JPH07227729A - Device and method for fastening screw - Google Patents

Abstract

PURPOSE:To provide a screw fastening device, which can easily judge that the set data for additional fastening is appropriate or not and which can easily correct that data. CONSTITUTION:Screw fastening is performed by a motor-driven driver 16 with the torque T1 required for seating a screw, and thereafter, additional screw fastening is performed by the torque T2 larger than the torque T1, and additional fastening is repeated till the rotating angle of the screw by the additional fastening is settled within a predetermined allowable rotating angle. A first display unit 15 for displaying the number of times of additional thread fastening, a second display unit 15 for displaying the rotating angle of the screw by the additional fastening of last time when the rotating angle of the screw is settled within the allowable rotating angle, and setting switches 9, 10, 11, 12, with which an operator can set at least one of additional fastening torque T2 of the motor-driven driver 16, the allowable rotating angle and the allowable number of times of additional fastening from outside are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw tightening device and a screw tightening method for performing additional tightening after a screw is seated.

[0002]

2. Description of the Related Art Conventionally, when tightening a screw, it is generally performed that the head of the screw is once seated and then a torque is further shocked to tighten the screw. As a device for automatically tightening and re-tightening such a screw, for example, a device disclosed in Japanese Patent Publication No. 61-5857 is known. In this device,
Tighten the screw with the torque T1 required for seating with an electric screwdriver, and when the head of the screw is seated, return the torque to approximately 0, and add a tightening torque T2 larger than the torque T1 again to tighten the screw. ing. Then, if the rotation angle of the screw head at the time of this additional tightening becomes smaller than the preset allowable angle, the additional tightening is finished, and if it is larger than the allowable angle, the rotation angle of the screw head is increased. The tightening is repeated until is smaller than the allowable angle. And by tightening less than a predetermined number of times,
If the rotation angle of the screw head is within the allowable value, consider it as a good product, and if the rotation angle of the screw head is not within the allowable value even after repeated retightening the specified number of times, this is a defective product. To judge. By tightening the screw by such a method, the loosening torque of the screw can be secured to a value equal to or more than a required value.

[0003]

However, in the above-mentioned conventional example, whether the workpiece tightened by screwing is good or defective, that is, whether the rotation angle of the screw head finally retightened is within the allowable value. It was not possible to determine how many times the retightening was performed or what value the rotation angle of the screw head became in the final retightening.

Therefore, there are the following problems. (1) Generally, if the accuracy of the screw and the machining accuracy of the pilot hole (or internal thread) of the screw are good, the retightening should be done only once, but after the retightening is performed several times, Since it is not known whether the rotation angle of is within the allowable value, such a defect cannot be found even when there is a problem in the accuracy of the screw or the machining accuracy of the prepared hole of the screw and the number of times of tightening is increased. (2) Also, the allowable rotation angle of the screw during retightening is empirically determined so that the required loosening torque can be obtained, and is input to the device in advance, but this rotation allowable angle is actually appropriate. It cannot be determined whether or not the value is For example, assume that the allowable rotation angle is set to 30 ° from empirical data. At this time, if the retightening rotation angle when the screw is screwed into the actual component is around 30 °, the retightening rotation angle will vary around 30 ° due to variations in the screw itself and the prepared hole. There are many cases where the angle exceeds 30 °, and the number of cases judged as defective products increases. However, when the tightening rotation angle is about 30 ° and an appropriate loosening torque can be obtained from the processing accuracy of the lot of screws, the dimensional accuracy of the prepared hole, the material of the parts, etc., the tightening rotation angle is, for example, It is conceivable that among the products judged to be defective at 31 °, those which are originally good products are included. In such a case, obviously, the initial setting value of the allowable rotation angle is inappropriate, and it is considered appropriate to reset the allowable rotation angle to about 40 °, for example. Conventionally,
Even in such a case, it was difficult to determine whether the allowable rotation angle needs to be corrected because the rotation angle of the screw during the final retightening was not known, and it was judged that the originally good product was a defective product. The product yield was poor. Further, even when it is found that the allowable rotation angle needs to be corrected, the built-in program needs to be rewritten to make the correction, which results in poor work efficiency.

In addition to the above-mentioned problems, in the past, there were the following problems because the torque was rapidly supplied at the rising and falling of the torque in the tightening process. (1) By increasing the number of times of additional tightening, metal fatigue of the bit increases and bit damage occurs. (2) The force that lifts the bit acts instantly, causing galling of the screw head. (3) When the twist of the bit when re-tightening is suddenly returned,
The energy generated by the twisting of the bit acts as a repulsive force and acts as a counteraction, causing problems such as loosening the screw in reverse.

