JP7185382B2 - Cable inspection method for indirect spot welding equipment - Google Patents

Description

The present invention relates to a method for inspecting cables provided in an indirect spot welding apparatus.

Spot welding includes direct spot welding in which multiple metal plates are sandwiched between a pair of electrodes and energized, and one electrode (welding electrode) and the other electrode (ground electrode) are brought into contact with different points and energized. Indirect spot welding is known (see Patent Document 1 below, for example).

JP 2006-198676 A

For direct spot welding, a welding gun 104 having a pair of electrodes 102 and 103 and a transformer 105 is provided at the tip of a robot arm 101, as shown in FIG. A current supplied from an external power supply is supplied to a transformer 105 via a cable 106 provided along the robot arm 101, and is converted into a large current (see thick dotted line) by the transformer 105 to generate a pair of electrodes 102 and 103. energized in between. In this case, the cable 106 along the robot arm 101 carries a small current (see thin dotted line) before being converted by the transformer 105 .

On the other hand, in the case of indirect spot welding, as shown in FIG. 9, a welding electrode 202 is provided at the tip of a robot arm 201, and a ground electrode is attached to a pressure device (for example, a cylinder 208) provided separately from the robot arm 201. 203 is provided. In this case, a current supplied from an external power supply via a cable 210 is converted into a large current by a transformer 205 provided on the fixed side (for example, the floor), and the cable 207→welding electrode 202→workpiece W→ground. It flows through the path of electrode 203 →cable 206 .

In the indirect spot welding apparatus as described above, a large current (see the thick dotted line) converted by the transformer 205 flows through the cables 206 and 207 during welding. The cables 206 and 207 themselves vibrate due to the magnetic field generated by this large current, and the cables 206 and 207 may break. In particular, since the cable 207 connecting the transformer 205 and the welding electrode 202 is bent and stretched each time the robot arm 201 is moved, there is a high risk of disconnection. If the cable 207 is disconnected, the current value supplied to the work decreases, resulting in defective welding, so the production line needs to be temporarily stopped to replace the cable 207, resulting in a decrease in productivity.

In view of the above circumstances, the problem to be solved by the present invention is to avoid the stoppage of the production line due to cable breakage in indirect spot welding, thereby preventing a decrease in productivity.

In order to solve the above problems, the present invention provides a welding electrode attached to the tip of a robot arm, a ground electrode provided at a location other than the robot arm, and an electric current flowing between the welding electrode and the ground electrode. 1. A method for inspecting the cable of an indirect spot welding apparatus comprising a transformer for generating a current that flows through the welding electrode and a flexible cable electrically connecting the transformer and the welding electrode, the cable and determining whether or not the cable is broken based on the resistance value of the energization path.

As described above, in the present invention, the resistance value of the current path including the cable connecting the welding electrode and the transformer is measured. judge. In this way, by monitoring the state of the cable (degree of disconnection), it is possible to replace the cable before a fatal disconnection occurs in the cable and welding defects occur. It is possible to avoid a situation that suddenly stops the line.

In the above-described method, for example, an electric path including the cable can be formed by bringing the welding electrode into contact with the conductor connected to the transformer. At this time, if a material (metal) melted at the time of welding adheres to the tip of the welding electrode, the contact resistance with the conductor increases, so the resistance value of the current-carrying path including the cable increases. In this case, even if the resistance value of the current-carrying path exceeds a predetermined value, whether it is due to an increase in the contact resistance between the welding electrode and the conductor or due to an increase in the resistance value of the cable (i.e., disconnection of the cable) is determined. difficult to distinguish.

Therefore, the welding electrode is polished to remove the metal adhering to the tip, and immediately after that (specifically, after polishing and before the next welding point is welded), the welding electrode is brought into contact with the conductor. , to form a current-carrying path including a cable. In this case, since the resistance value of the energization path is obtained by eliminating the influence of the metal adhering to the tip of the welding electrode, it is possible to more accurately determine the presence or absence of disconnection of the cable from the resistance value of the energization path.

As described above, according to the present invention, disconnection of a cable can be detected in advance, so that stoppage of the production line due to cable replacement can be avoided, and a decrease in productivity can be prevented.

