JPS6220786B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric tightening device, such as a nut runner, in which the tightening narc value is set using the current value of the electric motor as a power source as a guide, and in particular, the present invention relates to an electric tightening device such as a nut runner, etc. This is to prevent malfunction.

In an electric tightening device such as a nut runner, the tightening bit is driven by an electric motor, and the tightening torque is set using the relationship A∝T (A: current, T: torque). The motor is configured to stop when the current flowing through the motor reaches a set current value.

However, according to this method, since the starting current of the motor is very large, a malfunction occurs in which the starting current reaches a set current value immediately after the start of operation, causing the motor to stop.

Therefore, in order to prevent this malfunction, a soft start has been conventionally performed to protect the components and to suppress the starting current to a small value.

However, it is very difficult to reliably prevent malfunctions when the tightening torque is low, that is, when the set current value is low, or when the starting current becomes large due to a larger motor, and moreover, the soft start time must be lengthened. However, there is a problem in that the tightening work is very time-consuming, and the work efficiency is significantly reduced, especially in continuous work.

The present invention has been made in view of these circumstances, and includes a control section that drives an electric motor as a power source, and a detection section that detects the current flowing through the motor, and a detection signal from the detection section and a detection section. A reference signal corresponding to a set torque is compared, and when the detection signal exceeds the set torque, the control section is operated to stop the electric motor, and a soft start function is formed in the control section. It is an object of the present invention to provide an electric tightening device that reliably prevents malfunctions during startup by forming a function of changing the level of the reference signal for a certain period of time after the motor is started.

The present invention will be explained below based on an embodiment shown in the drawings.

FIG. 1 is a block diagram showing the configuration of an electric tightening device according to the present invention, and FIG. 2 is a diagram showing an example of its electric circuit. Further, FIG. 3 is a diagram showing the electrical characteristics of the tightening device according to the present invention, and FIG. 4 is a diagram showing the electrical characteristics of the conventional tightening device.

In FIG. 1, 1 is an electric motor as a power source, and 2 is a control circuit constituting a control section for driving the electric motor 1, which is equipped with a soft start function.

3 is a detection circuit that detects the current flowing through the motor 1;
Reference numeral 4 denotes an amplifier circuit that amplifies the output signal of the detection circuit 3, and the detection circuit 3 and the amplifier circuit 4 constitute a current detection section.

The torque setting circuit 5 is configured to be able to set a reference signal according to the tightening torque of the electric motor 1, and the torque setting circuit 5 and the amplifier circuit 4 are each connected to a comparison circuit 6.

Further, a reference signal correction circuit 7 having a timer function is connected to the torque setting circuit 5, and the reference signal correction circuit 7 starts operating at the same time as the control circuit 2 starts the electric motor 1, and sets the torque for a certain period of time after starting. A correction signal is output to circuit 5,
The torque setting circuit 5 is configured to change the signal level of the reference signal using this correction signal and output it to the comparison circuit 6.

In this way, the reference signal correction circuit 7 and the torque setting circuit 5 form a function of changing the signal level of the reference signal for a certain period of time.

Then, the comparison circuit 6 compares the detection signal of the amplifier circuit 4 with the reference signal of the torque setting circuit 5, and when the former is at a high level, outputs a stop signal to operate the control circuit 2 and control the electric motor 1. It is configured to stop.

Next, explanation will be given based on the electric circuit shown in FIG.

The control circuit 2 includes a triax 11 connected in series to the electric motor 1 and a drive section 12 that drives and controls the triax 11.
is designed to drive the triax 11 in a soft start manner.

The detection circuit 3 includes a detection resistor 13 connected in series to the motor 1 and the triax 11, and a diode 14 for rectifying the output.

The amplifier circuit 4 includes an amplifier 15 and a smoothing capacitor 16
The output signal from the detection circuit 3 is amplified to form a detection signal, which is output to the comparison circuit 6.

The torque setting circuit 5 is configured to set the comparison reference voltage of the comparator 18 constituting the comparison circuit 6, that is, the signal level of the reference signal, by adjusting the voltage division ratio with a variable resistor 17.

The reference signal correction circuit 7 also includes a charging resistor 1.
9, capacitor 20, amplifier 21, diode 2
A charging timer formed by a resistor 19 and a capacitor 20 is connected to the negative input of the amplifier 21, and the output side is connected to the torque setting circuit 5 via a diode 22. .

The charging timer formed by the resistor 19 and the capacitor 20 starts operating at the same time as the motor 1 is started (by the control circuit 2) when the switch S is turned on, and the CR
The charging waveform voltage determined by a constant is inverted and amplified by an amplifier 21, and output as a correction signal to the torque setting circuit 5 to change the voltage division ratio, thereby increasing the signal level of the reference signal.

On the other hand, the timer time at this time is sufficient if it can secure only the time during which the detection signal is affected by the starting current.