Furthermore, in the conventional screw tightening device, when an error is displayed, an LED is arranged for each error item, and which error occurs by checking which item LED is lit. I was deciding what I did. Therefore, there is also a problem that the control unit becomes large in size in order to increase the number of display contents due to the planar arrangement of the LEDs.

Further, the conventional electric motor control circuit is constituted by an analog circuit as a motor current control circuit as shown in FIG.

However, in this conventional example, the circuit is complicated because it is composed of three boards, a digital board, an analog board, and a servo board. In addition, an analog circuit is not easy to electrically adjust, requires specialized skills, and requires a long adjustment time. And for these reasons, it was expensive.

Therefore, the present invention has been made in view of the above problems, and a first object thereof is to easily determine whether or not the setting data for the additional tightening is appropriate, and An object of the present invention is to provide a screw tightening device capable of easily correcting data.

A second object of the present invention is to provide a screw tightening device capable of easily finding an abnormality such as a poor accuracy of a screw or a defective prepared hole.

A third object of the present invention is to provide a screw tightening device which increases the number of error display items while preventing the control unit from increasing in size.

A fourth object of the present invention is to provide a screw tightening device which simplifies the structure of the control circuit of the motor and facilitates the adjustment, thereby reducing the cost of the device.

A fifth object of the present invention is to provide a screw tightening method capable of preventing the bit or the head of the screw from being damaged when performing the additional tightening and securely performing the additional tightening.

[0014]

In order to solve the above-mentioned problems and to achieve the object, a screw tightening device of the present invention tightens the screw with a torque T1 required for seating the screw by an electric screwdriver, and thereafter. And the screw is tightened with a tightening torque T2 larger than the torque T1, and the screw tightening device repeats the tightening operation until the rotation angle of the screw by this tightening falls within a predetermined allowable rotation angle. In the first display means for displaying the number of times of the retightening of the screw, and for displaying the rotation angle of the screw in the final retightening when the rotation angle of the screw is within the allowable rotation angle. An operator can externally set at least one of the second display means, the tightening torque T2 of the electric screwdriver, the allowable rotation angle, and the allowable number of times of the additional tightening. Setting means, based on the set data by said setting means is characterized by comprising control means for controlling the tightening operation of the screw.

Further, in the screw tightening device according to the present invention, the first display means and the second display means are one.
And a display for displaying the number of times of the additional tightening and a state for displaying the rotation angle of the screw in the final additional tightening. It is characterized by further comprising means.

In the screw tightening device according to the present invention, the control means continuously performs a tightening step of tightening the screw with the torque T1 and a tightening step of tightening the screw with the torque T2. It is characterized in that it is provided with an automatic mode to be performed by the above, and a manual mode in which the tightening step and the additional tightening step are independently performed by using an external switch as a trigger.

Further, in the screw tightening device according to the present invention, the control means interrupts the screw tightening operation when an abnormal situation such as a break of the motor or a break of the encoder is detected.

In the screw tightening device according to the present invention, when the control means detects the abnormal situation,
It is characterized by further comprising a third display means for displaying the type of the abnormal situation.

Further, in the screw tightening device according to the present invention, the third display means comprises a 7-segment LED.

Further, in the screw tightening method of the present invention, the armature current value of the electric screwdriver is increased from the no-load current value I1 to the current value I2 for generating the torque required for the seating of the screw, and the screw is screwed into the screw. After the head of the person is seated, the armature current value is decreased from the current value I2 to the no-load current value I3, and the armature current is again increased to the retightening current value I4 which is larger than the current value I2. In the screw tightening method for retightening, when increasing the armature current value from the no-load current value I3 to the retightening current value I4,
And when the retightening current value I4 is decreased to the no-load current value I3, y = ax + b (a and b are constants) at the beginning of rising and falling of the armature current value.
When the armature current value is changed linearly as shown by the linear equation, and 70% of the difference between the current value I3 and the current value I4 is reached, y = cx ² + d (c and d are constants), It is characterized in that the armature current value is changed in a curved shape represented by the following equation.

[0021]

As described above, since the screw tightening device according to the present invention is configured, the number of times of the additional tightening of the screw is actually displayed by displaying the number of times of the additional tightening of the screw by the first display means. You can determine what was done. Thus, the operator can immediately determine the accuracy of the screw or the component or the like when there are many parts that have not been refastened once, and the problem can be found early. .

