JPH0321310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a bolt tightening machine that uses a load control washer to tighten a bolt with a predetermined tightening torque.

Conventionally, bolts are tightened at a predetermined tightening load using a load control washer that plastically deforms at a predetermined tightening load that is lower than a target tightening load within the elastic deformation range of the bolt. As this load control washer, for example, LC washer (trade name) manufactured by Nippon Steel Corporation and Nippon Steel Bolten Corporation is known.

FIG. 1 is a diagram showing the state in which such a load control washer is used, and FIG. 1A shows the state before tightening, and B shows the state after tightening. In these figures, numerals 1 and 2 are bodies to be tightened, 3 is a bolt passing through these bodies 1 and 2, 4 is a load control washer, and 5 is a nut. As the nut 5 is tightened from the state shown in A of the figure, the washer 4 undergoes plastic deformation and becomes flat, resulting in the state shown in B.
During the process of plastic deformation of the washer 4, the axial force of the bolt 3 becomes substantially constant, so the tightening torque during that time also becomes substantially constant. If the tightening is stopped at a target tightening load that is slightly increased from this constant value, the tightening axial force can be brought to a predetermined value determined by the type of washer 4.

On the other hand, when a DC series motor is used for a bolt tightening machine, focusing on the fact that the tightening torque and current are proportional, the change in current with respect to the tightening angle (or time) during tightening is within a predetermined range. Conventionally, it has been considered to detect that the load control washer 4 is being plastically deformed because the load control washer 4 has become sufficiently small to fit within the range. Curve A in FIG. 2A is a diagram showing the relationship of the motor current I of the soft-started motor with respect to the tightening angle θ in an ideal state. This motor current I corresponds to the tightening torque T. In this figure, point a is the plastic deformation start point of washer 4 (the point at which the washer starts to collapse), and point b is the plastic deformation end point (LC
point c indicates the tightening target point, and point d indicates the yield point of the bolt. Here, points a to b
At the tightening angle θ ₁ between the two, the motor current and the tightening torque T become approximately constant.

In actual bolt tightening, point a can be reliably detected because it is an inflection point determined by the characteristics of the LC washer, but point b is the contact surface of the washer, the object to be tightened, the nut, and the threaded part. The curve changes from B, C, and D due to the influence of friction, etc., and sometimes point b cannot be detected. Therefore, a method of tightening by a set angle θ ₂ after detecting point a may be considered, but in this case, it is usually necessary to install a pulse detector on the main body of the bolt tightening machine in order to detect the pulse (angle). However, the drawback was that the equipment, including the controller, was complicated and expensive. For this reason, a method of tightening for a certain set time after detecting point a may be considered, but in this case, the power supply voltage (voltage applied to the motor)
When the torque changes, the tightening speed of the electric motor also changes, resulting in the drawback that bolts, etc. cannot be tightened with accurate axial force. For example, as shown in FIG. 2B, the motor current changes with respect to time t as shown by curve F when the power supply voltage is high and curve G when it is low. Therefore, even if the timer is set to the time t _A between the plastic deformation start point a ₁ and the tightening target point c ₁ of the washer 4, when the power supply voltage becomes low, the set time becomes t _B (washer 4
The bolt cannot be tightened with accurate axial force unless the time between the plastic deformation start point a ₂ and the tightening target point c ₂ is (t _A < t _B ). In addition, in Fig. 2 A and B, point S (corresponding to torque T _SL ) is larger than the starting current (or torque) at the time of soft start, and the current (or torque) at plastic deformation starting points a, a ₁ , a ₂ is ) indicates a point smaller than

In order to eliminate the above-mentioned drawbacks, the present invention uses a timer with a voltage correction circuit to adjust the timer time even when the power supply voltage fluctuates, so that bolts can be tightened with accurate axial force, ie points c ₁ , c ₂ , etc. The object of the present invention is to provide a bolt tightening machine that has the following features.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 3 is an overall configuration diagram showing an embodiment of the present invention. In this figure, 10 indicates a DC series motor, and this motor 10 has a field winding 11 and a rotor 1.
2. The rotation of the rotor 12 tightens the nut 5 (see FIG. 1). 13 is a forward/reverse selector switch for the electric motor 10; 14 is a start switch; 15 is a control element circuit (thyristor, etc.); 16
1 is a phase control circuit, and 17 is a gate cutoff circuit.
18 is a plastic deformation start point detection circuit, 22 is a current detector, 23 is a timer with a voltage correction circuit, and 28 is a torque setting device (torque T _SL ).

