WO2006137553A1

WO2006137553A1 - Method for nondestructive testing of shielded signal wire

Info

Publication number: WO2006137553A1
Application number: PCT/JP2006/312676
Authority: WO
Inventors: Eiji Kashio; Yoshinobu Sugita; Keisuke Ayabe
Original assignee: Honda Motor Co., Ltd.
Priority date: 2005-06-21
Filing date: 2006-06-20
Publication date: 2006-12-28
Also published as: JP2007003214A

Abstract

A nondestructive testing method whereby the degree of degradation of a shielded signal wire can be determined merely by moving an eddy current sensor (11) along a shielded signal wire (20).

Description

DESCRIPTION

METHOD FOR NONDESTRUCTIVE TESTING OF SHIELDED SIGNAL WIRE

TECHNICAL FIELD

The present invention relates to a method for nondestructive testing of a signal wire in which the degree of degradation of a shielded signal wire is tested.

BACKGROUND ART Various electrical wires are routed in manufacturing equipment. Electrical wiring becomes damaged over the course of prolonged use. This damage is referred to as degradation.

The proper functioning of manufacturing equipment is maintained by examining the degree of degradation of the electrical wiring periodically or as needed, and replacing the wiring according to the degree of degradation.

Electrical wiring is tested according to a testing method such as the one described in Japanese Patent Laid-Open Publication No. 5-296943, for example. This conventional testing method involves preparing an image diagnostic device 104 and a test rod 103 provided with a backdrop plate 102 and a camera 101 at the top end thereof, as shown in FIG. 9. Reference data are stored in advance in this image diagnostic device 104. A tester 105 carries the image diagnostic device 104 and moves the distal end of the test rod 103 along an electrical wire 106, and an image of the electrical wire 106 is captured by the camera 101. The image data obtained from this imaging are compared with the reference data by the image diagnostic device 104. This comparison determines whether the electrical wire 106 has degraded. The conventional testing method described above is used to determine the outer appearance, i.e., the surface condition of the electrical wire 106 based on image data, and is therefore adapted for testing bare wiring.

Besides bare wiring, electrical wiring also includes coated wiring. This coated wiring includes unshielded wires and shielded wires. Shielded wire is preferably used for signal wires in order to protect against the effects of noise. In coated wiring such as a shielded signal wire, the test subject is under the coating layer, and is therefore difficult to test using the abovementioned conventional testing method. Destructive testing methods and non-destructive testing methods are considered as techniques that can be used in place of the conventional testing method. A convenient destructive testing method involves peeling off the coating and visually examining the internal wire or shielding, but this method is impractical because the wire then becomes unusable.

Conventional non-destructive testing methods include X- ray imaging methods, gamma-ray imaging methods, and ultrasonic flaw detection methods, but the testing devices used in all of these methods are large, a trained tester is needed to perform the test, and testing costs are increased. - 1 -

Among coated wires that are difficult to test, shielded signal wires have low strength compared to power supply wires. Large numbers of these shielded signal wires are placed in the joints of robots, for example. Since significant wear occurs in the shielded signal wires due to the repeated flexing of robot joints, nondestructive testing becomes even more necessary.

There has therefore been a need for a more convenient method of nondestructive testing of shielded signal wires. DISCLOSURE OF THE INVENTION

According to an aspect of the present invention, there is provided a method for nondestructive testing of a signal wire in which the degree of degradation of a shielded signal wire is tested, the method comprising the steps of: obtaining an output from an eddy current sensor by bringing the sensor into contact with a reference shielded signal wire and determining a reference value on the basis of the output from the sensor; obtaining a measured value by bringing the eddy current sensor into contact with a shielded signal wire being tested; and determining that the measured value is abnormal when differs from the reference value by an amount equal to or greater than a specific value, and determining that the measured value is normal in other conditions.

A normal or abnormal condition is determined by bringing an eddy current sensor into contact with a shielded signal wire and comparing the output of the sensor with a reference value. Eddy current sensors are widely used as compact rangefinders or compact displacement meters; are inexpensive and widely available; are more convenient to use than X-ray imaging, gamma-ray imaging, and ultrasonic flaw detection; and require no special training. Preferably, the shielded signal wire comprises a signal wire used to control equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a side view of the eddy current tester according to the present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; FIG. 3 is a schematic view of the control device shown in FIG. 1;

FIGS. 4A and 4B are basic diagrams of the eddy current sensor shown in FIG. 1;

FIGS. 5A and 5B are diagrams describing the manner in which a shielded signal wire used as a reference is tested using the eddy current tester shown in FIG. 1;

FIGS. 6A through 6D are diagrams describing the manner in which a shielded signal wire subjected to a bending test is tested using the eddy current tester shown in FIG. 1; FIG. 7 is a graph showing the relationship between the measurement position and the sensor output; FIG. 8 is a flow diagram of the control performed by the control device shown in FIG. 3; and

FIG. 9 is a diagram describing a conventional electrical wire testing method. BEST MODE FOR CARRYING OUT THE INVENTION

The eddy current tester 10 shown in FIG. 1 is composed of an eddy current sensor 11, a sensor housing 12 in which the eddy current sensor 11 is housed, a signal wire holder 13 that is connected to this sensor housing 12 and holds a signal wire 20 together with the sensor housing 12, a handle 15 mounted to the sensor housing 12 via a coupling fitting 14, and a control unit 30 housed in this handle 15.

