JP5396097B2 - Chile detection misjudgment prevention method - Google Patents

Description

  The present invention relates to a method for preventing misdetection of dust detection in resistance welding such as spot welding.

  2. Description of the Related Art Conventionally, many welding robots that perform spot welding work are arranged at predetermined locations on a workpiece conveyed by a conveyance device in a production line for welding and assembling a car body of an automobile. These welding robots include a spot welding gun having a shape suitable for a preset welding location of a workpiece.

  In this type of welding robot, the resistance value is monitored while the welding current is applied. By monitoring this resistance value, it is known that if dust is generated during welding current application, the resistance value is greatly reduced.

  When such dust occurs, the strength of the welded portion may be insufficient even when the preset welding current is energized for a preset energization time. This is because the growth rate of the nugget decreases due to the generation of dust, and the size of the nugget becomes small.

  For this reason, if the resistance value decreases during energization, the welding robot determines that dust has occurred, and preset dust generation such as stopping the welding current, lowering the welding current, raising the welding current, etc. It is programmed to perform time processing (see Patent Document 1).

  By the way, if foreign matter such as dust is caught between the materials to be welded, the initial resistance of resistance welding becomes very large compared to the time when normal resistance welding is started, and then the resistance rapidly decreases due to melting of the dust. is there.

JP 2006-55893 A

  However, such a rapid decrease in resistance value may cause the welding robot to erroneously determine that dust has occurred. When such a misjudgment is made, the welding robot stops the welding current, lowers the welding current, increases the welding current, or performs a preset process when dust occurs.

  If the processing at the time of occurrence of dust based on such an erroneous determination is performed, a malfunction may occur such as stopping the welding operation unnecessarily or changing the welding current to an abnormal value.

  The present invention has been made in view of the above-described problems, and prevents an erroneous determination that a sudden decrease in the resistance value caused by the inclusion of foreign matter such as dust is the occurrence of dust. It is an object of the present invention to provide a method for preventing dust detection misjudgment that can prevent malfunction caused by performing processing when dust occurs based on the judgment.

  The dust detection error determination prevention method of the present invention monitors a resistance value (for example, a resistance value r described later) during resistance welding, and a change amount of the resistance value per unit time (for example, a resistance value change amount rd described later). ) Is a threshold value (for example, a threshold value L described later) or more, a method for preventing erroneous detection of dust detected by a device that detects the occurrence of dust, an upper limit of the resistance value at the start of normal resistance welding And a second step of determining whether or not the resistance value during resistance welding has exceeded the upper limit threshold (step S1 described later). A step (for example, step S3 to be described later), and when the resistance value exceeds the upper threshold value, a period during which the resistance value exceeds the upper threshold value, and a predetermined value after the resistance value is equal to or lower than the upper threshold value The period until time T elapses, h The third step is not performed calculation of detection (e.g., step S6 will be described later), characterized in that it comprises a and.

  According to the present invention, it is possible to prevent a sudden decrease in the resistance value caused by the entrapment of foreign matter such as dust from being erroneously determined as the occurrence of dust, and the processing at the time of occurrence of dust is performed based on such erroneous determination. It is possible to prevent malfunctions that occur.

  According to the present invention, it is possible to prevent a sudden decrease in the resistance value caused by the entry of foreign matter such as dust from being erroneously determined as occurrence of dust, and processing at the time of occurrence of dust is performed based on such erroneous determination. It is possible to prevent malfunctions that occur.

It is a schematic explanatory drawing of the spot welding apparatus which enforces the dust detection misjudgment prevention method concerning the present invention. It is a flowchart in one Embodiment of the dust detection misjudgment prevention method which concerns on this invention. It is a detailed flowchart about step S7 shown in FIG. It is a timing chart which shows the relationship between the energization time of the welding current and the interelectrode resistance in the dust detection misjudgment prevention method according to the embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic explanatory view of a spot welding apparatus 10 that implements the dust detection misjudgment prevention method according to the present invention.

  The spot welding apparatus 10 includes a pair of electrode tips 3 and 4 that pressurize the overlapped members 1 and 2 to flow welding current, and a pressurizing device (not shown) that applies a desired pressure to the electrode tips 3 and 4. ), A power supply device (not shown) for supplying a desired welding current to the welded members 1 and 2 pressurized by the pressurizing device via the electrode tips 3 and 4, and a control device 5 for controlling them. Is provided.

  In the spot welding apparatus 10 configured in this manner, a nugget is caused by flowing a welding current set in advance according to welding conditions to the members to be welded 1 and 2 through the electrode tips 3 and 4 for a preset energization time. 6 grows at a predetermined speed and welding is performed.

The control device 5 detects the occurrence of dust according to the flowcharts of FIGS.
First, in the flowchart of FIG. 2, in step S <b> 1, the upper limit of the interelectrode resistance range is set as the upper limit threshold by the control device 5. Here, the “range of resistance between electrodes” is a range in which the resistance between electrodes can normally be taken at the moment when resistance welding is started when welding a member to be welded in a normal state without any abnormalities such as biting of dust. That is.
Specifically, for example, a value of 50 to 500 μΩ is set as the upper limit threshold value.