The plastic deformation start point detection circuit 18 includes a first comparator 3
1, an analog switch AS, a delay circuit 20, a plastic deformation start point setter 29, and a second comparator 32.

This plastic deformation start point detection circuit 18 compares the signal A detected by the current detector 22 and the signal corresponding to the torque T _SL set in the torque setting device 28 using a first comparator, and determines that the signal A is higher. If it is large, the signal from the first comparator 31 turns on the analog switch AS. When this analog switch AS turns on, signal A is transmitted to the plastic deformation start point setter 29 and the delay circuit 2.
Output to 0. Delay circuit 20 inputting signal A
outputs the signal E delayed by a certain time constant to the second comparator 32. The plastic deformation start point setter 29 which receives the signal A outputs the signal A' divided by the set voltage division ratio A'/A to the second comparator 32. The plastic deformation start point setter 29 sets the partial pressure ratio A'/A so that the intersection a' of the curve A' and the curve E coincides with the plastic deformation start point a. Partial pressure ratio
When A'/A is made smaller, the intersection a' approaches the straight line near the point S (the point where the washer has not yet begun to collapse),
When the partial pressure ratio A'/A is increased, the intersection point a' approaches the point where the current (or torque) is approximately constant (the point where the washer is collapsing), and in both cases, the starting point for measuring the rotation angle (or time) is This does not coincide with the actual plastic deformation starting point a, and the starting point for measuring the rotation angle (or time) becomes unstable. Note that the partial pressure ratio A′/A is
Once the washer is fixed, it is enough to set it once, but if the type of washer (size, material, heat treatment method, etc.) changes,
You can change the setting values accordingly. Further, the second comparator 32 inputs the signal A' and the signal E, and when the signal E is larger (points a ₁ , a ₂ etc. in FIG. 2 B),
A signal is output to the timer 23 with voltage correction circuit.
The timer 23 with voltage correction circuit is connected to the voltage correction circuit 2.
4, a timer body 25, a time setter 26, a third comparator 33, and a subtracter 34. The time setting device 26 of this timer 23 with voltage correction circuit has v ₁
is set, is activated by a signal from the plastic deformation start point detection circuit 18, and outputs a signal to the gate cutoff circuit 17 at a predetermined timer time. The gate cutoff circuit 17 is activated by a signal from the timer 23 with voltage correction circuit, outputs a cutoff signal G to the control element circuit 15, turns off the control element circuit 15, and stops the motor. The voltage correction circuit 24 of the timer 23 with voltage correction circuit is a circuit that adjusts the signal v ₂ so that the tightening angle θ ₂ remains constant even if the voltage of the power supply 27 fluctuates. That is, the signal v ₂ from the voltage correction circuit 24 and the signal v ₁ from the time setter 26 are subtracted by the subtracter 34, and the difference (v ₁ - v ₂ ) is sent to the third comparator 33 as the signal v ₃ . Output.

On the other hand, the signal from the plastic deformation start point detection circuit 18 is output to the timer main body 25, and the signal _v4 is output from the timer main body 25 to the third comparator 33.

The third comparator 33 inputs the signals V ₃ and v ₄ and
When v ₄ is larger than v ₃ (when the tightening angle reaches θ ₂ ), a signal is output to the gate cutoff circuit 17 to cut off the gate of the control element circuit 15. Furthermore, it is clear from FIG. 4 that when the power supply voltage fluctuates, the timer time fluctuates. In this Figure 4, the horizontal axis is time t,
The vertical axis represents the magnitude of the signal _v3 from the subtracter 34. That is, v ₁ is a set value set in the time setter 26, and v ₄ is determined by the resistor R and capacitor c of the timer main body 25 and varies according to the curve shown in the figure. Therefore, when the power supply voltage fluctuates and v ₂ becomes large and v ₃ becomes v ₃ ′, the timer time becomes short to t _A , and when v ₂ becomes small and v ₃ becomes v ₃ ″, the timer time becomes short. The timer 23 with a voltage correction circuit operates so that tB becomes as long as _tB .

