JPH0638986B2 - Method of detecting nut shortage in nut welder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for detecting a nut shortage in an automatic nut welding machine.

[Conventional technology]

FIG. 6 is a front view of the automatic nut welding machine, FIG. 7 is a side view thereof, 1 is a welding machine main body, 2 is a welding transformer connected to the welding machine main body 1 through a secondary cable 3, 4 Is a suspender thereof, and 5 is a control device including a welding timer, a thyristor and the like. The welder body 1 has a fixed electrode 6 and a movable electrode 7 facing the fixed electrode 6. The fixed-side electrode 6 is fixed on a base 8 via a bracket 9, and an insert electrode 6a is detachably provided on the upper part. (See FIG. 8). On the other hand, the movable electrode 7 is supported by a pressure cylinder 11 attached to a column 10 so as to be vertically movable,
An electrode tip 7b is detachably provided at the tip of the electrode arm 7a attached to the end of the cylinder output rod 11a. Reference numeral 12 denotes a work guide rail for feeding an object to be welded (a panel material on which a weld nut is welded; hereinafter referred to as "workpiece") W in a predetermined posture, and 13 denotes a supply pipe 1.
3a is a nut supply device for automatically supplying the weld nut N housed in 3a to a predetermined position. A locating pin 14 for nut positioning is provided so as to be able to move up and down by being inserted through the fixed-side electrode 6, and the pin tip 14a is driven by the locating cylinder 15 to project and retract on the upper surface of the fixed-side electrode insert 6a. The W and the nut N are positioned.

FIG. 8 shows a conventional nut shortage detecting means 16 provided in the automatic nut welding machine. Reference numeral 17 is a mounting bracket, 18 is an arm swingably supported by the bracket 17, 19 is a proximity switch (or limit switch) mounted on the bracket 17 facing one end of the arm 18, and 20 is the arm. It is a dog attached to the movable side electrode arm 7 a so as to be engageable with the other end of 18.

The nut shortage detection method using the nut shortage detection means 16 is as follows. That is, when welding nuts,
First, the movable electrode 7 is moved downward from the upper limit (welding gun return limit) level Lo to the welding level L _l by the stroke length Sp, and the weld nut N placed on the work W is inserted into the insert electrode 6a and the electrode. The chip 7b is pressed and pressed (see FIG. 9 (a)). At this pressurization stroke Sp, the dog 20 of the nut detecting means 16 has the upper limit level 20.
Since a stroke to the welding level 20Lo from lo, the one end 18a of the arm 18 to be linked to the dog 20 is moved from the return limit level 18Lo to the welding level 18L _l, opposite the proximity switch 19. The proximity switch 19 detects this and sends a signal to the control device. Based on the signal, it is determined that "a nut is present", and the connection gun is energized to perform welding. However, when the weld nut N is not on the work W, the movable electrode 7 moves down from the upper limit level Lo to the abnormal level L ₂ by the stroke length S _Q , and the electrode tip 7b directly contacts the work W. (Fig. 9 (b)
reference). Therefore abnormal "no nut" is pressurized stroke of the movable electrode 7 is increased by the height To of the nut N, the difference arises from the normal by To = S _Q -Sp. At this time, the dog 20 makes a stroke from the upper limit level 20Lo to the abnormal level 20L ₂ . Therefore, one end 1 of the arm 18
Since 8a has moved from the return limit level 18Lo to the abnormal level 18L ₂ and is disengaged from the proximity switch 19, the welding gun is not energized.

[Problems to be solved by the invention]

In such a conventional welding nut lacking detection method, the difference in the pressurization stroke length of the movable electrode 7 of the welding gun is controlled by the proximity switch (or limit) via the arm 18 of the nut lacking detection means 16. It has been decided to detect the presence or absence of a nut by detecting with a switch or the like. However, the fixed-side insert electrode 6a and the movable-side electrode tip 7b are worn and deformed each time welding is repeated, and therefore are polished to correct them. Therefore, the normal welding level L ₁ gradually moves down. Therefore, in order to prevent the pressing stroke Sp in the normal state (with a nut) from approaching the pressing stroke S _Q in the abnormal state (without a nut) and making the determination difficult, the nut shortage detecting means 16 is performed every time the electrode is polished. Proximity switch 19
Alternatively, there is a problem that the level of the dog 20 has to be adjusted.

The present invention has been made in order to solve such a conventional problem, and even if the stroke length of the welding gun changes due to electrode wear, the nut missing item can always reliably identify the presence or absence of the nut missing item. It is intended to provide a detection method of.

[Means for solving problems]

The present invention that achieves the above object, in a nut welding machine that repeats a cycle in which a workpiece and a weld nut supplied onto a fixed-side electrode are welded by pressurizing them with a vertically movable counter electrode, when the counter electrode is pressed. The stroke length of the nut is detected for each welding cycle, and the detected stroke length of the previous cycle is used as a reference value to compare with the detected stroke length of the current cycle to determine the presence or absence of a nut defect. This is a product detection method.