Further, by displaying the rotation angle of the screw in the final retightening by the second display means, the proper value of the rotation angle of the retightening can be determined according to the actual accuracy of the screw and parts, materials and the like. be able to. Therefore, based on the information of the first display means and the information of the second display means, the operator determines the additional tightening torque of the electric driver, the allowable rotation angle at the time of additional tightening, the allowable number of times of additional tightening, and the like. The proper value of can be known. Then, based on this, by setting the appropriate value from the outside by the setting means,
The optimum parameters for additional tightening can be set easily without rewriting the internal program.

Further, by sharing the first display means and the second display means by one display means, the control device can be downsized as compared with the case where a large number of display means are provided. In addition, by providing an automatic mode in which the operation from screw tightening to additional tightening is performed continuously and a manual mode in which screw tightening and additional tightening are performed independently, the torque and allowance for initial tightening of the device can be increased. At the time of setting parameters such as rotation angle and allowable number of times, retightening is experimentally performed in the manual mode, and if screw tightening is continuously performed after the parameters are set, select the automatic mode to continuously Since the screws can be tightened, continuous tightening operation and parameter setting for the additional tightening can be smoothly performed.

Also, the error display is a 7-segment LE.
By displaying a number by D, it is possible to display many kinds of error displays on one display device, so that the control device can be downsized.

Further, by using the CPU as the control means, the motor current, the motor rotation number, and the motor rotation angle can all be controlled by software, and the control circuit can be simplified so that one board is provided. A significant cost reduction can be realized by reducing the electrical adjustment of the analog circuit.

Further, since the screw tightening method of the present invention is configured as described above, the torque can be smoothly changed at the end of the rising portion and the falling portion of the torque during the additional tightening. It is possible to prevent damage to the bit and the head of the screw, and to prevent the screw from loosening due to the twisting reaction force of the bit.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present screw tightener.
Is a torque control box, 2 is a motor power indicator, 3 is an automatic / manual changeover switch, 4 is a screw tightening start switch, 5 is a tightening process start switch, 6 is an additional tightening process start switch, 7 is a reset switch, and 8 is stop. A switch, 9 is a digital rotary switch for setting tightening torque, 10 is a digital rotary switch for setting additional tightening torque, 11 is a digital rotary switch for setting allowable additional tightening angle, 12 is a DIP switch for setting maximum number of additional tightening, and 13 and 14 are LED for OK / NG display,
Reference numeral 15 is a 2-digit 7-segment LED, 16 is a screw tightening motor, 17 is a screw tightening bit to be controlled, and 18 is a screw tightening upper and lower cylinder.

In the above structure, the tightening and retightening conditions for screw tightening are set in advance by the digital rotary switches 9, 10, 11 and the DIP switch 12, and the screw tightening start switch 4 is used to start the operation. After the screw is tightened with the set tightening torque, the additional tightening is performed within the set number of times by the arbitrarily set additional tightening torque and the allowable additional tightening angle. The tightening torque is 1.
The tightening torque is set to a value of about 4 times, and the tightening torque is set to a value of about 1.5 times the tightening torque. The allowable number of times of additional tightening is set to, for example, about three times. Further, the allowable rotation angle of the screw during the additional tightening is initially set to a value that is empirically considered to be appropriate. However, it goes without saying that these values are not limited to this and may be changed as necessary.

FIG. 2 shows an embodiment for performing torque control. 20 is a CPU, 21 is a ROM, 22 is an I / O port for inputting external inputs and various switches, and 23.
Is I / for outputting digital data for motor control
O port, 24 is a D / A converter for converting digital data into voltage, 25 is a motor drive amplifier, 26 is a motor current feedback circuit, 16 is a DC motor for screw tightening, 27
Is a rotary encoder directly connected to the motor shaft,
Reference numeral 28 is an input / output port with an external device.

In the above structure, the tightening torque, the additional tightening torque, and the additional tightening allowable angle are set in advance by the digital rotary switches 9, 10 and 11, and when the start switch 4 is pressed, the program is set based on these setting data. The series of screw tightening sequences described above are executed, and the OK / NG judgments of 13 and 14 are output.
Further, the tightening start switch 5 and the additional tightening start switch 6 execute only the tightening step and the additional tightening step, respectively.

Reference numeral 3 is an automatic / manual changeover switch. In the case of manual operation, the above-mentioned switches 4, 5 and 6 are made effective, and in the case of automatic, a command corresponding to the switches 4, 5 and 6 by 28 external I / Os is issued. Validate.

