CN110961773B

CN110961773B - Seam welding device and seam welding method

Info

Publication number: CN110961773B
Application number: CN201910927787.9A
Authority: CN
Inventors: 伊贺上光隆; 河合泰宏; 儿玉哲也; 乾秀二郎
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2018-09-28
Filing date: 2019-09-27
Publication date: 2021-09-24
Anticipated expiration: 2039-09-27
Also published as: JP2020055009A; JP6728291B2; CN110961773A

Abstract

The invention provides a seam welding apparatus and a seam welding method. The seam welding apparatus (10) includes a first determination unit (18c) and a second determination unit (18d), wherein the first determination unit (18c) determines whether or not there is an abnormality in the detection result of a workpiece position detection sensor (16) that detects the positions of the edge portions of the two flanges (13, 15); when the first determination unit (18c) determines that there is an abnormality in the detection result of the workpiece position detection sensor (16), the second determination unit (18d) determines the cause of the abnormality based on the state of variation in the detection result of the workpiece position detection sensor (16). According to the present invention, it is possible to monitor the presence or absence of an abnormality in the detection result of the workpiece position sensor, and to determine the cause of the abnormality when the abnormality occurs.

Description

Seam welding device and seam welding method

Technical Field

The present invention relates to a seam welding apparatus (seam welding device) and a seam welding method for seam welding a plurality of workpieces by sandwiching the plurality of overlapped workpieces between a pair of roller electrodes (roller electrodes) to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating the pair of roller electrodes.

Background

Japanese patent application No. 6250555 discloses a seam welding apparatus (seam welding device) that seam welds a plurality of workpieces by sandwiching the overlapped workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating the pair of roller electrodes.

The seam welding apparatus disclosed in japanese patent laid-open No. 6250555 detects the positions of the edge portions of a plurality of workpieces by a sensor, and controls the axis orientation (the orientation of the axes) of a pair of roller electrodes based on the detection result.

Disclosure of Invention

In the seam welding apparatus described in japanese patent application laid-open No. 6250555, even when the sensor erroneously detects, the position information indicates a normal range, and therefore, abnormality detection cannot be performed. Even when abnormality detection is possible by adding some mechanism, it takes time to identify the cause of the abnormality, and a corresponding amount of time is required for the cause of the abnormality to be identified.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a seam welding apparatus and a seam welding method capable of monitoring the presence or absence of an abnormality in the detection result of a workpiece position sensor and capable of determining the cause of the abnormality when the abnormality occurs.

A first aspect of the present invention is a seam welding apparatus for seam welding a plurality of workpieces by sandwiching the plurality of workpieces that are stacked with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating, the seam welding apparatus including an electrode holding mechanism that holds the pair of roller electrodes so that an axial orientation of the pair of roller electrodes can be changed, a workpiece position detection sensor, and a control unit; the workpiece position detection sensor detects positions of edge portions of a plurality of the workpieces; the control section controls energization to the pair of roller electrodes and controls the electrode holding mechanism in accordance with a detection result of the workpiece position detection sensor, the control section including a first determination section and a second determination section, wherein the first determination section determines whether or not there is an abnormality in the detection result of the workpiece position detection sensor; when the first determination unit determines that there is an abnormality in the detection result of the workpiece position detection sensor, the second determination unit determines the cause of the abnormality based on the state of variation in the detection result of the workpiece position detection sensor.

A second aspect of the present invention is a seam welding method including a seam welding start step of starting seam welding by sandwiching a plurality of overlapped workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes while rotating, a workpiece position detection step, a first determination step, and a second determination step; in the workpiece position detecting step, positions of edge portions of the plurality of workpieces are detected by a workpiece position detecting sensor; in the first determination step, it is determined whether or not there is an abnormality in the detection result of the workpiece position detection sensor; in the second determination step, when it is determined in the first determination step that there is an abnormality in the detection result of the workpiece position detection sensor, the cause of the abnormality is determined based on the state of variation in the detection result of the workpiece position detection sensor.

According to the present invention, the control unit can take countermeasures in accordance with various situations by monitoring the presence or absence of an abnormality in the detection result of the workpiece position detection sensor and determining the cause of the abnormality (failure) when the abnormality occurs. This can reduce the time required to cope with the failure.

The above objects, features and advantages will be readily understood by the following description of the embodiments with reference to the accompanying drawings.

Drawings

Fig. 1 is a diagram illustrating an overall configuration of a seam welding apparatus according to the present embodiment.

Fig. 2A is a side view of a vehicle body to be welded including the seam welding apparatus. Fig. 2B is a partial cross-sectional view showing a state in which a seam welding apparatus seam-welds a welded portion (a pair of flanges) of a vehicle body.

Fig. 3 is a diagram for explaining a method of controlling the axial orientation of the roller electrode pair (a method of correcting the welding locus of seam welding).

Fig. 4 is a block diagram showing a control configuration of the seam welding apparatus.

Fig. 5 is a diagram for explaining a method of determining whether there is an abnormality in the sensor output from the average value of the control amounts of the axial orientations of the roller electrode pairs.

Fig. 6A is a diagram showing sensor outputs and variance values when there is an abnormality in the sensor outputs due to the abnormality cause 1. Fig. 6B is a diagram showing the sensor output and the variance value when there is an abnormality in the sensor output due to the abnormality cause 2. Fig. 6C is a diagram showing the sensor output and the variance value when there is an abnormality in the sensor output due to the abnormality cause 3.

