JPS62114779A - Detecting method for nut lacking in nut welding machine - Google Patents

Abstract

PURPOSE:To surely detect the presence or absence of a nut lacking by making the detected stroke length of the preceding cycle the reference value and by comparing it with the detected stroke length in the current cycle. CONSTITUTION:The standard stroke length while until the electrode tip 7b at movable side abutting to the nut with its descent is set as the reference value Sp0 at the 1st time by setting a work W and nut on an insert electrode 6a. The work is then fed on the electrode 6a and the nut is fed on the set work W. With the descent of the electrode 7 at movable side the electrode tip 7b presses by abutting to the nut. The stroke length of the electrode 7 is outputted by a stroke detecting means 21 and the movement is detected by the control device. This value is stored as the 1st time pressure stroke observation value Sp1. Whether the pressure stroke is normal or not is judged by comparing the observation value Sp1 with the initial value Sp0. The nut is welded on the work by passing a big current between electrodes 6 and 7 by setting the 1st time observation value Sp1 as the 2nd time reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting a missing nut in an automatic NAND welding machine.

[Conventional technology]

FIG. 6 is a front view of the automatic nut welding machine, and FIG. 7 is a side view thereof, in which 1 is the welding machine main body, 2 is a welding transformer connected to the welding machine main body 1 via the secondary cable 3, and 4 5 is a control device including a welding timer, a thyristor, etc. The welding machine main body 1 has a fixed electrode 6 and a movable electrode 7 opposed thereto. There are 12 fixed side electrodes 8
It is fixed on the top via a bracket 9, and an insert electrode 6a is removably provided on the top (see Fig. 8).
. On the other hand, the movable electrode 7 is supported by a pressurizing cylinder 11 attached to a column 10 so as to be able to move up and down, and the electrode arm 7 attached to the end of the cylinder outlet lla.
An electrode tip 7b is removably provided at the tip of a. 12 is a work guide rail that feeds the object to be welded (panel material to which weld nuts are welded, hereinafter referred to as "work") W while keeping it in a predetermined posture; 13 is a supply vlSa
This is a nut supplying device that automatically supplies a weld nut N stored therein to a predetermined position. Note that a locate pin 14 for nut positioning is inserted through the fixed side electrode 6.
is provided so as to be movable up and down, and the tip end 14a of the bin is driven by the locating cylinder 15 to protrude and retract from the surface of the fixed electrode insert 6al-, thereby positioning the workpiece W and the nut N.

FIG. 8 shows a conventional nut missing detection means 16 provided in the automatic nut welding machine.

17 is a mounting bracket; 18 is an arm movably pivoted on the bracket 17; 19 is a proximity switch (or limit switch) attached to the bracket 17 facing one end of the arm 18; 20 is the above-mentioned Arm 1
8 is a dog attached to the movable electrode arm 7a so as to be engageable with the other end of the movable electrode arm 7a.

A method for detecting a missing nut using this nut missing detecting means 16 is as follows. In other words, during NAND welding,
First, the movable electrode 7 moves downward by the stroke length Sp from the upper limit (return limit of the welding gun) level Lo to the welding level L1, and moves the weld nut N that has been tied onto the workpiece W to the insert electrode 6a and the electrode tip 7b. Apply pressure by pressing between (see Figure 9(a)). At this pressurizing stroke Sp, the dog 20 of the NAND detection means 16 is at the upper limit level 20.
Since the stroke is made from Lo to the welding level 20Lo, one end 18a of the arm 18 linked to the tongs 20 moves from the return limit level 18Lo to the welding level 18L1 and faces 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 "the nut is present" and the welding gun is energized to perform welding. However, the weld nut N is the workpiece W.
If not, the movable electrode 7 moves downward by the stroke length SQ from the upper limit level Lo to the abnormal level L2, and the electrode tip 7b directly contacts the workpiece W (Fig. 9(b)).
reference). Therefore, in the event of an abnormality of "no Nando", the movable static control 8
The pressurizing stroke of i7 becomes longer by the height To of the nut H, and there is a difference from the normal state by To=SQ-5p. At this time, the dog 20 strokes from the upper limit level 20Lo to the abnormal level 20L2. Therefore, one end 1 of arm 18
8a moves from the return limit level 18Lo to the abnormal level 18L2 and is removed from the proximity switch 19.
The welding gun is not energized.

