JPH0435970B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power tool that controls the duty ratio of a tool drive motor connected to a battery through a switching element and has improved performance when the motor is locked. be.

(Prior Art) Conventionally, in order to protect the motor from burnout or regulate the torque of the motor, it is necessary to set the load current to an overload current value or a current value corresponding to a preset torque.
For example, when the set current values 11, 12, and 13 shown in FIG. 1 are reached, the switching element is turned off to cut off the power supply.

(Problem to be Solved by the Invention) However, in this case, depending on the set current value, there is a risk that the large current at the time of starting the motor may exceed the set current value, causing malfunctions such as turning off the switching element. Also, if the power supply voltage is lower than the rated value, the specified lock current, that is, the current of the set current value, will not flow through the motor even when the motor is locked, and a lock current that is less than the set current value will continue to flow through the motor. However, there was a drawback that the motor could burn out.

Furthermore, if the locking torque can be adjusted in response to the screw tightening force, etc., the current value when the switching element is off must also be adjusted separately, which means that there are two adjustment points, making the work complicated. In the end, only the locking torque is adjusted.

As a result, a lock current continues to flow through the motor during the lock state, and if this lock state continues for a long time, the motor will burn out.

Furthermore, if the torque/rotation speed characteristic of the motor can be adjusted by adjusting only one point, for example, as shown in Fig. 3 using the duty ratio control shown in Fig. 2, the lock current will flow through the motor when the motor is locked. If the battery continues to flow, the battery energy is wasted, which not only accelerates the discharge of the battery, but also causes problems in work due to the heating of the power tool due to the heat generated by the motor.

Therefore, an object of the present invention is to alleviate the decrease in the rotational speed of the motor as the motor load increases.
An object of the present invention is to provide a power tool capable of cutting off power supply to the motor regardless of the magnitude of the lock current when the motor is locked when the motor is driven with the desired torque/rotation speed characteristic shown in FIG.

(Means for Solving the Problem) That is, the present invention provides a power tool that controls the duty ratio of a switching element connected to a battery via a tool drive motor in response to load fluctuations of the motor. A lock detector that changes the output voltage by increasing the voltage across the switching element due to a reduction in the back electromotive force of the motor when the motor is locked or close to lock; A corresponding motor lock detection comparator is provided which compares the output voltage with a preset reference voltage and changes the output when the output voltage from the lock detector exceeds the reference voltage. The switching element is activated by a change in the output of the motor lock detection comparator when the output voltage from the motor exceeds the reference voltage.
It is on power tools that are held in the OFF state.

(Example) Next, the configuration of an example of the present invention is shown in FIGS. 4 to 7.
This will be explained using figures.

When a power tool, for example, a battery pack (not shown) is inserted into the battery insertion hole 1, the main switch SW1 with a forward/reverse switch function is turned on, and the motor M1 is rotated through the gear train 2. For example, inside the body case 5 of a battery-driven electric drill 4 that rotates a drill chuck 3, there is a variable resistor VR1 whose resistance value is adjusted by a dial 6, and a motor M1 that is operated by adjusting the variable resistor VR1. An electric control circuit 7 is attached to control the .

A power switch SW1, a motor M1, and a power control power MOS FET transistor FET1 for the motor M1 are connected in series to the battery pack of the electric drill 4 constructed as described above, that is, the power supply battery B.

The gate terminal of transistor FET1 has operational amplifiers OP1 and OP2, resistors R1 to R4, and capacitor C1.
The output from the triangular wave generator 8 is input to the inverting terminal of an open collector operational amplifier OP3 forming a comparator 9.

The non-inverting terminal of operational amplifier OP3 is connected to motor M1.
The voltage between the drain and source of the transistor FET1, which has increased due to a decrease in the back electromotive force of the motor M1 due to a load being applied to the motor M1 and the rotational speed of the motor M1, is applied to the resistors R9 to R14 and the offset voltage adjustment variable resistor VR1. , capacitor C7, diode
It is input as a reference voltage via the reference voltage generation circuit 10 of the amplifier, which is composed of D5 and operational amplifier OP4.

The output from the comparator 9, into which the output from the triangular wave generator 8 and the output (reference voltage) from the reference voltage generation circuit 10 are input, is connected to the gate terminal of the transistor FET1 via the resistor R5.

