JPS6013797B2 - 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 tapping screw into a prepared hole in a mating material made of a solid material such as a thin iron plate and controlling the tightening torque.

Conventionally, the load current of the DC motor that rotates the driver bit is detected, compared with the amount of electricity corresponding to the desired tightening torque set in advance, and when the two match, the DC motor is stopped and the screw threading torque is adjusted. A screw tightening torque control device that reliably maintains the set torque detects the load current through a capacitor in order to prevent malfunctions caused by the instantaneous starting current that occurs when the DC motor starts when the screw tightening start switch is turned on. , the load current is detected only when the load current continues to flow for a certain period of time. Therefore, the load current during screw tightening work is passed for a certain period of time in the same way as the starting current, and even after the load current reaches the desired value, the driver bit rotates and over-tightens the screw, causing the screw tightening torque to reach the set value. There are disadvantages such as the inability to maintain The present invention aims to eliminate the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings.

In Figures 1 and 2, numeral 1 is a DC motor that rotates a driver bit (not shown) and tightens a screw held at the tip of a chuck (not shown); A constant voltage circuit 2 is connected to control the number of motors, and power for driving the DC motor is supplied to the armature winding of the DC motor. The constant voltage circuit 2 includes two Darlington-connected NPN transistors Trl and Tr2, two Zener diodes ZD1 and ZD2, and a resistor RI, and a lightning voltage cutting circuit 3 is connected to the constant voltage circuit 2. . The lightning pressure switching circuit 3 consists of an NPN transistor Tr3 that is activated by a female thread forming completion detection signal, which will be described later.
It 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 threading the screw, and detects the load current of the DC motor 1, which increases when the rotation of the driver bit is blocked during screw threading. It is configured to detect tightening torque.

A noise filter 5 is connected to the current detection section 4 to remove noise generated by brushes (not shown) of the DC motor.

This noise filter 5 uses an active filter including an operational amplifier OPI. 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 includes resistors R2, R4, variable resistor R5, and capacitor CI.
The voltage value is configured to be arbitrarily set in accordance with the desired tightening torque. Further, the first setting circuit 7 together with the comparison circuit 6 constitutes a determination circuit which transmits a digital signal at the moment when the actual attaching torque reaches the set torque. The comparison circuit 6 includes resistors R6, R
7, R8 diode DI and NPN transistor Tr
It is connected to a waveform shaping circuit 8 consisting of 4.

The waveform shaping circuit 8 is connected to one input of the first NAND circuit 9 via the inverter lnVI, and when the gate of the first NAND circuit 9 is open, the output of the waveform shaping circuit 8 is connected to the switch circuit 1.
01 is added, and the constant voltage circuit 2 is turned off. Said switch circuit 1 OR circuit OR1
, inverters lnV2, lnV3, a flip-flop circuit FF1 (hereinafter referred to as FF circuit), and an NPN transistor Tr5, and a first NAND circuit 9.
Regardless of the output of the screw tightening failure detection device (not shown)
The constant voltage circuit 2 is turned off by the defect detection signal, 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. On the other hand, the current detection section 4 is connected to a peak voltage holding circuit 12 via a noise filter 5.

This peak voltage holding circuit 12 includes a capacitor C2, a resistor R9, and an NPN transistor Tr6, and is connected to a timer circuit 14 via a voltage drop detection circuit 13. The voltage drop detection circuit 13 is composed of a comparator M1 and a resistor RIO, and is configured to send an activation signal to the timer circuit 14 when the detected voltage of the current detection section 4 becomes lower than the peak voltage of the peak voltage holding circuit 12. It is composed of
The timer circuit 14 includes resistors 11, 12, 13, 14, diodes D2, D3, a capacitor C3, a Zener diode ZD3, and an NPN transistor Tr7, and the detected voltage is the first setting value of the first setting circuit 7. It is configured to be reset until it descends once. Further, this timer circuit 14 is configured such that the detected voltage is the second setting circuit 1.
The timer circuit 14 is configured to be reset until it reaches the second set value of No. 5, and the timer circuit 14 will not operate unless the detected voltage rises to a predetermined value, so that the female thread forming completion detection signal will not be transmitted. It is configured. This second setting value has a value lower than the first setting value, and is selected such that the detection voltage does not reach when a female thread is not formed. The timer circuit 14 is connected to one input of a second NAND circuit 16 via an inverter lnV4.

The output of a startup reset circuit 17 (to be described later) is connected to the other input of the second NAND circuit 16, and the gate of the second NAND circuit 16 is opened when a predetermined period of time has elapsed after the start of screw tightening.
The output signal of the timer circuit 14 is the female thread forming completion detection circuit 1.
8. The female thread forming completion detection circuit 18 consists of an FF circuit FF2, the "Q" output of which is connected to the voltage switching circuit 3 via an inverter lnV5.

On the other hand, the "Q" output of this FF circuit FF2 is connected to the input of the first NAND circuit 9 connected to the switch circuit 101, and the signal of the judgment circuit transmitted to the switch circuit 10 is transmitted to the first NAND circuit 9. Pass through by opening and closing the gate,
Or it is configured to block it. Next, the main parts of the present invention will be explained.

