JPS6036909B2 - Screw tightening torque control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vertical screw torque control device for screwing a tatupin screw into a pilot hole of a fastened object made of a soft metal plate such as a thin iron plate, and controlling the vertical torque of the screw.

Conventionally, when tightening a screw with a predetermined vertical torque, the load current of the DC motor that rotates the driver bit is detected, and the load current of the DC motor that rotates the driver bit is detected. There is a method of controlling the screw tightening torque by stopping the DC motor. With this method, when starting the DC motor that rotates the driver bit, if a starting current larger than the set value is generated in the DC motor, the starting current will stop the DC motor and the screw pin will screw into the thin plate. However, the screw tightening is completed before the screw is fully tightened, resulting in defects such as poor thread attachment. As a method for eliminating this drawback, there is an apparatus described in Samuraiko Akihiro-15360.

This device uses a comparison circuit to compare the load current and the set value in order to prevent the DC motor from stopping due to the starting current and to stop the DC motor immediately when the load current reaches the set value. Once the load current reaches the set value, the gate circuit opens for the first time after a predetermined period of time has elapsed, and when the load current reaches the set value again, the output of the comparison circuit passes through the gate circuit and stops the DC motor. has been done. According to this device, if the set value is smaller than the load current, it is possible to prevent the DC motor from stopping due to the starting current when the power is turned off, and also to stop the DC motor immediately when the load current reaches the desired set value. Tightening torque can be accurately controlled to the set value. However, if the set value is larger than the starting current, the gate circuit will not open depending on the starting current, and the DC motor will be stopped after the load current reaches the set value and a predetermined period of time has elapsed. , the driver bit continues to rotate even after the set value is reached, and the torque is higher than the set value, causing the screw to be tightened, resulting in drawbacks such as the inability to perform accurate torque control. In addition, with this device, when a self-tapping screw is inserted so that its leg passes through a thin plate, it is necessary to form a female thread in the thin plate with its leg before the seat surface of the self-tapping screw contacts the thin plate. Initial torque is generated, and at the initial current stage corresponding to this initial torque, an initial current larger than the set value continues to be generated for an extremely long time, and this initial current causes the DC motor to stop, causing this type of fastening. In this case, there is a drawback that torque control cannot be performed. In order to eliminate this drawback, we recently installed an initial reset circuit that outputs a signal after a predetermined period of time has passed since the start of screw tightening, and also outputs a signal when the initial torque generated when the leg of a self-tapping screw forms a female thread in a thin plate reaches its peak. A method has been devised to control the vertical torque by providing a peak detection circuit that outputs a peak detection circuit, and stopping the DC motor when the load current matches the set value only after receiving signals from the initial reset circuit and the peak detection circuit. has been done.

This device controls the tightening torque by transmitting a female thread forming completion detection signal the moment the initial torque reaches its peak and drops to the set value. If the load current flowing outside the DC motor increases even slightly, such as when a screw is wedged between a screw and a female thread, it may match the above-mentioned setting value, and the DC motor may not start even after the female thread has been formed. However, there are disadvantages in that the tightening of the screws is stopped and screw tightening is subsequently stopped, leading to defects such as screw lifting. 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, reference numeral 1 denotes a DC motor that rotates a driver bit (not shown) and tightens a tuft pin screw held at the tip of a chuck (not shown). A constant voltage circuit is connected to the DC motor 1 to control the rotation speed, and power for driving the DC motor is supplied to the armature winding of the DC motor 1. The constant voltage circuit 2 includes two Darlington-connected NPN transistors Tr, , T.
r2, two Zener diodes ZD, ZD2, and a resistor R, and a lightning pressure control circuit 3 is connected to this constant voltage circuit 2. The lightning pressure switching circuit 3 is an NPN transistor Tr that is activated by a female thread forming completion detection signal, which will be described later.
3, and is configured to switch the output voltage of the constant voltage circuit 2 into two stages. A detection resistor R2 is connected in series to the armature winding as a current detection unit 4, and detects the load current of the DC motor 1, which increases due to the rotation of the driver bit being blocked when tightening a tapping screw, and performs tapping. It is configured to detect the under-tightening torque of the screw. A noise filter 5 is connected to the current detection section 4, and a brush (not shown) of the DC motor 1 is connected to the noise filter 5.

