JPH0424174B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to a nut tightening machine.

Conventional Example Configuration and Its Problems When tightening a nut onto a screw shaft, a conventional nut tightening machine rotates the nut in the tightening direction while pressing the nut against the screw shaft and screwing it in.

At this time, poor tightening occurred due to misalignment and inclination angle between the screw shaft and the nut.

Figures 11 to 15 and Figure 6 show data from experiments on tightening JIS standard hexagonal nuts M3 regarding these various factors, defective rates and defective states of nut tightening;
This will be explained below using FIGS. 8 and 10.

Figure 11 is a graph showing the relationship between the lowering speed of a box bit holding a nut and the tightening failure rate.
At a descending speed of ~150 mm/sec, approximately 1% of the diagonal tightening defects shown in FIG. 6 (defect A shown in the figure) occur.

Figure 12 is a graph of the relationship between the inclination angle of the screw shaft with respect to the nut and the tightening defect rate, which is approximately 0.5% at an inclination angle of 0°.
A diagonal tightening defect (defect A shown in the figure) occurs,
At 7 degrees, the nut will not be tightened at an angle, or the nut, screw shaft, and box bit will be distorted, resulting in a defect where the nut is inserted only halfway as shown in Figure 8 (defect B shown in the figure).

Figure 13 is a graph showing the relationship between the misalignment of the nut and screw shaft and the tightening defect rate.
mm, as shown in Figure 10, the nut does not enter the screw shaft while rotating on the screw shaft (defect C in the diagram), or even if it does, the screw shaft cannot be fully tightened by about 12 mm within the set time of 4 seconds. Defects (defect D in the figure) occur from about 25%.

FIG. 14 is a graph showing the relationship between the downward thrust of the nut and the defective rate.Although the influence is relatively small, diagonal tightening defects generally occur (defect A in the figure).

FIG. 15 is a graph showing the relationship between the number of rotations of the nut and the defective rate.Although the influence is small, diagonal tightening defects (defects A in the figure) generally occur.

On a normal production line, due to variations in the workpiece or the jig that fixes the workpiece, the inclination angle of the screw shaft is ±1°, the misalignment is ±0.25mm, the descending speed is 150mm/sec, and the number of rotations.
The tightening conditions were 600 rpm and 3 kg of downward thrust.
As can be seen from the above experimental data, approximately 2% of diagonal tightening defects occur.

In addition, when tightening volume nuts that fix the volume used in radios, stereos, etc., the screw shaft is large and the thread pitch is small, so there is a high probability of diagonal tightening failure, which is 5 to 6% on a normal production line. defects are occurring.

In other words, the nut often fails to be tightened diagonally, but since the nut is embedded in the screw shaft, a separate tool must be used to release the nut, which is very troublesome.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, the present invention provides a nut tightening device that automatically releases the nut even if the nut is improperly tightened diagonally without bothering the human operator.

Structure of the Invention The present invention comprises a detection means for determining whether or not a nut has started to be properly screwed into a screw shaft, and a means for canceling a malfunction in diagonal tightening of a nut, and the present invention reliably releases a malfunction in tightening of a nut. It has the unique effect of doing.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is a nut supply section, 2 is an escapement section, 3 is a catch section, 4 is a driver section, and 5 is an elevating section. They are fed into the catcher section 3 one by one. By the operation of the elevating part 5, the driver part 4 descends while sucking the nut of the catch part 3, and reaches the top of the screw shaft 6.

In FIG. 2, reference numeral 7 denotes a box bit which has a fitting hole at its tip that fits into the outer shape of the nut N. 8 is a suction pipe, 9 is a guide pin that fits into the threaded hole of the nut N, and reaches the vacuum source (not shown) through the gap 12 between the bit holder 10 and the vacuum pipe 11, and the tip of the box bit 7. adsorbs Nut-N. Detection switches 13 and 14 are activated by a dog 15 to detect the height of the driver section 4.

The operation of the nut tightening device configured as described above will be described below, focusing on a flowchart showing the operation after the driver part 4 is lowered and the nut is positioned on the screw shaft.

FIG. 9 is a flowchart of a control section showing an embodiment of the present invention, which will be explained based on this figure and FIGS. 4 to 8. Detection switches 13, 1 in FIGS. 5 to 8
4 is shown on the screw shaft for ease of explanation.