The operation of the circuit is such that command data is output from the CPU 20 and the D / A conversion 2 is performed via the I / O port 23.
4, the motor drive amplifier 25 is operated to control the motor 16, and the encoder 27 directly connected to the motor controls the angle. The CPU 20 controls the operation of the motor while feeding back the current value by the motor current feedback circuit 26 and constantly comparing it with the tightening data or the additional tightening data.

FIG. 3 shows a first circuit example of the display, which is an IC
30 is a CPU which is the center of screw tightening control, and IC31 is I
/ O port, IC32 is an inverter, IC33 is a driver for 7-segment LED, and LED display 34 is a 7-segment LED for displaying data.

In the above configuration, the CPU 30 outputs data such as the number of additional tightening, the final additional tightening angle, the error number, etc. to the I / O port 31 in performing screw tightening control, and the IC 3
The logic is inverted via 2, and IC33 has a 7-segment LE.
The D34 is controlled to display the above various data.

FIG. 4 is a main flowchart of software for controlling the screw tightening device of this embodiment, FIGS. 5 to 8 show a subroutine, and FIGS. 9 to 11 show interrupt processing.

In the above software configuration, FIG. 4 is a main flow chart which is capable of automatically starting up when the power is turned on and executing each operation divided by the subroutine by each switch input described above.

FIG. 5 is a flowchart for performing GO / NG determination by executing a series of screw tightening steps in the automatic mode, that is, the tightening step and then the additional tightening step.

FIG. 6 is a detailed flowchart of the tightening process, and FIG. 7 is a detailed flowchart of the tightening process.

FIG. 8 shows the calculation of parameters used in the additional tightening step, and the calculation of each parameter from the additional tightening conditions.

FIG. 9 shows interrupt processing for detecting disconnection of the encoder signal cable or the electric power line of the motor.
At the time of starting the tightening process, a minimum command is output to the motor. If a normal encoder output is input, it is determined as OK, and if it is not input, it is determined that the motor cable or the encoder cable is broken.

FIG. 10 is a flow chart of interrupt processing as disconnection detection of the encoder when the A phase or B phase of the encoder is lost.

FIG. 11 is a flowchart of interrupt processing by the operation of the eddy current detection circuit or the emergency stop.

Next, FIGS. 12 to 15 show an embodiment of a method for supplying power to the screw tightening motor at the time of retightening. (1) is a linear curve (straight line) up to 70% of rising. ), (2) represents an approximate quadratic curve up to the rising point, (3) represents a linear curve (straight line) up to 70% of the falling point, and (4) represents a quadratic curve up to the falling point. It represents a curve.

(1) is a method of adding torque at the time of rising, which is a current of a value calculated by the linear expression of y = ax + b until 70% of the difference between the no-load current I3 and the tightening current I4 is reached. To the motor.

In (2), y = cx when 70% is exceeded.
A current having a value calculated by the quadratic equation of ² + d is applied to the motor.

(3) is a method of reducing the torque at the time of falling, and shows a decrease in the current value due to the value calculated by the linear expression of y = ax + b until it reaches 70%.

In (4), when 70% is exceeded, y = c
It shows a decrease in the current value due to the value calculated by the quadratic expression of x ² + d.

At the time of the additional tightening, as shown in FIG. 15, the operations (1) to (4) are repeated until the rotation angle of the screw by the additional tightening falls within the allowable rotation angle.

The peculiar effect of the above configuration is that bit breakage, screw head scoring, etc. are prevented and torque can be reliably transmitted.

As described above, since the screw tightening device of this embodiment is constructed, the 2-digit 7-segment LED
By displaying the number of times of the retightening of the screw in real time, it is possible to judge how many times the retightening is actually performed. Thus, the operator can immediately determine the accuracy of the screw or the component or the like when there are many parts that have not been refastened once, and the problem can be found early. .

Further, by displaying the rotation angle of the screw in the final retightening by the same 7-segment LED as above, the proper value of the rotation angle of the retightening can be determined by the accuracy of the screw and parts, the material, etc. can do. Therefore, based on the information on the number of times of additional tightening and the information on the final additional tightening angle, the operator determines an appropriate value such as the additional tightening torque of the electric screwdriver, the allowable rotation angle at the time of additional tightening, and the allowable number of times of additional tightening. You can know. And
Based on this, digital rotary switches 9, 10, 11
Thus, by setting the above appropriate value from the outside, the optimum parameter for the additional tightening can be easily set without rewriting the internal program or the like.

