JPH0575556B2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention is used for tightening bolts, etc.
Concerning improvements to the AC nut runner.

(Prior Art) Many parts of automobiles and the like are assembled by fastening them with bolts or the like. When fastening with bolts or the like, the tightening torque must be appropriate from the viewpoint of product reliability.

In other words, if the tightening torque is insufficient, the tightening may be insufficient and cause loosening, and if the tightening torque is too strong, it may lead to bolt breakage or destruction of the fastening member. It causes problems in terms of sexuality.

Therefore, it is necessary to tighten bolts or the like with appropriate torque and strictly.

Generally, as shown in FIG. 3, an AC nut runner rotates the main shaft 4 by decelerating the rotation of the AC motor 1 using a reduction unit 2, and tightens the main shaft 4 or the reduction unit 2 using a torque sensor 3. Detects and outputs torque. Then, this output signal is input to the controller 5 to operate the driver 6, and when a certain torque is reached, the rotation of the AC motor 1 is stopped.

Conventionally, in the above AC nut runner, as shown in Fig. 4, the rotation speed of the AC motor is kept constant until the bolt is seated and after it is seated until a predetermined tightening torque is reached (line B). The AC motor was stopped when a predetermined torque was detected by the torque sensor. Curve A in the figure shows the tightening torque.

(Problem to be solved by the invention) As mentioned above, conventionally, the number of rotations of the AC motor until the bolt is seated is the same as the number of rotations of the AC motor from the time the bolt is seated until the specified tightening torque is reached. Since I was trying to tighten it by changing the number of rotations, I had the following problem.

In other words, if you increase the rotation speed of the AC motor (10 to 20 rpm) in order to shorten the time required for tightening as much as possible, the torque overrun will become larger and more, resulting in excessive tightening.
On the other hand, if the number of rotations of the AC motor is reduced in order to optimize the torque overrun and increase the tightening accuracy, there is a problem in that it takes a long time to tighten the bolts, which reduces productivity.

In this way, as the rotation speed of the AC motor increases, the torque overrun increases in proportion to this, so there is a limit to increasing the rotation speed of the AC motor, and beyond that limit the time required to tighten the bolts will increase. There is a conflict between bolt tightening accuracy and improving productivity by shortening bolt tightening time, and it is impossible to satisfy both at the same time. There is.

The present invention aims to provide an AC nut runner that minimizes the torque overrun, improves torque accuracy, increases product reliability, and shortens the time required for fastening to improve productivity. It is something.

(Means for Solving the Problem) A means according to the present invention for solving the above problem is to reduce the rotation of the AC motor in a reduction unit to rotate the main shaft, and to tighten the main shaft to a constant torque using a torque sensor. In the AC nut tranner that was made like this,
Find the current deviation between the set AC motor command current and the AC motor armature current during engagement, and calculate the voltage required to supply this deviation current.
As the tightening torque increases when applied to the AC motor.
This is characterized by the provision of a control device that reduces the rotational speed of the AC motor.

(Operation) The present invention calculates the current deviation between the set command current of the AC motor and the armature current of the AC motor during engagement, and applies the voltage necessary to supply this deviation current to the AC motor. I did it like this,
A deviation current that changes according to the tightening torque of the AC motor is supplied to the AC motor, and the AC motor is automatically controlled by the tightening control device to reduce the rotation speed as the torque increases.

As a result, the bolt tightening torque is not generated until the bolt is seated, so the armature current of the AC motor is maintained at the current when no tightening torque is being generated, rotating at high speed, and the bolt is seated. The time required for the bolt to tighten is shortened, and after the bolt is seated, bolt tightening torque is generated, so the rotation of the AC motor slows down to follow the increase in tightening torque, making it possible to prevent torque overrun. Become.

(Example) An example of the present invention will be described in detail below. Figure 1 is a diagram showing the relationship between tightening torque, motor rotation speed, and time from the point when the bolt is seated and torque begins to be generated. Curve A is the tightening torque, and curve B is the motor rotation speed. The rotation speed and line C indicate the set torque.

Figure 2 is an electric circuit diagram for actually implementing the relationship shown in Figure 1, where 7 is a current deviation detection circuit, 8 is a motor armature current detector, and 9 is a circuit for outputting a current command signal I _R. Volume, 10, 11, 12
are respectively amplifiers for amplification.

As shown in Figure 3, in the AC nut runner, the AC motor 1 is rotated when tightening bolts.
This rotation is decelerated by the deceleration section 2 to rotate the main shaft 4.

The operation of this embodiment configured in this way will be described next. The person operating the AC nut runner adjusts the volume 9 in advance to determine the current command signal I _R. Setting of this current command signal I _R is performed as follows. At the design stage, the nominal diameter of the bolt is determined, and in other words, the tightening strength of the fastened object is determined, so the bolt tightening torque should naturally be set to the tightening strength determined at the design stage. There must be. And the Natsu runner is a current command signal
The larger I _R is set, the larger the torque capacity becomes, and it is possible to tighten to a large torque. On the other hand, it is necessary to increase the rotational speed of the AC motor 1 in order to shorten the time required to tighten bolts and improve productivity. Generally, the rotation speed of a motor is proportional to the current, so this AC motor 1
The rotation speed increases as the current command signal I _R increases, the deviation ΔI from the motor current signal I _M increases, and the voltage V ₀ applied to the motor increases.

The current command signal I _R is thus set based on the relationship between the tightening torque and the tightening time.