1 is a side view of an indirect spot welding device; FIG. Fig. 3 is a cross-sectional view of a cable; FIG. 2 is a side view showing how a welding electrode is ground in the indirect spot welding apparatus of FIG. 1; FIG. 2 is a side view showing how the indirect spot welding apparatus of FIG. 1 inspects a cable for disconnection; It is a graph which shows the relationship between the resistance value of an electric conduction path for an inspection, and the frequency|count of an inspection. It is a side view of an indirect spot welding device according to another embodiment. FIG. 11 is a side view of an indirect spot welding device according to still another embodiment; It is a side view of a direct spot welding device. It is a side view of an indirect spot welding device according to a comparative example.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The indirect spot welding apparatus shown in FIG. and a polishing device 5 for polishing the welding electrode 2 .

The welding electrode 2 is arranged by the robot arm 1 at an arbitrary three-dimensional position within the movable range of the robot arm 1 and in an arbitrary posture. In this embodiment, a cylinder 6 as a pressure device is provided at the tip of the robot arm 1 and the welding electrode 2 is attached to the pin of the cylinder 6 . By projecting or retracting the pin of the cylinder 6, the welding electrode 2 moves in its own axial direction (vertical direction in FIG. 1).

The ground electrode 3 is attached to a pin of a cylinder 7 as a pressure device provided on the fixed side (for example, the floor). By projecting or retracting the pin of the cylinder 7, the ground electrode 3 moves in its own axial direction (vertical direction in FIG. 1).

Welding electrode 2 and transformer 4 are electrically connected via a flexible cable 8 . In the illustrated example, a cable 8 is provided along the robot arm 1 and can be deformed to follow the robot arm 1 . Specifically, as shown in FIG. 2, the cable 8 includes a conductor bundle 8a formed by twisting a large number of conductors (copper wires) 8a1 and a flexible tube 8b covering the outer periphery of the conductor bundle 8a. , and a cooling medium 8c (for example, cooling water) flowing between the wire bundle 8a and the tube 8b.

The ground electrode 3 and the transformer 4 are electrically connected via a conductor. In this embodiment, the ground electrode 3 and the transformer 4 are connected via a bus bar 9 made of a conductive rigid body such as metal (for example, copper) (see FIG. 1). Even when the earth electrode 3 is moved up and down by the cylinder 7, the bus bar 9 and the earth electrode 3 are maintained in a conductive state. The transformer 4 is connected to an external power source (not shown) via a cable 10 .

Welding by the above indirect spot welding apparatus is performed in the following procedure. First, a work including the metal plates W1 and W2 is set on a set table (not shown). In this state, the cylinder 7 is driven to raise the ground electrode 3 and bring the ground electrode 3 into contact with the metal plate W2 from below. After that, the robot arm 1 is driven to place the welding electrode 2 above the overlapping portion of the metal plates W1 and W2, the cylinder 6 is driven to lower the welding electrode 2, and the welding electrode 2 separates the metal plates W1 and W2. Press the polymerization section from above. In this state, the current supplied through the cable 10 is converted into a large current by the transformer 4 and passed between the welding electrode 2 and the ground electrode 3, whereby the metal plate W1, The contact portion of W2 is melted and joined by resistance heat generation.

According to the indirect spot welding as described above, even when the overlapped portions of the metal plates W1 and W2 cannot be sandwiched, the overlapped portions can be welded. In addition, while maintaining the ground electrode 3 in contact with the metal plate W2, the robot arm 1 can move the welding electrode 2 to another location to weld a plurality of points.

As the welding is repeated, the molten material of the metal plate W1 adheres to the tip of the welding electrode 2 . If metal adheres to the tip of the welding electrode 2 in this manner, the quality of welding may be degraded. Therefore, as shown in FIG. The base material (copper) of the welding electrode 2 is exposed by polishing with the device 5 to remove the metal adhering to the tip.

When performing indirect spot welding as described above, the large current converted by the transformer 4 passes through the cable 8, the welding electrode 2, the metal plates W1 and W2, the ground electrode 3, and the bus bar 9, and the welding current path M1. flow (see Figure 1). At this time, since the bus bar 9 is formed of a rigid body, it is hardly damaged even if a large current flows. On the other hand, since the cable 8 is flexible, when the large current converted by the transformer 4 flows, the cable 8 itself vibrates due to the magnetic field generated at this time. Also, since the cable 8 deforms following the robot arm 1 , it is bent and stretched in order to drive the robot arm 1 . As described above, there is a risk that part of the wire bundle 8a of the cable 8 will break due to the vibration and bending/stretching of the cable 8 .

The indirect spot welding apparatus described above has an inspection mechanism for inspecting the presence or absence of disconnection of the cable 8 as described above. The inspection mechanism includes, for example, as shown in FIG. 13. The inspection ground electrode 11 is attached to, for example, the polishing device 5 in an insulated state. The calculation unit 13 has a calculation unit 13a, a determination unit 13b, and an alarm unit 13c.

