JPS6039515B2 - Screw tightening torque control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a screw tightening torque control device for screwing a tatu pin screw into a prepared hole of an object to be fastened such as a thin plate and controlling the tightening torque.

Conventionally, when screwing a tatsu pin screw into a prepared hole in a fastened object, especially a thin plate, using an electric driver having a driver bit that receives rotation from a DC motor, the head bearing surface of the tatsu pin screw is covered after the female thread is cut into the prepared hole. A constant voltage is applied to the DC motor until the vertical torque of the tuft pin screw reaches a predetermined vertical torque when it comes into contact with the surface of the fastener.

Therefore, even if the voltage supply to the DC motor is stopped at the moment when the tapping torque of the tapping screw reaches the set vertical torque, the inertia of the DC motor is large, and even after the voltage supply is stopped, the tapping screw continues to rotate. The drawback is that the tightening torque reaches a set value or more. As a device for eliminating this drawback, there is a device described in Tokusekki Publication No. 53-9960. This device is configured to switch the voltage supplied to the DC motor just before the end of bolt fastening, lower the rotation speed of the DC motor, and reduce the influence of inertia of the DC motor when bolt fastening is finished. . With this device,
In order to detect immediately before the end of engagement, the present invention is configured to detect a value in which the value of the load current flowing through the DC motor approaches a desired set value. Therefore, when starting the DC motor that rotates the driver bit, if a starting current larger than the DC motor external setting value is generated, this starting current will erroneously detect just before the end of fastening, and the current will not be supplied to the DC motor. This causes disadvantages such as the voltage being switched, making it impossible to perform proper tightening work, and the DC motor rotating at a low speed from this point on, resulting in an extremely long cycle time.
In addition, with this device, when a self-tapping screw is inserted into a thin plate so that its leg passes through it, an initial torque is generated when forming a female thread in the thin plate using the leg, and a torque corresponding to this initial torque is generated. Since an initial current larger than the set value occurs at the initial current stage, when this initial current approaches the set value even though the seat surface of the tapping screw is not in contact with the thin plate, it is mistakenly detected that the fastening is about to end. At this point, the supply voltage of the DC motor is switched, and even in the case of this type of fastening, it is not possible to perform proper vertical mounting, and the DC motor rotates at low speed from the middle of forming the female thread. However, there are drawbacks such as extremely long cycle times.
The present invention aims to eliminate the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings. In FIGS. 1 and 2, 1 gives rotation to a driver bit (not shown);
This is a DC motor with a tapping screw held at the tip of a chuck (not shown) installed vertically.A constant voltage circuit 2 is connected to the DC motor 1 to control the number of rotations, and a DC voltage is applied to the armature winding of the DC motor 1. Motor drive power is being supplied. The constant voltage circuit 2 consists of two Darlington-connected NPN transistors Tr, Tr2, two Zener diodes ZD, ZD2, and a resistor R, and two Zener diodes ZD, ZD2. It is configured to be able to supply a voltage determined by the Zener voltage. A detection resistor R2 is connected in series to the armature winding as a current detection unit 3, and the current increases as the driver bit is prevented from rotating when the screw wire is attached. It is configured to detect the load current flowing through the armature winding to detect the tightening torque of the tapping screw. A noise filter 4 is connected to the current detection section 3,
Brush of DC motor 1 (not shown).

) is removed. This noise filter 4 uses an active filter including an operational amplifier bp. This noise filter 4 is connected to the positive terminal of the comparison circuit 5, and the negative terminal is connected to the resistor R3.
, R4, a variable resistor R5, and a capacitor C, a first setting circuit 6 is connected thereto. This first setting circuit 6 is configured such that its voltage value can be arbitrarily set in accordance with a desired vertical torque, and together with the comparison circuit 5, a digital signal is generated at the moment when the actual vertical torque reaches the set torque. It constitutes a judgment circuit that sends out a signal. The judgment circuit includes a resistor R6.
, R7, R8 diodes D, and a waveform shaping circuit 7 consisting of an NPN transistor Tr3.