Fig. 7 is a diagram showing the cause of an abnormality corresponding to the variance value of the sensor output when there is an abnormality in the sensor output.

Fig. 8 is a flowchart for explaining the operation of the seam welding apparatus.

Detailed Description

Hereinafter, a seam welding apparatus and a seam welding method according to the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a diagram showing an example of the structure of the seam welding apparatus 10. The seam welding apparatus 10 is an apparatus for seam welding a plurality of overlapped workpieces. Specifically, the seam welding apparatus 10 is an apparatus that performs continuous spot welding on a plurality of overlapped workpieces by sandwiching the workpieces by a pair of

roller electrodes

12A and 12B to which a voltage (pulse voltage) is applied and moving the pair of

roller electrodes

12A and 12B relative to the workpieces while rotating the workpieces.

Fig. 2A is a view showing a vehicle body B including a plurality of workpieces to be welded by the seam welding apparatus 10. Fig. 2B is a view of the seam welding apparatus 10 viewed from the welding direction of seam welding in the vicinity of the pair of

roller electrodes

12A and 12B. As an example, as shown in fig. 2A and 2B, the plurality of workpieces to be welded by the seam welding apparatus 10 are a flange 13 of an inner member and a flange 15 of an outer member in a center pillar 11 of a vehicle body B. Fig. 2B shows a IIB-IIB cross section of the center pillar 11 of fig. 2A. Hereinafter, the flange 13 and the flange 15 are also collectively referred to as "flange pair FP".

As shown in fig. 1, the seam welding apparatus 10 includes an electrode holding mechanism 14, a workpiece position detection sensor 16, a control unit 18, a display unit 19, and an operation unit 21 in addition to the pair of

roller electrodes

12A and 12B.

The electrode holding mechanism 14 holds the pair of

roller electrodes

12A, 12B in such a manner that the axial orientation of the pair of

roller electrodes

12A, 12B can be changed.

The electrode holding mechanism 14 is, for example, a multi-joint robot (here, a six-axis robot having six joints (a first joint 14a, a second joint 14b, a third joint 14c, a fourth joint 14d, a fifth joint 14e, and a sixth joint 14 f)). In the electrode holding mechanism 14, a first shaft portion 17A (a shaft portion on the distal end side relative) and a second shaft portion 17B (a shaft portion on the proximal end side relative) which are coaxially arranged with each other are connected to each other by a first joint portion 14a so as to be relatively rotatable around an axis.

A support structure 9 is attached to the distal end of the first shaft portion 17A, and the support structure 9 rotatably supports each of the pair of

roller electrodes

12A and 12B. The support structure 9 supports the pair of

roller electrodes

12A and 12B such that their axes are substantially parallel to each other and their outer peripheral surfaces face each other.

Specifically, the support structure 9 includes a support member 9a, and the support member 9a has 3 recesses 9a1, 9a2, and 9a3 arranged in the longitudinal direction (the direction connecting the distal end and the proximal end) and each opened in the side surface. A motor 9b having a rotating shaft 9c is fixed to the recessed portion 9a1 on the distal end side of the support member 9a, and the roller electrode 12A is coaxially fixed to the rotating shaft 9 c. A motor 9d is provided in a recess 9a2 in the middle (between the distal end and the proximal end) of the support member 9a so as to be slidable in the longitudinal direction of the support member 9 a. A roller electrode 12B is coaxially fixed to a rotary shaft 9e of the motor 9 d. The rotation shaft 9c and the rotation shaft 9e are substantially parallel to each other and substantially orthogonal to the axes of the first shaft portion 17A and the second shaft portion 17B.

The motor 9d is driven by a cylinder 9f straddling the recess 9a3 on the base end side of the support member 9a and the intermediate recess 9a 2. Further, a through hole through which the cylinder 9f is inserted is formed in a wall between the recess 9a3 on the base end side of the support member 9a and the intermediate recess 9a 2. The moving direction (sliding direction) of the motor 9d, that is, the extending and contracting direction of the cylinder 9f is substantially parallel to the arrangement direction of the pair of

roller electrodes

12A, 12B (longitudinal direction of the support member 9 a). The roller electrode 12B fixed to the rotating shaft 9e of the motor 9d is movable in an axial direction including a direction approaching the roller electrode 12A fixed to the rotating shaft 9c of the motor 9B and a direction separating from the roller electrode 12A by the expansion and contraction operation of the cylinder 9 f. Accordingly, the pair of

roller electrodes

12A and 12B can sandwich the flange pair FP having an arbitrary thickness within a predetermined range. Further, it is also possible to cope with the thickness variation of the flange pair FP in seam welding. The motor 9b and the motor 9d are controlled by the control unit 18.

The first joint portion 14a incorporates a drive portion including a motor. The support member 9a and the pair of

roller electrodes

12A, 12B are integrally rotated about the axes of the first shaft portion 17A and the second shaft portion 17B by the driving force of the motor. That is, the shaft orientations of the pair of

roller electrodes

12A and 12B are changed synchronously by the driving force of the motor. As a result, the first joint section 14a is operated, whereby the axial orientation of the pair of

roller electrodes

12A and 12B can be changed. Hereinafter, the pair of

roller electrodes

12A and 12B is also collectively referred to as "roller electrode pair REP".