In step S2, the control device 5 starts monitoring the resistance value. That is, the resistance value is detected every predetermined time.
Specifically, the control device 5 detects the resistance value at time t1 and sets this resistance value to r1, and detects the resistance value at time t2 after a unit time from time t1 and sets this resistance value to r2. The control device 5 similarly detects the resistance value every unit time from the start to the end of spot welding.

In step S3, it is determined whether or not the resistance value monitored by the control device 5 exceeds the upper limit threshold value.
If this determination is NO, the number of determinations in step S3 is stored, and the process proceeds to step S4. If YES, the process proceeds to step S6.

In step S4, the control device 5 determines whether or not the determination in step S3 is the first time. That is, it is determined whether or not it is the first determination that the resistance value is determined to be equal to or lower than the upper limit threshold in the determination in step S3.
If this determination is NO, the process proceeds to step S5, and if YES, the process proceeds to step S7.

When the determination in step S4 is NO and the process proceeds to step S5, in step S5, it is determined whether or not a predetermined time has elapsed since the resistance value monitored by the control device 5 is equal to or less than the upper limit threshold value.
In this case, the resistance value monitored by the control device 5 initially exceeded the upper threshold value, but thereafter became equal to or lower than the upper threshold value. Therefore, the time from when the resistance value becomes equal to or less than the upper limit threshold until it matches the resistance value during normal welding is set as a predetermined time.

This time varies depending on the type of material to be welded. Moreover, it also differs depending on the type of foreign matter bitten, such as dust. Examples of foreign substances include sealer and dust. When the gap between the plates such as high-tensile material is large, the resistance may suddenly drop at the moment of familiar contact. Therefore, what is most likely to occur and what has the longest time are experimentally obtained.
Specifically, for example, a time of 2 to 50 μs is set as a predetermined time from when the resistance value becomes equal to or lower than the upper limit threshold, and it is determined whether or not this time has elapsed.
If this determination is NO, the process proceeds to step S6, and if YES, the process proceeds to step S7.

When the determination in step S3 is YES and the process proceeds to step S6, the control device 5 does not perform the dust detection calculation in step S6.
In this case, since the resistance value monitored by the control device 5 exceeds the upper limit threshold value, the process returns to step S3 without performing the dust detection calculation.

If the determination in step S5 is NO and the process proceeds to step S6, the control device 5 does not perform the dust detection calculation in step S6.
In this case, after the resistance value monitored by the control device 5 first exceeds the upper threshold value, the time is equal to or lower than the upper threshold value, and the time from when the resistance value is lower than the upper threshold value until the resistance value during normal welding is reached. Therefore, the process returns to step S3 without performing the dust detection calculation.

  That is, the period during which the resistance value monitored by the control device 5 exceeds the upper limit threshold, and the period from when the resistance value is equal to or lower than the upper limit threshold to when the resistance value during normal welding elapses is controlled. The apparatus 5 returns to step S3 without performing the dust detection calculation.

  On the other hand, if the determination in step S5 is YES and the process proceeds to step S7, the control device 5 performs a dust determination calculation in step S7.

If the determination in step S4 is YES and the process proceeds to step S7, the control device 5 performs a dust determination calculation in step S7.
In this case, the resistance value monitored by the control device 5 is not more than the upper threshold value from the beginning.

  The calculation of dust determination in step S7 will be described with reference to the flowchart of FIG.

  In step S71, it is determined whether or not the amount of change per unit time of the resistance value monitored by the control device 5 is equal to or greater than a threshold value. That is, the control device 5 detects the resistance value every unit time, and calculates the change amount per unit time of the resistance value based on the two resistance values separated by the unit time. Then, it is determined whether or not the calculated resistance value change amount per unit time is equal to or greater than a threshold value.

This threshold value represents the degree of decrease in the resistance value that decreases when dust occurs, in terms of the amount of change in the resistance value per unit time.
If this determination is YES, the process proceeds to step S72, and if this determination is NO, the process proceeds to step S74.

  In step S72, the control device 5 determines that the dust is present.

In step S73, the control device 5 performs processing for dust. That is, the control device 5 is pre-programmed as processing for dust, for example, processing for stopping the welding current, processing for reducing the welding current, processing for increasing the welding current, etc. I do.
Then, after a predetermined process is performed on dust, the welding operation is finished.

  On the other hand, when the determination in step S71 is NO and the process proceeds to step S74, in step S74, the controller 5 determines that it is not dust.

  Subsequently, in step S75, the control device 5 determines whether or not the welding is finished. That is, the control device 5 refers to a preset welding program and determines whether or not the welding has been completed.

