JPH07243821A - Inspection of wire - Google Patents

Abstract

PURPOSE:To provide a method for judging whether a joint part in which the intermediate part is connected by a crimp-style terminal with another wire is good or defective. CONSTITUTION:A peeled part of conductor 1 is connected with the end of another wire by means of a crimp-style terminal, and its joint part 1a is illuminated with a transmissive illumination, then its gradation picture is obtained. The obtained picture is binarized and the edge of outer circumference of the joint part is traced to calculated the tilt of approximate straight line formed by a plurality of close picture elements, and when the tilt has a specified value or more, the boundary of the peeled part and the end position of the crimp-style terminal are judged based on the central position of the line as a changing position. Further, the joint part is illuminated with a ring illumination ad the change in brightness of an object within a picture is detected so as to judge the deformation of the crimp-style terminal and also judge whether the joint part is normal or defective.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case where a wire terminal is crimped to an intermediate stripping portion where the coating of the intermediate portion of the wire is stripped to a certain length, and an end where the coating of another wire is stripped. The present invention relates to a method for inspecting a linear material for inspecting the quality of a connection portion.

[0002]

2. Description of the Related Art When wire terminals are crimped to each other, for example, in the middle of a trunk wire, by using a metal terminal, that is, a crimping terminal,
As shown in FIG. 23, the coating 2 of the portion to be connected to the main line 1 (hereinafter referred to as “intermediate peeling portion”) is stripped off over a predetermined length to bare the core wire 3 and the coating 5 of the branch wire 4 is removed. The terminal of the core wire 6 is exposed by stripping off the terminal for a predetermined length, and as shown in FIG. 24 (a) or FIG.
Alternatively, the core wire 6 of the branch wire 4 is pressure-bonded to the core wire 3 of the main wire 1 by means of 8.

When the core wire 3 of the trunk wire 1 and the core wire 6 of the branch wire 4 are connected by the crimp terminal 7, the core wire crimping portion 7a crimps the core wires 3 and 6 as shown in FIG. 7c
Needs to grip each end of the coatings 2, 5 and to see the ends of the coatings 2, 5 slightly. However, as shown in FIG. 3B, for example, a neck hanging crimping defect may occur in which the end of the coating 5 of the branch wire 4 is not gripped by the grip portion 7c.

When the core wire 3 of the trunk line 1 and the core wire 6 of the branch line 4 are connected by the crimping terminal 8, the core wire crimping portion 8a securely connects the core wires 3 and 6 as shown in FIG. 25 (a). It is necessary to crimp and form the bell mouths 8b, 8b at both ends. However, as shown in FIG.
Part of the plurality of wires 6a forming the core wire 6 of the branch wire 4 protrudes from the core wire crimping portion 8a, and the core wire does not protrude, as shown in FIG.
The terminal of the sheath 5 is bitten into the core wire crimping portion 8a of the crimping terminal 8 as shown in FIG. 5, and the terminal does not have bellmouths at both ends of the core wire crimping portion 8a of the crimping terminal 8 as shown in FIG. Deformation and failure without bell mouth will occur.

[0005]

Conventionally, when the ends of the branch wires are connected by crimp terminals in the middle of such a trunk line, each inspection of the connection portion of the crimp terminals has been conducted by visual inspection. However, along with the automation of the entire wire material processing apparatus, it has been demanded to automate the inspection of the connection portion by such a crimp terminal.

An apparatus or method for inspecting the quality of a crimping terminal in which a crimping terminal is connected to the end of a core wire by stripping off the coating on the end of the coated wire is disclosed in, for example, JP-A-5-157526.
There is a terminal crimping position inspection device disclosed in Japanese Patent Publication No. This device irradiates slit-shaped laser light from above the crimping portion of the crimping terminal, captures the reflected light into the camera from diagonally above, and captures the captured image as light traces of irregularities on the outer diameter of the terminal, and changes It measures and inspects the quality of the crimped state. However, this inspection apparatus can inspect when the object to be inspected is accurately positioned, but it requires a mechanical mechanism, which makes the inspection apparatus expensive. In addition, there is a problem in that it is not possible to inspect for the protrusion of the core wire due to a single slit light trace.

The present invention has been made in view of the above points, and connects a core wire at a portion where a coating is stripped off in the middle of a wire and a terminal of a core wire where a terminal of a coating of another wire is stripped by a crimp terminal. An object of the present invention is to provide a method for inspecting a linear material that optically inspects the quality of the connected portion.