) is excluded. This noise filter 5 uses an active filter including an operational amplifier bp. This noise filter 5 is connected to a positive terminal of a comparator circuit 6, and a first setting circuit 7 is connected to its negative terminal. The first setting circuit 7 is a resistor R3, R
Consisting of a variable resistor 4 or 5 and a capacitor C, the voltage value thereof is configured to be arbitrarily set in accordance with the desired tightening torque, and together with the comparison circuit 6, the actual tightening torque reaches the set torque. A determination circuit is configured that transmits a digital signal at the moment when the The comparison circuit 6 includes a resistor R
6, R7, R8, a diode D, and an NPN transistor Tr4.

The waveform shaping circuit 8 is connected to one input of the first NAND circuit 9 via an inverter lnV, and when the gate of the first NAND circuit 9 is open, the output of the waveform shaping circuit 8 is applied to the switch circuit 10', and the above-mentioned It is configured to turn off the voltage circuit 2. The switch circuit 10 is an OR circuit
,, inverter lnV2, flip-flop circuit FF,
(hereinafter referred to as an FF circuit) and an NPN transistor T, and regardless of the output of the first NAND circuit 9, a driver bit rotation stop command signal is sent from a screw tightening defect detection circuit (not shown). If received, the constant voltage circuit 2 is turned off, and the constant voltage circuit 2 is turned on by the operation switch 11. Further, the gate of the first NAND circuit 9 is opened and closed in response to a female thread forming completion detection signal, which will be described later. Further, a starting reset circuit 12 is connected to the switch circuit 1 to distinguish between the starting current generated at the moment when the constant voltage circuit 2 is turned on and the load current of the DC motor 1 at the time when the initial torque is generated. .

This startup reset circuit 12 is an inverter lnV3 resistor R
7, R, o, R, . The FF circuit F in the switch circuit 10 includes capacitors C2 and C3 and a comparator MP.
After receiving the signal from the "Q" output of F, no signal is transmitted from the comparator CMP for a predetermined period of time, so that a female thread forming completion detection signal, which will be described later, is not transmitted. Next, the main parts of the present invention will be explained.

The current detection section 4 is connected to a peak voltage holding circuit 13 via a noise filter 5. The peak voltage holding circuit 13 consists of a capacitor C4, a resistor R,2, and an NPN transistor Tr6, and a comparator CM circle 2 and a resistor R,3.
The timer circuit 1 is connected via the voltage drop detection circuit 14 configured with
5. The voltage drop detection circuit 14 is configured to transmit an activation signal to the timer circuit 15 when the detected voltage of the current detection unit 4 becomes lower than the peak voltage of the peak voltage holding circuit 13, and is configured to transmit an activation signal to the timer circuit 15, and A peak detection circuit is constituted by the drop detection circuit. The timer circuit 15 includes resistors R, 4, R, 5, R,
6, R, 7, diodes D2, D3, cosodenser C5,
Zener diode m3 and NPN transistor Tr
7, and is configured to be reset until the detected voltage of the current detection section 4 once drops to the first setting value of the first setting circuit 7. Further, this timer circuit 15 is configured to be reset until the detected voltage reaches a second set value of the second setting circuit 16, and if the detected voltage does not rise to a predetermined value, the timer circuit 15 is not activated. Therefore, the internal thread forming completion detection signal is configured not to be transmitted. This second set value has a value lower than the first set value, and a value that the detection voltage does not reach when not forming a female thread is selected. The timer circuit 15 is an inverter ln.
V4, and this inverter lnV4 is connected to the second
It is connected to one input of the NAND circuit 17. This second
The output of the startup reset circuit 12 is connected to the other input of the NAND circuit 17, and when a predetermined period of time has elapsed after the start of tapping and threading, the gate of the second NAND circuit 17 is opened, and the output signal of the timer circuit 15 indicates that the female thread forming is completed. The signal is configured to be sent to the detection circuit 18. Female thread forming completion detection circuit 1
8 consists of an FF circuit FF2, the "Q" output of which is connected to the exposure voltage switching circuit 3 of the constant voltage circuit 2 via an inverter lnV5.