The torque setting device 28 has plastic deformation starting points a ₁ and a _{2 .}
etc., this point (a ₁ , a ₂ etc.)
Set a torque (T _SL ) that is smaller than the current (or torque) of and larger than the starting current (or torque) at soft start, and compare the detection signal of the current detector 22 and the signal from this torque setting device 28. Then, the signal from the current detector 22 is transmitted to the torque setting device 2.
When the signal becomes larger than 8, turn on the analog switch AS. As a result, the plastic deformation start point detection circuit 18 starts operating.

Next, the operation of this embodiment will be explained.

First, set v ₁ in the time setter 26 of the timer 23 with voltage correction circuit, and then apply a torque (T _SL ) smaller than the torque at the plastic deformation start points a ₁ , a ₂ , etc. to the torque setter 28 to start the plastic deformation. The partial pressure ratio is set in the starting point setter 29.
A'/A is set, and the forward/reverse changeover switch 13 is turned on to either the forward rotation side or the reverse rotation side (Figure 3 shows the state in which it is turned on to the forward rotation side). After that, when the start switch 14 is turned on, the phase control circuit 16 is activated, the thyristor etc. of the control element circuit 15 are turned on, the electric motor 10 is rotated, the nuts etc. are tightened, and the tightening torque is set in the torque setting device 28. When the torque exceeds the specified torque (T _SL ), the analog switch AS turns ON, the plastic deformation start point detection circuit 18 starts operating, and the signal A detected by the current detector 22 is sent to the plastic deformation start point setter 2.
The signal A' divided by 9 and the delayed signal E delayed by a time constant in the delay circuit 20 are sent to the second comparator 3.
2, and when the signal E becomes larger than the signal A' (points _a1 , _a2, etc. in FIG. 2B), a signal is output to the timer 23 with a voltage correction circuit. This timer 23 with voltage correction circuit is connected to the plastic deformation start point detection circuit 1.
It is activated by a signal from 8 and outputs a signal to the gate cutoff circuit 17 at a timer time determined according to fluctuations in the power supply voltage. The gate cutoff circuit 17 is activated by a signal from the timer 23 with voltage correction circuit, and outputs a cutoff signal G to the control element circuit 15.
is turned off to stop the electric motor 10. Further, the timer 23 with a voltage correction circuit has a voltage correction circuit 24.
and timer body 25, time setting device 26, and subtractor 3
4, the timer time is adjusted even if the power supply voltage fluctuates and the motor speed fluctuates, and θ ₂
is corrected almost constant. That is, when the power supply voltage decreases, the timer time value increases to _tB , and when the power supply voltage increases, the timer time value decreases to _tA .

As described above, the present invention operates with a torque _TSL smaller than the torque at the plastic deformation starting point of the load control washer, and generates a signal A obtained by dividing the signal detected by the current detector by the plastic deformation starting point setter 29. ′ is compared with signal E with a certain time constant delay, and the point where signal E becomes larger is set as the plastic deformation start point (point a ₁ , a _2, etc.) and a timer with a voltage correction circuit is activated to start plastic deformation. Equipped with a point detection circuit, tightening is stopped at a timer time determined according to fluctuations in the power supply voltage, so even if the power supply voltage fluctuates, the timer time of the timer with a voltage correction circuit is adjusted, ensuring accuracy at all times. The bolt can be tightened with a certain tightening axial force, and the device is simpler than the conventional example.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing how the load control washer is used, Fig. 2 A and B are change curves of motor current with respect to rotation angle and time, Fig. 3 is an overall configuration diagram showing an embodiment of the present invention, Fig. 4 The figure shows a curve of voltage change over time. 4... Load control washer, 10... DC series motor, 14... Start switch, 15... Control element circuit, 16... Phase control circuit, 17... Gate cutoff circuit, 18... Plastic deformation start point detection Circuit, 22...
...Current detector, 23...Timer with voltage correction circuit, 27...Power source, 28...Torque setting device.

Claims (1)

[Claims] 1. In a bolt tightening machine that is equipped with a DC series motor and tightens bolts using a load control washer that plastically deforms at a load lower than the target tightening load, the set torque T _SL is smaller than the torque at the starting point of plastic deformation of the load control washer. A plastic deformation start point detection circuit that starts operating when the above condition is reached and detects the plastic deformation start point, and operates based on a signal from this plastic deformation start point detection circuit,
and a timer with a voltage correction circuit that adjusts the timer time according to fluctuations in power supply voltage, and the bolt is characterized in that tightening is stopped after a time set by the timer with the voltage correction circuit from the plastic deformation starting point. Tightening machine.