JPH11138456A - Battery-powered fastening tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately operate an automatic stopping function even if a battery-powered fastening tool uses a gear shift switch, by preventing the automatic stopping function from being operated in the start-up of a motor. SOLUTION: This battery-powered fastening tool for fastening screws by rotating a tool by a motor to be driven by a battery is provided with a cancel circuit 24 to be set while starting current is allowed to flow to the motor, a latch circuit 26 to be set if the applied battery voltage Vb is the specified voltage V2 or less when the cancel circuit 24 is reset, and to be reset when the battery is detached from a battery-powered fastening tool and the battery voltage Vb is not applied, and a switch FET connected between the battery and the motor and for releasing the connection of the battery and the motor when the latch circuit 26 is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw driver for tightening screws such as screws, nuts and bolts,
The present invention relates to a tightening tool such as a torque wrench and an impact wrench, and more particularly to a battery-type tightening tool in which a motor is driven by a battery.

[0002]

2. Description of the Related Art In the case of a battery-operated fastening tool, if a fastening operation is performed in a state where the remaining capacity of a battery is less than a predetermined value, fastening of screws becomes insufficient due to an insufficient fastening torque. There is a problem that screws will be loosened in the future. Japanese Patent Application Laid-Open No. 7-1350 proposes a battery-operated tightening tool that takes this measure. If the battery voltage drops below a predetermined voltage at the time of starting the motor, the battery-operated fastening tool determines that the remaining capacity of the battery is insufficient, and forcibly turns off a switch connected between the battery and the motor. . That is, when the remaining capacity of the battery is insufficient, the automatic stop function is operated so that the fastening tool does not operate even if the operation switch is turned on. As a result, the fastening operation is not performed in a state where the remaining capacity of the battery is insufficient, and the fastening failure of the screws is eliminated. The auto stop function is reset at the timing when the battery with insufficient remaining capacity is removed from the fastening tool.

[0003]

However, when the motor is started with an ON-OFF type operation switch, the battery voltage at the time of starting decreases substantially in the same manner. Has a different tendency to decrease depending on how the trigger is pulled. For example, when the trigger is slowly pulled, the starting current of the motor is relatively small, and the battery voltage gradually decreases as shown by the dotted line in FIG. 2, and its lower limit does not become so low. On the other hand, when the trigger is suddenly pulled, the starting current of the motor becomes large, and the battery voltage drops sharply as shown by the solid line in FIG.

Therefore, when the automatic stop function is added to a battery-operated fastening tool with a speed change switch, it is not possible to determine the remaining battery capacity shortage due to a battery voltage drop when the motor is started. Therefore, the invention described in claim 1 enables the remaining battery capacity to be determined from the change in the battery voltage at the time of load, so that the auto stop function can be properly operated even in a battery-type fastening tool with a shift switch. That is the purpose.

[0005]

The above object is achieved by a battery-operated fastening tool having the following features. That is, the invention according to claim 1 is a battery-operated fastening tool for fastening a screw by rotating a tool by a motor driven by a battery, and a cancel circuit that is set while a starting current is flowing through the motor. When the applied battery voltage is equal to or less than a predetermined voltage when the cancel circuit is reset, the battery is set when the battery is removed from the battery-operated tightening tool, and reset when the battery voltage is not applied. And a switch that is connected between the battery and the motor and that disconnects the battery from the motor when the latch circuit is set.

According to the present invention, the cancel circuit is set while the starting current is flowing through the motor, so that the latch circuit is not set even if the battery voltage drops below a predetermined voltage. For this reason, the switch is maintained in the conductive state, and the automatic stop function does not work. On the other hand, after the motor is started, the cancel circuit is reset, so the tightening torque is applied to the motor and the load current increases,
When the remaining capacity of the battery is insufficient and the battery voltage falls below a predetermined value, the latch circuit is set. As a result, the switch is turned off, and the auto stop function operates. That is, the auto stop function does not operate when the motor is started, but operates when the load current of the motor increases. For this reason, the auto-stop function operates properly even with a battery-operated tightening tool that uses a shift switch, and unlike the conventional case, the inconvenience of operating the auto-stop function in a state where the remaining battery capacity is not insufficient. Disappears. Since the latch circuit is reset when a battery with insufficient remaining capacity is removed from the battery-powered fastening tool, the battery-powered fastening tool can be used by setting the battery again after charging. .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG.
A battery-operated fastening tool according to a first embodiment of the present invention will be described with reference to FIGS. The battery-operated fastening tool according to the present embodiment determines whether the remaining battery capacity is insufficient by comparing the battery voltage with a predetermined voltage at the time of the impact when the load current of the motor increases, and determines whether the remaining battery capacity is insufficient. When it is determined that there is a shortage, the auto stop function is operated. As a result, the automatic stop function can be accurately operated even in a battery-operated tightening tool using the speed change switch.

