JPS6055272B2 - Bolt tightening method using load control washers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bolt tightening method that uses a load control washer that plastically deforms under a predetermined tightening load and controls the amount of tightening by a digital calculation device.

BACKGROUND OF THE INVENTION Conventionally, a bolt is tightened with a predetermined tightening load using a load control washer that plastically deforms with a predetermined tightening load within the elastic deformation range of the bolt.

As this load control washer, for example, (1) washer (trade name) manufactured by Nippon Steel Corporation and Nippon Steel Bolten Corporation is known. FIG. 1 is a diagram showing possible states of such a load control washer, where A shows the state before tightening and B shows the state after tightening.

In these figures, reference numerals 51 and 52 are bodies to be tightened, 53 is a bolt passing through these bodies 51 and 52, 54 is a load control washer, and 55 is a nut. As the nut 55 is tightened from the state shown in A in the figure, the washer 54 undergoes plastic deformation and becomes flat, resulting in the state shown in B. During this process of plastic deformation of the washer 54, the axial force of the bolt 53 becomes substantially constant, so the tightening torque during that time also becomes substantially constant. Therefore, if the tightening is stopped at the end of the plastic deformation range of the washer 4, the tightening torque can be set to a predetermined value determined by the type of the washer 54. FIG. 2A shows the relationship between tightening torque T and tightening time t, in which point A in the figure indicates the starting point of plastic deformation of the load control washer 54, and point B indicates the ending point of plastic deformation.

In this manner, the tightening torque T is approximately constant in the plastic deformation range between points A and B. Various methods have been proposed in the past to detect this plastic deformation range A-B.
Since all conventional methods perform signal processing using analog circuits, it is difficult to maintain accurate calculation results during processing, and tightening torque is detected using the drive current of the electric motor. Since the drive current is smoothed during the process, a phase lag occurs in the signal processing, resulting in a drawback that the bolt or nut cannot be tightened with high accuracy.

Furthermore, when using a load control washer, it is necessary to detect the start and end points of plastic deformation, but when an analog circuit is used, separate circuits are required for each detection point. For this reason, there was also the problem that the number of parts increased. Particularly in such analog circuits, adjustments such as temperature compensation are troublesome and productivity is extremely low. This invention was developed in view of these circumstances, and it is possible to detect the end point of plastic deformation with high precision, control tightening with a predetermined axial force with high precision, and furthermore, the number of parts is small and temperature compensation, etc. The purpose of the present invention is to provide a bolt tightening method using a load control washer that allows for very easy adjustment.

In order to achieve such an object, the present invention uses a load control washer that plastically deforms under a predetermined tightening load, and in a method in which the amount of tightening by an electric motor is controlled by a digital calculation device, the tightening torque is a threshold value determination step for determining that a set threshold smaller than the deformation start torque of the washer has been exceeded; and a deformation step for detecting the deformation start point of the washer based on the increase rate of the tightening torque becoming less than or equal to a predetermined value. The electric motor is configured to include a start point detection step and a stop determination step for outputting a tightening stop signal when a predetermined tightening amount is tightened from the deformation start point, and the electric motor is stopped by the tightening stop signal. be. Furthermore, there are cases where the screw threads of the bolts and nuts are deformed, making it difficult to screw them in smoothly, or where the bolts and nuts rotate together, making it difficult to tighten them.

A second object of the present invention is to provide a bolt tightening method using a load control washer that promptly detects the abnormality and generates an alarm when there is an abnormality in the tightening. In order to achieve this second objective, the present invention is provided in at least one of the steps,
An abnormality detection step is added in which an abnormality is detected and an alarm is generated and a tightening stop signal is output because the time required for the determination condition of that step to be met is outside the set time range.