The signal wire 20 shown in FIG. 2 may, for example, be a shielded coated wire composed of eight twisted wires 21, a shield 22 for

all of these twisted wires 21 at once, and an insulating coat 23 for covering the shield 22.

The signal wire 20 is placed between the sensor housing 12 and the signal wire holder 13. The signal wire holder 13 is then brought into proximity with the sensor housing 12. This operation causes the signal wire 20 to approach the eddy current sensor 11. A screw 27 is tightened once the distance between the signal wire 20 and the eddy current sensor 11 has reached a prescribed value. The eddy current tester 10 can thereby be moved along the signal wire 20 as indicated by the arrow X shown in FIG. 1.

The structure of the control unit 30 will next be described. As shown in FIG. 3, the control device 30 is provided with a reference value setting unit 31 for setting a reference value, a normal/abnormal determination unit 32 for comparing a measured value with the reference value set by the reference value setting unit 31 and determining whether a normal or abnormal state exists, and a warning unit 33 for issuing a warning when the existence of an abnormal state is determined by the normal/abnormal determination unit 32. The handle 15 is furthermore provided with an input unit 34 for allowing a differentiating maximum value and a differentiating minimum value to be set in the reference- value setting unit 31 by entering an allowable difference with respect to the reference value, and a switching switch 35 for selectively transferring the sensor output obtained by the eddy current sensor 11 to the reference value setting unit 31 or the normal/abnormal determination unit 32.

The warning unit 33 emits an audible or visible warning and notifies the tester that an abnormality has been detected. The operating principle of the eddy current sensor 11 will next be described.

As shown in FIG. 4A, a high-frequency current is fed to a sensor coil 42 by an oscillator 41 of the eddy current sensor 11. A high-frequency magnetic field 43 is then generated in the sensor coil 42. As the distance between the sensor coil 42 and the shield 22 decreases, the effect of the high-frequency magnetic field 43 increases, and the eddy current 44 generated in the shield 22 increases. The impedance of the sensor coil 42 changes under the influence of this eddy current 44. The change in voltage that is based on this change in impedance is applied to an LC resonance circuit made up of the sensor coil 42 and a capacitor C. The voltage change thus applied is detected at high frequency by a detection circuit 45. The voltage Vl thus detected at high frequency is converted by a linearizer 46 to a voltage V2 that is proportional to a displacement equal to distance LLO. This voltage V2 is amplified by an amplifier 47 and delivered as a sensor output (output voltage) V. As a result, a graph is obtained that shows the relationship between the distance and the sensor output, as shown in FIG. 4B. The sensor naturally has a specific measurement range, and since the sensor output is proportional to the distance within this measurement range, the distance can be found on the basis of the sensor output.

A shielded signal wire used as a reference is first tested using the eddy current tester 10 configured as described above. As shown in FIG. 5A, a shield 22 is aligned in the shielded signal wire (new signal wire, for example) used as a reference. An eddy current sensor 11 indicated by an imaginary line is brought into proximity with the shield 22. The sensor output of the eddy current sensor 11 at this time is V3, as shown in FIG. 5B.

The shielded signal wire is then tested following a bending test. -S-

In the shield 22 of the shielded signal wire subjected to a bending test, parts of the shield 22 have separated from adjacent parts of the shield 22 and have become coarser, as shown in FIG. 6A. The eddy current sensor 11 indicated by the imaginary line is therefore brought into proximity with the coarse portions of the shield 22. The sensor output of the eddy current sensor 11 at this time is V4, as shown in FIG. 6B. This output V4 is larger than V3.

In the shield 22 of the shielded signal wire subjected to a bending test, some parts of the shield 22 are overlapped with the adjacent parts of the shield 22 and are too densely packed, as shown in FIG. 6C . The eddy current sensor 11 indicated by the imaginary line is brought into proximity with the densely packed portions. The sensor output of the eddy current sensor 11 at this time is V5, as shown in FIG. 6D. This output V5 is smaller than V3.

The reasons for the above results are as follows. Since parts of the shield 22 shown in FIG. 6A have become unraveled, the eddy currents occurring in the shield 22 are markedly smaller than the eddy currents occurring in the shield 22 shown in FIG. 5A. The sensor output increases with increased magnitude of the eddy current.

