JPH0323310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a strength detection bolt tightening machine that enables fastening with accurate yield strength 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, it is not possible to tighten with an accurate load. In addition, the axial force method is not practical because it is impossible to actually measure the bolt axial force.

The proof stress method is a method of tightening bolts so that the permanent elongation is 0.2%, which is theoretically very preferable. However, in the past, the rate of increase in tightening torque after passing the bolt's elastic range was 1/2 to 1/2 of the maximum rate of increase.
The moment when the set value reached 1/3 was considered to be the proof stress, and the tightening was stopped. For this reason, if the rate of change in tightening torque changes due to differences in tightening conditions depending on the type of washer or to be tightened, it will not be possible to tighten with accurate proof stress, and variations will still occur in the tightening load. There was a problem. Furthermore, the tightening stop point is detected from the second derivative of the tightening torque, but in this case there is a problem in that malfunctions are likely to occur due to noise.

(Purpose of the Invention) The present invention was made in view of the above circumstances, and provides a proof force detection bolt tightening machine that allows the fastening load to be controlled with high precision at all times even when the tightening conditions change. The purpose is to provide

(Structure of the Invention) According to the present invention, the object is to provide a bolt tightening machine using a prime mover with a means for detecting an amount equivalent to bolt tightening torque, and a first-order lag circuit for determining the first-order lag amount of the amount equivalent to bolt tightening torque. , a subtracter that calculates the difference between the tightening torque equivalent amount at a predetermined point in the bolt elasticity range and its primary lag amount, and a first hold circuit that calculates and stores the increase rate of the tightening torque equivalent amount based on this difference. and a second hold circuit that stores an amount equivalent to a tightening torque at a starting point located after the time when the rate of increase in the elastic range of the bolt is stored;
a setting means for outputting an integral start signal after tightening an amount equivalent to a predetermined tightening angle from the starting point and setting an amount equivalent to a predetermined tightening torque for determining the rate of increase and the starting point; an integrating circuit that starts integrating the rate of increase;
an addition circuit that calculates the sum of the tightening torque equivalent amount at the starting point and the integral value output by the integrating circuit;
and a comparison circuit that outputs a tightening stop signal when determining that the output of the adding circuit has become equal to an amount equivalent to the tightening torque, and stops tightening based on the tightening stop signal. Achieved by detection bolt tightening machine.

(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, reference numeral 10 denotes a DC series motor, and the bolts are tightened by the rotation of this motor 10. This electric motor 10 includes an AC power source 12, a thyristor 14,
It forms a closed circuit together with the current detection resistor 16 and the main switch 18. Tightening torque T is electric motor 10
is proportional to the current i. This current i, that is, the tightening torque T, is detected by a resistor 16 as torque equivalent amount detection means. Note that in order to eliminate the influence of the starting current of the motor 10, a soft start circuit is provided in the gate circuit of the thyristor 14,
It is desirable to configure the output of the resistor 16 to be cut off for a predetermined period of time by a timer.

This embodiment detects the proof strength of a bolt in an analog manner, and is formed entirely of an analog circuit.

First, a rise rate detection circuit that calculates and stores the rise rate of the tightening torque within the elastic range based on the tightening torque T within the bolt elastic range and its primary delay amount will be described.

20 and 22 are first and second primary delay circuits, which respectively include series resistors 20a and 22a, parallel capacitors 20b and 22b, and operational amplifier 20.
c, 22c. The time constant of the first delay circuit 20 is set to be extremely small compared to the time constant of the second delay circuit 22. In particular, the time constant of the first primary delay circuit 20 is preferably set as small as possible to eliminate high frequency noise of the current i. Of course, if there is no noise, the first primary delay circuit 20 is not necessary. Second primary lag circuit 2
2 can be switched by a switch having a normally open contact SW1 and a normally closed contact SW11, and the normally open contact SW
When the normally closed contact SW11 is closed, the second primary delay circuit 22 with a large time constant operates, and when the normally closed contact SW11 is closed, it becomes a circuit with a small time constant that is almost the same as the first primary delay circuit 20.

24 is the output of these first-order delay circuits 20 and 22.
This is a subtraction circuit that calculates the difference between A ₁ and A ₂ (A ₁ - _{A 2} ). 26 is the output of this subtraction circuit 24 (A ₁ −A ₂ )
The point is to find the increase rate K of the tightening torque from .

Within the elastic range of the bolt, if the delay time of the first primary delay circuit 20 is minute, the change in the output A ₁ can be considered to be linear, so A ₁ = Kt (K is the spring constant) On the other hand, The time constant of the second primary lag circuit 22 is T=
If it is RC, the characteristic equation of its output A ₂ is RdA ₂ /dt+A ₂ /C=Kt Therefore, A ₂ =KT(e ^-t/T -1)+Kt A ₁ -A ₂ =KT(1-e ^{- t/T} ) Here, for example, if t is the time constant T, then A ₁ −A ₂ =0.632KT ∴K=(A ₁ −A ₂ )/0.632T Also, if t is 2T, then K=(A ₁ −A ₂ )/0.863T In any case, once t is determined, K can be found by calculation.