The waveform shaping circuit 7 is connected to one input of the first NAND circuit 8 via an inverter lnv, and when the gate of the first NAND circuit 8 is connected, the output of the waveform shaping circuit 7 is applied to the switch circuit 9, It is configured to turn off the voltage circuit 2. The switch circuit 9 includes an off circuit OR, inverters lnv2, lnv3, FF circuit FF, and NP.
It is composed of an N-type transistor Tr4, and is configured so that, regardless of the output of the first NAND circuit 8, if the rotation of the driver bit stops for some reason, the constant voltage circuit 2 will be turned off. , the constant voltage circuit 2 is also configured to be turned on by the operation switch 10. Said first
The gate of the NAND circuit 8 is opened and closed in response to a female thread cutting completion signal, which will be described later. Next, the main parts of the present invention will be explained.

The output of the current detection section 3 is configured to be applied to a peak voltage holding circuit 11 via a noise filter 4. Moreover, this peak voltage holding circuit 11 includes resistors R3, R,
o It is composed of capacitors C2, C3, diodes D2, and operational amplifier bp2, comparator CMP, resistors, . It is connected to a timer circuit 13 via a voltage drop detection circuit 12 consisting of A peak detection circuit is configured by the circuit and the voltage drop detection circuit. The timer circuit 13 is composed of a resistor, R, 3, R, 4 diodes D3, D4 capacitors, a Zener diode ZD3, and the detected value of the current detecting section 3 is the first one.
The timer circuit 13 is reset until the voltage falls below the set value, and if the peak voltage does not reach the voltage set by the second setting circuit 14, no signal is sent from the second comparison circuit 20, and the timer circuit 13 does not operate. It is configured as follows. Further, the peak voltage is configured to be reset when the tightening torque reaches the set tightening torque. The timer circuit 13 is connected to an inverter lnv4 via a waveform shaping circuit 15, and is further connected to one input of a second NAND circuit 16.

The gate of this second NAND circuit 16 is the initial reset circuit 1
7, it will be opened after a predetermined period of time has passed after the start of screw tightening.
The output signal of the timer circuit 13 is detected by the internal thread cutting completion detection circuit 1.
It is configured to send to 8. This internal thread cutting completion detection circuit 18 is comprised of an FF circuit FF2, the Q output of which is connected to the eagle pressure switching circuit 19 via an inverter lnv5. This voltage switching circuit 19 is composed of an NPN type transistor Tr5, whose emitter terminal is connected to a Zener diode ZD, , Z disposed in series with the constant voltage circuit 2.
The constant voltage circuit 2 is connected to the intermediate point of the constant voltage circuit 2, and is configured such that when a "1" level signal is applied to the pressure switching circuit 19, the output voltage of the constant voltage circuit 2 is switched. On the other hand, the Q of the FF circuit FF2 is
The output is connected to the other input of the first NAND circuit 8,
The signal from the determination circuit is configured to be passed through or blocked. In the above screw tightening torque control device,
A signal is applied to the switch circuit 9 by the operation switch 10,
When the FF circuit FF is reset, a predetermined voltage is generated in the constant voltage circuit 2 and applied to the DC motor 1.

At this time, a starting current flows through the armature winding, but the initial reset circuit 17 prevents the peak voltage holding circuit 11 from working for a predetermined period of time. Therefore, the timer circuit 13 also does not operate, and no signal is sent to the female thread cutting completion detection circuit 18. Therefore, in the FF circuit FF2 of the female thread cutting completion detection circuit 18, Q, Q
No change occurs in the output, the voltage of the constant voltage circuit 2 is maintained,
The gate of the first NAND circuit 8 is also closed, and the ON signal is continuously sent from the switch circuit 9 to the constant voltage circuit 2. Next, when the driver bit connects to the head of the tapping screw held at the tip of the chuck and starts screwing the tapping screw into the thin plate so that its leg passes through, the initial torque is the first when cutting an internal thread into the pilot hole. exceeding the setting value of setting circuit 6,
A signal is emitted from the comparison circuit 5.

However, since the voltage drop detection circuit 12 does not operate at the gate of the first NAND circuit 8 and no signal is emitted from the internal thread cutting completion detection circuit 18, the signal from the comparison circuit 5 does not pass through the first NAND circuit 8. Therefore, no voltage is applied to the switch circuit 9. Therefore, the DC motor 1 continues to rotate at the same speed. When the female thread is cut into the prepared hole of the thin plate, the pin screw 1 is screwed in with a low screwing torque, so that the detection voltage of the current detection unit 3 decreases.