The structure of the electrode holding mechanism 14 is not limited to the above structure, and may be another structure as long as the pair of

roller electrodes

12A, 12B are held so that the axial orientation of the pair of

roller electrodes

12A, 12B can be changed.

As shown in fig. 2B, the workpiece position detection sensor 16 detects the positions of the edge portions of the two workpieces, i.e., the edge portions of the flange pair FP. More specifically, the workpiece position detection sensor 16 detects the position of the end face of the edge of the flange pair FP. Hereinafter, the end surface of the edge of the flange pair FP is also referred to as "detected surface DS". The workpiece position detection sensor 16 is attached to a wall between the front end side recess 9a1 and the middle recess 9a2 of the support member 9a so as to face the detection surface DS. That is, the workpiece position detection sensor 16 is disposed between the rotary shaft 9c and the rotary shaft 9 e. The detected surface DS is not limited to the end surface of the edge of the flange pair FP, and may be another surface of the edge of the flange pair FP.

The workpiece position detection sensor 16 includes a light irradiation unit 16a, a light receiving unit 16b, and a distance calculation unit 16 c. The light irradiation section 16a irradiates light to the detection surface DS and its peripheral region (for example, each roller electrode). The light irradiation section 16a includes: a light emitting element such as a laser diode; and a light deflector for deflecting and scanning the light from the light emitting element. That is, the light irradiation section 16a scans the detection surface DS and the peripheral region thereof with light. The light receiving unit 16b has a light receiving element such as a photodiode, and receives light emitted from the light irradiating unit 16a and reflected on the detection surface DS and its peripheral region.

The distance calculation unit 16c includes, for example, a CPU. The distance calculation unit 16c calculates a time difference between the emission time of the light irradiation unit 16a and the reception time of the light reception unit 16b for each scanning position during scanning of the detection surface DS and the peripheral region thereof. The distance calculation unit 16c converts the minimum value of the calculation results of the time difference into a distance, and outputs the converted value to the control unit 18 (fig. 1) as the distance to the detected surface DS (the detection result of the workpiece position detection sensor 16). In addition, during scanning of the detection surface DS and its peripheral region, the detection surface DS is located at the position closest to the workpiece position detection sensor 16.

The light irradiation unit 16a, the light receiving unit 16b, and the distance calculation unit 16c are housed in a package (package)16e having a substantially U-shaped cross section and having a light transmission window 16d provided at an opening end thereof. Specifically, the light irradiation unit 16a, the light receiving unit 16b, and the distance calculation unit 16c are mounted on the same substrate disposed on the bottom surface of the package 16 e. The light (emission light) emitted from the light irradiation section 16a is incident on the detection surface DS and its peripheral region through the light transmission window 16 d. The light (reflected light) reflected on the detection surface DS and its peripheral region enters the light receiving unit 16b through the light transmission window 16 d. In another embodiment, the distance calculation unit 16c may not be provided, and the control unit 18 may assume the function of the distance calculation unit 16 c.

The structure and arrangement of the workpiece position detection sensor 16 are not limited to those described above, and may be changed as appropriate. The workpiece position detection sensor 16 may be an image sensor including an imaging sensor (image sensor) and an image processing unit, for example. In this case, the image processing unit performs edge detection processing on the output image (distance image) of the imaging sensor, thereby detecting the position of the edge of the flange pair FP. The workpiece position detection sensor 16 may be a stereo image sensor including two imaging sensors, for example. In this case, the distance to the edge of the flange pair FP can be detected from the parallax value obtained from the outputs of the two imaging sensors. The light irradiator 16a and the light receiver 16b may be housed in different packages. The light irradiation section 16a may not have an optical deflector. In this case, light may be irradiated onto the detection surface DS and the peripheral region thereof using a light-emitting element array in which a plurality of light-emitting elements are arranged. The light irradiation section 16a may have a lens for suppressing diffusion of light from the light emitting element. In this case, the lens may be provided on the package 16e so as to be exposed without providing the light transmission window 16 d. The light receiving unit 16b may have a lens for collecting light incident on the light receiving element. In this case, the lens may be provided on the package 16e so as to be exposed without providing the light transmission window 16 d.

The control unit 18 shown in fig. 1 controls the energization to the pair of

roller electrodes

12A, 12B, and controls the electrode holding mechanism 14 based on the detection result (hereinafter also referred to as "sensor output") of the workpiece position detection sensor 16. The control unit 18 includes, for example, a CPU.

Seam welding is performed by moving a pair of roller electrodes to which a voltage (pulse voltage) is applied relative to a plurality of overlapped workpieces (for example, a pair of flanges) while rotating the pair of roller electrodes along a desired welding locus of the plurality of workpieces. However, in actual seam welding, since the distance between the seam welding apparatus and the plurality of workpieces stacked on each other varies finely with the passage of time, if the roller electrode pair is moved while being held in one state (in a state in which the axis orientation is fixed), the roller electrode pair may deviate from a target range centered on a desired welding trajectory.

Therefore, the control section 18 controls the electrode holding mechanism 14 based on the sensor output of the workpiece position detection sensor 16. Specifically, as shown in fig. 3, the controller 18 controls the axial orientation (angle) of the roller electrode pair REP, that is, the steering angle of the roller electrode pair REP, based on the sensor output so that the roller electrode pair REP does not deviate from the target range TR centered on the desired welding locus DWT.