The nut N held by the box bit 7 shown in FIG. 2 descends onto the screw shaft 6, as shown in FIG. 4.
When the nut N is properly screwed into the screw shaft 6, the detection switch 13 is turned on. Next, when the electric screwdriver 15, which is the rotational drive source for the box bit 7, reaches a predetermined torque, it outputs an AT signal, and if this AT signal turns ON, it is further determined whether the detection switch 14 is turned ON. If it is tight as shown in Figure 7, the detection switch 14
turns ON and tightening is completed.

On the other hand, as shown in FIG. 8, if the screw shaft 6 is screwed in only halfway due to poor machining or the like, the detection switch 14 will not turn on and it will be determined that the tightening height is incorrect.

Returning to the front, detection switch 13 is ON and AT
If the signal does not come out, set timer TR2 to the estimated time that the nut will be sufficiently tightened.
Rotate clockwise until timer TR2 turns on,
If the AT signal still does not come out, it is determined that the screw is defective, with either the nut or the threads of the screw shaft being damaged.

Going back further, if the nut N is wedged diagonally into the screw shaft 6 as shown in Fig. 6 from the state shown in Fig. 4, the detection switch 13 will not turn on and the AT signal will not turn on.
It becomes ON.

This condition is determined to be a skew defect at the initial stage of tightening.
Rotate counterclockwise for the time set by timer TR3 to release the diagonal tightening of nut N. In other words, if the diagonal tightening is defective, the rotation is always done in the opposite direction. If the AT signal is generated due to counterclockwise rotation, the release is defective.

When the diagonal tightening of the nut N is released, the state shown in FIG. 6 returns to the state shown in FIG. 4. As a result, tightening is started again and the operations described above are repeated. I is the number of times of tightening; for example, if I=3, tightening can be attempted three times.

The final good product rate after n tries is P _o , n+1
Letting the final good product rate after multiple attempts be P _o+1 , it is expressed as P _o+1 = P _o + (100−P _o ) P _o /100.

If the good product rate at one time is P ₁ = 98%, the good product rate after 2 tries is P ₂ = 99.96%, and the good product rate after 3 tries is P ₃ = 99.9992%, which is extremely high quality. . An example is shown in FIG.

As described above, according to this embodiment, the nut is comprised of a detection means for determining whether or not the nut has started to be correctly screwed into the screw shaft, and a means for releasing a defective jam. It is possible to provide a nut tightening device that automatically releases the nut even if it occurs.

In this embodiment, the switch 13 that detects the height of the nut and the AT signal of the electric screwdriver are used as detection means to determine whether the nut has started to be screwed into the screw shaft correctly, but it is also possible to use a timer relay. It is also possible.

Effects of the Invention As described above, the present invention provides a detection means for determining whether or not a nut has started to be correctly screwed into a screw shaft, and a means for releasing a malfunctioning nut from diagonal tightening. Even if a problem occurs, the release can be automatically performed, and its practical effects are great.

[Brief explanation of drawings]

Fig. 1 is a partially sectional front view of an embodiment of the present invention, Figs. 2 and 3 are enlarged sectional views of main parts of Fig. 1, and Figs. 4 to 8 and 10 show the tightened state of the nut. FIG. 9 is a flowchart of the control section of the first embodiment of the present invention, and FIGS. 11 to 16 are graphs showing experimental data. 4...driver part, 5...lifting part, 6...screw shaft, 7...box bit, 13, 14...detection switch, 16...electric screwdriver, N...nut, I...predetermined number of times.

Claims (1)

[Claims] 1. A box bit having a fitting part with a nut of the object to be tightened, an electric screwdriver that communicates with the box bit and outputs an AT signal when a predetermined torque is reached, and an elevating section that lifts and lowers the electric screwdriver and the box bit. a first position detection sensor that detects the position of the box bit when the nut begins to be screwed into the screw shaft; and a first position detection sensor that detects the position of the box bit when the nut has been tightened to a predetermined length of the screw shaft. If the AT signal turns on without the second position detection sensor and the first position detection sensor turning on, it is determined that the nut is improperly attached to the screw shaft, and the electric screwdriver is reversed. A nut tightening device equipped with a control unit that rotates the nut and then rotates it in the forward direction.