If welding has not ended, the determination in step S75 is NO, and the process returns to step S71.
While the determination in step S71 is NO, the process proceeds to step S74, and further to step S75. While the determination in step S75 is NO and the process proceeds to step S71, the amount of change in resistance value per unit time is less than the threshold value. Continue to maintain state. That is, a normal welding operation that does not generate dust is performed.

  When the welding is completed, the determination in step S75 becomes YES, so that the welding operation is normally completed.

FIG. 4 is a timing chart showing the relationship between the welding current application time and the interelectrode resistance in the dust detection error determination prevention method according to the embodiment.
In FIG. 4, the solid line indicates the energization time when the resistance between the electrodes is abnormally high at the start of the welding operation by biting foreign matter such as dust between the workpieces, and then the resistance is reduced to a normal value by melting the dust. And the interelectrode resistance.
For comparison, the broken line indicates the relationship between the energization time and the interelectrode resistance when dust is generated during the welding operation and the welding operation is not normally performed.
Furthermore, a two-dot chain line indicates the relationship between the energization time and the interelectrode resistance when the welding operation is normally performed.

As shown by the solid line in FIG. 4, when dust is caught in the initial stage of the welding operation, it is determined as follows according to the flowchart shown in FIG.
That is, the control device 5 detects the resistance value r every unit time.

At time t1, the resistance value r1 is detected. Since the resistance value r1 exceeds the upper limit threshold UL, it is determined that the calculation for dust detection is not performed.
At time t2 after the unit time, the resistance value r2 is detected. Further, at time t3 after unit time, the resistance value r3 is detected. Since both the resistance values r2 and r3 exceed the upper limit threshold UL, it is determined that the calculation for dust detection is not performed.

  At time t4 after the unit time, the resistance value r4 is detected. The resistance value r4 coincides with the upper limit threshold UL, but since the predetermined time T has not elapsed since the coincidence, it is determined that the calculation of dust detection is not performed.

At time t5, the resistance value r5 is detected. The resistance value r5 matches the resistance value during normal welding. In this case, since the elapsed time from the time t4 to the time t5 is equal to the predetermined time T, it is determined that the dust detection calculation is performed.
Thereafter, the calculation of dust detection is repeated every unit time until welding is completed.

In FIG. 4, the length of the predetermined time T from when the resistance value monitored by the control device 5 becomes equal to or lower than the upper threshold value until the resistance value during normal welding coincides with the resistance value is determined by the control device 5 every unit time. It is shown equal to the length of the unit time for detecting r.
However, there is no correlation between the length of the predetermined time T and the length of the unit time, and usually the lengths of both are different.

As shown by the broken line in FIG. 4, when dust occurs during the welding operation, the following determination is made according to the flowchart shown in FIG.
The description from time t1 to time t5 is omitted.

  At time t6, the resistance value (r6) is detected, and at time t7 after the unit time, the resistance value (r7) is detected. Then, the difference between the resistance value (r6) and the resistance value (r7) is calculated as the resistance value change amount rd6. Since the resistance value change amount rd6 is not equal to or greater than the threshold value L, it is determined not to be dust.

  At time t8 after the unit time, the resistance value (r8) is detected. Then, the difference between the resistance value (r7) and the resistance value (r8) is calculated as the resistance value change amount rd7. Since the resistance value change amount rd7 is equal to or greater than the threshold value L, it is determined to be Chile.

According to this embodiment, there are the following effects.
(1) While the abnormal resistance value caused by foreign object biting such as dust is generated by the control device 5, the resistance value caused by foreign object biting is drastically reduced by not performing the dust detection calculation. Can be prevented from being erroneously determined to be the occurrence of dust.

  (2) Based on misjudgment of dust generation, the welding current is stopped, lowered, raised, etc. As a result of processing when dust generation occurs, welding work is stopped uselessly or the welding current is set to an abnormal value. It is possible to prevent malfunction such as changing.

  (3) It is possible to prevent welding failure from occurring due to a malfunction as a processing result based on an erroneous determination of occurrence of dust.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

DESCRIPTION OF SYMBOLS 1, 2 ... Member to be welded 3, 4 ... Electrode tip 5 ... Control apparatus 6 ... Nugget 10 ... Spot welding apparatus

Claims (1)

Dust detection that monitors the resistance value during resistance welding and prevents erroneous determination in a device that detects the occurrence of dust when the amount of change in the resistance value per unit time is equal to or greater than a threshold based on the calculation of dust detection A method for preventing misjudgment,
A first step of setting the upper limit of the resistance value at the start of normal resistance welding as an upper threshold;
A second step of determining whether or not a resistance value during resistance welding exceeds the upper limit threshold;
When the resistance value exceeds the upper limit threshold at the start of resistance welding, a period during which the resistance value exceeds the upper limit threshold, and a period until a predetermined time elapses after the resistance value is equal to or less than the upper limit threshold, A third step not performing the calculation of the dust detection;
A method for preventing misdetection of dust detection, comprising:

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