At this time, the detected voltage becomes lower than the peak voltage held by the peak voltage holding circuit 11, and a signal is transmitted from the voltage drop detection circuit 12 and applied to the timer circuit 13. When the detected voltage becomes equal to or less than the first setting value of the first setting circuit 6, the timer circuit 13 is activated, and after a predetermined period of time has elapsed, the timer circuit 13 is activated.
emits a signal and sends the signal to the internal thread cutting completion detection circuit 18 through the waveform shaping circuit 15. Therefore, the FF circuit FF2 of the female thread cutting completion detection circuit 18 is set, its output signals are both inverted, and the Q output operates the tortoise pressure switching circuit 19, reducing the output voltage of the constant voltage circuit 2 to a predetermined value, and Lower the rotation speed of motor 1. Further, the FF circuit FF
The Q output of 2 is applied to the first NAND circuit 8 and its gate is connected. Thereafter, the DC motor 1 rotates at a low speed to screw in the tapping screw. When the seat surface of the tapping screw comes into contact with the thin plate and the vertical screw attachment is completed, the detected voltage of the current detecting section 3 becomes equal to the reference value of the comparator circuit 5. Therefore, a signal is transmitted from the comparison circuit 5 and applied to the first NAND circuit 8. At this time, since the gate of the first NAND circuit 8 is open, this signal passes through the first NAND circuit 8 and is applied to the switch circuit 9. Therefore, an off signal is applied from the switch circuit 9 to the constant voltage circuit 2, the output voltage of the constant voltage circuit 2 becomes zero, and the DC motor 1 is stopped. At this time, since the rotation of DC motor 1 is low, the rotational inertia of DC motor 1 is 4
- If the voltage supply stops, the rotation of the DC motor 1 will stop almost instantaneously. As explained above, the present invention connects a DC motor to a driver bit that screws a Tatsupin screw into a prepared hole in a thin plate so that its leg passes through, and after a predetermined period of time has elapsed since the start of vertical screwing, the load current Once the voltage has reached a peak, it is detected that the tapping screw has completed forming a female thread on the thin plate, and after a predetermined period of time has elapsed from this point, the voltage supplied to the DC motor is switched. Not only does the supply voltage to the DC motor not change depending on the starting current when the power is turned on, but when a tapping pin screw is fastened to a thin plate so that its leg passes through, the seating surface of the tapping screw may become a thin plate. Even if the setting value is low and the initial current generated when the self-tapping screw forms a female thread on a thin plate exceeds the setting value, the supply voltage to the DC motor will be switched during the process of forming the female thread. Since the supply voltage to the DC motor can be switched after the female thread has been reliably formed, it is extremely economical, the cycle time is shortened to the minimum, and the torque is eliminated from the influence of the inertia of the DC motor. It has the advantage of being able to be controlled.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the present invention, FIG. 2 is an electric circuit diagram of the present invention, and FIG. 3 is a time chart at each point in FIG. 1... DC motor, 2... Constant voltage circuit, 3... Current detection unit, 4... Noise filter, 5... Comparison circuit, 6... First setting circuit, 7... Waveform shaping circuit, 8... First NAND circuit, 9...
...Switch circuit, 10... Operation switch, 11
...Peak voltage holding circuit, 12...Voltage drop detection circuit, 13...Timer circuit, 14--...
Second setting circuit, 15... Waveform shaping circuit, 16...
... Second NAND circuit, 17 ... Initial reset, 18 ... Female thread cutting completion detection circuit, 19 ... Tortoise pressure switching circuit, 20 ... Second comparison circuit. Figure 3 Figure 1 Figure 2

Claims (1)

[Claims] 1 Connect a DC motor to a driver bit that screws a pin screw into a prepared hole in a thin plate so that its leg passes through it, and connect a constant voltage circuit that supplies a constant high or low voltage to the DC motor. , a comparison circuit is provided that supplies a high voltage to the DC motor, detects the load current flowing through it, and compares the detected value with a preset value corresponding to the desired screw tightening torque, so that the load current is A screw tightening torque control device configured to switch the output of the constant voltage circuit to a low voltage until the set value is reached, reduce the rotation of the DC motor, and stop the DC motor when the load current reaches the set value. An initial reset circuit is provided which outputs a signal when a predetermined time elapses after the start of screw tightening, and a peak detection circuit is provided which outputs a signal when the afterload current reaches a peak upon receiving the output of the initial reset circuit, A screw tightening torque control device further comprising a voltage switching circuit that receives a signal from the peak detection circuit and switches the output of the constant voltage circuit from a high voltage to a low voltage.