The present invention will be described in detail below based on Examples. This invention allows various methods for the operation up to detecting the deformation start point A (hereinafter referred to as the first half operation) and the operation for detecting a predetermined tightening amount after the deformation start point A (hereinafter referred to as the second half operation). These operation methods before and after the deformation start point A are possible, and embodiments can be constructed by variously combining these operation methods before and after the deformation start point A. For this reason, below is an example of the first half of the operation until the deformation start point A is detected,
The second half of the operation after the deformation start point A will be explained separately. FIG. 3 is a block diagram showing a first embodiment of a bolt tightening device according to the present invention, and FIGS. 4 and 5 are flowcharts showing an example of the first half operation of this embodiment device, respectively.

In FIG. 3, reference numeral 1 is an AC power supply, and this power supply 1
The power is supplied to a closed circuit consisting of a switch 2, a semiconductor switch 3, and a DC series motor 4.

5 is a rotation angle detector that outputs an angle pulse P (Δθ) for each tightening rotation angle Δθ of bolts and nuts as the electric motor 4 rotates; 6 is a signal detector; A strain gauge is attached to the part that receives the tightening reaction force, and the tightening torque is detected by converting the strain caused by the tightening reaction force into an electrical signal.

7 is an AD converter that converts this electrical signal indicating the tightening torque into a digital signal T.

8 is a digital arithmetic unit, and this arithmetic unit 8 is connected to the fourth,
Predetermined rotation angles are sequentially performed according to the flowchart shown in FIG.

Reference numeral 9 denotes a memory (ROM) that stores an arithmetic program for the arithmetic unit 8 to perform predetermined arithmetic operations, 10 an input/output device for setting various setting values such as a threshold value Tth, data related to volts, and 11. 2 is a phase control circuit, and 2 is a gate pulse generation circuit.

Based on the tightening stop signal S generated by the arithmetic device 8, the phase control circuit 11 stops the gate pulse generation circuit 12 from generating the gate pulse G and starts the semiconductor switch 3, thereby controlling the power supply of the motor 4. cut off. A power supply voltage detector 13 detects the closing of the switch 2 and outputs a calculation start signal to the calculation device 8.

Next, an embodiment of the first half operation shown in FIG. 4 will be described.

First, the input/output device 10 sets a threshold value Tth of the tightening torque T within the elastic range of the bolt, a predetermined value ΔTO that is sufficiently smaller than the maximum value ΔTO~ of the increase rate ΔT of the tightening torque T within this elastic range; Various other values are set for detecting tightening abnormalities. The threshold T. h is a value sufficiently smaller than the final target tightening torque T8 corresponding to the yield point A. When switch 2 is closed, power supply voltage detector 1
3 detects the closing of this switch 2 and sends a calculation start signal to the calculation device 8. The arithmetic device 8 sequentially reads programs from the memory 9 based on this arithmetic start signal and starts executing the series of arithmetic operations shown in FIG. First, the arithmetic unit 8 sends a tightening operation start signal to the phase control circuit 11, and the gate pulse generation circuit 12 generates a phase-controlled gate pulse G. Therefore, the semiconductor switch 3 has a trigger pulse G
The motor 4 is ignited in phase synchronized with the motor 4, and a drive current begins to flow to the motor 4, which starts rotating. As the bolt is tightened, the rotation angle detector 5 outputs an angle pulse P (Δ0) at every predetermined rotation angle Δ0. Further, the AD converter 7 continues to output the ever-changing tightening torque T as a digital signal. The arithmetic unit 8 reads the threshold value Tt set by the input/output device 10, and also reads the digitalized tightening torque T for each angle pulse P (Δθ) and compares the two (step 100). New tightening torques T are sequentially read and this comparison operation is repeated until the tightening torque T exceeds the threshold value Tth.

On the other hand, the arithmetic unit 8 has a built-in clock pulse generator and integrates the required time t after the start of tightening. When the time t required until the condition in step 100 is met exceeds the set time t1, this is determined in step 102, and a warning is issued as the bolt is rotating together with the nut (step 104), and the tightening is stopped. Further, if the time T2 required for the condition in step 100 to be satisfied is less than or equal to the set time T2,
This is determined in step 106, and a warning is issued as the bolt or nut is locked due to deformation of the screw thread or the like (step 104), and the tightening is stopped.
That is, in steps 102, 104, and 106, the time t required for the tightening torque T to reach the threshold value Tth is T2
An abnormality detection step in which an abnormality is detected and an alarm is generated because it is outside the range of <t1, and a tightening stop signal S is sent to the phase control circuit 11 to open the semiconductor switch 3 and cut off the power to the motor 4. It is becoming. The calculation device 8 calculates a certain rotation angle θ.