Fig. 4 is a block diagram showing a control configuration of the control unit 18. As shown in fig. 4, the control unit 18 includes an energization control unit 18a, a mechanism control unit 18b, a first determination unit 18c, and a second determination unit 18 d.

The mechanism control unit 18b controls the electrode holding mechanism 14 based on the sensor output of the workpiece position detection sensor 16. Specifically, the mechanism control unit 18b calculates the control amount CA of the electrode holding mechanism 14 based on the sensor output, sends the calculation result to the first determination unit 18c, and outputs the calculation result to the electrode holding mechanism 14 as needed. The electrode holding mechanism 14 controls the axis orientation (steering angle) of the roller electrode pair REP using the inputted control amount CA. The control amount CA is a difference between a target value of the shaft angle (shaft orientation) of the roller electrode pair REP output from the sensor and the shaft angle of the roller electrode pair REP at that point in time (at the time of control). The control amount CA has positive and negative values depending on the control direction of the axial orientation of the roller electrode pair REP.

The first determination unit 18c determines whether or not there is an abnormality in the detection result (sensor output) of the workpiece position detection sensor 16. The first determination unit 18c determines whether or not there is an abnormality in the sensor output based on the control amount CA from the mechanism control unit 18 b.

Here, as shown in fig. 5, the control unit 18 controls the control amount CA of the electrode holding mechanism 14 (the control amount of the axial orientation of the roller electrode pair REP) based on the sensor output to take the normal distribution ND. When the sensor output is not abnormal, the average Ave of the normal distribution ND is smaller than the predetermined threshold Th. Therefore, when the average Ave of the normal distribution ND is equal to or greater than the threshold Th, it can be determined that the sensor output is abnormal. Here, the threshold Th is, for example, an average Ave +4 σ. Where σ is the standard deviation of the normal distribution ND.

Therefore, the first determination unit 18c shown in fig. 4 determines that there is an abnormality in the sensor output when the average value of the control amounts CA is equal to or greater than the threshold Th. The case where the average value Ave of the control amounts CA is equal to or greater than the threshold value Th is exemplified by the case where a foreign substance adheres to the light transmission window 16d of the workpiece position detection sensor 16 shown in fig. 2B. In addition, the following cases can be mentioned: in the mechanism control unit 18b, a teaching demonstration (teaching) corresponding to the shape of the workpiece is performed so that the roller electrode pair REP machines the target range TR, but the teaching demonstration for the workpiece varies depending on the workpiece change or the like.

The energization control unit 18a shown in fig. 4 controls energization of the roller electrode pair REP. Specifically, the energization control unit 18a controls energization of the roller electrode pair REP based on the determination result of the first determination unit 18 c.

Here, when seam welding is continued with an abnormality in the sensor output, there is a concern that the roller electrode pair REP greatly deviates from the desired welding trajectory DWT. Therefore, when the first determination unit 18c determines that there is an abnormality in the sensor output, the energization control unit 18a stops energization of the roller electrode pair REP, thereby stopping seam welding.

When the first determination unit 18c determines that there is an abnormality in the sensor output, the second determination unit 18d determines the cause of the abnormality based on the variance value DV (variation) of the sensor output. The second determination section 18d receives the detection result of the workpiece position detection sensor 16 and calculates a variance value DV output from the sensor. The variance value DV of the sensor output indicates the degree of variation in the sensor output value. The variance value DV of the sensor output is the average of the squares of the differences between the respective sensor output values and the average of the sensor output values. The second determination unit 18d may determine the cause of the abnormality based on another value indicating the variation state of the sensor output, such as the standard deviation of the sensor output (the square root of the positive square of the variance value DV), instead of the variance value DV indicating the variation state of the sensor output.

Specifically, when the variance value DV is not within the predetermined range PR (see fig. 7), the second determination unit 18d determines that a foreign object is attached to the workpiece position detection sensor 16. The second determination unit 18d outputs the determination result to the display unit 19. The display unit 19 displays the input determination result on a screen (for example, displays "foreign matter is attached to the workpiece position detection sensor 16"). Alternatively, a voice output unit including a speaker may be provided instead of or in addition to the display unit 19, and the result of the determination by the second determination unit 18d may be output by voice via the voice output unit.

Fig. 6A to 6C are diagrams for explaining the causes 1 to 3 of abnormality in which sensor outputs are different from each other. In each of fig. 6A to 6C, Ta represents a target distance between the workpiece position detection sensor 16 and the detection surface DS (a distance at which the roller electrode pair REP can be positioned on the desired welding locus DWT).

In the example shown in fig. 6A, for example, fine foreign matter adheres to a large area (for example, contaminated with dust, oil, or the like) of the light transmission window 16d of the workpiece position detection sensor 16 at a high density (abnormality cause 1). In this case, the light emitted from the light irradiator 16a is scattered by the light transmission window 16d, and the light reflected on the detection surface DS and its peripheral region is scattered by the light transmission window 16 d. Therefore, the variance value DV of the sensor output becomes large (more specifically, larger than the upper limit PRu of the predetermined range PR (see fig. 7)). At this time, if the axis orientation of the roller electrode pair REP is controlled according to the sensor output, the roller electrode pair REP may deviate from the target range TR.

Therefore, when the variance value DV is larger than the upper limit PRu of the predetermined range PR, the second determination unit 18d determines that foreign matter is attached to the workpiece position detection sensor 16 over a wide range, and outputs the determination result to the display unit 19. The display unit 19 displays the input determination result on a screen (for example, displays "dirt adheres to the workpiece position detection sensor").

