JPS61270083A - Axial-tension control bolting machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an axial force management bolt tightening machine that enables tightening with accurate axial force at all times.

(Prior Art) Various methods have been proposed in the past for tightening bolts with a predetermined load. Because the rotation angle method is inaccurate in detecting the snug point, and the torque method has variations in the coefficient of friction, both methods are unable to tighten with accurate loads.

The proof stress method is a method of tightening bolts so that the permanent elongation of the bolt is 0.2%, which is theoretically very preferable. However, in the past, the point at which the rate of increase in tightening torque after passing through the bolt's elastic range reached a set value of 1/2 to 1/3 of the maximum rate of increase was considered to be the proof stress, and the tightening was stopped. I was trying to stop it.

For this reason, when tightening with washers or objects to be tightened, if the rate of change in tightening torque changes due to differences in conditions, it is not possible to tighten with accurate proof stress, and with indication tightening, the load may vary. There was a problem that occurred. There are also methods that detect the tightening stop point from the second derivative of the tightening torque.
In this case, the beginning of the song was likely to cause malfunctions due to noise.

In addition, with the axial force method, it is actually impossible to directly measure the axial force of the port while tightening, so the conventional method is to predict the axial force using the differential value (torque coefficient) of the tightening torque. (For example, Japanese Patent Publication No. 54-22640
). However, since this requires a differentiating circuit, there is a problem in that malfunctions are likely to occur due to noise.

On the other hand, when actually tightening bolts, preliminary tightening may be performed prior to the final tightening. Since the tightening torque is different for final tightening and preliminary tightening, if two dedicated tightening machines were used for final tightening and preliminary tightening, there would be a problem that the operating rate of the tightening machines would decrease. Ta.

(Purpose of the Invention) The present invention was made in view of the above circumstances, and provides an axial force management bolt tightening system that is less prone to malfunction due to noise and that enables high-precision tightening with the desired axial force at all times. The primary purpose is to provide opportunities. A second object of the present invention is to provide an axial force management port tightening machine that can perform pre-tightening as needed to increase the operating rate.

(Structure of the invention)
1 According to the present invention, the first object is to provide a bolt tightening machine using a prime mover, in which tightening within the elastic range of the bolt is based on the torque equivalent amount and its primary delay amount. a maximum rate of increase detection circuit that determines and stores the maximum rate of increase; a multiplier circuit that multiplies the maximum rate of increase by a predetermined constant; The tightening is accomplished by an axial force management port tightening machine which is equipped with a comparison circuit that outputs a stop signal upon determining this, and stops tightening based on the tightening stop signal.

The second purpose is to add a comparator to the above configuration to determine a tightening torque lower than the calculation start point of the first-order delay amount, and to select either the output of this comparator or the tightening stop signal. This is achieved by adding a pre-tightening selection change-over switch that stops the tightening process, and by using this change-over switch, it is possible to switch between pre-tightening and main tightening.

(Embodiment) FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is a diagram of its tightening characteristics.

In FIG. 1, 10 is a DC motor, and the bolts are tightened by the rotation of this motor 10. This electric filO forms a closed circuit with the AC power supply 12, the thyristor 14, the current detection resistor 16, and the main switch 18. The tightening torque T is proportional to the current i of the electric motor 10. This current i, that is, the tightening torque T is detected by the resistor 16. Further, the tightening speed of the electric motor 10 is determined from the applied voltage of the electric motor, that is, the conduction rate of the thyristor 14 and the current i.

In this embodiment, the tightening speed is controlled to be constant at least within the elastic range during tightening. Note that in order to eliminate the influence of the starting current of the motor 10, a soft starter circuit may be provided in the gate circuit of the thyristor 14, or a soft starter circuit may be provided in the gate circuit of the thyristor 14.
It is preferable to configure the output of the filter to be cut off for a predetermined period of time by a timer.

The port tightening machine of this embodiment is entirely formed of analog circuits.

First, the maximum rate of increase detection circuit (2) that calculates and stores the maximum rate of increase K of the tightening torque based on the tightening torque T within the elastic range of the bolt and its primary lag amount will be explained.