The current measuring unit 12 has, for example, a non-contact type measuring probe 12a provided on the outer periphery of the busbar 14, and a measuring device 12b for measuring the value of the current flowing through the busbar 14 according to the signal from the measuring probe 12a. A toroidal coil, for example, can be used as the measuring probe 12a. The toroidal coil is arranged on the outer circumference of an inspection energization path M2, which will be described later, and is arranged on the outer circumference of the bus bar 14 in the illustrated example. In this case, current flows through the toroidal coil due to the magnetic field generated by the current flowing through the busbar 14, and the current value flowing through the busbar 14 is measured by detecting the current value of the toroidal coil with the measuring device 12b. The toroidal coil is preferably provided at a location where the current values of both the inspection current path M2 and the welding current path M1 can be measured. In the illustrated example, a toroidal coil (measurement probe 12 a ) is provided on the transformer 4 side of the bus bar 14 at the junction with the bus bar 9 connected to the ground electrode 3 . In addition, for example, a toroidal coil may be provided on the outer circumference of the cable 8 .

The inspection of the cable 8 by the inspection mechanism is performed in the following procedure. First, by bringing the welding electrode 2 into contact with the ground electrode 11 for inspection, an electric conduction path for inspection M2 including the cable 8 is formed. In the present embodiment, the electric conduction path for inspection M2 is formed through the cable 8, the welding electrode 2, the ground electrode 11 for inspection, and the bus bar . In this manner, by simply bringing the welding electrode 2 into contact with the ground electrode 11 for inspection, the energization path for inspection M2 can be easily formed without requiring operations such as circuit switching. At this time, by lowering the earth electrode 3 by the cylinder 7 and separating it from the metal plate W2, it is possible to reliably prevent the current for inspection from flowing to the earth electrode 3 side.

In this state, a minute current is passed through the inspection energization path M2, and the current measuring unit 12 measures the value of the current flowing through the bus bar 14 at this time, that is, the value of the current flowing through the inspection energization path M2. In this way, the current value of the current measuring path M2 for inspection and the voltage value (secondary voltage value) of the transformer 4 measured by the current measuring unit 12 are transmitted to the calculating unit 13 . Then, the calculation unit 13 a of the calculation unit 13 calculates the resistance value of the inspection energization path M<b>2 from the current value of the inspection energization path M<b>2 and the voltage value of the transformer 4 . Then, the determination unit 13b determines whether or not the resistance value of the inspection energization path M2 calculated by the calculation unit 13a exceeds a predetermined threshold value (upper limit value). It is transmitted to the part 13c and an alarm is issued.

Of the members forming the inspection energization path M2 shown in FIG. The resistance of the member is very low. Therefore, the resistance value of the inspection conducting path M2 is mainly determined by the resistance value of the cable 8 and the resistance value of the contact portion between the welding electrode 2 and the inspection ground electrode 11. As shown in FIG.

In this embodiment, immediately after the welding electrode 2 is polished by the polishing device 5 (specifically, after polishing and before welding the next welding point), the welding electrode 2 is brought into contact with the inspection ground electrode 11 for inspection. A current-carrying path M2 is formed, and its resistance value is measured. In this case, the welding electrode 2 is brought into contact with the inspection ground electrode 11 in a state in which the metal (such as zinc) adhering to the welding electrode 2 is removed and the base material (copper) of the welding electrode 2 is well exposed. Therefore, the energization state of the contact portion between the welding electrode 2 and the inspection ground electrode 11 can be stabilized, and the resistance value at this contact portion can be stabilized. Accordingly, it can be considered that the change in the resistance value of the inspection energization path M2 is mainly caused by the change in the resistance value of the cable 8. By inspecting whether or not the resistance value of the cable 8 exceeds a predetermined value, it is possible to determine whether or not the cable 8 has a disconnection of a predetermined value or more.