In this embodiment, time t ₁ at point A within the elastic region is set in advance in the timer 28, and at this time t ₁ the normally open contact is
Close SW1 and start inputting the tightening torque T to the second primary delay circuit 22, and at time t ₂ (i.e. t ₂ - t ₁ = α) when a predetermined time t = α has passed from this time t ₁ , the state is normally closed. Contact SW2 is opened and (A ₁ −
A ₂ ) is stored in the first hold circuit 26. Note that the amplification factor of the operational amplifier 26c is set so that its output becomes K.

The timer 28 detects the time t ₃ at which time γ has elapsed from the starting point B, that is, the point A, at which the output A ₁ of the first primary delay circuit 20 is within the elastic range of the bolt, and this time.
A signal is outputted from t ₃ to t ₄ after a time period β corresponding to a predetermined tightening angle has elapsed. This signal at time _t4 is an integration start signal.
It goes without saying that the set time of the timer 28 can be set to a value such as loosening of the bolt.

30 is the second hold circuit, normally closed contact SW
3, the output _A1 of the first primary delay circuit 20 is sequentially stored. The normally closed contact SW3 opens based on the signal output by the timer 28 at time _t3 . As a result, the second hold circuit 30 has a tightening torque at a starting point B within the elastic range of the bolt, as shown in FIG.
You will remember T ₂ .

32 is an integrating circuit. This integration circuit 32 integrates the rate of increase K over time t via a normally open contact SW4 which is closed in response to an integration start signal output by the timer 28 at time _t4 . That is, the integration is started with the time _t4 when the tightening is done by a predetermined tightening angle equivalent from the starting point B as the integration start point C.

34 is an adder circuit, which calculates the sum of the output Kt of this integrating circuit 32 and the output T ₂ of the second hold circuit 30. The output Kt+T ₂ of this adder circuit 34 means a straight line extending with a slope K from the integration starting point C. This output is the output of the first primary lag circuit 20.
It is compared with A ₁ by a comparator circuit 36. This comparison circuit 36 sends a tightening stop signal to the gate circuit 38 of the thyristor 14 to stop tightening when both match (fastening stop point D).

Generally, if the type of bolt, tightening thickness, etc. are determined, the elongation under load that will result in a predetermined permanent elongation can be determined in advance. Normally, this permanent elongation is set at 0.2% at the length where tensile force is applied, but
It may be set to 1% of the idle screw length (the length of the threaded portion of the portion to which tensile force is applied).
In any case, once a predetermined elongation ε is determined, the tightening angle ψ required to generate this elongation ε is determined.
The predetermined tightening angle equivalent amount (t ₄ - t ₃ )=β stored in the timer 28 in this embodiment is calculated by converting this tightening angle ψ
By setting the time to be equal to , it becomes possible to tighten with proof stress in accordance with the theory.

Note that if the delay time of the first primary delay circuit 20 with respect to the actual tightening torque T is sufficiently small and this delay can be ignored, the predetermined tightening angle equivalent amount (t ₄ - t ₃ ) will be as described above. It is sufficient to set it so that it matches the tightening angle ψ. But this first
Of course, if the delay of the primary delay circuit 20 cannot be ignored, this predetermined tightening angle equivalent amount (t ₄ - t ₃ ) must be set shorter than the time corresponding to the tightening angle ψ. .

In the above embodiment, the timer 28 is set at times t ₁ , t ₂ , t ₃ ,
_t4 is stored, and the integrating circuit 32 integrates K with respect to time. However, in the present invention, the rotation angle θ of the electric motor 10 is detected, the timer stores the amount equivalent to a predetermined tightening angle in θ, and the integrator may be integrated over θ.

Further, the first-order delay amount in the present invention may be calculated digitally at every predetermined time or every predetermined rotation angle, and may be constructed entirely or partially by a digital circuit.

Furthermore, in the embodiment, the second primary lag circuit 2
Although the time point A and the starting point B at which the prime mover torque starts to be input to the circuit 2 are determined by the timer 28 from the time starting from the start of tightening, the present invention is not limited to this, and the first primary delay circuit It is sufficient that points A and B fall within the elastic range of the output of 20.

For example, the tightening torques at points A and B within the elastic range are preset in a setting device, the output of this setting device is compared with the output of the first primary lag circuit, and the point when the two become equal is determined at points A and B. It may also be the starting point B. Third
The figure is a configuration diagram showing an example of such a case.