The battery-operated fastening tool according to the present embodiment includes a battery pack BP as shown in a main part circuit diagram of FIG. The battery pack BP contains cells of a nickel-cadmium battery and is housed in a battery housing (not shown) of a battery-operated fastening tool. The battery accommodating portion is provided with contacts CN1 and CN2, and when the battery pack BP is accommodated in the battery accommodating portion, the battery pack B
The contacts CN1 and CN2 of P are the contacts CN1 and C of the battery housing.
Automatically connected to N2. The battery pack BP can be charged, and when charging, the battery pack BP is taken out of the battery housing.

The charged battery pack BP is housed in the battery housing of the battery-operated fastening tool, and contacts CN1 and CN of each other.
2 is connected, the battery pack BP, the shift switch SW
1, forward / reverse switch SW2a, SW2b, motor M
And the motor drive circuit in which the switch FET is connected in series is completed. The speed change switch SW1 includes a contact portion that switches between a contact and b contact, a variable resistor RX, and a trigger (not shown). When the tool user pulls the trigger, the contact portion changes to the a contact. As the switching is performed, the variable resistor RX changes, and the comparison circuit 1 described later
4 decreases. Conversely, when the trigger is returned to the original position, the contact switches to the contact b and the terminal voltage VR becomes maximum.

The a-contact and the b-contact of the shift switch SW1 are mounted between the CN1 (+ side) of the battery pack BP and the motor M. When the shift switch SW1 is switched to the a-contact side, the motor M And the battery pack BP are connected. Therefore, if the switch FET is in the ON state, power is supplied to the motor M. Also, the shift switch S
When W1 switches to the contact b side, a braking circuit for the motor M is formed. Also, the variable resistor RX of the speed change switch SW1
Are incorporated in a comparison circuit 14 of the transmission circuit 10 described later.

The forward / reverse switch SW2a, SW2b
Is a switch for switching the rotation direction of the motor M. When the switch is switched to the de-e contact side, a current in the forward direction flows through the motor M, and when the switch is switched to the cf contact side, the motor is rotated. A reverse current flows through M. The switch FET is a field-effect transistor operated by a transmission circuit 10 and a control circuit 20 described later, and turns on and off a drive circuit of the motor M separately from the transmission switch SW1.

Next, the transmission circuit 10 for controlling the switch FET will be described. The transmission circuit 10 is a circuit that outputs a pulse signal of a constant frequency while changing the pulse width, and operates the switch FET based on the pulse output. The transmission circuit 10 includes a triangular wave generation circuit 12, a comparison circuit 14, and a transistor 16,
The breakdown voltage A of the Zener diode ZD1 is used as a constant voltage source for those circuits 12, 14, 16. The triangular wave generation circuit 12 operates the capacitor C by the operation of the operational amplifier OP1.
1 is a circuit for generating a triangular wave of a constant frequency while charging / discharging 1 regularly, and its output voltage VT is input to the minus side of the operational amplifier OP2 of the comparison circuit 14.

The comparison circuit 14 calculates the voltage V of the triangular wave.
T is compared with the terminal voltage VR of the variable resistor RX, and when triangular wave voltage VT> terminal voltage VR, a low voltage (L) is output;
High voltage (H) when triangular wave voltage VT <terminal voltage VR
Is output. For this reason, when the trigger of the shift switch SW1 is greatly pulled and the resistance value of the variable resistor RX decreases,
The terminal voltage VR of the variable resistor RX decreases and the low voltage (L)
Is longer, and the time of the high voltage (H) is shorter. Conversely, when the terminal voltage VR of the variable resistor RX is increased by reducing the amount of pulling the trigger, the time of the low voltage (L) is short and the time of the high voltage (H) is long.