−1 and the rotation angle θ after the predetermined rotation angle Δθ. The respective tightening torques L-1 and Tn are stored in a built-in memory (RAM).
), and these tightening torques L-1 and Tn are sequentially rewritten as the rotation angle progresses. The calculation device 8 calculates the difference ΔL between the tightening torques Tn-1 and Tn at each predetermined rotation angle Δθ.
is calculated (step 108), and this operation is repeated until this difference ΔTn becomes equal to or less than the predetermined value ΔTO stored in advance (deformation start point detection step 110). The time t required until the condition of step 110 is satisfied is the same as that of steps 112 and 114, as in steps 102 and 106.
The difference ΔTn is also compared with the set value モ,T2″ and the presence or absence of a tightening abnormality is determined.The difference ΔTn is also the increase rate of the tightening torque T with respect to the rotation angle θ, and this difference ΔTn is determined in step 110.
If the following conditions are satisfied and no tightening abnormality is detected in steps 112 and 114, the tightening torque Tn is further increased at this time.
It is determined whether or not the value is within the range of pre-stored set values T,, T2 (step 116), and if it is within the range W1 to T2, it is assumed that the tightening is proceeding normally and will be described later. Perform the second half of the action. Next, another embodiment of the first half operation will be explained with reference to FIG.

In this embodiment, the maximum rate of increase in tightening torque within the elastic range is stored, and the deformation starting point A is detected when the rate of increase becomes less than a predetermined percentage of this maximum rate of increase. Difference ΔT in tightening torque between predetermined rotation angles Δθ. , that is, calculate the rate of increase (step 200), and when this difference ΔTn is increasing or constant, (
Step 202), convert the difference ΔTn to the maximum increase rate ΔT, . a.
(step 204), and this maximum increase rate ΔT
．． ．． ax is sequentially replaced by the newly determined difference ΔTn. Steps 206 and 208 are steps 102 and 1.
This is an abnormality detection step similar to 06. As a result, the memory (RAM) built into the arithmetic unit 8 stores the maximum increase rate ΔT corresponding to the slope of the maximum slope M in FIG. ．． ax is stored. When the condition of step 202 is satisfied and the difference ΔTn starts to decrease, the difference ΔTrr. (Step 2)
10) This difference ΔTm is the maximum value ΔT. ．． These steps 210 and 212 are repeated until the value becomes less than or equal to a predetermined value C·ΔTmax, which is the product of aO and a constant C (0<C×1) (deformation start point detection step 212). Furthermore, the fifth
In the figure, the same steps as in Figure 4 are given the same symbols, so
That explanation cannot be repeated. 4 and 5 above, the embodiment shows the tightening torque T by converting the output of the strain gauge for obtaining the tightening reaction force into a digital signal using the AD converter 7.
However, according to the present invention, the tightening torque T can be determined using various methods.

FIGS. 6 and 7 are a block diagram and a first half operation flowchart showing another embodiment.

In this embodiment, the tightening torque T is calculated from the motor torque characteristic equation based on the motor current 1M and the angular velocity. Note that in FIG. 7, each step for abnormality detection is omitted. In FIG. 6, 20 is a current detection resistor connected in series to the motor 4, and 22 is this resistor 2.
The motor current is detected from the voltage across 0 and is converted into a digital signal 1.

24 is a second digital arithmetic device that calculates the tightening torque Tn and angular velocity ω at any rotation angle 0n using this digital signal 1D; 26 is a storage for the arithmetic program of this second arithmetic device; memory. In this figure, the same parts as in FIG. 3 are given the same reference numerals, so their description will not be repeated. Next, the operation of this embodiment will be explained based on FIG.