[Action]

The pressurization stroke length of the counter electrode is detected every time the welding cycle is performed, and the pressurization stroke length of the current cycle is always obtained using the pressurization stroke length of the immediately preceding cycle as a reference value.

Therefore, the reference pressure stroke length is constantly updated, and the influence of wear of the welding electrode is completely eliminated.

〔Example〕

1 to 3 are views showing an embodiment of the present invention, and FIG. 1 is a side view of a main part of a nut welding machine equipped with a nut shortage detection means used in the method of the present invention. The figure is a structural cross-sectional view of the nut shortage detection means. The same or corresponding parts as in the conventional case are designated by the same reference numerals.

In the figure, reference numeral 21 is a known stroke detecting means used for detecting the lack of nut of the present invention, and a rod 23 attached integrally to the electrode arm 7a of the movable electrode 7 via a bracket 22, and this rod. A detection head portion 25, which is inserted through the column 23 and fixed to the column 10 via a bracket 24, is provided.

FIG. 2 shows an example of a concrete structure of the stroke detecting means 21 for detecting the displacement amount by utilizing the differential change of the variable magnetic resistance. The rod 23 has a concentric magnetism. The body portions 26 are incorporated alternately with the non-magnetic body portions 27 at an equal pitch P. On the other hand, in the detection head unit 25, a primary excitation coil 28 and a secondary induction coil 29 are arranged at fixed positions in the magnetic shield core 30. Now, when the primary excitation coil 28 is AC-excited (input) with 1 Sinωt and 1 Cosωt, the magnetic body portion 26 in the rod 23,
Due to the combination with the non-magnetic body portion 27, the magnetic resistance becomes 1 as the rod 23 moves (that is, the displacement of the movable side electrode 7).
The change is repeated for each pitch P. This change in the magnetic resistance appears as a change in the induced voltage to the secondary induction coil 29 (output), and the secondary coil induced voltage output value E is [Where X is the amount of movement of the rod 23]. Now, paying attention to this phase, the movement amount X of the rod 23 is transferred as compared with the primary excitation input 1 Sinωt. Therefore, if the input and the output are compared and the phase difference is digitally taken out via the converter, an output proportional to the linear displacement amount X of the rod 23 (and thus the stroke length of the movable electrode 7) is obtained. Absolutely obtained within 1 pitch range. Even if the pitch exceeds 1 pitch, the magnetic material portion 26 is continuously arranged, so that the movement amount X can be calculated by counting the pitch.
Can be detected by absolute.

Hereinafter, a nut shortage detection method using the stroke detection means 21 will be described based on the process flowchart of FIG.

First, the power of the automatic nut welding device is turned on (step). Next, in step, the initial value S of the pressurization stroke Sp
Set po as the first reference value. This is because the work W and the weld nut N are placed on the insert electrode 6a,
This is a reference stroke length until the electrode tip 7b of the movable side electrode 7 descends from the upper limit level Lo and comes into contact with the weld nut N in a state where the electrode tip 7b of the movable side electrode 7 is positioned and set through the locate pin 14, and the insert electrode 6a and the electrode tip 7b.
It is set for the controller only during the first cycle when the is replaced with a new one. In step, the work W is supplied to a predetermined position on the insert electrode 6a of the fixed-side electrode 6 via the work guide rail 12. The cycle start button is pressed in step. As a result, the first welding cycle starts, and in the step, the weld nut N is supplied from the automatic nut supply device 13 onto the work W previously positioned and set on the insert electrode 6a.

The nut N and the work W are correctly positioned by the locate pin 14 which is vertically moved by the locate cylinder 15 for nut positioning. Then, in a step, the pressurizing cylinder 11 is operated, and the movable side electrode 7 moves to the upper limit level Lo.
From the beginning, the end face of the electrode tip 7b comes into contact with the upper surface of the nut N to apply pressure. In step, stroke length of movable electrode 7 (pressurization stroke length Spn; n = 1,)
However, the stroke detection means 21 described above outputs the change as the secondary coil induced voltage change, and the movement amount X is detected by the control device. The value is stored in the memory in the control device as the first pressurization stroke actual measurement value Sp _l .
In step, by comparing this pressure stroke Found Sp _l pressurized stroke initial value Spo is a predetermined reference value in step, whether the pressure stroke is normal or not. If the pressure stroke actual measurement value Sp _{1 of} the first circuit and the pressure stroke initial value Spo are substantially equal (Sp _l ≈Spo), it is determined that the pressure stroke is normal and the process proceeds to the next step. In step, the first pressurization stroke measured value Sp ₁ is set as the second pressurization stroke reference value. That is,
The measured data Sp ₁ is transferred to the address for storing the pressure stroke reference value in the memory, and the previous reference value Spo is updated. In the step, a large current is passed between the fixed electrode 6 and the movable electrode 7 from the transformer 2 via the secondary cable 3 to weld the nut N onto the work W. In this welding, the melting portion Nm (see FIG. 4) of the nut N is melted, so that the height (thickness) of the nut N changes from To to T ₁ before and after the welding. This change in thickness To-T _l causes the movable electrode 7 to move downward while the nut is being pressed.
Detected by 1. In step, it is judged whether or not the change in the thickness of the nut N is normal.