The output of the comparison circuit 14 is the transistor 1
6 is input to the base. Therefore, when a high voltage (H) is input to the base, the collector and the emitter conduct, and the voltage of the collector becomes a low voltage (L). Conversely, when a low voltage (L) is input to the base, the collector and the emitter are cut off and the voltage of the collector becomes a high voltage (H). Here, since the collector of the transistor 16 is connected to the gate terminal of the switch FET via a resistor, when a low voltage (L) is input to the base of the transistor 16, the switch FET is turned on and the base of the transistor 16 is high. When the voltage (H) is input, the switch FET turns off.

Therefore, when the tool user reduces the amount of pulling the trigger, the ON time of the switch FET is shortened, the average voltage applied to the motor M is reduced, and the rotation speed is reduced. Conversely, if the tool user increases the amount of pulling the trigger, the ON time of the switch FET increases, the average voltage applied to the motor M increases, and the rotation speed increases.

Next, the control circuit 20 will be described. The control circuit 20 is an auto-stop circuit for forcibly turning off and holding the switch FET when the remaining charge capacity of the battery pack BP becomes insufficient, and includes a comparison circuit 22, a cancel circuit 24, and a latch circuit 26. . The comparison circuit 22 includes an operational amplifier OP3, and a voltage Vb obtained by dividing the battery voltage is applied to a plus terminal of the operational amplifier OP3.
(Hereinafter, simply referred to as battery voltage Vb). Further, a breakdown voltage V2 of the second Zener diode ZD2 (hereinafter, referred to as a determination voltage V2) is input to a minus terminal of the operational amplifier OP3.

Here, the judgment voltage V2 is determined by the battery pack BP
Is a voltage for determining whether or not the remaining charge capacity of the battery pack BP is insufficient. When the remaining charge capacity of the battery pack BP is appropriate, even at the time of impact (when the screws are tightened while making an impact). Battery voltage Vb is set to a value that does not drop below that voltage. That is, if the minimum value when the battery voltage Vb decreases at the time of impact is Vbmin, Vbmin> V2. Conversely, if the remaining charge capacity of the battery pack BP is insufficient, the minimum value Vbmin of the battery voltage Vb at the time of impact is Vbmin ≦ V2. That is, the determination voltage V2 corresponds to the predetermined voltage of the present invention.

The comparison circuit 22 determines that battery voltage Vb> voltage V
If it is 2, a high voltage (H) is output, and if battery voltage Vb ≦ voltage V2, a low voltage (L) is output. Then, the output of the comparison circuit 22 is input to the cancel circuit 24 and the latch circuit 26. The cancel circuit 24 includes a knot circuit 24n, a one-shot circuit 24y, and a NAND circuit 24d. The cancel circuit 24
When the low voltage (L) is input from the comparison circuit 22 to the low voltage (L), the low voltage (L) is converted into the high voltage (H) by the knot circuit 24n and input to the one-shot circuit 24y (IN in the figure). ) Is done. One shot circuit 24y
Outputs the high voltage (H) for a certain period of time (OUT in the figure) from the timing when the high voltage (H) is input.

Here, the time during which the one-shot circuit 24y outputs the high voltage (H) is set longer than the time during which the starting current flows through the motor M and shorter than the impact time. The output (OUT) of the one-shot circuit 24y is input to one input terminal of a NAND circuit 24d. An output Qb of a latch circuit 26 described later is input to the other input terminal of the NAND circuit 24d.
The output T of the NAND circuit 24d, that is, the output T of the cancel circuit 24 is input to the R1 terminal of the latch circuit 26.

The latch circuit 26 is a flip-flop circuit in which two NAND circuits are combined, and the output of the comparison circuit 22 is input to the S1 terminal. The output T of the cancel circuit 24 is input to the R1 terminal of the latch circuit 26 as described above. Further, the latch circuit 2
6 is input to the NAND circuit 24d of the cancel circuit 24 and the switch FE as described above.
Input to the gate terminal of T. FIG. 5 is a truth table of the latch circuit 26.