By closing the switch 2, the arithmetic unit 8 is switched to the phase control circuit 1.
1. The semiconductor switch 3 is ignited via the gate pulse circuit 12 to start the electric motor 4. The AD converter 22 quantizes the voltage across the resistor 20 indicating the motor current at an extremely shorter period than the AC power supply 1 to generate a digital signal 1 . shall be. The second arithmetic unit 24 receives this digital signal 1. The effective value h=ΣID of the current is calculated by integrating over a half cycle or one cycle of the AC power source 1, while the angle pulse (
The angular velocity ω is calculated from the reciprocal 1/N of the number N of clock pulses accumulated within the time interval of Δθ) (step 300).
. This second arithmetic unit 24 also calculates the rotation angle θ at which two consecutive angle pulses P(ΔO) are output. Calculate the angular acceleration dω/t from the difference in angular velocity at −1 and θo (
Step 302). On the other hand, the output torque T of a DC motor is as follows.

Here, Φ is the magnetic flux and k is a constant. However, the torque T that actually contributes to tightening in an electric motor tightening machine is affected by inertia during speed fluctuations (Jd) and friction torque (T
, ), the following equation is obtained.

The second calculation device 24 calculates the actual tightening torque T by calculating the equation (1) (step 304).

The arithmetic unit 8 reads the tightening torque T output from the second arithmetic unit 24 based on the angle pulse P (ΔO), and performs the same calculation as in the embodiment shown in FIG. 5 above.

As described above, since the operation in the second half of FIG. 7 is completely the same as that in FIG. 5, the same steps are given the same reference numerals and the description thereof will not be repeated. In this embodiment, as shown in FIG. 6, the rotation angle 0 is determined by the rotation angle detector 5, and the rotation angle 0 is determined by the number of clock pulses N accumulated between the angle pulses P (Δ0) outputted by the rotation angle detector 5. The velocity ω was calculated, and this angular velocity ω is as shown in the example shown in Figs.
It may be configured to be calculated from a speed characteristic equation of the motor based on the motor current M and the motor voltage M. FIG. 8 is a block diagram of this embodiment, and FIG. 9 is a flowchart showing the first half of the operation.

In FIG. 8, 30 represents the motor voltage as a digital signal V. 32 is a second digital arithmetic unit,
Reference numeral 34 denotes a memory that stores an arithmetic program for this arithmetic unit 32. In this figure, the same parts as those in FIGS. 3 and 6 are given the same reference numerals, so the description thereof will not be repeated. In this embodiment, when a current flows through the motor 4 by closing the switch 2, the motor current and the voltage are respectively A.
The D converters 22 and 30 convert the signal into quantized digital signals 1D and VD at a period much shorter than the AC power supply period.

The second arithmetic unit 32 sequentially reads these digital signals 1DVD and integrates them over a half cycle or one cycle of the AC power supply to calculate an effective value 1M=ΣID (step 400 in FIG. 9). Generally, the angular velocity ω of a series-wound commutator motor is determined by the following speed characteristic equation.

of Here, R is the armature resistance, Φ is the magnetic field, and K is a constant.

Although the magnetic field Φ is generally a function of the current 1M, it is assumed that its changing characteristics are stored in the memory 34 in advance. Second
The arithmetic unit 32 sequentially reads the current and voltage (9) output from the oil converters 22, 30 and calculates the angular velocity ω by calculating the equation (2) (step 402). is calculated to calculate the tightening torque T that contributes to actual tightening (step 404).

The second arithmetic unit 32 outputs this tightening torque T every half cycle or every cycle of the power supply. The arithmetic unit 8 sequentially reads the torque T output from the second arithmetic unit 32 at predetermined time intervals, and performs the same operation as in each of the embodiments described above.

In the embodiments shown in FIGS. 1 to 9 above, the angular velocity ω changes as the tightening progresses, but the present invention can also be applied to a system in which the angular velocity ω is controlled to be constant.