In the example shown in fig. 6B, for example, foreign matter (granular solid or liquid) is locally adhered to the light transmission window 16d of the workpiece position detection sensor 16 (abnormality cause 2). In this case, there is a fear that light from the light irradiation section 16a is reflected by the foreign substance and received by the light receiving section 16 b. That is, there is a fear that the workpiece position detection sensor 16 detects the position of the foreign substance rather than the position of the detection surface DS. In this case, since the axis orientation of the roller electrode pair REP is controlled according to the distance from the foreign matter, the roller electrode pair REP may deviate from the target range TR. In the case of fig. 6B, since the workpiece position detection sensor 16 detects the position of the foreign object adhering to the light transmission window 16d located at a certain distance from the light irradiation section 16a, the sensor output hardly fluctuates (is shown as a substantially fixed value). Therefore, the variance value DV of the sensor output becomes extremely small (more specifically, smaller than the lower limit PRl of the predetermined range PR (see fig. 7)).

Therefore, when the variance value DV is smaller than the lower limit PRl of the predetermined range PR, the second determination unit 18d determines that a foreign object is locally attached to the workpiece position detection sensor 16, and outputs the determination result to the display unit 19. The display unit 19 displays the input determination result on a screen (for example, displays "dust adheres to the workpiece position detection sensor").

The second determination unit 18d determines that foreign matter is attached to the workpiece position detection sensor 16 over a wide range when the variance value DV is larger than the upper limit PRu of the predetermined range PR (see fig. 7), and determines that foreign matter is attached to the workpiece position detection sensor 16 locally when the variance value DV is smaller than the lower limit PRl of the predetermined range PR. For example, the second determination unit 18d may determine only whether the variance value DV is within the predetermined range PR (whether a foreign object is attached to the workpiece position detection sensor 16) and notify the determination result (for example, display the determination result on the display unit 19). For example, the second determination unit 18d may determine only one of whether the variance value DV is larger than the upper limit PRu of the predetermined range PR (whether foreign matter is widely attached to the workpiece position detection sensor 16) and whether the variance value DV is smaller than the lower limit PRl of the predetermined range PR (whether foreign matter is locally attached to the workpiece position detection sensor 16), and notify the determination result (for example, display on the display unit 19).

In the example shown in fig. 6C, a deviation of the teaching demonstration input to the mechanism control unit 18b (a state where appropriate teaching demonstration is not performed in accordance with the shape of the workpiece) occurs in the electrode holding mechanism 14 (abnormality cause 3). In this case, as shown in fig. 6C, the sensor output gradually gets away (monotonically decreases) from the target distance Ta (the target distance between the workpiece position detection sensor 16 and the detection target surface DS) with the passage of time. In this case, if the axis orientation of the roller electrode pair REP is controlled based on the sensor output, the roller electrode pair REP may deviate from the target range TR (see fig. 3).

Therefore, in the case where the variance value DV is within the prescribed range PR, the second determination portion 18d determines that a deviation of the demonstration teaching, which sets the electrode holding mechanism 14 so that the roller electrode pair REP moves in accordance with the desired welding locus DWT, has occurred.

Further, a case is also considered in which even though the exemplary teaching itself has no problem, the followability of the electrode holding mechanism 14 to the exemplary teaching becomes poor and an abnormality occurs in the sensor output. Therefore, when the variance value DV of the sensor output is within the predetermined range PR, the second determination unit 18d may determine that "the followability of the electrode holding mechanism 14 to the demonstration teaching is deteriorated or the demonstration teaching itself has a problem" and notify the determination result (for example, display the result on the display unit 19).

Next, the operation of the seam welding apparatus 10 configured as described above will be described with reference to the flowchart of fig. 8.

In the first step S1, the operator starts seam welding by the seam welding apparatus 10. Specifically, the operator controls the electrode holding mechanism 14 to clamp the flange pair FP by the roller electrode pair REP, and then sends a welding start trigger signal to the controller 18 via the operation unit 21. More specifically, the operator appropriately moves (slides) the motor 9d that drives the roller-type electrode 12B to rotate via the operation unit 29, and appropriately operates the first joint unit 14a, the second joint unit 14B, the third joint unit 14c, the fourth joint unit 14d, the fifth joint unit 14e, and the sixth joint unit 14f, thereby causing the pair of roller-

type electrodes

12A, 12B to sandwich the flange pair FP.

The controller 18, which has received the welding start trigger signal, applies a voltage to the roller electrode pair REP, and controls the electrode holding mechanism 14 to start moving the roller electrode pair REP along the desired welding locus DWT of the flange pair FP. Specifically, the controller 18 operates the motors 9B and 9d to rotate the pair of

roller electrodes

12A and 12B in opposite directions, and appropriately operates the first joint portion 14a, the second joint portion 14B, the third joint portion 14c, the fourth joint portion 14d, the fifth joint portion 14e, and the sixth joint portion 14f, thereby starting the movement of the roller electrode pair REP along the desired welding locus DWT of the flange pair FP.

In the next step S2, the workpiece position detection sensor 16 detects the position of the detection surface DS, and outputs the detection result (sensor output) to the mechanism control unit 18 b.

In the next step S3, the mechanism control unit 18b calculates the control amount CA of the axial orientation of the roller electrode pair REP based on the sensor output, and sends the calculation result to the first determination unit 18 c.