If the amount of decrease in thickness corresponds to the height of the fusion zone Nm of the weld nut N, it is determined to be normal, and the process proceeds to step.
In the step, the pressurizing cylinder 11 is operated in the opposite direction to raise the movable side electrode 7 to release the welding gun pressurization, and in the step, the work W after the nut welding is fixed via the work guide rail 12. After carrying out from the side electrode 6 and incrementing the counter (not shown) by +1 in step, the process returns to step and shifts to the second cycle starting from work supply. In the second and subsequent cycles, the reference value of the pressurizing stroke is the pressurizing stroke length measured by the stroke detecting means 21 in the cycle immediately before that. Thus, the pressure stroke reference value is automatically updated every cycle, so that the wear of the electrode during welding and the change in the pressure stroke length due to polishing to correct it are completely corrected. Therefore, it is not necessary to adjust the level of the stroke detection means 21 one by one when determining whether the pressurization stroke is normal or abnormal in the step. In step, if the pressurization stroke reference value and the actually measured value are not substantially equal to each other, it is determined that the pressurization stroke is abnormal, the process proceeds to step, and the progress of the cycle is stopped. After that, the operator operates the manual operating means (not shown) to move the pressurizing cylinder 11 upward (step), retract the movable electrode 7, and then the nut N is put on the work W in step. Check visually if there is any. If it is confirmed that the nut N has not been inserted, it is confirmed in step whether or not it is the first cycle (for example, the display of the cycle number display board is confirmed).

In the case of the first cycle, it is possible that there is a supply failure due to the nut catching in the nut supply device 13, so in order to repeat the cycle again, move to the step and press the cycle button to automatically supply the nut automatically. Start with On the other hand, if it is confirmed in step that the nut N has been put on the work W, or if it is confirmed that the nut N is the second time or later, there is something wrong with the nut welding device. Therefore, turn off the power (step) and inspect the entire device (step). Then, after the abnormal part is found and repaired, it is possible to start from the step again. In addition, when it is determined in step that the thickness change due to the melt pressurization of the nut N is abnormal, the process shifts to step to stop the cycle, and then a check process by a series of operator manual operations up to step is performed. Be implemented.

In the above embodiment, the stroke detecting means 21 of the lot 2 is used.
Although 3 is attached to the electrode arm 7, a magnet may be embedded in the rod 11a of the pressure cylinder 11 and the detection head 25 may be incorporated in the rod 11a, as shown in FIG. Stroke detecting means 21 used in the present invention
Is not limited to that shown in FIGS. 1 and 2, and various other known non-contact type linear displacement amount measuring devices can be used.

According to this embodiment, whether or not the nut is supplied can be reliably determined regardless of the amount of wear of the welding electrode, and by measuring the difference in the thickness of the nut before and after welding, the quality of the welded state of the nut can be determined. It is also possible to judge. Also, by setting the wear limit value of the electrode tip in advance, the tip use limit or the tip replacement time based on wear is determined,
It is also possible to display automatically.

〔The invention's effect〕

As described above, according to the present invention, in the nut welder, the stroke length of the movable side electrode of the welding gun is measured for each cycle, and the stroke length of the immediately previous cycle is always used as a reference value for the current cycle. Since it is determined whether the stroke length is normal or abnormal, it is possible to reliably detect the presence or absence of a missing weld nut without adjustment regardless of the amount of electrode wear.

[Brief description of drawings]

FIG. 1 is a view showing a usage mode of a stroke detecting means which can be used in the nut missing item detecting method of the present invention, FIG. 2 is a sectional structure view of the stroke detecting means, and FIG. 3 is a nut missing item detecting method of the present invention. FIG. 4 is a side view of the weld nut, FIG. 5 is another usage mode view of the stroke detecting means, FIG. 6 is a front view of the nut welding machine, FIG. 7 is a side view thereof, and FIG. FIG. 9 is a diagram showing a usage mode of a conventional nut shortage detection means in a nut welder, and FIG. 9 is an operation diagram of the nut welder. FIG. 9A shows a case with a nut, and FIG. Indicate the case. 6: Fixed side electrode 7: Counter electrode (movable side electrode) N: Weld nut W: Work piece

Claims (1)

[Claims] 1. A nut welding machine for repeating a cycle in which a work and a weld nut supplied onto a fixed-side electrode are pressed and welded by a vertically movable counter electrode, and a stroke length when the counter electrode is pressed is varied. A method for detecting a nut shortage, characterized by detecting for each welding cycle and comparing the stroke length detected in the previous cycle as a reference value with the stroke detected in the current cycle to determine the presence or absence of a nut shortage.