Next, the operation of the battery-operated fastening tool according to the present embodiment will be described in time series with reference to FIGS.
When replacing the battery pack BP, the trigger of the shift switch SW1 is not pulled, so that the contact portion is switched to the contact b side, and no voltage is applied to the motor M. In this state, when the charged battery pack BP is set, the output of the comparison circuit 22 changes to the high voltage (H) at the moment of the setting (see timing in FIG. 3). However, since the application of the voltage to the S1 terminal of the latch circuit 26 is delayed by the action of the capacitor CS, the S1 terminal becomes a low voltage (L). Therefore, the Qa terminal of the latch circuit 26 becomes a high voltage (H). Further, since the application of the voltage to the R1 terminal of the latch circuit 26 is delayed due to the function of the capacitor CT, the R1 terminal becomes a low voltage (L). Therefore, the output Qb of the latch circuit 26 becomes the high voltage (H), the high voltage (H) is applied to the gate terminal of the switch FET, and the switch FET is turned on. When the output Qb of the latch circuit 26 is at a high voltage (H),
The reset state of the latch circuit 26, and when the output Qb is at the low voltage (L), will be referred to as the set state of the latch circuit 26.

On the other hand, the input (IN) is input to the one-shot circuit 24y of the cancel circuit 24 by the function of the knot circuit 24n.
Becomes a low voltage (L). Therefore, the output (OUT) of the one-shot circuit 24y also becomes the low voltage (L). However, the NAND circuit 24d includes the one-shot circuit 2
4y and the output Q of the latch circuit 26.
Since the high voltage (H) is input, the output of the NAND circuit 24d, that is, the output T of the cancel circuit 24 becomes the high voltage (H). Note that when the output T of the cancel circuit 24 is at a high voltage (H), the reset state of the cancel circuit 24, and conversely, when the output T is at a low voltage (L),
This is referred to as a set state of the cancel circuit 24.

Next, after a certain time has passed since the battery pack BP was set, the capacitors CS and CT
Is charged (see timing in FIG. 3), a high voltage (H) is applied to the S1 terminal of the latch circuit 26, and thus the Qa terminal of the latch circuit 26 changes to a low voltage (L).
On the other hand, since the high voltage (H) is applied to the R1 terminal of the latch circuit 26 from the cancel circuit 24, the output Qa of the latch circuit 26 does not change and remains at the high voltage (H).
Remains. For this reason, the switch FET is kept in the ON state.

Next, when the trigger of the speed change switch SW1 is pulled to tighten the screws, the contact portion is switched to the a contact side, and electric power is supplied to the motor M. As a result, a starting current flows through the motor M, and the motor M
Rotates (see activation in FIG. 2). Here, FIG. 2 is a graph showing a change in the battery voltage Vb when the screws are tightened by the battery-operated fastening tool according to the present embodiment, and FIG. 2A shows that the remaining charge capacity of the battery pack BP is sufficient. In the case of (b), FIG. (B) shows the case where the remaining charge capacity is reduced but not insufficient, and FIG. (C) shows the case where the remaining charge capacity is insufficient.

When the motor M is started, the speed change switch SW1
Is slowly pulled, the width of the pulse output from the transmission circuit 10 gradually increases. For this reason, the time during which the switch FET is turned on gradually increases, and the average value of the voltage applied to the motor M gradually increases.
As a result, the motor M is started slowly and the starting current becomes relatively small, and the battery voltage Vb gradually decreases as shown by the dotted line in FIG. Further, when the starting current decreases with the rotation of the motor M, the battery voltage Vb slowly increases to a predetermined value. At this time, unless the battery voltage Vb falls below the determination voltage V2, the states of the comparison circuit 22, the cancellation circuit 24, and the latch circuit 26 do not change.
For this reason, the operation of the battery-operated fastening tool is continued as it is.