[0008]

In order to achieve the above object, according to the present invention, the end of the core wire of another wire is crimp-connected to the core wire of the stripped part in the middle of the wire material by transillumination through a crimp terminal. The connection portion is illuminated to obtain its grayscale image, the grayscale image is binarized to trace the edge of the outer periphery of the connection portion, and the inclination of the approximate straight line of a plurality of adjacent pixels is calculated. The position of the boundary of the peeled portion and the position of the end of the crimp terminal is discriminated using the center point when the value becomes a certain value or more as a change point.

Further, a ring light is used to illuminate the connecting portion where the end of the core wire of another wire material is crimp-connected to the core wire of the stripped portion in the middle of the wire material with a crimp terminal to obtain an image, and the object in the image is obtained. The deformation of the crimp terminal is discriminated from the change in the brightness of the object to judge the quality of the connection portion. Furthermore, the connection part where the end of the core wire of another wire material is crimp-connected to the core wire of the stripped part in the middle of the wire material through transmissive illumination is illuminated to obtain the grayscale image, and the grayscale image is
The value is processed to trace the edge of the outer periphery of the connection portion, the slope of the approximate straight line of a plurality of adjacent pixels is calculated, and the peeling is performed with the middle point when the slope becomes a certain value or more as the change point. The boundary of the part and the position of the end of the crimp terminal are discriminated, and the connection part is illuminated by a ring illumination, and the deformation of the crimp terminal is discriminated from the change in the brightness of the object in the image to judge the quality of the connection part. It is made to be discriminated.

[0010]

The connection part of the wire is illuminated with transmitted illumination, the grayscale image is binarized to trace the edge of the outer periphery of the connection part, and the inclination of the approximate straight line of a plurality of pixels in the vicinity is calculated, The position at the boundary of the peeled portion and the end of the crimp terminal is determined by using the middle point when the inclination becomes a certain value or more as the change point. Further, the connection portion is illuminated by ring illumination, and the deformation of the crimp terminal is determined by the brightness change in the obtained image. Thereby, the quality of the connecting portion of the wire is determined.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an outline of an inspection apparatus for carrying out the method for inspecting a connecting portion of a linear material according to the present invention.
Is the core wire of the peeling part where the intermediate coating of the wire is stripped off,
A device for inspecting the quality of a connection part in which the end of the core wire from which the end of the coating of another wire has been stripped off is crimped and connected by a crimp terminal. The illumination part 11 illuminates the connection part of the wire, and the illuminated connection part is a camera. The image processing unit 12 and the image processing unit 12 which pick up the image, capture the image, and perform image processing to determine pass / fail.
And a display unit (CRT) 14 for displaying the process and result of image processing. The inspection start, the inspection, and the inspection result (pass / fail result) are controlled and monitored via the control unit 13. The image processing unit 12 receives necessary data of the inspection object (connection portion) from the control unit 13 at the time of initializing, waits for a start signal, processes, and outputs a result. Then, the process and result of the processing are displayed on the display unit 14.

It is indispensable to perform processing efficiently and easily in inspection. For this reason, characterization of the data to be processed, for example, something that serves as a standard such as "is easily distinguishable" and "has regularity" is required. In addition, the feature amount of data may be affected by the surrounding environment, and before the data is taken in, that is, how to perform the previous process is also an important factor. In particular, the feature amount of data in image processing is greatly influenced by how the optical system using the illumination, the lens, the camera, etc. is configured.

According to the present invention, an object to be inspected, that is, a connecting portion of a wire is caught as a shadow, image data of grayscale is image-processed, and the quality of the connecting portion and the crimping terminal of the crimping terminal are evaluated by the brightness change due to the unevenness of the surface of the crimp terminal. Inspect the quality of deformation. Therefore, the illumination unit 11 is a transmissive illumination and a ring illumination, and is configured as shown in FIG. That is, the lens 16 and the light projector (light source) 17 of the camera 15 are arranged and fixed so as to be spaced apart and face each other, and the connecting portion 1a of the wire 1 is horizontally arranged at substantially the center. Further, on the lens 16 side, a ring-type light projector 18 is arranged outside the lens 16.