[Problem that the invention seeks to solve]

In such a conventional welding tool shortage detection method, the difference in the pressurizing stroke length of the movable side electrode 7 of the welding gun is
The presence or absence of Nando's is determined by detecting with a proximity switch (or limit switch) or the like via the arm 18 of the Nando's missing item detection means 16. However, the fixed insert electrode 6a and the movable electrode chimp 7b are worn and deformed each time welding is repeated, so they are polished to correct this. Therefore, the normal welding level L gradually moves downward. Therefore, the pressurizing stroke Sp when normal (with nut) is the pressurizing stroke SQ when abnormal (without nut).
There is a problem in that the level of the proximity switch 19 or the dog 20 of the nut missingness detection means 16 must be adjusted every time the electrode is polished in order to prevent it from becoming too close to the nut and making the determination difficult.

This invention was made to solve these conventional problems, and even if the stroke length of the welding gun changes due to electrode wear, it can always be reliably identified whether there is a missing nut or not. The purpose is to provide a detection method for

[Means for solving problems]

This invention achieves the above object in a nut welding machine that repeats a cycle of pressurizing and welding a workpiece and a welded band supplied onto a fixed electrode with a counter electrode made by Kitashita Town. In addition to detecting the stroke length of each welding cycle, the detected stroke length of the previous cycle is 2! This nut missing item detection method is characterized in that the presence or absence of a nut missing item is determined by comparing the half value with the detected stroke length in the current cycle.

[Operation] The pressurizing stroke length of the counter electrode is detected every welding cycle, and the pressurizing stroke length of the current cycle is always determined using the pressurizing stroke length of the previous cycle as a reference value.

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

〔Example〕

1 to 3 are diagrams showing one embodiment of the present invention, in which FIG. 1 is a side view of essential parts of a nut welding machine equipped with a NAND missing item detection means used in the method of this invention, and FIG. The figure is a structural sectional view of the nut missing item detection means. Note that the same reference numerals are given to parts that are the same as or equivalent to the conventional ones.

In the figure, reference numeral 21 denotes a known stroke detection means used for detecting missing nuts according to the present invention, which includes a rod 23 integrally attached to the electrode arm 7a of the movable electrode 7 via a bracket 22, and , a detection head portion 25 through which a door 23 is inserted and fixed to the column 10 via a bracket 24.

FIG. 2 shows an example of the specific structure of the stroke detection means 21 that detects the amount of displacement using differential changes in variable magnetic resistance. The body portion 26 is mated with the non-magnetic material portion 27 at an equal pitch P. On the other hand, in the detection head section 25, a -order excitation coil 28 and a secondary induction coil 29 are arranged at fixed positions in the magnetic shield core 30. Now, -
The sub-excitation coil 28 is set to l Sinωt and I Cos
When AC excitation (input) is performed at ωt, the rod 2
3 (that is, the displacement of the movable electrode 7), the magnetic resistance repeats changes for each pinch P. This change in magnetic resistance results in a change in induced voltage to the secondary induction coil 29 (output), and the secondary coil induced voltage output value E
is E=Sin(ωt-2w), (where X is the amount of movement of the rod 23.) If we focus on this phase now, we can see that the amount of movement of the rod 23 is X compared to the -th order excitation human force I Sinωt. Therefore, if the above input and output are compared and the phase difference is extracted digitally via a converter, an output proportional to the linear displacement 1X of the rod 23 (and by extension, the stroke length of the movable electrode 7) can be obtained. can be obtained absolutely within the range of 1 pitch.Furthermore, even beyond 1 pitch, the magnetic body portion 26 is still disposed, so
By counting the pitches, the amount of movement x can be detected in absolute terms.