When the trigger of the shift switch SW1 is quickly pulled, the width of the pulse output from the shift circuit 10 increases rapidly. For this reason, the time during which the switch FET is turned on is quickly increased, and the average value of the voltage applied to the motor M is also increased quickly. As a result, the motor M is started up quickly, the starting current is increased, and the battery voltage V
b sharply decreases as shown by the solid line in FIG. Further, when the starting current decreases with the rotation of the motor M, the battery voltage Vb rapidly increases to a predetermined value. At this time, when the battery voltage Vb falls below the determination voltage V2 (see FIG. 2).
(B), see timing in FIG. 3), the output of the comparison circuit 22 becomes a low voltage (L), and the S1 terminal of the latch circuit 26 becomes the low voltage (L) with a slight delay due to the action of the capacitor CS. Therefore, the Qa terminal of the latch circuit 26 also changes to the high voltage (H) with a slight delay.

Since the output of the comparison circuit 22 is also input to the cancellation circuit 24, a high voltage (H) is applied to the input (IN) of the one-shot circuit 24y by the function of the knot circuit 24n. Therefore, the high voltage (H) is output (OUT) from the one-shot circuit 24y for a certain period of time. Therefore, the NAND circuit 24d includes the one-shot circuit 2
4y and the output Q of the latch circuit 26.
b, the high voltage (H) is input to the NAND circuit 24.
The output T of d becomes a low voltage (L). That is, the cancel circuit 24 is set. As a result, the R1 terminal of the latch circuit 26 becomes the low voltage (L), and the output Qb of the latch circuit 26 is maintained at the high voltage (H). Therefore, the battery voltage Vb is determined by the starting current of the motor M.
Is lower than the determination voltage V2, the latch circuit 26 is maintained in the reset state, and the switch FET is not turned off. For this reason, the switch FET is controlled by the transmission circuit 10, and the operation of the battery-operated fastening tool is continued as it is.

Next, as the starting current of the motor M decreases, the battery voltage Vb rises, and the battery voltage Vb falls to the determination voltage V2.
If the voltage is higher than the reference voltage (see the timing in FIG. 3), the output of the comparison circuit 22 becomes a high voltage (H).
A high voltage (H) is applied to the S1 terminal of No. 6. As a result, the Qa terminal of the latch circuit 26 changes to a low voltage (L). On the other hand, the input (IN) of the one-shot circuit 24y becomes a low voltage (L) when the output of the comparison circuit 22 becomes a high voltage (H), but the one-shot circuit 24y is reset after a lapse of a predetermined time. The predetermined time is set longer than the time during which the starting current flows. Therefore, the output T of the cancel circuit 24 is still at the low voltage (L), and the R1 terminal of the latch circuit 26 is also at the low voltage (L). Therefore, the latch circuit 2
The output Qb of No. 6 is maintained at the high voltage (H), and the operation of the battery-operated fastening tool is continued as it is.

When the one-shot circuit 24y is reset in a state where the battery voltage Vb is higher than the determination voltage V2 (see timing in FIG. 3), the output T of the cancel circuit 24 becomes a high voltage (H). Therefore, the latch circuit 2
6 becomes high voltage (H), but the latch circuit 2
Since the Qa terminal of No. 6 is held at the low voltage (L),
The output Qb of the latch circuit 26 is kept at the high voltage (H). In this way, when the operation of the battery-operated fastening tool is continued and the screwing of the screws is almost completed and the impact is started, a large torque of the motor M is applied, so that the load current increases. Thereby, the battery voltage Vb decreases again.

However, when the battery voltage Vb is equal to the judgment voltage V2
If not lower, the comparison circuit 22 and the cancellation circuit 2
4 and the state of the latch circuit 26 do not change, so that the operation of the battery-operated fastening tool is continued. Then, the tightening of the screws is completed with the impact being performed for a certain period.

In this manner, the tightening of the screws using the battery-operated fastening tool is repeatedly executed, and the battery pack BP
When the remaining charge capacity of the battery is insufficient, the impact is started, and the battery voltage Vb falls below the determination voltage V2 (see timing in FIG. 4). As a result, the output of the comparison circuit 22 becomes a low voltage (L), and the low voltage (L) is applied to the S1 terminal of the latch circuit 26. As a result, the Qa terminal of the latch circuit 26 changes to the high voltage (H). The low voltage (L) output of the comparison circuit 22 is input to the cancel circuit 24, and the high voltage (H) is applied to the input (IN) of the one-shot circuit 24y by the function of the knot circuit 24n.