For example, there is a device that takes advantage of the fact that the armature back electromotive force is proportional to the angular velocity ω, and controls the angular velocity ω to be constant by controlling the conduction angle of the semiconductor switch 3 according to changes in this back electromotive force. FIG. 10 is a flowchart of the first half of the operation in which the speed ω is kept constant in this manner.

In this embodiment, the motor voltage is converted into a digital signal V using an oil converter.
After setting this to D, the effective value VM of the voltage is obtained by integrating it over a half cycle or one cycle of the AC power supply (step 500), and the motor current is calculated using the speed characteristic equation (2) above. (Step 502), and further, using this charging, the tightening torque T is calculated by the equation (1) (Step 504). Hereinafter, tightening is performed by calculations exactly the same as in the embodiment shown in FIG. 9 above. In the embodiment shown in FIGS. 3 to 5, both the threshold value determination step 100 and the deformation start point determination step 110, 212 include abnormality detection steps 102, 106 and 1 for detecting abnormality in tightening.
Since steps 12 and 114 are provided, abnormality detection becomes more reliable, but in this invention, steps 100 or 110 and 2 are provided.
12 may be provided with this abnormality detection step. In these embodiments, it is determined in step 116 whether the tightening torque at the deformation start point A is within a predetermined range, and in the embodiment of FIG.
Since abnormality detection steps 206 and 208 are also provided in steps 200, 202, and 204), tightening abnormalities can be detected more reliably, and reliability is further improved. Next, the deformation starting point A
An example of the subsequent operation (second half operation) will be described.

In the embodiment shown in FIG. 11, the time t at the deformation start point A is set to Ta.
(step 600), and calculates the time T. from this time Ta as the starting point. = t-Ta (step 602
), the time when the time exceeds the pre-stored time Ts is regarded as the deformation end point B (stop determination step 604), and the tightening is stopped. The embodiment shown in FIG. 11 has a very simple configuration because it can utilize one timer built into the arithmetic unit 8, but it can be combined with the embodiments of the first half operation shown in FIGS. 3 to 9 above in which the tightening speed changes. In this case, the detection of the deformation end point B is likely to be inaccurate.

However, when combined with the embodiment of FIG. 10 in which the torque speed is stepped at a constant rate, the tightening can be stopped precisely at the deformation end point B, which is preferable. In the second half operation example of FIG. 12, the rotation angle θ at the deformation start point A is stored as θ1 (step 650), and the rotation angle θ is calculated from this rotation angle θ1 as the starting point.

=0-08 and the angular velocity ω at that time. (see the embodiment in FIG. 7) is first stored as an initial value (step 652).
and performs inertia compensation as described below) step 65
4). That is, if friction is omitted, the equation of motion during tightening is as follows.

Here, J is the inertia rate seen from the output shaft of the motor, 0 is the tightening angle after the bolt starts to be tightened, E is the spring constant of the bolt, T is the torque of the electric motor, and t is time.

Since T becomes zero after the power is cut off, the following holds true at this time.

If we solve this equation under the initial conditions of t=o, O=00, and dθ/Df=ωo, we get 1.

Here β2=E/J, φ=Tan-1(θoβ/ωo)
It is. From this formula (3), the maximum value θ of the tightening angle θ after the power is cut off. ~ becomes.

On the other hand, the maximum bolt tightening torque T, . Since aO is at the maximum value 0max of the tightening angle θ, it is as follows.

Here, if the speed fluctuation rate of the motor immediately before the power is shut off is small, the tightening torque T immediately before the power is shut off.