The projector 17 is a flat-plate type projector in which the irradiation section 17a has a flat plate shape and irradiates a main line (hereinafter referred to as a "wire") 1 with parallel rays as indicated by an arrow. The floodlight 17 is
The irradiation part 17a has a uniform surface emission, and by using this as transmitted light, the shade of the connection part 1a can be captured. The camera 15 is, for example, a camera of a type using a CCD solid-state image sensor, and the input image from the lens 16 is a binary image of white and black as a brightness gradation of 0 to 255 steps, that is, binarized and a corresponding signal is obtained. Output.

The projector 18 has a ring shape and is shown in FIG.
The inner surface 18 of the open end 18a facing the connecting portion 1a as shown in FIG.
b is taper-expanded at a predetermined angle to form an inclined surface, and an irradiation portion 19 is annularly provided over the entire circumference at substantially the center of the inclined surface 18b. That is, the projector 18 has an angled illumination portion, and illuminates the surface of the object (connection portion) from the lens 16 side to emphasize the unevenness.

Further, in the inspection device 10, the illumination unit 11 and the image processing unit 12 are fixed, and thus the wire rod 1 obtained.
The image data of the connection part of is only one direction. Therefore,
A mechanism for mechanically rotating the wire rod 1 is provided so that image data of the connecting portion 1a from multiple directions can be taken in. That is, as shown in FIGS. 4A to 4C, the wire rod 1 (connecting portion 1a)
Is rotated to capture an image of 360 ° from 3 directions in 120 ° increments.

5 to 7 show an example of a rotary gripping mechanism 20 for gripping and rotating the wire 1. Rotating gripping mechanism 2
0 is a support plate 2 provided with notches 22a, 22a that are opened in a substantially U-shape on each upper end of the base 21 and take in a wire rod.
2 and 22 are vertically provided at a predetermined interval, and each of the support plates 22 and 22 has a disk-shaped notch 22a on the inner side thereof.
22a, a pair of discs 23, 23 that are open to the outer periphery and have notches 23a, 23a for taking in the wire rod at the center are rotatably supported. Rotating shaft 24
Is rotatably and horizontally supported by the support plates 22 and 22, and gears 25 and 25 fixed to the rotary shaft 24 mesh with the teeth engraved on the outer peripheral surfaces of the discs 23 and 23. These discs 23, 23 are rotated.

The gripping mechanism 26, 26 has support plates 22, 22.
Is arranged outside and fixed to the corresponding discs 23, 23, and rotates integrally with these discs 23, 23 to grip the wire 1 and hold it at the center position. Further, outside the gripping mechanisms 26, 26, support members 27, 27 having a bifurcated shape and supporting the wire rod are vertically provided. The drive motor 28 is mounted on the base 21, connected to the rotary shaft 24 via a joint, and connected to the disc 23 via gears 25, 25.
It is designed to rotate 23.

The support plates 22, 22 are attached to the holding mechanism 2
The camera 15 is provided on one side with respect to the connecting portion 1a of the wire rod 1 which is held horizontally at the central positions of the disks 23, 23 by the reference numerals 6, 26.
The lens 16 and the light projector 18 are fixed to the other side of the light projector 17 so as to face each other at predetermined intervals. As a result, the camera 15 can capture the image of the 360 ° connection portion 1a from the three directions in 120 ° increments, as shown in FIGS. 4A to 4C, in a fixed state. That is, the inspection device 10 inspects three screens for one connection portion 1a and treats this as one cycle process. The processing time required to inspect one screen is
Maximum is about 0.8 seconds.

The inspection of the connection part is complicated because the object is composed of two wire rods and crimp terminals, and the formation of the captured image also changes every time. Therefore, it is necessary to extract the feature quantity as stable as possible, and the configuration of the illumination system is important. Therefore, a configuration is adopted in which the transmissive illumination by the flat type projector 17 and the ring illumination (reflective illumination) by the ring type projector 18 are combined.

The connection portion 1a is inspected by crimping the core wire 3 of the wire rod 1 and the end of the core wire 6 of the branch wire (hereinafter referred to as "wire rod") 4 as shown in FIG. 13 (b) or (c). The portion crimped and connected by 8 is captured as an image to be inspected. FIG. 8 shows an inspection flow from image acquisition to inspection result output. As is clear from this flow, the inspection flow starts from image capturing and is performed step by step for each block of the inspection method. That is, when the image capture signal is input (step S1), the object detection window is set (step S2), the inspection method 1 (step S3), the inspection method 2 (step S4), and the connection portion 1a are set.
The quality of the inspection result is output (step S5).