As described above, by periodically measuring the resistance value of the current conducting path M2 for inspection (for example, each time the welding electrode 2 is polished), the breakage state of the cable 8 can be monitored. As a result, since the cable 8 can be replaced before the cable 8 is fatally broken, it is possible to avoid the sudden stoppage of the production line due to the defective welding due to the breakage of the cable 8.例文帳に追加

FIG. 5 shows the relationship between the number of times of inspection and the resistance value of the inspection energization path M2. In this way, as the number of inspections increases, the disconnection of the cable 8 increases, so the resistance value of the inspection energization path M2 increases. Then, when the resistance value of the inspection energization path M2 exceeds a predetermined threshold value R1 (the point indicated by the arrow in the drawing), the alarm unit 13c issues an alarm. At this time, if the threshold value R1 of the resistance value of the inspection energization path M2 is set to a value close to the resistance value R2 at which welding failure occurs, the production line is immediately stopped and the cable 8 is replaced when the alarm is issued. need to be done. Therefore, it is desirable to set the threshold value R1 of the resistance value of the inspection energization path M2 to a value somewhat lower than the resistance value R2 at which welding defects occur (for example, 80% or less of the resistance value R2). In this case, even if the resistance value of the inspection energization path M2 exceeds the threshold value R1 and an alarm is issued, the production is continued for a while, and when the production line is periodically stopped (for example, after the end of production on that day, (during maintenance of the production line, etc.), the cable 8 can be replaced.

The invention is not limited to the above embodiments. For example, in the above-described embodiment, the current value of the secondary-side energization path (inspection energization path M2) after being converted by the transformer 4 is measured. It is also possible to measure the current value of the primary-side energization path before the measurement and multiply it by the conversion factor of the transformer 4 to obtain the current value of the inspection energization path M2.

Further, in the above embodiment, the resistance value calculated from the secondary voltage of the transformer 4 is used to determine whether or not the cable 8 is broken. In this case, the presence or absence of disconnection of the cable 8 is determined by using the resistance value of the section including the contact portion between the welding electrode 2 and the ground electrode 11 for inspection as well as the cable 8 in the conducting path for inspection M2. Become. Therefore, for example, if metal adheres to the tip of the welding electrode 2 and the resistance value of the contact portion between the welding electrode 2 and the inspection ground electrode 11 increases, the resistance value of the above-mentioned section also increases, so that the cable 8 can be broken. There is a risk of erroneously judging that it has occurred.

Therefore, it is preferable to measure the voltage in a section of the inspection energization path M2 that includes the cable 8 and does not include the contact portion between the welding electrode 2 and the inspection ground electrode 11, and use the resistance value calculated from this voltage. . For example, as shown in FIG. 6, a voltage measuring device 15 measures the voltage near both ends of the cable 8 (specifically, the voltage between the near end of the cable 8 on the transformer 4 side and the welding electrode 2). can do. Alternatively, as shown in FIG. 7, the voltage between the welding electrode 2 and the inspection ground electrode 11 is measured by a voltage measuring device 15, and the difference between this voltage and the secondary voltage of the transformer 4 can be used. . By using the resistance value calculated from these voltages, the presence or absence of disconnection of the cable 8 can be accurately determined without being affected by the state (resistance value) of the contact portion between the welding electrode 2 and the inspection ground electrode 11. be able to.

In addition, in the above-described embodiment, the presence or absence of disconnection of the cable 8 is determined based on the resistance value of the inspection energization path M2. Whether or not the cable 8 is disconnected may be determined based on the resistance value of M1. In this case, a mechanism (the inspection ground electrode 11 and the bus bar 14) for forming the inspection energization path M2 becomes unnecessary. However, since the resistance value of the welding energization path M1 varies depending on the plate assembly, welding conditions, etc., it may not be possible to determine whether or not the cable 8 is disconnected from this resistance value. In such a case, as in the above-described embodiment, an inspection energization path M2 that does not weld (that is, does not pass through a work) is formed, and disconnection of the cable 8 is detected based on the resistance value of this inspection energization path M2. It is preferable to determine the presence or absence of

1 Robot arm 2 Welding electrode 3 Earth electrode 4 Transformer 5 Polishing device 6 Cylinder 7 Cylinder 8 Cable 9 Bus bar 10 Cable 11 Inspection ground electrode 12 Current measurement unit 13 Calculation unit 13a Calculation unit 13b Judgment unit 13c Alarm unit 14 Busbar M1 For welding Electricity path M2 Electricity path for inspection W1, W2 Metal plate

Claims (1)

a welding electrode attached to the tip of a robot arm; a ground electrode provided at a location other than the robot arm; a transformer for generating a current to flow between the welding electrode and the ground electrode; A method for inspecting a cable of an indirect spot welding device comprising a flexible cable electrically connecting a welding electrode, the method comprising:
a step of measuring a resistance value of an energization path including the cable; and a step of determining whether or not the cable is broken based on the resistance value of the energization path ,
After polishing the welding electrode and before welding the next welding point, the welding electrode is brought into contact with a conductor connected to the transformer to form an energization path including the cable. A cable inspection method for welding equipment.

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