Therefore, the high voltage (H) is output (OUT) from the one-shot circuit 24y for a certain period of time. Therefore, the one-shot circuit 24y is connected to the NAND circuit 24d.
And the high voltage (H) of the output Qb of the latch circuit 26 are input, and the output T of the NAND circuit 24d becomes the low voltage (L). As a result, the R1 terminal of the latch circuit 26 becomes the low voltage (L), and the output Qb of the latch circuit 26 is maintained at the high voltage (H).
Therefore, even when the impact starts and the load current increases and the battery voltage Vb falls below the determination voltage V2, the latch circuit 26 does not turn off the switch FET.

However, when the one-shot circuit 24y is reset after a certain period of time (see timing in FIG. 4), the output T of the NAND circuit 24d becomes a high voltage (H), and the R1 terminal of the latch circuit 26 High voltage (H) is applied. At this time, if the battery voltage Vb is lower than the determination voltage V2, a low voltage (L) is applied to the S1 terminal of the latch circuit 26, so that the Qa terminal of the latch circuit 26 is maintained at the high voltage (H). Therefore, the output Qb of the latch circuit 26 changes to a low voltage (L), and the latch circuit 26 is set. As a result, the gate terminal of the switch FET becomes low voltage (L), the switch FET is turned off, and power supply to the motor M is stopped. That is, the automatic stop function of the battery-operated fastening tool operates.

When the power supply to the motor M is stopped, the high voltage (H) is applied to the S1 terminal of the latch circuit 26 because the battery voltage Vb rises above the determination voltage V2.
At this time, the output Qb of the latch circuit 26 is at the low voltage (L).
Therefore, the Qa terminal of the latch circuit 26 remains at the high voltage (H). Since a high voltage (H) is applied to the R1 terminal of the latch circuit 26, the latch circuit 2
The output Qb of No. 6 is maintained at the low voltage (L). Therefore, once the output Qb of the latch circuit 26 becomes a low voltage (L), the output Qb is maintained until the latch circuit is reset, that is, until the battery pack BP is removed.
b is kept at the low voltage (L).

As described above, according to the battery-operated fastening tool according to the present embodiment, when the motor M is started, the cancel circuit 24 is set.
The latch circuit 26 will not be set even if it falls below 2. For this reason, the switch FET is kept conductive, and the auto stop function does not operate. However, when the battery voltage Vb drops below the determination voltage V2 at the time of impact, the latch circuit 26 is set with the cancel circuit 24 reset, and the auto stop function operates. That is, the auto stop function does not operate when the motor M is started, but operates when a load is applied to the motor M. For this reason, the auto-stop function also operates properly even with a battery-operated tightening tool that uses a shift switch,
The inconvenience of operating the auto stop function in a state where the remaining capacity of the battery is not insufficient is eliminated.

[Second Embodiment] A battery-operated fastening tool according to the present embodiment is obtained by partially modifying the structure of a cancel circuit 34, as shown in FIG. It is the same as the structure of the battery-operated fastening tool according to the first embodiment. The cancellation circuit 34 of the battery-operated fastening tool according to the present embodiment includes a comparison circuit 34n, a one-shot circuit 3
4y, and a NAND circuit 34d. The comparison circuit 34n includes an operational amplifier OP4, and a voltage Vc obtained by dividing a voltage applied to both ends of the switch FET is input to a plus terminal of the operational amplifier OP4. Further, the breakdown voltage V3 of the third Zener diode ZD3 is input to the minus terminal of the operational amplifier OP4.

When starting the battery-operated fastening tool, the shift switch S
When the contact portion of W1 switches to the a contact, the switch FET
Because the transmission circuit 10 repeatedly turns on and off the motor drive circuit by the operation of the transmission circuit 10, a voltage Vc substantially equal to the battery voltage is generated across the switch FET. Here, since V3 <Vc, the comparison circuit 34 is activated when the motor M is started.
n outputs a high voltage (H) and the one-shot circuit 3
Reference numeral 4y outputs the high voltage (H) for a certain period from the timing when the high voltage (H) is input.