At this time, since one cycle processing is limited to several seconds and the time required for inspection is limited, invalid data is omitted from the processing.
It needs to be as concise as possible. With that in mind,
When capturing an image, after detecting the inspection object on the screen,
The window of the necessary data part is cut off, and the other data is invalid. In this connection inspection,
You can turn off about one-third of the screen.

Next, the window setting method will be described. As shown in FIG. 9, the shadow of the wire rod 1 (connecting portion 1a) is captured as an image by transmission illumination by the projector 17 of the illumination unit 11. At this time, a portion other than the wire rod enters the camera 15 as a direct light, and a brightness value (for example, a brightness of 0 to 255 is set).
The value expressed as the gradation of the stage) is constant at the maximum brightness. As a result, the luminance becomes darker in the portion of the wire, and a window having a certain vertical distance d, d is cut out as indicated by dotted lines I, I with the points P, P where the luminance changes abruptly. The vertical lines of the solid lines II and II (in the diameter direction of the wire) represent the background luminance value with the dotted lines III and III.
The vertical line of III represents the brightness value of the darkest wire rod portion.

The inspection method 1 measures the change position at the boundary (indicated by an arrow) between the coating 2 and the core wire 3 of the stripped portion of the wire rod 1 shown in FIG. 10 to measure the length (width dimension) of the stripped portion. To do. This measurement is performed by changing the unevenness of the image, and is performed by binarizing the image. Since the background portion has uniform brightness, the threshold value is fixed and only the object can be detected as shown in FIG. After binarization, arrow A,
As shown in B, the edge of the outer periphery of the connection portion (target object) is traced, and a plurality of adjacent pixels (odd number), for example, the inclination of the approximate straight line V of 5 pixels is calculated as shown in FIG. The center point q at the time of tilting is taken as the change point of the object.
This change point is, for example, a boundary between the peeled portions, that is, a stepped portion between the coating 2 and the core wire 3. This inspection method 1 is shown in FIG.
As shown in (a) to (c), the width dimension of the peeling portion (FIG. (A)), the resin biting and protruding margin of the connection portion (FIG. (B),
(C)) is inspected. In addition, the core wire protrusion and neck suspension crimping are also inspected.

The inspection method 2 inspects the deformation of the crimping terminal of the connection portion 1a based on the change in the gradation of the image. That is, as shown in FIG. 14, when the irradiation section 19 of the ring type projector 18 irradiates the surface of the crimp terminal 8 with light from an oblique direction, the brightness of the uneven surface section is emphasized as shown in FIG. Therefore, the deformation of the crimp terminal is inspected by measuring the position of this luminance change. At this time, if the portion where the ring-type light projector 18 irradiates light is the entire circumference, the edge portion of the crimp terminal 8 becomes bright and the original edge portion due to binarization cannot be obtained. Then, the crimp terminal 8 by the projector 18
The irradiation part is limited to the irradiation part 19 as shown in FIG.
The portion of the predetermined range θ excluding the vicinity of both ends of the crimp terminal 8 is masked.

Further, in the captured image, the side surface portion in the longitudinal direction of the crimp terminal is not necessarily parallel to the horizontal direction, so that it is necessary to rotate the image as a software process because of the processing time. Therefore, the inclination of the side surface of the crimp terminal is calculated from the edge data obtained by the inspection method 1, and the image data is rotated by that angle to make the crimp terminal horizontal. Then, a rectangular window is cut out with a size that fits within the terminal area of the image (FIG. 17 (a),
(B)), analysis is performed based on the data in the window, and the deformation of the terminal is inspected. The crimp terminal 8 includes bell mouths 8b and 8b (FIGS. 14 and 1) at both ends of the core crimping portion 8a.
The brightness of the reflected light from 5) is the highest.

Then, by these inspection methods 1 and 2,
It is possible to inspect whether the crimping terminal is crimped, whether the core wire protrudes, or the resin bite crimps. If the captured image is in good condition, then check for terminal deformation, terminal twice crimping, core wire allowance, and neck hanging crimping. Is possible. Of course, each of these inspection methods has its own inspection judgment criteria (depending on the size of the image, etc.), and therefore the captured image to be inspected is
It is necessary to be within the criteria.