In the next step S4, the first determination unit 18c determines whether or not the control amount CA is equal to or greater than the threshold Th, that is, whether or not there is an abnormality in the sensor output. If the determination is negative, the process proceeds to step S5, and if affirmative, the process proceeds to step S8.

In step S5, the first determination unit 18c determines that the sensor output is normal (no abnormality in the sensor output).

In the next step S6, the control unit 18 controls the axial orientation of the roller electrode pair REP in accordance with the calculated control amount CA. Specifically, the mechanism control unit 18b outputs the control amount CA calculated in step S3 to the drive unit of the first joint unit 14a of the electrode holding mechanism 14. Accordingly, the axial orientation of the roller electrode pair REP is controlled (changed) by the control amount CA.

In the next step S7, the control unit 18 determines whether seam welding is completed. Specifically, the controller 18 determines that seam welding is completed when determining that the roller electrode pair REP has reached the end of the desired welding trajectory DWT based on the control amount of each joint of the electrode holding mechanism 14. If the determination here is affirmative, the flow ends, and if the determination here is negative, the flow returns to step S2.

In step S8, the first determination unit 18c determines that the sensor output is abnormal (sensor output is abnormal).

In the next step S9, the control unit 18 stops seam welding. Specifically, the current supply controller 18a stops the current supply to the roller electrode pair REP.

In the next step S10, the second decision portion 18d calculates the variance value DV of the sensor output.

In the next step S11, the second determination portion 18d determines whether the variance value DV is larger than the upper limit PRu of the prescribed range PR. If the determination is affirmative, the process proceeds to step S12, and if the determination is negative, the process proceeds to step S13.

In step S12, the second determination unit 18d determines that foreign matter is adhering to the workpiece position detection sensor 16 (e.g., the light transmission window 16d) over a wide range, and notifies the determination result (displays it on the display unit 19). After confirming the determination result displayed on the display unit 19, the operator can promptly take countermeasures such as cleaning and replacement of the workpiece position detection sensor 16. After the execution of step S12, the flow ends.

In step S13, the second determination section 18d determines whether the variance value DV is smaller than the lower limit PRl of the prescribed range PR. If the determination is affirmative, the process proceeds to step S14, and if the determination is negative, the process proceeds to step S15.

In step S14, the second determination unit 18d determines that a foreign object is locally attached to the workpiece position detection sensor 16 (e.g., the light transmission window 16d), and notifies the determination result (displays it on the display unit 19). After confirming the determination result displayed on the display unit 19, the operator can promptly take countermeasures such as cleaning and replacement of the workpiece position detection sensor 16. After the execution of step S14, the flow ends.

In step S15, the second determination unit 18d determines that the deviation of the teaching demonstration target range TR has occurred in the electrode holding mechanism 14, and notifies the determination result (displays it on the display unit 19). After confirming the determination result displayed on the display unit 19, the operator can promptly take countermeasures for suppressing the deviation of the demonstration teaching. After the execution of step S15, the flow ends.

Next, the effect of the seam welding apparatus 10 configured as described above will be described.

The seam welding apparatus 10 of the present embodiment is a seam welding apparatus that seam welds two

flanges

13 and 15 by sandwiching the two flanges 13 and 15 (a plurality of workpieces) that are overlapped with each other between a pair of

roller electrodes

12A and 12B to which a voltage is applied and moving the pair of

roller electrodes

12A and 12B relative to the two

flanges

13 and 15 while rotating the pair of roller electrodes. The seam welding apparatus 10 has an electrode holding mechanism 14, a workpiece position detection sensor 16, and a control section 18, wherein the electrode holding mechanism 14 holds a pair of

roller electrodes

12A, 12B in such a manner that the axial orientation of the

roller electrodes

12A, 12B can be changed; the workpiece position detection sensor 16 detects the positions of the edge portions of the two flanges 13, 15 (the positions of the detection surfaces DS); the control unit 18 controls the energization to the pair of

roller electrodes

12A, 12B, and controls the electrode holding mechanism 14 based on the detection result of the workpiece position detection sensor 16. The control section 18 includes a first determination section 18c and a second determination section 18d, wherein the first determination section 18c determines whether or not there is an abnormality in the detection result of the workpiece position detection sensor 16; when the first determination unit 18c determines that there is an abnormality in the detection result of the workpiece position detection sensor 16, the second determination unit 18d determines the cause of the abnormality based on the variance value DV of the detection result of the workpiece position detection sensor 16.

Accordingly, the control unit 18 can determine the cause of an abnormality (failure) in the detection result of the workpiece position detection sensor 16 and take countermeasures in accordance with various situations. This can reduce the time required to cope with the failure.

When the variance value DV is not within the predetermined range PR, the second determination unit 18d determines that a foreign object is attached to the workpiece position detection sensor 16. Accordingly, the cause of an abnormality (failure) in the detection result of the workpiece position detection sensor 16 can be identified by classifying the cause of an abnormality into a case where a foreign object is attached to the workpiece position detection sensor 16 and another case.

When the variance value DV is larger than the upper limit PRu of the predetermined range PR, the second determination unit 18d determines that foreign matter is attached to the workpiece position detection sensor 16 over a wide range. Accordingly, when the variance value DV is larger than the upper limit PRu of the predetermined range PR, it is considered that foreign matter adheres to the workpiece position detection sensor 16 over a wide range and the workpiece position detection sensor 16 cannot detect the edge portions of the two

flanges

13 and 15 to be detected, and therefore such appropriate determination can be made.