Since there is no torque load on the AC motor 1 until the bolt is seated, the armature current of the AC motor 1 is small. The armature current at this time is detected by the motor armature current detector 8, amplified by the amplification amplifier 12, and inputted to the current deviation detection circuit 7 as a motor current signal I _M , and the current deviation ΔI=I _R − _{I M}
calculations are performed. This current deviation ΔI is the amplifier 1
0, G is amplified by ₁ times, and further G is amplified by ₂ times by the power amplifier 11, so that the motor applied voltage V ₀ = [G ₁・
_G2・ΔI] is applied to the AC motor 1.

Here, until the bolt is seated, the armature current of the AC motor 1 is small, so the current deviation ΔI is large. Therefore, the motor applied voltage V ₀ becomes large, and the AC motor 1 is in a state where there is no torque load. The armature current is maintained, and the AC motor 1 rotates at high speed until the bolt is seated to tighten the bolt.

Next, when the bolt is seated and the tightening torque starts to increase, the AC
The armature current of motor 1 increases. The armature current, which increases as the tightening torque load increases, is detected by the motor armature current detector 8, amplified by the amplification amplifier 12, and inputted to the current deviation detection circuit 7 as a motor current signal I _M. , current deviation ΔI
The calculation =I _R -I _M is performed.

In this calculation, the motor current signal I _M increases as the tightening torque load increases, so the current deviation ΔI decreases as the tightening torque load increases.
As a result, the current deviation ΔI is amplified by G1 _times in the amplifier 10, and further amplified by G2 _times in the power amplifier 11, and applied to the AC motor 1 as the motor applied voltage _V0 = [ _G1・_G2・ΔI]. Applied motor voltage V ₀
As the tightening torque load increases, the armature current decreases, and the rotational speed of the AC motor 1 also decreases as the tightening torque load increases.

In Fig. 1, this relationship is between curve A representing the increase in tightening torque and curve B representing the motor rotation speed, and _one hour after the bolt is seated due to the setting of the current command signal I _R. The set torque (line C) is just reached. AC motor 1 at this time
The number of revolutions is N ₁ .

At this point, the torque sensor 3 shown in FIG. 3 detects this set torque C, inputs a stop signal for the AC motor 1 to the controller 5, and outputs it to the driver 6.
Stop AC motor 1.

As described above, when the tightening torque reaches the set torque C, the rotational speed of the AC motor 1 reaches _N1 and is at a low speed, so that the rotation of the AC motor 1 can be easily stopped. This makes it possible to accurately stop the AC motor after the stop time _t2 , and allows accurate retightening T _r without causing torque overrun.

Note that the applied voltage V ₀ may be reduced by intermittently chopping a constant voltage using a PWM (pulse width modulation) method.

In this way, the armature current of the AC motor 1 is maintained in a state where no tightening torque load is applied until the bolt is seated, and the armature current of the AC motor 1 is rotated at high speed to shorten the bolt tightening time, and the bolt is seated. Since the tightening torque load increased, the armature current of the AC motor 1 was decreased to slow down the rotation of the AC motor 1 as the tightening torque load increased.
Turn off the armature current of AC motor 1 and stop it.
Unlike tightening by the inertial force of AC motor 1, AC
By controlling the armature current of the motor 1 and controlling its rotation speed, it becomes possible to adjust the tightening times t ₁ and t ₂ and shorten the bolt tightening time.
Moreover, it becomes possible to obtain highly accurate bolt tightening torque.

(Effects of the invention) As detailed above, according to the AC nut runner according to the present invention, the current deviation between the set command current of the AC motor and the armature current of the AC motor during the engagement is determined, and this deviation current is calculated. Since the voltage necessary to supply the voltage is applied to the AC motor,
A deviation current that changes according to the tightening torque of the AC motor is supplied to the AC motor, and the AC motor can be automatically controlled by the tightening control device to reduce the rotation speed as the torque increases. This can prevent torque overrun and greatly improve the accuracy of bolt tightening torque.

This automatic control prevents torque overrun by reducing the rotation of the AC motor from the time when the bolt is seated, which generates a deviation current, as the tightening torque increases. While this does not occur, the AC motor can rotate at high speed and the time required to tighten bolts can be shortened.

In this way, by improving torque accuracy and shortening the time required for tightening, product reliability is increased, and
It can improve productivity and has excellent industrial effects.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing one embodiment of the present invention. Figure 1 is a diagram showing the relationship between tightening torque, motor rotation speed, and time, and Figure 2 is the same as Figure 1. FIG. 3 is an electrical circuit diagram for achieving the relationship shown.
FIG. 3 is a block diagram shown to explain a general AC nut runner, and FIG. 4 is a diagram showing the relationship between conventional tightening torque and motor rotation speed. 1...AC motor, 2...Reduction unit, 3...Torque sensor, 4...Main shaft, 5...Controller, 6
...Driver, 7...Electrical deviation detection circuit, 8...
Motor armature current detector, 9...volume.

Claims (1)

[Claims] 1. In the AC nut runner, which reduces the rotation of the AC motor with a reduction part to rotate the main shaft, and uses a torque sensor to tighten the torque to a constant level,
Find the current deviation between the set AC motor command current and the AC motor armature current during engagement, and calculate the voltage required to supply this deviation current.
As the tightening torque increases when applied to the AC motor.
AC nut runner equipped with a control device that reduces the rotation speed of the AC motor.