Because the shield 22 shown in FIG. 6C is densely packed, the eddy current occurring in the shield 22 is markedly stronger than the eddy current occurring in the shield 22 shown in FIG. 5A. The sensor output decreases with increased magnitude of the eddy current. Even when the actual distance is the same, the sensor output decreases when the shield 22 is densely packed, and increases when the shield 22 is coarse.

Specifically, by monitoring the sensor output, the coarseness or density of the shield 22 can be detected.

It can also be determined that the shield 22 is abnormally coarse when the sensor output is larger than the reference sensor output, or that the shield 22 is abnormally dense when the sensor output is smaller than the reference sensor output.

A method for the nondestructive testing of a shielded electrical wire will be described hereinafter. This method is based on the flaw determination principle described above.

In FIG. 1, a new shielded electrical wire 20 or one that is used as a reference is placed in the eddy current tester

10. The sensor output is thereby recorded, and a sensor output reference value V3 is specified from this record.

This reference value V3 is entered as a horizontal line in the graph shown in FIG. 7. The sensor output appears as a small waveform such as the curve indicated by the reference symbol Vact . A certain vertical range must therefore be allowed for the sensor output. Otherwise, a normal condition would frequently be misdiagnosed as an abnormality, and the reliability of the test would be compromised. An upper allowable difference of Δl is therefore estimated for the reference value V3, and a differentiating upper limit V6 is established. This upper limit Vβ is entered as a horizontal line in the graph shown in FIG. 7. A lower allowable difference of Δ2 is also estimated for the reference value V3, and a differentiating lower limit V7 is established. This lower limit V7 is entered as a horizontal line in the graph shown in FIG. 7.

As shown in FIG. 1, the eddy current tester 10 is brought into proximity with the shielded signal wire 20 as the test subject, and the measured value Vact of the sensor output is obtained. When this measured value Vact is superposed on the graph in FIG. 7, Vact substantially coincides with V3 from point Pl to point P2. Vact is above V6 from point P2 to point P3. Vact is below V7 from point P4 to point P5.

Since Vact is above V6 from point P2 to point P3, the shield can be considered to be extremely coarse, and the existence of an abnormal region A can be recognized.

Since Vact is below V7 from point P4 to point P5, the shield can be considered to be extremely dense, and the existence of an abnormal region B can be recognized.

A destructive test or other follow-up test may be performed for the shielded signal wire in which abnormal regions A and B were found. Specifically, the presence of an abnormal region can be determined merely by bringing the eddy current tester of the present invention into proximity with a shielded signal wire. Since this test is nondestructive, there is no risk of damaging the signal wire.

The non-destructive testing method of the present invention will next be described according to FIG. 8. In step 01 (hereinafter indicated as ST) , the eddy current sensor is placed against a shielded signal wire as a reference, and a reference value V3 is set on the basis of the resultant sensor output. Then, in ST02, an allowable difference is entered for the sensor output reference λralue V3 by the input unit (FIG. 3), and a differentiating upper limit Vb is set. In ST03, an allowable difference is entered for the sensor output reference value V3 by the input unit (FIG. 3), and a differentiating lower limit V7 is set. In ST04, a measured value Vact from the shielded signal wire that is the test subject is- obtained by the eddy current sensor. It is determined in ST05 whether V7 < Vact < V6. If V7 < Vact < V6, the process will proceed to ST08, and if Vact < V7 or Vact > V6, the process will proceed to ST06. A warning signal is issued by the normal/abnormal determination unit (FIG. 3) in ST06. In ST07, an audible or visible warning is issued. It is determined in ST08 whether measurement is completed. The test is completed when measurement is completed, and the process will proceed to ST04 if measurement is not completed.

In the present embodiment, a warning was issued to the tester based on the reference value or measured value thus obtained. A configuration may also be adopted whereby this reference value or measured value is transferred to a processing device using a wireless LAN (Local Area Network) or the like, and this reference value or measured value is recorded, classified, plotted, and otherwise processed by the processing device.

The reference value and measured value were described as voltages in the present embodiment, but the sensor output may also be read as a distance when an eddy current displacement meter is used. The reference value and the actual value may also be a voltage, a distance, or any type of value equivalent thereto .

INDUSTRIAL APPLICABILITY . As described above, the present invention is useful for the nondestructive testing of shielded signal wires that are used to control equipment.

Claims

1. A method for nondestructive testing of a signal wire in which the degree of degradation of a shielded signal wire is examined, said method comprising the steps of: obtaining an output from an eddy current sensor by bringing the sensor into contact with a reference shielded signal wire and determining a reference value on the basis of the output from the sensor; obtaining a measured value by bringing the eddy current sensor into contact with a shielded signal wire being tested; and determining that the measured value is abnormal when the measured value differs from the reference value by an amount equal to or greater than a specific value, and determining that the measured value is normal in other conditions.

2. The method of claim 1, wherein the shielded signal wire comprises a signal wire used to control equipment.