When the variance value DV is smaller than the lower limit PRl of the predetermined range PR, the second determination unit 18d determines that a foreign object is locally attached to the workpiece position detection sensor 16. Accordingly, when the variance value DV is smaller than the lower limit PRl of the predetermined range PR, it is considered that the workpiece position detection sensor 16 detects foreign matter locally adhering to the workpiece position detection sensor 16, instead of detecting the edge portions of the two

flanges

The second determination unit 18d determines that foreign matter is locally attached to the workpiece position detection sensor 16 when the variance value DV is larger than the upper limit PRu of the predetermined range PR, and determines that foreign matter is locally attached to the workpiece position detection sensor 16 when the variance value DV is smaller than the lower limit PRl of the predetermined range PR. When the variance value DV is larger than the upper limit PRu of the predetermined range PR and when the variance value DV is smaller than the lower limit PRl of the predetermined range PR, appropriate determinations can be made corresponding to each.

When the variance value DV is within the predetermined range PR, the second determination unit 18d determines that the deviation of the teaching demonstration of the teaching target range TR occurs in the electrode holding mechanism 14. Accordingly, deviations from the exemplary teachings can be motivated.

The first determination unit 18c determines whether or not there is an abnormality in the detection result of the workpiece position detection sensor 16 based on the control amount CA of the electrode holding mechanism 14 based on the detection result of the workpiece position detection sensor 16. Accordingly, for example, by a simple method of comparing the average value Ave of the control amounts CA with the threshold value Th, it is possible to determine whether or not there is an abnormality in the detection result of the workpiece position detection sensor 16.

When the first determination unit 18c determines that there is an abnormality in the detection result of the workpiece position detection sensor 16, the control unit 18 stops seam welding. Accordingly, it is possible to prevent the seam welding from being continued in a state where the pair of

roller electrodes

12A, 12B is greatly deviated from the desired welding trajectory DWT (in a state where the pair of

roller electrodes

12A, 12B is deviated from the target range TR).

The seam welding method of the present embodiment includes a seam welding start step of starting seam welding by sandwiching two flanges 13, 15 (a plurality of workpieces) overlapped with each other between

roller electrodes

12A, 12B to which a voltage is applied and moving the pair of

roller electrodes

12A, 12B while rotating the pair of

roller electrodes

12A, 12B; in the workpiece position detecting step, the positions of the edge portions of the two

flanges

13, 15 are detected by the workpiece position detecting sensor 16; in the first determination step, it is determined whether or not there is an abnormality in the detection result of the workpiece position detection sensor 16; in the second determination step, when it is determined in the first determination step that there is an abnormality in the detection result of the workpiece position detection sensor 16, the cause of the abnormality is determined based on the variance value DV of the detection result of the workpiece position detection sensor 16.

Accordingly, in the second determination step, the cause of abnormality (failure) in the detection result of the workpiece position detection sensor 16 can be determined, and countermeasures can be taken in accordance with various situations. This can reduce the time required to cope with the failure.

If the variance value DV is not within the predetermined range PR, it is determined in the second determination step that foreign matter has adhered to the workpiece position detection sensor 16. Accordingly, the cause of an abnormality (failure) in the detection result of the workpiece position detection sensor 16 can be notified separately from the case where a foreign object is attached to the workpiece position detection sensor 16 and the other cases.

In the second determination step, when the variance value DV is larger than the upper limit PRu of the predetermined range PR, it is determined that foreign matter is attached to the workpiece position detection sensor 16 over a wide range. Accordingly, when the variance value DV is larger than the upper limit PRu of the predetermined range PR, it is considered that foreign matter adheres to the workpiece position detection sensor 16 over a wide range and the workpiece position detection sensor 16 cannot detect the edge portions of the two

flanges

In the second determination step, when the variance value DV is smaller than the lower limit PRl of the predetermined range PR, it is determined that a foreign object is locally attached to the workpiece position detection sensor 16. Accordingly, when the variance value DV is smaller than the lower limit PRl of the predetermined range PR, it is considered that the workpiece position detection sensor 16 detects foreign matter locally adhering to the workpiece position detection sensor 16, instead of detecting the edge portions of the two

flanges

In the second determination step, when the variance value DV is larger than the upper limit PRu of the predetermined range PR, it is determined that foreign matter is attached to the workpiece position detection sensor 16 over a wide range, and when the variance value DV is smaller than the lower limit PRl of the predetermined range PR, it is determined that foreign matter is locally attached to the workpiece position detection sensor 16. Therefore, in the case where the variance value DV is larger than the upper limit PRu of the predetermined range PR and in the case where the variance value DV is smaller than the lower limit PRl of the predetermined range PR, appropriate determinations corresponding to each can be made.

When the variance value DV is within the predetermined range PR, it is determined in the second determination step that a deviation of the teaching demonstration of the teaching target range TR occurs in the electrode holding mechanism 14. Accordingly, deviations from the exemplary teachings can be motivated.

In the first determination step, it is determined whether or not there is an abnormality in the detection result of the workpiece position detection sensor 16 based on the control amount CA of the axes of the pair of

roller electrodes

12A, 12B based on the detection result of the workpiece position detection sensor 16. Accordingly, for example, by a simple method of comparing the average value Ave of the control amounts CA with the threshold value Th, it is possible to determine whether or not there is an abnormality in the detection result of the workpiece position detection sensor 16.