Therefore, the high voltage (H) from the one-shot circuit 34y and the high voltage (H) from the output Qb of the latch circuit 26 are input to the NAND circuit 34d. Becomes a low voltage (L). That is, the cancel circuit 34 is set, and when the motor M starts, the battery voltage Vb becomes equal to the determination voltage V2.
Even if it becomes smaller, the auto stop function does not work.

On the other hand, after the motor M is started, the cancel circuit 34 is reset by the one-shot circuit 34y. Therefore, if the battery voltage Vb becomes smaller than the determination voltage V2 at the time of impact, the auto stop function operates. After the motor M is started, the switch FET is in the ON state, so that Vc ≒ 0 <V3, and the cancel circuit 34 is not set. As described above, in the present embodiment, similarly to the case of the first embodiment, the automatic stop function can be properly operated in the battery-operated fastening tool with the shift switch.

[Third Embodiment] In a battery-operated fastening tool according to this embodiment, as shown in FIG. 7, a voltage Vc input to a cancel circuit 34 is connected in series with a switch FET. The battery is taken out by a shunt resistor SH, and the other structure is the same as the structure of the battery-operated fastening tool according to the second embodiment. Therefore, when the battery-operated fastening tool is started, the contact portion of the speed change switch SW1 is set to a
When the contact is switched, a voltage Vc is generated on the plus side of the shunt resistor SH when the switch FET is on. Since the resistance value of the shunt resistor SH is set so that Vc> V3, when the motor M starts, the high voltage (H) is output from the comparison circuit 34n, and the one-shot circuit 34y outputs the high voltage (H). ) Outputs a high voltage (H) for a fixed time from the input timing.

For this reason, the cancel circuit 34 is set when the motor M is started. During this time, even if the battery voltage Vb becomes lower than the determination voltage V2, the automatic stop function does not operate. Further, after the motor M is started, the cancel circuit 3 is activated by the one-shot circuit 34y.
4 is reset, the battery voltage Vb
Is smaller than the determination voltage V2, the automatic stop function operates. After starting motor M, switch FET
Is in the ON state, Vc hardly changes and the cancel circuit 34 is not set. in this way,
In the present embodiment, as in the case of the first embodiment, the automatic stop function can be accurately operated also in the battery-operated tightening tool using the speed change switch.

[0042]

According to the present invention, even with a battery-operated tightening tool using a speed change switch, the inconvenience that the automatic stop function operates when the remaining battery capacity is not insufficient is eliminated, and the automatic stop function operates properly. Become like For this reason, the time during which the battery-operated fastening tool can be used in one charge becomes longer.

[Brief description of the drawings]

FIG. 1 is a main part circuit diagram of a battery-operated fastening tool according to a first embodiment of the present invention.

FIG. 2 is a graph showing a change in battery voltage when a screw is tightened by the battery-operated fastening tool according to the first embodiment of the present invention, and FIG. FIG. (B) shows a case where the remaining charge capacity is low but not insufficient, and FIG. (C) shows a case where the remaining charge capacity is insufficient.

FIG. 3 is an operation explanatory view of the battery-operated fastening tool according to the first embodiment of the present invention.

FIG. 4 is an operation explanatory view of the battery-operated fastening tool according to the first embodiment of the present invention.

FIG. 5 is a truth table of the latch circuit of the battery-operated fastening tool according to the first embodiment of the present invention.

FIG. 6 is a main part circuit diagram of a battery-operated fastening tool according to a second embodiment of the present invention.

FIG. 7 is a main part circuit diagram of a battery-operated fastening tool according to a third embodiment of the present invention.

[Explanation of symbols]

 M motor 10 transmission circuit 22 comparison circuit 24 cancellation circuit 26 latch circuit FET switch SW1 transmission switch

Claims (1)

[Claims] 1. A battery-operated tightening tool for tightening screws by rotating a tool by a motor driven by a battery, wherein a cancel circuit is set while a starting current is flowing through the motor, and the cancel circuit is reset. Is set when the applied battery voltage is equal to or lower than a predetermined voltage, and then is set when the battery voltage is no longer applied, and a latch circuit is connected between the battery and the motor. And a switch for disconnecting the battery from the motor when the latch circuit is set.