Returning to FIG. 1, the image signal output from the camera 15 in the image processing unit 12 is the camera adapter 30.
Is input to the image processing device 31 via. The image processing device 31 binarizes and shades the input image signal, outputs the result, and displays it on the display unit 14. The inspection start, the inspection, and the inspection result (pass / fail result) are controlled and monitored via the control unit 13. The image processing device 31 receives necessary data of the inspection object (wire material) from the control unit 13 at the time of initialization, waits for a start signal, binarizes and shades the input image signal, and outputs the result. Then, the process of the image processing device 31 and the result are
It is displayed on the display unit 14.

A method of inspecting the connecting portion will be described below with reference to the timing flows shown in FIGS. 18 and 19 and the operation timing charts shown in FIGS. First, at the time of the inspection initial, the control unit (sequencer) 13 sends data necessary for inspection such as an initial signal, an inspection start signal, and a data writing signal to the image processing device 31 (see FIG. 2).
0 (e), (a), (c)). When an initial signal is input from the control unit 13 (step S1 in FIG. 18) and then an inspection start signal is input (step S2), the image processing device 31 starts reading necessary data (step S3, FIG. 20 (b)) and read the data (steps S4, S5, FIG. 20 (d)). Next, the image processing device 3
1 sets the number of inspections (step S6 in FIG. 19) and determines whether or not the cycle start signal is input from the control unit 13 (step S7). When the cycle start signal is not input, the process proceeds to step S9 and the inspection is performed. Wait until the start. The number of inspections in step S6 is
Three times for inspecting the connection portion by 120 ° in 360 °. 20. In FIG. 20, reference numeral (SI) indicates a signal on the sequencer side, and reference numeral (image) indicates a signal on the image processing apparatus side.

When the image processing apparatus 31 receives an inspection start signal (FIG. 21 (a)) from the control section 13 (step S9), the image processing apparatus 31 starts operating and the first position of the connection section from the camera adapter 30, that is, 0. A rotary gripping mechanism for fetching an image signal at a position (FIG. 4A) (step S10, FIG. 21D), starting processing of the selected pattern (step S11), and gripping and rotating the wire 1 at the same time. 20 (Fig. 5
~ Fig. 7), the timing of the start of rotation (Fig. 2)
1 (a)). The determination result of step S12 is negative (NO)
The adjacent image processing apparatus 31 ends the first image processing (step S13) and returns to step S7. The number of inspections is subtracted by 1 to be 2, and the second inspection, that is, the inspection of the connection portion at the position rotated by 120 ° (FIG. 4B) is performed (steps S9 to S13). Rotating gripping mechanism 20
Rotates the wire 1 from the inspection start position of FIG. 4A (FIG. 18C), and the image processing apparatus 31 has a connection portion of 0 °.
The image is sequentially captured and processed every time it is rotated by 120 °.

The image processing device 31 reads the inspection result (FIGS. 22A to 22C), and the inspection number is the predetermined number (3).
When the number of times reaches, the inspection is ended, the read inspection result is output to the control unit 13 (step S14), the image processing is ended (step S15), and the process proceeds to step S16. When the initial signal (FIG. 20 (e)) is output in step S16, the image processing device 31 performs step S16.
2, the process returns to step S6 when no output is made. Then, the inspection result is displayed on the display unit 14,
The quality of the connection between the wire rods 1 and 4 is determined.

[0032]

As described above, according to the present invention, the connection portion in the case of crimp-connecting the end of the stripped core wire of another wire rod to the core wire of the stripped portion in the middle portion of the wire rod via the crimp terminal It becomes possible to automate the determination of pass / fail, it is possible to quickly and favorably determine the pass / fail of the connection part,
This has the effect of improving work efficiency.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an inspection apparatus for carrying out an inspection method for a linear material according to the present invention.

FIG. 2 is a cross-sectional view showing an outline of an illuminating unit for transmitting illumination and ring illuminating the wire rod of FIG.

FIG. 3 is an enlarged cross-sectional view of the ring type projector of FIG.

FIG. 4 is an explanatory view of rotating the wire rod of FIG. 1 by 360 ° and inspecting the connection portion every 120 ° from three directions.

5 is a plan view showing an embodiment of a rotary gripping mechanism for rotating the wire rod of FIG. 4. FIG.

FIG. 6 is a front view of FIG.

FIG. 7 is a side view of FIG.

FIG. 8 is a flowchart showing an outline of an inspection procedure in the present invention.