In this figure, 40a is the tightening torque T ₁ at point A, 4
2a is a setting device for setting the tightening torque _T2 at the starting point B, and 40b and 42b are comparators. Point A is determined based on the output of the comparator 40b, SW1 is closed, and SW2 is opened after the time α set by the timer 28A. Further, the timer 28B starts counting based on the output of the comparator 42b, and sends a signal to the normally open contacts SW4 and SW5 to start the integration after the elapse of time β corresponding to a predetermined tightening angle. In this case, since the output of the setting device 42a becomes the tightening torque at the starting point B, this setting device 42a
If the output of
It becomes possible to omit 0. In addition, SW5 is starting point B
This is provided to prevent the comparison circuit 36 from outputting a tightening stop signal. Also, in Figure 3, the same parts as in Figure 1 are given the same symbols, so
I won't repeat that explanation.

In the present invention, in FIG. 2, t ₁ =t ₃ may be set. In this case, it is necessary to set α<β. By doing so, the timer 28 in the embodiment of FIG. 1 becomes simple, and the setter 42a and comparator 42b in the embodiment of FIG. 3 become unnecessary. Furthermore, in the present invention, it goes without saying that t ₂ =t ₃ may be set.

(Effects of the Invention) As described above, the present invention calculates the rate of increase of the tightening torque equivalent amount within the elastic region based on the tightening torque equivalent amount and its primary lag amount, and performs a predetermined tightening process from a starting point within the elastic region. After tightening the angle equivalent amount, the rate of increase within this elastic range is integrated and added to the tightening torque equivalent amount at the starting point, and this added value is compared with the tightening torque equivalent amount. Therefore, the tightening end point can be detected in accordance with the definition of proof stress, making it possible to perform highly accurate tightening.

[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. DESCRIPTION OF SYMBOLS 10... DC series motor, 16... Resistor as torque equivalent amount detection means, 20... First primary lag circuit, 22... Second primary lag circuit, 24... Subtractor,
26...first hold circuit, 28, 28A, 28B
...Timer as setting means, 30... Second hold circuit, 32... Integrating circuit, 34... Adding circuit, 36...
Comparison circuit, I...Increase rate detection circuit, B...Starting point, C...
Integration start point, t ₄ ...Integration start signal, B...Start point.

Claims (1)

[Claims] 1. In a bolt tightening machine using a prime mover, there is provided a means for detecting an amount equivalent to bolt tightening torque, a first-order lag circuit for determining a first-order lag amount of the amount equivalent to bolt tightening torque, and a first-order delay circuit for determining a first-order lag amount of the amount equivalent to bolt tightening torque; a subtracter that calculates the difference between the tightening torque equivalent amount at a point in time and its primary lag amount; a first hold circuit that calculates and stores the increase rate of the tightening torque equivalent amount based on this difference; a second hold circuit that stores an amount equivalent to a tightening torque at a starting point located after the time point at which the increase rate is stored; and a second hold circuit that outputs an integration start signal after tightening an amount equivalent to a predetermined tightening angle from the starting point; a setting means for setting a predetermined tightening torque equivalent amount for determining the increase rate and the starting point; an integrating circuit that starts integrating the increase rate based on the integration start signal; and a setting means for setting the tightening torque equivalent amount at the starting point and the The method includes an addition circuit that calculates the sum of the integral value outputted by the integration circuit, and a comparison circuit that determines that the output of the addition circuit has become equal to an amount equivalent to the tightening torque and outputs a tightening stop signal. A strength detection bolt tightening machine characterized by stopping tightening based on a tightening stop signal. 2. The strength-detecting bolt tightening machine according to claim 1, wherein the prime mover is a DC series-wound motor, and the motor current is an amount equivalent to the tightening torque. 3. The subtracter calculates the difference between the first primary lag circuit having a small time constant and the second primary lag circuit having a large time constant. Strength detection bolt tightening machine. 4. The strength detection bolt tightening machine according to claim 3, wherein the delay time of the first primary delay circuit is approximately zero. 5. According to any one of claims 1 to 4, wherein the predetermined tightening angle equivalent amount is set by the tightening time, and the integrating circuit integrates the rate of increase of the tightening torque equivalent amount over time. The strength detection bolt tightening machine described. 6 The amount equivalent to the specified tightening angle is set by the tightening angle,
5. The strength detecting bolt tightening machine according to claim 1, wherein the integrating circuit integrates the rate of increase of the tightening torque equivalent amount with respect to the tightening angle. 7. The strength detection bolt tightening machine according to any one of claims 1 to 6, wherein the predetermined tightening angle equivalent amount is set to give a permanent elongation of 0.2% to the bolt. . 8. Claim 3 or 4, characterized in that the starting point within the elastic range is defined as the point in time when the output of the first primary delay circuit becomes equal to the tightening torque preset by the setting device. Strength detection bolt tightening machine described in .