Further, by providing an automatic mode for continuously performing the operation from tightening the screw to the additional tightening and a manual mode for independently performing the tightening and the additional tightening of the screw,
Torque for tightening at the beginning of equipment operation, allowable rotation angle,
At the time of setting parameters such as the allowable number of times, experimentally perform additional retightening in the manual mode.When continuously tightening the screws after setting the parameters, select the automatic mode to continuously tighten the screws. Since tightening can be performed, continuous tightening operation and parameter setting for additional tightening can be smoothly performed.

In addition, the error display is a 7-segment LE.
By displaying a number by D, it is possible to display many kinds of error displays on one display device, so that the control device can be downsized.

Further, at the end of the rising portion and the falling portion of the torque at the time of retightening, the torque is allowed to change smoothly to prevent damage to the bit or the head of the screw, and to prevent the torsion reaction force of the bit. It is also possible to prevent the screws from loosening.

Further, the structure of the digital board, the analog board, and the servo board may be one torque control board to simplify the board. Also, since the electrical adjustment of the analog circuit was mostly replaced by software, the adjustment time was reduced by about 95%. With these, a total cost reduction of about 50% can be realized. In addition, since the torque control is made softer, adjustment deviation due to drift of the analog circuit is eliminated, and high quality can be maintained.

The present invention can be applied to modifications and variations of the above embodiments without departing from the spirit of the present invention.

For example, in the above embodiment, the case where the method of gradually changing the current at the time of the rise and the fall of the torque is applied to the tightening of the screw has been described, but the present invention is not limited to this. It can be applied to other fields such as how to apply a pin driving torque in a pin driving machine.

Further, what gives the curve of the retightening current is not limited to a quadratic equation such as y = ax ² + b, but any function that can gently reach without reaching the target value without causing overshoot. Other functions are also acceptable.

[0060]

As described above, according to the screw tightening device and the screw tightening method of the present invention, the first display means
By displaying the number of times of the retightening of the screw in real time, it is possible to judge how many times the retightening is actually performed. Thus, the operator can immediately determine the accuracy of the screw or the component or the like when there are many parts that have not been refastened once, and the problem can be found early. .

Further, by displaying the rotation angle of the screw in the final retightening by the second display means, the proper value of the rotation angle of the retightening can be determined according to the actual accuracy of the screw and parts, materials and the like. be able to. Therefore, based on the information of the first display means and the information of the second display means, the operator determines the additional tightening torque of the electric driver, the allowable rotation angle at the time of additional tightening, the allowable number of times of additional tightening, and the like. The proper value of can be known. Then, based on this, by setting the appropriate value from the outside by the setting means,
The optimum parameters for additional tightening can be set easily without rewriting the internal program.

Further, by sharing the first display means and the second display means by one display means, the control device can be downsized as compared with the case where a large number of display means are provided.

By providing an automatic mode for continuously performing the operation from tightening the screw to the additional tightening and a manual mode for independently performing the tightening and the additional tightening of the screw,
Torque for tightening at the beginning of equipment operation, allowable rotation angle,
At the time of setting parameters such as the allowable number of times, experimentally perform additional retightening in the manual mode.When continuously tightening the screws after setting the parameters, select the automatic mode to continuously tighten the screws. Since tightening can be performed, continuous tightening operation and parameter setting for additional tightening can be smoothly performed.

Also, the error display is a 7-segment LE.
By displaying a number by D, it is possible to display many kinds of error displays on one display device, so that the control device can be downsized.

Further, by using the CPU as the control means, the motor current, the motor rotation speed, and the motor rotation angle can all be controlled by software, and the control circuit can be simplified so that one board is provided. A significant cost reduction can be realized by reducing the electrical adjustment of the analog circuit.

Further, at the end of the rising portion and the falling portion of the torque during the retightening, the torque is made to vary smoothly to prevent damage to the bit and the head of the screw, and to prevent the torsion reaction force of the bit. It is also possible to prevent the screws from loosening.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a screw tightening device according to the present invention.

FIG. 2 is a diagram showing an example of a circuit for performing torque control.

FIG. 3 is a diagram showing a first circuit example of a display device.

FIG. 4 is a main flowchart of software for controlling the screw tightening device according to the present exemplary embodiment.

FIG. 5 is a flowchart of a subroutine of software for controlling the screw tightening device according to the present exemplary embodiment.

FIG. 6 is a flowchart of a subroutine of software for controlling the screw tightening device according to the present exemplary embodiment.