On the other hand, the "Q" output of the FF circuit FF2 is connected to the input of the first NAND circuit 9 connected to the switch circuit 10,
The signal from the determination circuit transmitted to the switch circuit 10 is configured to be passed through or blocked by opening and closing the gate of the first NAND circuit 9. In the above-mentioned vertical screw torque control device, the switch circuit 10 includes an operation switch 1.
When the signal 1 is applied to reset the FF circuit FF, a predetermined voltage of the constant voltage circuit 2 is applied to the DC motor 1 as shown in FIG. 3a.

At this time, a starting current flows through the armature winding, but the starting reset circuit 12 prevents the peak voltage holding circuit 13 from working for a predetermined period of time, as shown in FIG. 3d. Therefore, even if the starting current exceeds a predetermined set value, the timer circuit 15 does not operate, and no signal is sent to the female thread forming completion detection circuit 18. Therefore,
In the FF circuit FF2 in the female thread forming completion detection circuit 18,
Q", "Q" outputs do not change and the voltage of the constant voltage circuit 2 is maintained, the gate of the first NAND circuit 9 is also closed, and the constant voltage circuit 2 is turned on from the switch circuit 10. The signal is sent continuously. Next, when the driver bit engages the tip of the chuck with the head of the tapping screw and starts screwing the tapping screw into the thin plate so that its legs penetrate, the initial torque generated when forming the female screw into the pilot hole. but,
As shown in FIGS. 3b and 3c, the set value of the first setting circuit 7 is exceeded, and a signal is transmitted from the comparator circuit 6.

However, while the detection voltage is rising, the peak voltage is equal to that of the detection circuit, so no signal is transmitted from the voltage drop detection circuit 14. Therefore, the timer circuit 15 does not operate, and no signal is sent from the female thread forming completion detection circuit 18, and the first
The gate of the NAND circuit 9 is closed, and the signal from the comparison circuit 6 does not pass through the first NAND circuit 9. Therefore, there is no change in the switch circuit 1, and the DC motor 1 continues to rotate. When the female thread is formed into the prepared hole of the thin plate, the bolt pin screw is screwed in with a low screwing torque, so that the detection voltage of the current detection unit 4 decreases.

At this time, the detected voltage becomes lower than the peak voltage of the peak voltage holding circuit 13, and a signal is transmitted from the voltage drop detection circuit 14 and applied to the timer circuit 15, as shown in FIG. When the detected voltage further decreases and once becomes equal to or less than the first set value, the reset of the timer circuit 15 is released, and the timer circuit 15 operates as shown in FIG. 3g. A predetermined period of time has elapsed since the detected fog pressure dropped to the first set value, the detected voltage has dropped sufficiently below the first set value, and chips, dust, etc. are caught between the tatsu pin screw and the female thread. Only after the detection voltage reaches a value that does not reach the first set value does the third
As shown in FIG. h, a signal is sent to the female thread forming completion detection circuit 18. Therefore, the FF circuit FF2 of the female thread forming completion detection circuit 18 is set, and its output signal is inverted. Therefore, as shown in FIG. 3i, the "Q" output operates the tortoise voltage switching circuit 3 via the inverter lnV5, halving the output voltage of the constant voltage circuit 2, and lowering the rotational speed of the DC motor 1. . Further, as shown in FIG. 3J, the "Q" output is applied to the first NAND circuit 9, and its gate is opened. Thereafter, the DC motor 1 rotates at a low speed to screw in the tapping screw.