Hereinafter, a method for detecting Nando's out-of-stock items using the stroke detection means 21 described in L will be explained based on the process flowchart of FIG. 3.

First, turn on the power to the automatic nut welding equipment (step ■
). Next, in step ■, the initial value Sp of the pressurizing stroke Sp
Set o as the first reference value. This involves inserting the workpiece W and the weld nut N into the insert electrode 6a-),
This is the standard 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 when the electrode tip 7b of the movable side electrode 7 is positioned and set via the locating pin 14, and the insert electrode 6a and the electrode tip 7b
This is set for the control device only during the first cycle when the device is replaced with a new one. In step (2), the workpiece W is supplied to a predetermined position on the insert electrode 6a of the stationary electrode 6 via the workpiece guide rail 12. At step ■, the cycle start button is pressed. As a result, the first welding cycle begins, and in step (2), the automatic nut supply device 13 supplies the welt nut N to the workpiece W that has been previously positioned and placed on the insert electrode 6a.

The nut N and workpiece W are correctly positioned by a locate pin 14 which is vertically operated by a nut positioning locate cylinder 15. Subsequently, in step (2), the pressurizing cylinder 11 is operated, and the movable side electrode 7 is brought to the hill limit level LO.
The end surface of the electrode tip 7b comes into contact with the upper surface of the nut N, and pressure is applied. At step ■? +7 Stroke length of moving side electrode 7 (pressurizing stroke length S pn ;
n=1, ) is the stroke detection means 21 mentioned above.
This is output as a change in the secondary coil induced voltage, and the movement ψX is detected by the control device. The value is 11 for the first time
is stored in the memory within the control device as the actual pressurization stroke value Spl. In step (8), it is determined whether or not the pressurizing stroke is normal by comparing it with the pressurizing stroke initial value Spo, which is the reference value set in this pressurizing stroke actual Δ11 value Sp1'tstep (reference value). If the pressure stroke actual value SPI of the first circuit and the pressure stroke initial value Spa are almost equal (Sp+嬌5po), it is determined that the pressure stroke is normal and the process moves to the next step (2).Step In (2), set the first pressurization stroke actual measurement value SPI as the second pressurization stroke reference value.In other words, move the actual measurement data SPI to the pressurization stroke reference value storage address in the memory, and set the previous reference value. Update Spo. In step [Co.], a large current is passed from the transformer 2 through the secondary cable 3 between the fixed side electrode 6 and the movable side electrode 7 to weld the nut N onto the workpiece W. During welding, the molten part Nm of the nut N (see Figure 4)
melts, the height and thickness of the nut N changes from TO to T1 before and after welding. This thickness change To-T1
Since this lowers the movable electrode 7 while the nut is being pressurized, it is detected by the stroke detection means 21 in step (3).

In step @, it is determined whether the change in the thickness of the nut N is normal or not.

If the thickness reduction amount corresponds to the height of the melted part Nm of the weld nut N, it is determined to be normal, and the process moves to step (2).

In step (2), the pressure cylinder 11 is operated in the opposite direction to raise the movable electrode 7, thereby releasing the welding gun pressure, and in step [phase], the nut welding is completed via the work guide rail 12. After the workpiece W is carried out from above the stationary electrode 6 and a counter (not shown) is incremented by +1 in step [stock], the process returns to step (2) and the second cycle starts from supplying the workpiece. In the second and subsequent cycles, the pressurization stroke length measured via the stroke detection means 21 in the immediately preceding cycle is used as the reference value of the pressurization stroke. In this way, since the pressure stroke reference value is automatically updated every cycle, changes in the pressure stroke length due to electrode wear during welding and polishing to correct the wear are completely compensated for.

Therefore, there is no need to adjust the level of the stroke detection means 21 each time when determining whether the pressurizing stroke is normal or abnormal in step (3).