FIG. 7 is a flowchart of a subroutine of software for controlling the screw tightening device according to the present exemplary embodiment.

FIG. 8 is a flowchart of a subroutine of software for controlling the screw tightening device according to the present exemplary embodiment.

FIG. 9 is a flowchart showing an interrupt process in the screw tightening device of the present embodiment.

FIG. 10 is a flowchart showing interrupt processing in the screw tightening device of the present embodiment.

FIG. 11 is a flowchart showing interrupt processing in the screw tightening device of the present embodiment.

FIG. 12 is a diagram showing a method of supplying power to a screw tightening motor during additional tightening.

FIG. 13 is a diagram showing a method of supplying power to the screw tightening motor during additional tightening.

FIG. 14 is a diagram showing a method of supplying power to the screw tightening motor during additional tightening.

FIG. 15 is a diagram showing a method of supplying power to the screw tightening motor during additional tightening.

FIG. 16 is a diagram showing a conventional motor current control circuit.

[Explanation of symbols]

1 Torque control box 2 Motor power indicator 3 Changeover switch 4 Screw tightening start switch 5 Tightening process start switch 6 Retightening process start switch 7 Reset switch 8 Stop switch 9 Tightening torque setting digital rotary switch 10 Additional tightening torque setting digital rotary Switch 11 Digital rotary switch for setting the additional tightening allowable angle 12 Dip switch for setting the maximum number of additional tightening 13, 14 OK / NG display LED 15 2 digit 7 segment LED 16 Screw tightening motor 17 Screw tightening bit 18 Upper and lower cylinders for screw tightening

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[Procedure amendment]

[Submission date] April 27, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

FIG. 11 is a flowchart of interrupt processing by the operation of the overcurrent detection circuit or the emergency stop.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Satoshi Satoshi Shimomaruko 3-30-2 Ota-ku, Tokyo Canon Inc. (72) Inventor Tadahiro Nishikubo 3-30-2 Shimomaruko Ota-ku, Tokyo Canon Incorporated (72) Inventor Koji Kusuda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (7)

[Claims] 1. An electric screwdriver tightens the screw with a torque T1 required for seating the screw, and then a retightening torque T2 larger than the torque T1 is used to retighten the screw. In a screw tightening device that repeatedly performs the retightening operation until the rotation angle falls within a predetermined allowable rotation angle, a first display unit that displays the number of times of the retightening of the screw, and a rotation angle of the screw are Second display means for displaying the rotation angle of the screw in the final tightening when the screw is within the allowable rotation angle, the tightening torque T2 of the electric screwdriver, the allowable rotation angle, and the tightening allowance. The tightening operation of the screw based on the setting means by which the operator can set at least one of the number of times from the outside and the data set by the setting means. Screwing apparatus characterized by comprising a control means for controlling. 2. The first display means and the second display means are configured by sharing one display means, and a state in which the display means displays the number of times of the additional tightening. The screw tightening device according to claim 1, further comprising switching means for switching between a state in which the rotation angle of the screw is displayed in the final tightening. 3. The automatic mode in which the control means successively performs a tightening step of tightening the screw with the torque T1 and a tightening step of tightening the screw with the torque T2, and the tightening step. The screw tightening device according to claim 1, further comprising a manual mode in which the additional tightening process is independently performed by using an external switch as a trigger. 4. The screw tightening device according to claim 1, wherein the control means interrupts the screw tightening operation when an abnormal situation such as a motor wire break or an encoder wire break is detected. 5. The screw tightening device according to claim 4, wherein the control means further comprises third display means for displaying the type of the abnormal situation when the abnormal situation is detected. 6. The screw tightening device according to claim 5, wherein the third display means comprises a 7-segment LED. 7. The electric current value of an electric screwdriver is increased from a no-load current value I1 to a current value I2 for generating a torque required for seating a screw, the screw is screwed in, and after the head of the screw is seated, the screw head is seated. In the screw tightening method, the armature current value is decreased from the current value I2 to the no-load current value I3, and the armature current is again increased to the retightening current value I4 larger than the current value I2 to retighten the screw. When the armature current value is increased from the no-load current value I3 to the retightening current value I4 and when the retightening current value I4 is decreased to the no-load current value I3, the rise and rise of the armature current value is performed. At the beginning of the fall, y =
The electric current value is linearly changed by a linear expression of ax + b (a and b are constants), and the electric current value I3 and the electric current value I4 are changed.
When the difference reaches 70%, y = cx ² + d (c, d
Is a constant) and the armature current value is changed in a curved line represented by a quadratic equation.