Further, in the figure, 23 is a rectifying diode, 24 is a resistor, and 25 is a smoothing capacitor, each of which constitutes a DC power supply section.

In the above configuration, when the switch S is turned on after the tightening bit (not shown) connected to the electric motor is attached to the object to be tightened, the control circuit 2 is operated and the electric motor 1 is soft-started to perform tightening. Start working.

At the same time as the tightening starts, the current flowing through the motor 1 changes to resistance 1.
3, and this detection signal changes over time, drawing a characteristic curve as shown by the solid line in FIG.

In the figure, _t1 is a section where the starting current is applied, _t2 is a light load section that does not lead to tightening, and _t3 is a section where tightening is performed.

Although the motor ₁ is soft-started in the section t1, the influence of the starting current is still large, and the detection signal has a mountain-shaped characteristic with a large peak value.

In section _t2 , the influence of the starting current disappears, but there is also a light load state in which the threaded part of the nut etc. is engaged and rotating and does not reach tightening, so the characteristics are almost flat.

In section _t3 , the clamping state is reached, so the detection signal gradually increases as the load increases, that is, the clamping resistance increases.

Then, the tightening torque value is set in the interval _t3. Conventionally, as shown in FIG. 4, the signal level _L1 of the reference signal was constant regardless of the passage of time, so for example, As already explained, when the torque setting value is low, such as at point _P1 , the detection signal reaches the signal level _L1 of the reference signal at point _P0 in section _t1 , which causes malfunction.

However, according to the present invention, the timer circuit starts operating at the same time as the electric motor 1 is started, and the comparison reference voltage of the comparator 18 increases, so that the signal level of the reference signal increases.
This means that L ₁ is increased to signal level L ₂ in section t ₁ , and after almost the timer time set corresponding to section t ₁ has elapsed, signal level L ₁ is increased according to the set tightening torque. Therefore, malfunctions due to starting current can be reliably prevented, and tightening can be performed at the set torque value.

Furthermore, since the influence of the starting current can be eliminated by changing the signal level of the reference signal, the soft start time can be shortened and the tightening work efficiency can be greatly improved.

In addition, by using the CR charging circuit as in this embodiment to correct the signal level of the reference signal and inverting and amplifying the charging waveform voltage based on the CR constant, it is possible to
Correction can be performed that approximates the attenuation characteristic of the detection signal at _t1 .

Then, the detection signal and signal level in section t ₂
By bringing the difference χ ₁ from L ₁ closer to the difference χ ₀ between the detection signal and the signal level L ₂ in the interval t ₁ ,
Work can be performed with relatively few tightening errors even in the section _t1 .

Therefore, with this configuration, the tightening time is short, for example, it is possible to tighten items that have already been tightened with a certain amount of torque without loosening them, or it is possible to tighten sections for high-speed tightening. In this case, tightening is completed at t ₁ , there is little tightening error, and the work can be completed without fear of breakage due to excessive tightening.

As explained above, the gist of the present invention is to control the tightening torque value using the relationship A∝T, and to control the tightening torque value in a section where the detection signal fluctuates due to the influence of the motor starting current. The purpose is to change the signal level of the reference signal so that the influence of the starting current can be ignored, and to prevent malfunctions caused by the starting current.

Therefore, as long as the idea of the present invention is not departed from, the present invention can be implemented by changing the mode as appropriate. For example, the signal system may be reversed, or the component parts may be changed as appropriate. can.

According to the present invention, it is possible to obtain an electric tightening device which has excellent advantages such as being able to reliably prevent malfunctions in which the electric motor stops immediately after starting, and improving tightening work efficiency. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an electric tightening device according to the present invention, and FIG. 2 is a diagram showing an example of its electric circuit. Further, FIG. 3 is a diagram showing the electrical characteristics of the tightening device according to the present invention, and FIG. 4 is a diagram showing the electrical characteristics of the conventional tightening device. DESCRIPTION OF SYMBOLS 1...Electric motor, 2...Control circuit, 3...Detection circuit, 4...Amplification circuit, 5...Torque setting circuit, 6
...Comparison circuit, 7...Reference signal correction circuit.

Claims (1)

[Claims] 1. A control unit that drives an electric motor of a power source, and a detection unit that detects the current flowing through the electric motor, and a detection signal from the detection unit and a reference signal according to a set torque. When the detection signal exceeds the set torque, the control unit is operated to stop the electric motor, and the control unit is provided with a soft start function to suppress the starting current. A correction signal is generated at the same time as the motor is started until the end of the detection signal, and this correction signal is added to the reference signal to change the level of the reference signal so that the control section does not operate due to the detection signal. Features electric tightening device. 2. The electric motor according to claim 1, wherein the correction signal is formed by a charging timer using a resistor and a capacitor, and the signal level of the reference signal is changed by approximating the attenuation characteristic of the detection signal due to the starting current. Tightening device.