In the second determination step, when the first determination step determines that there is an abnormality in the detection result of the workpiece position detection sensor 16, seam welding is stopped. Accordingly, it is possible to prevent the seam welding from being continued in a state where the pair of

roller electrodes

12A, 12B is deviated from the target range TR).

Claims

1. A seam welding apparatus for seam welding a plurality of workpieces by sandwiching the overlapped workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating, characterized in that,

has an electrode holding mechanism, a workpiece position detection sensor, and a control section, wherein,

the electrode holding mechanism holds a pair of the roller electrodes in such a manner that an axis orientation of the roller electrodes can be changed;

the workpiece position detection sensor detects positions of edge portions of a plurality of the workpieces;

the control section controls energization to the pair of roller electrodes and controls the electrode holding mechanism based on a detection result of the workpiece position detection sensor,

the control section includes a first determination section and a second determination section, wherein,

the first determination unit determines whether or not there is an abnormality in the detection result of the workpiece position detection sensor;

the second determination unit determines a cause of an abnormality based on a variation state of the detection result of the workpiece position detection sensor when the first determination unit determines that there is an abnormality in the detection result of the workpiece position detection sensor,

the second determination unit determines that a foreign object is attached to the workpiece position detection sensor when the value indicating the variation state is not within a predetermined range,

when the value indicating the fluctuation state is larger than the upper limit of the predetermined range, the second determination unit determines that foreign matter is attached to the workpiece position detection sensor in a wide range.

2. A seam welding apparatus for seam welding a plurality of workpieces by sandwiching the overlapped workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating, characterized in that,

when the value indicating the fluctuation state is smaller than the lower limit of the predetermined range, the second determination unit determines that a foreign object is locally attached to the workpiece position detection sensor.

3. A seam welding apparatus for seam welding a plurality of workpieces by sandwiching the overlapped workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating, characterized in that,

when the value indicating the fluctuation state is larger than the upper limit of the predetermined range, the second determination unit determines that foreign matter is attached to the workpiece position detection sensor in a wide range,

when the value indicating the variation state is smaller than the lower limit of the predetermined range, the second determination unit determines that a foreign object is locally attached to the workpiece position detection sensor.

4. A seam welding apparatus for seam welding a plurality of workpieces by sandwiching the overlapped workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes relative to the plurality of workpieces while rotating, characterized in that,

the second determination unit determines that the teaching of the electrode holding mechanism is deviated when the value indicating the variation state is between an upper limit and a lower limit of the predetermined range.

5. A seam welding apparatus according to any of claims 1 to 4,

the first determination unit determines whether or not there is an abnormality in the detection result of the workpiece position detection sensor based on the control amount of the electrode holding mechanism based on the detection result of the workpiece position detection sensor.

6. A seam welding apparatus according to any of claims 1 to 4,

the control unit stops the seam welding when the first determination unit determines that the detection result of the workpiece position detection sensor is abnormal.

7. A seam welding method is characterized in that,

comprises a seam welding starting step, a workpiece position detecting step, a first judging step and a second judging step, wherein,

in the seam welding starting step, seam welding is started by sandwiching the overlapped plurality of workpieces with a pair of roller electrodes to which a voltage is applied and moving the pair of roller electrodes while rotating;

in the workpiece position detecting step, positions of edge portions of the plurality of workpieces are detected by a workpiece position detecting sensor;

in the first determination step, it is determined whether or not there is an abnormality in the detection result of the workpiece position detection sensor;

in the second determination step, when it is determined in the first determination step that there is an abnormality in the detection result of the workpiece position detection sensor, a cause of the abnormality is determined based on a fluctuation state of the detection result of the workpiece position detection sensor,

in the second determination step, it is determined that a foreign object is adhered to the workpiece position detection sensor when the value indicating the variation state is not within a predetermined range,

in the second determination step, when the value indicating the fluctuation state is larger than the upper limit of the predetermined range, it is determined that foreign matter is attached to the workpiece position detection sensor in a wide range.

8. A seam welding method is characterized in that,

in the second determination step, it is determined that foreign matter is locally attached to the workpiece position detection sensor when the value indicating the variation state is smaller than the lower limit of the predetermined range.

9. A seam welding method is characterized in that,

in the second determination step, it is determined that,

when the value indicating the fluctuation state is larger than the upper limit of the predetermined range, it is determined that foreign matter is attached to the workpiece position detection sensor in a wide range,

when the value indicating the fluctuation state is smaller than the lower limit of the predetermined range, it is determined that a foreign object is locally attached to the workpiece position detection sensor.

10. A seam welding method is characterized in that,

in the second determination step, it is determined that the deviation of the teaching demonstration has occurred when the value indicating the variation state is between the upper limit and the lower limit of the predetermined range.

11. A seam welding method according to any of claims 7 to 10,

in the first determination step, it is determined whether there is an abnormality in the detection result of the workpiece position detection sensor based on the control amount of the shafts of the pair of roller electrodes based on the detection result of the workpiece position detection sensor.

12. A seam welding method according to any of claims 7 to 10,

in the second determination step, the seam welding is stopped when the first determination step determines that there is an abnormality in the detection result of the workpiece position detection sensor.