FIG. 9 is a diagram showing an example of a window set in the image processing of the present invention.

FIG. 10 is an explanatory diagram of a first-stage inspection method for a connecting portion (peeling portion) of a wire rod.

FIG. 11 is an explanatory diagram showing a state in which the image of the connection portion (peeling portion) in FIG. 10 is binarized.

12 is an explanatory diagram showing a method of detecting an edge of a peeling portion from the image of FIG.

FIG. 13 is a diagram showing inspection items by a first-stage inspection method of a connecting portion of a wire.

FIG. 14 is an explanatory diagram of a second-stage inspection method for a connecting portion of a wire rod.

FIG. 15 is a diagram showing a change in brightness of reflected light from the crimp terminal of FIG.

16 is an explanatory diagram for limiting the illumination range in the ring illumination of FIG.

17 is an explanatory diagram of image processing in the second-stage inspection method of FIG.

18 is a diagram showing a part of a timing flow of image processing in the inspection apparatus of FIG.

19 is a diagram showing the rest of the timing flow of FIG. 18. FIG.

FIG. 20 is a diagram showing an operation timing chart of the inspection apparatus of FIG. 1 at the time of inspection initials.

21 is a diagram showing an operation timing chart when the inspection of the inspection apparatus of FIG. 1 is started.

22 is a diagram showing an operation timing chart when the inspection result of the inspection device of FIG. 1 is output.

FIG. 23 is an explanatory diagram of a case where a branch line end is connected to the middle of a trunk line by a crimp terminal.

FIG. 24 is a diagram showing a first mode in which the trunk line and the branch line of FIG. 23 are connected by a crimp terminal.

25 is a diagram showing a second mode in which the trunk line and the branch line of FIG. 23 are connected by a crimp terminal.

[Explanation of symbols]

 1 wire rod (main line) 2, 5 coating 4 branch wire 3, 6 core wire 7, 8 crimping terminal 10 inspection device 11 illumination unit 12 image processing unit 13 control unit 14 display unit 15 camera 16 lens 17 flat plate type projector 18 ring type projector 20 Rotational gripping mechanism 30 Camera adapter 31 Image processing device

Claims (7)

[Claims] 1. A transmission image is used to illuminate a connecting portion where a terminal of a core wire of another wire is crimp-connected to a core wire of a stripped portion in the middle of the wire material through a crimping terminal to obtain a grayscale image, and the grayscale image is displayed as 2 The value is processed to trace the edge of the outer periphery of the connection portion, the slope of the approximate straight line of a plurality of adjacent pixels is calculated, and the peeling is performed with the middle point when the slope becomes a certain value or more as the change point. A method for inspecting a linear material, characterized in that the position of the boundary between the parts and the position of the end of the crimp terminal is determined. 2. An image is obtained by illuminating an image by illuminating the connecting portion, which is formed by crimping and connecting a terminal of a core wire of another wire material to a core wire of a stripped portion in the middle of the wire material, with a ring illumination, and an object in the image. A method for inspecting a linear material, characterized in that deformation of the crimp terminal is discriminated based on a change in luminance of an object to determine quality of the connection portion. 3. A transmission image is used to illuminate a connecting portion where a terminal of a core wire of another wire material is crimp-connected to a core wire of a stripped portion in the middle of the wire material through a crimping terminal to obtain a grayscale image thereof, and the grayscale image is displayed. The value is processed to trace the edge of the outer periphery of the connection portion, the slope of the approximate straight line of a plurality of adjacent pixels is calculated, and the peeling is performed with the middle point when the slope becomes a certain value or more as the change point. The position of the boundary of the part and the end of the crimp terminal is discriminated, an image is obtained by illuminating the connection part with ring illumination, and the deformation of the crimp terminal is discriminated from the change in the brightness of the object in the image to make the connection. A method for inspecting a linear material, characterized by determining the quality of a part. 4. The method for inspecting a linear material according to claim 1, wherein the number of pixels for obtaining the approximate straight line is an appropriate odd number within a range where the change point can be inspected. 5. The method for inspecting a linear material according to claim 4, wherein the number of pixels is five. 6. The method for inspecting a linear member according to claim 2, wherein the ring illumination limits an irradiation range to both ends of the crimp terminal and the vicinity thereof. 7. The method for inspecting a linear material according to claim 1, wherein the determination is performed within a range of 360 ° for each predetermined rotation angle by rotating the connecting portion.