So, in the end, it becomes as follows. Therefore, the rotation angle θ just before the power is cut off.

and angular velocity ω. If is known, the final rotation angle θ8 including the amount of additional tightening due to inertia is determined by formula (4), and the tightening torque T is similarly determined. and angular velocity ω. If is known, the final tightening torque Te
can be predicted using equation (5). 1st
The embodiment shown in FIG. 2 uses equation (4) above to set a certain rotation angle to 0. The final rotation angle θ8 when the power is cut off is predicted (step 654), and the predicted final rotation angle θ8 is predicted. Tightening is stopped when the rotation angle becomes equal to or larger than a pre-stored rotation angle θ8 (stop determination step 656). Furthermore, Figure 11 and Figure 1
In Figure 2, steps 606, 608, and 610 are the fourth and fifth steps.
This is a step for abnormality detection similar to the embodiment shown in the figure.

In the embodiment shown in FIG. 13, the deformation end point B is determined from the fact that the increase rate ΔT (step 700) of the tightening torque T exceeds a pre-stored set value ΔTO'' using a procedure similar to that of FIG. 4. (Stop determination step 702).

In the embodiment shown in FIG. 14, the minimum increase rate ΔTmi between the plastic deformation range A and B is determined by a procedure similar to that shown in FIG.

(steps 750, 752, 754), and the increase rate ΔT after the increase rate ΔTn starts increasing after the deformation end point B.
m (step 756) is a predetermined value C・ΔTmin (however, C
1), a tightening stop signal is output to stop tightening (stop determination step 758). 15th
In the illustrated embodiment, the angular velocity ω is calculated from the reciprocal of the number N of clock pulses within a predetermined rotation angle Δθ (step 800).
.

If the tightening speed is not controlled constant, the angular velocity ω will be approximately constant between the plastic deformation range A and B, and after the deformation end point B, the angular velocity ω will decrease as the tightening torque increases. The deformation end point B is detected (stop determination step 802). The first of the above
By appropriately combining the embodiments of the second half operation shown in Figures 1 to 15 with the embodiments of the first half operation shown in Figures 3 to 10, an optimal tightening method can be constructed for different bolt types and tightening conditions. be able to. In the present invention, as described above, all calculations are performed by digital signal processing, so compared to those using analog signals, there is no phase delay during signal processing or errors caused by the signal holding means, and tightening accuracy is significantly improved.

It should be noted that, in general, it is unavoidable that the tightening torque will have small fluctuations during tightening.

However, according to the present invention, when digitizing the tightening torque detected from current, strain gain, etc., it is quantized and converted into a digital signal at a cycle sufficiently shorter than the fluctuation cycle of this torque, and this digital signal is converted into a digital signal for an appropriate period of time. It is possible to easily average the width by just setting the program. As a result, according to the present invention, it is possible to average out the fluctuations in the tightening torque, thereby making it possible to manage the tightening torque more accurately. On the other hand, if an analog circuit were to perform the first half operation and the second half operation as in the present invention, separate circuits corresponding to each operation would be required, making the circuit configuration extremely complicated.

Furthermore, if an attempt is made to improve the reliability of temperature compensation, etc., productivity will be extremely poor and the device will be extremely expensive. However, according to the present invention, the number of parts is reduced, and temperature compensation measures can be taken very easily by setting the program. Therefore, it becomes possible to improve productivity and improve reliability of the device. In addition, if an abnormality detection step is provided in the threshold value determination step, deformation start determination step, or stop determination step to detect tightening abnormalities based on the time required to satisfy these determination conditions, it is possible to It is possible to reliably detect abnormalities.

Furthermore, since the present invention uses a digital arithmetic unit, an abnormality detection step can be provided by simply changing the program. In addition, by changing various setting values and programs, it is possible to flexibly deal with changes in the type of bolt and tightening conditions, which has the effect of being highly versatile.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing how the load control washer is used, Fig. 2 is its tightening characteristic diagram, Figs. 3, 6, and 8 are block diagrams of various embodiments of the present invention, and Figs. , 9 and 10 are flowcharts showing various embodiments of the first half operation, and 11th to 1st
FIG. 5 is a flowchart showing various embodiments of the second half operation. 4...Electric motor, 8...Digital arithmetic unit, 54...
・Load control washer, 100... Threshold value determination step, 1
02,106,112,114,606,608...
Abnormality detection step, 110, 212... Deformation start point detection step, 604, 656, 702, 75J8, 80
2...Stop determination step.