20 is a first-order delay circuit, which includes a series resistor 20a.

It is composed of a parallel capacitor 20b and an operational amplifier 20c.

22 is a subtraction circuit that calculates the difference (AI-A2) between the real-time tightening torque AI and the output A2 of the first-order delay circuit 20.

24 is a hold circuit that determines and stores the maximum increase rate K of the tightening torque from the output (AI-A2) of this subtraction circuit 22, and is an ideal field effect transistor 2 whose forward resistance is zero.
4a, an integrating capacitor 24b, and an operational amplifier 24c.

By the way, the feature of the present invention is that the difference (Al - A2 ) between the real-time tightening torque A1 and the output A2 of the first-order lag circuit 20
The point is to find the maximum increase rate K of the tightening torque based on .

Within the elastic range of the bolt, the real-time tightening torque A1
Since the change in is considered to be a straight line, AI = Kt (K is a constant) ---- (1) On the other hand, if the time constant of the first-order lag circuit 20 is τ = RC, the characteristic equation of the output A2 is, therefore, A2 = to τ(exp (-t/τ)-1)+KtAH
-A? = to? (1-exp (-t/τ)) Here, for example, if t is the time constant τ, AI - A2 = 0.632, τ,'', K = (AI - A2) / 0, 632
τ--(2) Also, if t is 2, then = (AI - A2 ) 10.863τ In any case, if t is determined, K can be obtained by calculation.

In this embodiment, the tightening torque T1 at a point A within the elastic region (the starting point for calculating the first-order lag amount) is set in advance in the setting device 26,
The time t1 at this point A is detected by the comparator 28. And this time 1. Close the normally open contact SWl and close the first-order delay circuit 20.
Apply the tightening torque T to 1 torque, and at this point t1
A predetermined time t=α is accumulated by the timer 30 which starts from
When l = α), the normally closed contact SW2 is opened, and (AI - A2) at this time is stored in the hold circuit 24.

Note that the amplification factor of the operational amplifier 24c is set so that its output becomes K.

The constant obtained in this manner indicates the maximum rate of increase in the tightening torque T.

Next, the principle of determining the tightening torque at a desired axial force using this maximum rate of increase K will be explained.

Generally, there is a relationship between the tightening torque T of a bolt and the axial force N as follows: T=D−N−−−(3). Here, D is the nominal diameter of the bolt, and k is the torque coefficient (constant).

From equation (3), k = T/ CD -N) ---- (4) If the rotation angle is θ and minute changes in T and N are taken, then T/N = dT/dN holds within the elastic region. Equation (4) is k = dT/ (D dN) Substituting Equation (5) into Equation (3), where (dN/dθ) is a constant determined by the dimensions and materials of the bolt and the fastened member. be. Also, N is the desired axial force. Therefore, if (dN/dO) is found in equation (8), the tightening torque T required for tightening with the desired axial force N is determined.

Therefore, it is understood that the tightening should be completed when the tightening torque T reaches the torque T determined by this equation (6).

Here, (dT/dθ) can be calculated using equation (1), that is, if the maximum rate of increase K is found from equation (2), then from equations (6) and (7), it is determined that the tightening angular velocity ω is constant here. If so, it is determined by T=a・K---1(i3).

Based on this principle, in the embodiment shown in FIG. 1, the real-time tightening torque T is multiplied by l/a by the multiplication circuit 32.

The output T/a of this multiplier circuit 32 is compared with the maximum rate of increase in a comparator circuit 34. The comparison circuit 34 determines that T/a= (point B in the second figure) and outputs a tightening stop signal S. This S is the gate circuit 3 of the thyristor 14
6, and the tightening is stopped.

As is clear from equation (8), the tightening torque T2 at the tightening stop point C is the torque at which tightening is performed with the desired axial force N.

In the above embodiment, the point A at which the input of the tightening torque T to the temporary delay circuit 20 is started is set in the setting device 26 and detected by the tightening torque T1. It is only necessary to set point A, that is, the starting point A for calculating the first-order lag amount, and it goes without saying that various methods for finding point A are possible.