When the seating surface of the tapping screw comes into contact with the object to be fastened and screw tightening is completed, the detected voltage matches the first set value.
Therefore, a signal is transmitted from the comparison circuit 6 and applied to the first NAND circuit 9. At this time, since the gate of the first NAND circuit 9 serves as a link, this signal passes through the first NAND circuit 9 as shown in FIG. 3 and is applied to the switch circuit 10. Therefore, the FF circuit FF is reset as shown in FIG.
The "Q" output is inverted and emits a "0" level signal, as shown in FIG. Due to this "Q" output, the output of the constant voltage circuit 2 becomes zero, and the DC motor 1 stops. At this time, the rotation speed of the DC motor 1 is low and its inertia is small, so if the voltage supply to the DC motor 1 is stopped, the rotation of the DC motor stops almost instantaneously. Further, as shown in FIG. 3n, the "Q" output is inverted to an "H" level signal, thereby turning off the peak voltage holding circuit 13. As explained above, the present invention connects a DC motor to a driver bit that screws a tapping screw into a prepared hole in a thin plate so that its leg passes through it, and when a predetermined period of time elapses after the start of screw threading, the load current Once it has reached its peak and it is detected that the female thread forming of the tatsu pin screw on the thin plate is completed, the load current of the DC motor will match the preset value corresponding to the desired vertical screw torque. Since the DC motor is configured to stop, the DC motor will not stop depending on the starting current when the DC motor wire is turned on, and the DC motor will stop as soon as the load current reaches the set value, regardless of the setting value. It has the advantages of being able to stop the motor, being extremely accurate, and being able to perform torque control. In addition, in the present invention, when a tapping screw is fastened to a thin plate so that its leg passes through, the desired tightening torque is low and the setting value is small, and the tapping screw is tightened until the seating surface of the tapping screw touches the thin plate. Even if the initial current generated when forming a female thread on a thin plate exceeds a set value, the bearing surface of a tapping screw can surely come into contact with the thin plate, and the self-tapping screw can be securely fastened to the thin plate at the set value. This has the advantage that there is no possibility of tightening defects such as screw lifting. In addition, the present invention allows the DC motor to operate without causing the load current to exceed the set value even if the load current flowing to the DC motor fluctuates slightly due to chips or dust, etc., being caught between the screw and the female thread during female thread forming. The screw tightening torque can be adjusted reliably without stopping.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview 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. DESCRIPTION OF SYMBOLS 1...DC motor, 2... Constant voltage circuit, 3... Voltage switching circuit, 4... Current detection unit, 5... Noise filter, 6... Comparison circuit, 7...
First setting circuit, 8... Waveform shaping circuit, 9... First NAND circuit, 10... Switch circuit, 11...
......Operation switch, 12...Start-up reset circuit, 13...Peak voltage holding circuit, 14...
...Voltage drop detection circuit, 15...Timer circuit, 1
6...Second setting circuit, 17...Second NAND circuit, 18...Female thread forming completion detection circuit. Figure 1 Figure 3 Figure 2

Claims (1)

[Claims] 1. A DC motor is connected to a driver bit, which is screwed into a pilot hole in a thin plate so that the leg of the screw passes through it, and the load current flowing through this DC motor is detected and the detected value is set to a preset desired value. A tightening torque control device is equipped with a comparison circuit that compares the screw tightening torque with a set value corresponding to the set value, and is configured to stop the DC motor using the output of this comparison circuit. In addition to providing an initial reset circuit to output,
A peak detection circuit that receives a signal from the initial reset circuit and outputs a signal when the afterload current reaches a peak is provided, and a timer that receives the signal from the peak detection circuit, measures time, and outputs a signal when the time is up. 1. A screw tightening torque control device comprising a circuit so as to stop the DC motor by the output of the comparator circuit only after receiving signals from the initial reset circuit and the timer circuit.