuation in flatness or the like of a bottom surface of the recess defining a bolt surface. Therefore, the accuracy of the ultrasonic measurement value is insufficient in the structure in which the probe is brought into close contact with the bottom surface of the recess.
In contrast, the bolt axial force measuring method of the present embodiment and the bolt 1 used in the method have a stepped portion 14c in the recess 5.
According to the bolt axial force measuring method and the bolt 1 used in the method, the probe 24 is supported by the step portion 14c, so that the gap 41 can be formed between the probe 24 and the bottom surface 6 of the recess 5. Therefore, according to the bolt axial force measuring method, the accuracy of the ultrasonic measurement value can be remarkably improved.
In addition, according to the bolt axial force measuring method of the present embodiment, the gap 41 is interposed with the propagation material 42 of the ultrasonic wave.
According to the bolt axial force measuring method, the attenuation of the ultrasonic wave in the gap 41 can be suppressed. Thus, according to the bolt axial force measuring method of the present embodiment, more accurate axial force measurement can be achieved.
In general, when the probe 24 is brought into contact with the surface of the bolt 1 (the bottom surface 6 of the recess 5) to measure the B echo, the oscillation origin (position 0) of the ultrasonic wave cannot be measured due to the vibration of the probe 24 itself at the time of the ultrasonic oscillation. Therefore, in the conventional bolt axial force measurement method, the B1 echo (the 1 st bottom echo) cannot be used for the axial force measurement, and the B echo after the B2 echo is stopped (after the 2 nd bottom echo) is measured for the axial force based on the vibration of the probe 24 itself. However, the B echo after the B2 echo is attenuated compared to the B1 echo, and there is a problem that the influence of noise is significant.
In contrast, in the bolt axial force measurement method according to the present embodiment, the gap 41 is provided, and the bolt axial force is measured based on the difference between the S1 echo and the B1 echo on the surface of the bolt 1. Thus, in the bolt axial force measurement method according to the present embodiment, the B1 echo having a smaller attenuation and a smaller noise than the B2 echo is used, whereby the accuracy of the bolt axial force measurement is further improved.
< effect of bolt axial force measuring device >
Further, the bolt axial force measuring device 10 of the present embodiment includes: an echo detection unit 31d that detects a head echo (Sn echo) and a bottom echo (Bn echo) of an ultrasonic pulse oscillating from the head side of the bolt 1 toward the bottom surface of the shaft portion of the bolt 1; and an axial force calculation unit 31b that calculates the axial force of the bolt 1 based on the time difference between the predetermined positions of the head echo and the bottom echo detected by the echo detection unit 31 d.
The echo detection unit 31d sets a head echo period G for the head echoSnAnd a bottom echo period G is set for the bottom echoBnIn fastening the bolt 1, the head echo period G is adjusted for the ultrasonic pulse of the multiple oscillationsSnAnd bottom echo period BSnPerforming tracking processing so that the prescribed position is located in the head echo period GSnAnd bottom echo period BSnAre moved independently in the same position.
Thus, in the bolt axial force measuring apparatus 10 of the present embodiment, the axial force (F) of the bolt 1 can be measured more reliably and accurately by tracking the head echo and the bottom echo independently without providing the reference cycle.
The bolt axial force measuring device 10 of the present embodiment further includes an amplitude correction unit (ultrasonic transmission/reception control unit 31f) that generates a head echo period GSnAmplitude of inner head echo (Sn echo) and bottom echo period GBnThe amplitude of the inner bottom echo (Bn echo) is corrected to be close to each other.
Thus, in the bolt axial force measuring device 10 according to the present embodiment, the head echo (Sn echo) and the bottom echo (Bn echo) can be displayed at substantially the same amplitude level regardless of whether the bottom echo (Bn echo) is attenuated or not.
In addition, the bolt axial force measurement of the present embodimentThe volume device 10 is characterized in that the amplitude correction unit includes at least one of a first amplitude correction unit 31f1 and a second amplitude correction unit 31f2, wherein the first amplitude correction unit 31f1 sets an amplitude increase for the entire time axis and corrects the head echo period G based on the amplitude increaseSnAnd bottom echo period GBnBoth amplitudes, the second amplitude correction unit 31f2 takes the head echo period GSnAnd bottom echo period GBnOne of them is used as a reference so as to make the head echo period GSnAnd bottom echo period GBnThe other amplitude of (3) is close to the head echo period GSnAnd bottom echo period GBnOne of the amplitudes is corrected.
Thus, in the bolt axial force measuring device 10 according to the present embodiment, the head echo (Sn echo) and the bottom echo (Bn echo) can be displayed at substantially the same amplitude level.
In the bolt axial force measuring device 10 according to the present embodiment, the echo detecting unit 31d determines that the amplitude of the head echo exceeds the first predetermined value LSThe first positive or negative peak value of the ultrasonic pulse is set as a head echo period, and the amplitude of the bottom echo is set to exceed a second predetermined value LBOne wavelength of the ultrasonic pulse centered on the first positive or negative peak is set as the bottom echo period.
The echo detector 31d sets a point having an amplitude of zero at a predetermined position before the positive or negative peak value with respect to the head echo period and the bottom echo period, respectively.
Thus, in the bolt axial force measuring device 10 according to the present embodiment, the range of the cycle of each echo is reduced and the backward setting is made longer than the predetermined position, so that the movement of each echo due to elongation or the like can be appropriately tracked.
The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments and can be implemented in various ways.
In the above embodiment, the fastening device 20 for fastening the head 3 of the bolt 1 by the socket 22 is described as an example, but the fastening device 20 of the present invention may be a member for fastening a nut (not shown) engaged with the bolt 1. The present invention can also be realized by a bolt axial force measurement program that causes a computer to function as the bolt axial force measurement device 10.