In addition, in this embodiment, the tightening angular velocity ω is determined by the thyristor 14 so as to tighten the electric motor 10 at a constant speed (therefore, ω is constant).
control the conduction rate. However, if this angular velocity ω is constant at least from point A to point C in Fig. 2, there is no problem in theory, and the key is to detect the tightening angular velocity ω during this period using another speed detector. During this time, the angular velocity ω may not be strictly constant, but may be approximately constant, and in this case, the value of a in equation (8) may be slightly changed.

FIG. 3 is a configuration diagram of another embodiment, and this embodiment is the second embodiment.
This enables pre-tightening with a lower tightening torque than point A in the figure. That is, the setting device 26
Connect the voltage dividing resistor 50 to
The value divided by 0 and the tightening torque AI are input to the comparator 52. Further, the output of the comparator 52 is sent to the gate circuit 36 via the pretightening selection switch SW2.

This embodiment works as follows. If the switch SW2 is in the state shown by the solid line in FIG. 3, the comparator 52 outputs the tightening stop signal S at the point where the torque T3 is smaller than the point A. Therefore, the tightening operation is stopped (preliminary tightening), but when the switch SW2 is switched, the state becomes the same as that shown in FIG. 1, and the original tightening (main tightening) is performed.

According to this embodiment, preliminary tightening can be performed by switching the switch SW2. In particular, since the torque T3 during pre-tightening is set lower than the torque T1 at point A, even if the device has a relatively large moment of inertia in its rotating parts, such as the electric motor 10,
The torque T1 at point A during the final tightening does not become smaller than the torque at the end of the preliminary tightening, and malfunctions during the final tightening can be prevented.

(Effects of the Invention) As described above, the present invention calculates the maximum rate of increase in the amount of tightening torque equivalent based on the amount of tightening torque change and its temporary delay amount, and sets a predetermined constant to this maximum rate of increase. The tightening end point is detected by multiplying the value and comparing it with the tightening torque. Therefore, the end point of tightening can be detected using the tightening torque at the desired axial force, and highly accurate tightening becomes possible. In addition, the pre-tightening selection switch allows pre-tightening and final tightening to be performed with one tightening machine, which dramatically improves the operating rate of the tightening machine.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a diagram of its tightening characteristics, and FIG. 3 is a block diagram of another embodiment. 10...DC motor. 20... Temporary delay circuit, 24... Subtractor, 24... Hold circuit, 30... Timer. 32...Multiplication circuit, 34...Comparison circuit, 52...Comparator, A...Calculation start point for primary lag amount, ■...Maximum increase rate detection circuit, SW2...Pre-tightening selection Switch for use.

Claims (3)

[Claims] (1) In a bolt tightening machine using a prime mover, the maximum rate of increase is detected by determining and storing the maximum rate of increase in the amount of tightening torque equivalent to the amount of tightening torque within the elastic range of the bolt and its primary lag amount. a multiplication circuit that multiplies the maximum rate of increase by a predetermined constant; and a comparison circuit that outputs a tightening stop signal upon determining that the tightening torque equivalent amount has become equal to the output of the multiplication circuit. An axial force management bolt tightening machine, characterized in that it stops tightening based on the tightening stop signal. (2) The axial force management bolt tightening machine according to claim 1, wherein the prime mover is an electric motor, and the tightening speed is controlled to be substantially constant within the elastic range of the bolt. (3) Maximum rate of increase detection in a bolt tightening machine using a prime mover, which calculates and stores the maximum rate of increase of the amount equivalent to tightening torque based on the amount equivalent to tightening torque within the elastic range of the bolt and its primary lag amount. a multiplication circuit that multiplies the maximum rate of increase by a predetermined constant; and a comparison circuit that outputs a tightening stop signal upon determining that the tightening torque equivalent amount has become equal to the output of the multiplication circuit. , a comparator for determining a tightening torque lower than the calculation start point of the first-order delay amount, and a pre-tightening selection changeover switch for selecting either the output of this comparator or the tightening stop signal to stop tightening. An axial force management bolt tightening machine, characterized in that the changeover switch enables switching between preliminary tightening and final tightening.