A startup reset circuit 17 is connected to the switch circuit 1M so as to distinguish between a startup current generated at the moment when the constant voltage circuit 2 is turned on by pressing the operation switch 11 and a load current generated during threading. . This startup reset circuit 17 includes an inverter lnV6, resistors R15, R16,
Consisting of R17 capacitors C4, C5 and comparator CMP2, "Q" of FF circuit FFI in the switch circuit 10
Upon receiving the signal from the output, no signal is transmitted from the comparator CMP2 for a predetermined time, the peak voltage holding circuit 12 is turned off, and the gate of the second NAND circuit 16 is closed.
The internal thread forming completion detection signal is configured not to be transmitted. In the screw tightening torque control device described above, a signal is applied to the switch circuit 10 by the operation switch 11, and the FF
When the circuit FFI is reset, a predetermined voltage of the constant voltage circuit 2 is applied to the DC motor 1.

At this time, a starting current flows through the armature winding, but after the operation switch is turned on, the "Q" output of the FF circuit FFI is connected to the inverter.
It is connected to the start-up reset circuit 17 via nV6, and is connected to the resistor R.
15. Apply MP to the comparator for the time determined by capacitor C4.
2 does not emit an output signal. Therefore, the NPN transistor Tr6 of the peak voltage holding circuit 12 is turned on, and the capacitor C2 is not charged. At the same time, the gate of the second NAND circuit 16 continues to close, and no signal is sent to the female thread forming completion detection circuit 18, so even if the starting current exceeds a predetermined set value, the peak voltage holding circuit 12 ,
The voltage drop detection circuit 13 also does not operate, and no activation signal is sent to the timer circuit 14. Therefore, in the FF circuit FF2 in the female thread forming completion signal detection circuit 18, no change occurs in the "Q" and "Q" outputs, and the voltage of the constant voltage circuit 2 is maintained.
When a predetermined period of time has elapsed after the operation switch is turned on, an output signal is transmitted from the comparator CMP2 of the startup reset circuit 17, and N
The PN type transistor Tr6 is turned off and the peak voltage holding circuit 12 is turned on.

At the same time, the gate of the second NAND circuit 16 is opened.
Prepare for the detection of the DC motor load current that occurs when threading. Next, when the driver bit aligns with the head of the screw at the tip of the chuck and begins to screw the screw into the pilot hole of the other village,
The initial torque generated when forming a female thread in a prepared hole reaches the desired set value, but while the initial torque detection voltage is rising, the voltage drop detection circuit 13 does not transmit an output signal, and the timer circuit 14 doesn't work either.

Therefore, the gate of the first NAND circuit 9 is closed, and the signal from the comparison circuit 6 does not pass through the first NAND circuit 9.
Therefore, even if the initial torque detection voltage exceeds the set value, the voltage applied to the DC motor 1 does not change. When the female thread is formed in the prepared hole of the object to be fastened, the 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 12, a signal is transmitted from the voltage drop detection circuit 13, and an activation signal is applied to the timer circuit 14. When the detected voltage further drops below the first set value, the reset of the timer circuit 14 is canceled and the timer circuit 1
4 is activated. A signal is transmitted to the female thread forming completion detection circuit 18 after a predetermined period of time has passed since the detection voltage has dropped to the first set value. Therefore, the FF circuit FF2 is set and its output signal is inverted. Therefore, the "Q" output operates the voltage switching circuit 3, which halves the output voltage of the constant voltage circuit 2 and lowers the rotational speed of the DC motor 1. The "Q" output is also applied to the first NAND circuit 9, opening its gate. Thereafter, the DC motor 1 rotates at a low speed to screw in the screw.

When the screw bearing surface contacts the mating material and screw tightening is completed,
The detected voltage corresponding to the tightening torque of the screw matches the desired 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 is open, this signal passes through the first NAND circuit 9 and is applied to the switch circuit 101. Therefore, the FF circuit FFI is reset, the "Q" output is inverted, and a "0" level signal is generated. Due to this "Q" output, the output of the constant voltage circuit 2 becomes zero, and the DC motor 1 stops at the moment the detected voltage reaches the desired set value, thereby ensuring the desired screw tightening torque. As explained below, the present invention detects the peak of the load current of the DC motor, and after the forming of the female thread on the mating material is completed, the load current reaches a set value corresponding to the desired screw threading torque. The DC motor is stopped instantaneously and the torque is controlled, and the peak of the load current is not detected for a predetermined period of time after the DC motor starts, so the starting current generated when the DC motor starts is reduced. Not only can the DC motor continue to rotate without stopping the DC motor even if it matches a predetermined set value, but the DC motor can also be stopped the moment the DC motor's load current matches the set value. This has the advantage of making it possible to reliably control the attaching torque.

[Brief explanation of drawings]

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. 1... DC motor, 2... Constant voltage circuit, 3... Lightning pressure 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... Peak voltage holding circuit, 13... Voltage drop detection circuit, 14...
Timer circuit, 15...Second setting circuit, 16...Second NAND circuit, 17...Start reset circuit, 18...Female thread forming completion detection circuit. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A torque control circuit that detects the load current of the DC motor that rotates the driver bit, compares it with the amount of electricity corresponding to a preset desired tightening torque, and stops the DC motor after the two match; a circuit that holds the peak of the current, a circuit that detects a drop in the load current,
and a circuit that detects the completion of forming the female thread on the mating material after the falling load current reaches the set value, and the screw tightening circuit that activates the torque control circuit after the forming of the female thread on the mating material is completed. What is claimed is: 1. A screw tightening torque control device, characterized in that the screw tightening torque control device is equipped with a circuit that causes a circuit that maintains the peak of the load current to operate after a predetermined period of time has elapsed after the start of screw tightening.