In step (2), if the pressurization stroke reference value and the actual measurement value are not substantially equal, it is determined that the pressurization stroke is abnormal, and the process moves to step 0 to stop the cycle. After that, the operator operates the manual operation means (not shown) to pressurize cylinder 1.
1 is raised (step O), the movable electrode 7 is retracted, and then, in step O, it is visually confirmed whether the nut N is placed on the workpiece W or not. If it is confirmed that the nut N is not inserted, it is confirmed in step O whether or not this is the first cycle (for example, the display on the cycle number display panel is confirmed).

If this is the first cycle, there may be a problem with the nut being caught in the nut feeding device 13, resulting in a feeding failure, so in order to repeat the cycle again, proceed to step ① and press the cycle button to turn the nut off automatically. Start with supply.

- On the other hand, if it is confirmed in step O that nut) N is being thrown onto the workpiece W, or if it is confirmed in step O that it is after the second time [], then the nut welding device is There may be an abnormality somewhere, so turn off the power (
Step O), carry out an inspection of the entire device (step (
9). After the abnormality is identified and repaired,
You will be able to start again from step ■. In addition, if it is determined in step @ that the thickness change due to the melting and pressurization of the nut N is abnormal, the process moves to step O to stop the cycle, and then a series of manual operations by the operator leading to step O are performed. A checking process is carried out.

Note that the above embodiment is based on lot 2 of the stroke detection means 21.
3 attached to the electrode arm 7, as shown in FIG. 5, a magnet may be embedded in the rod lla of the pressurizing cylinder 11, and the detection head 25 may be incorporated in the rod 11a. Stroke detection means 21 used in this invention
is not limited to those shown in FIGS. 1 and 2, and various other known non-contact linear displacement measuring devices can be used.

According to this embodiment, regardless of the amount of wear on the welding electrode, it is possible to reliably determine the presence or absence of nut supply, and furthermore, by measuring the difference in the thickness of the nut before and after welding, it is possible to determine whether the welding state of the nut is good or not. It is also possible to determine In addition, by setting the wear limit value of the electrode tip in advance, the tip usage limit or tip replacement time can be determined based on wear.
It is also possible to display it automatically.

〔Effect of the invention〕

As explained above, according to the present invention, in a nut welding machine, the stroke length of the movable side electrode of the welding gun is measured every cycle, and the stroke length of the immediately preceding cycle is always used as a reference value for the current cycle. Since the stroke length is determined to be normal or abnormal, it is possible to reliably detect the presence or absence of a missing weld nut without any adjustment, regardless of the magnitude of electrode wear.

[Brief explanation of drawings]

FIG. 1 is a usage diagram of a stroke detection means that can be used in the nut missingness detection method of the present invention, FIG. 2 is a cross-sectional structural diagram of the stroke detection means, and FIG. 3 is a diagram of the nut missingness detection method of the present invention. Flowchart showing an example, FIG. 4 is a side view of the weld-nand, FIG. 5 is a diagram of another usage mode of the stroke detection means, FIG. 6 is a front view of the nut welding machine, FIG. 7 is a side view thereof, and FIG. The figure is a usage diagram of a conventional nut missing detection means in a nut welding machine, and Figure 9 is an operation diagram of a nut welding machine.
indicates the case without nut. 6...Fixed side electrode 7...Counter electrode (movable side electrode) N...
・・・・・・Weld nut W・・・・・・Workpiece 4 Figure 5 Figure 8 Diagram Figure 9 (a) (b)

Claims (1)

[Claims] In a nut welding machine that repeats a cycle of pressurizing and welding a workpiece and weld nut supplied onto a fixed electrode with a vertically movable counter electrode, the stroke length of the counter electrode when pressurizing is detected for each welding cycle. At the same time, the detected stroke length of the previous cycle is used as a reference value and compared with the detected stroke length of the current cycle, thereby determining whether or not there is a nut missing item.