Claims (1)

[Claims] 1. A method in which a load control washer that plastically deforms under a predetermined tightening load is used and the amount of tightening by an electric motor is controlled by a digital calculation device, wherein the tightening torque is lower than the deformation start torque of the load control washer. a threshold value determination step for determining whether a small set threshold value has been exceeded; a deformation start point detection step for detecting a deformation start point of the washer based on the increase rate of the tightening torque; A bolt tightening method using a load control washer, comprising: a stop determination step of outputting a tightening stop signal when the bolt is tightened to a predetermined tightening amount, and the electric motor is stopped by the tightening stop signal. 2. A bolt tightening method using a load control washer according to claim 1, wherein the tightening torque is obtained by converting the output of a strain gauge that measures the motor reaction force of the electric motor into a digital signal using an AD converter. 3. A bolt tightening method using a load control washer according to claim 1, wherein the tightening torque is calculated from a motor torque characteristic equation based on motor current and angular velocity. 4. A bolt tightening method using a load control washer according to claim 3, wherein the angular velocity is determined by the number of clock pulses accumulated between angular pulses output by a rotation angle detector at every predetermined rotation angle. 5. A bolt tightening method using a load control washer according to claim 3, wherein the angular velocity is calculated from a speed characteristic equation of the motor based on the motor current and the motor voltage. 6 The motor is phase controlled so that the angular velocity is constant,
2. The bolt tightening method using a load control washer according to claim 1, wherein the tightening torque is calculated from a torque characteristic equation using the motor voltage and the motor current calculated from the motor voltage and the speed characteristic equation. 7. The bolt tightening method according to claim 1, wherein in the deformation start point detection step, the deformation start point of the washer is detected when the increase rate of the tightening torque becomes equal to or less than a pre-stored set value. 8 In the deformation start point detection step, the maximum increase rate of the tightening torque is memorized, and the deformation start point of the washer is detected when the increase rate of the tightening torque decreases by a predetermined percentage from this maximum increase rate. A bolt tightening method according to claim 1. 9. A bolt tightening method using a load control washer according to claim 1, wherein in the stop determination step, a predetermined tightening amount is determined from the elapsed time from the deformation start point. 10. A bolt tightening method using a load control washer according to claim 1, wherein in the stop determination step, the predetermined tightening amount is determined from the tightening rotation angle from the deformation start point. 11. The load control washer according to claim 1, wherein in the stop determination step, the increase rate of the tightening torque from the deformation start point is determined, and when this increase rate exceeds a predetermined value, the predetermined tightening amount is detected. Bolt tightening method using 12 In the stop determination step, the minimum increase rate of the tightening torque from the deformation start point is stored, and since the increase rate of the tightening torque has increased by a predetermined percentage from this minimum increase rate, the predetermined tightening amount is determined. A bolt tightening method according to claim 1, which detects. 13. In the stop determination step, the angular velocity from the deformation start point is calculated, and the predetermined tightening amount is detected from the fact that this angular velocity begins to decrease. Bolt tightening using the load control washer according to claim 1 Method. 14 In a method in which a load control washer that plastically deforms under a predetermined tightening load is used and the amount of tightening by an electric motor is controlled by a digital arithmetic device, a set threshold value is set such that the tightening torque is smaller than the deformation start torque of the load control washer. a threshold value determination step for determining whether the tightening torque has exceeded a predetermined value; a deformation start point detection step for detecting a deformation start point of the washer since the increase rate of the tightening torque has become less than a predetermined value; A stop determination step that outputs a tightening stop signal when a predetermined tightening amount is tightened, and a stop determination step that is provided in at least one of the steps described above, since the time required until the determination condition for that step is satisfied is within the set time range. and an abnormality detection step of detecting an abnormality and generating an alarm and outputting a tightening stop signal, and the load control washer is characterized in that the power to the electric motor is cut off in response to any of the tightening stop signals. Bolt tightening method used.