Moreover, the gate terminal of transistor FET1 is
Through resistor R5, diodes D1, D2 and resistor R8
and capacitor C2 absorb the noise from motor M1, and the power from battery B is connected to the square wave from operational amplifier OP1, diodes D3 and D4, and the capacitor.
A voltage boosted by C3 and C4 is applied.

In this connection state, the output of comparator 9 is ON.
When , the gate terminal of transistor FET1 is
Its gate terminal is grounded through resistor R5.
OFF, and when the output of comparator 9 is OFF, the gate terminal of transistor FET1 is connected to resistor R5,
Diode D3, D4 and capacitor C3, through R6
It is connected to the booster circuit consisting of C4 and turned ON.

Therefore, as the load on the motor M1 increases, the reference voltage of the comparator 9 increases, and the time during which the value of the triangular wave remains below the reference voltage becomes longer, and the ON time of the transistor FET1 also becomes longer. The effective value of the applied voltage also increases, the decrease in rotational speed of motor M1 is alleviated, and the desired torque:rotational speed characteristic shown in FIG. 6 is obtained.

In this way, between the gate and source of the transistor FET1 that controls the duty ratio of the motor M1,
A transistor Tr1 is connected that forcibly turns off the transistor FET1 when the motor M1 is stopped.

That is, an output voltage is generated between the drain and source of the transistor FET1 due to an increase in the voltage between the drain and source of the transistor FET1 due to a decrease in the back electromotive force of the motor M1 when the motor M1 is in a locked or nearly locked state. The lock detector 11 to be varied, in this case transistor Tr2
A lock detector 11 consisting of and resistors R18 and R19 is connected.

Further, between the output terminal of the lock detector 11 and the transistor Tr1, the output voltage from the lock detector 11 is connected to a reference voltage VR set in advance corresponding to the lock of the motor M1, in this case, a Siener diode ZD1. A motor lock detection comparator 12 that changes its output and turns on transistor Tr1 when the set reference voltage VR is exceeded; in this case,
Opamp OP5, resistors R15 to R17, and diodes
D6, Sienna diode ZD1 for setting reference voltage VR
A motor lock detection comparator 12 consisting of
is connected.

Next, the operation of this embodiment will be explained.

In the power tool control device configured as described above, when the main switch SW1 is turned on, the motor M1 is operated with the arbitrary torque/rotation speed characteristic as shown in FIG. 6, for example, adjusted by the variable resistor VR1. .

In this operating state, when the rotation speed of the motor M1 is at or above the motor lock stop state or the rotation speed close to the lock, the output voltage from the lock detector 11 is changed to the siener diode ZD1 because the back electromotive force of the motor M1 is high. The output from the motor lock detection comparator 12 is "L", so the transistor Tr1 is OFF and the motor M1 is operated with the torque/rotation speed characteristic shown in FIG.

Next, in this operating state, when the rotational speed of the motor M1 becomes almost locked, the back electromotive force of the motor M1 decreases, the drain-source voltage of the transistor FET1 increases, and the output from the lock detector 11 increases. When the voltage exceeds the preset reference voltage VR corresponding to the motor lock, the output of the motor lock detection comparator 12 becomes "H" and the transistor Tr1 is self-maintained in the ON state.

As a result, transistor FET1 turns OFF and motor M1 turns off the main switch.
The OFF state is maintained until the OFF/ON restart operation is performed, and wasteful energy consumption of battery B and heating of the power tool are effectively prevented.

Moreover, when the power supply is cut off,
This eliminates the need for troublesome work such as adjusting the lock current, and can significantly improve work efficiency when using a power tool.

(Effects of the Invention) The present invention provides a power tool that controls the duty ratio of a switching element, such as a transistor FET1, connected to a battery via a tool drive motor in response to load fluctuations of the motor. Or a lock detector that changes the output voltage by increasing the voltage across the switching element due to a reduction in the back electromotive force of the motor when the motor is in a state close to lock, and the output voltage from the lock detector corresponds to the motor lock. and a motor lock detection comparator that changes the output when the output voltage from the lock detector exceeds the reference voltage by comparing it with a preset reference voltage. The power tool is characterized in that the switching element is held in an OFF state by a change in the output of the motor lock detection comparator when the output voltage from the motor exceeds the reference voltage.

As a result, the present invention controls the duty ratio so that the amount of power supplied to the motor increases in response to an increase in the load, and increases the effective value of the voltage applied to the motor as the motor load increases. In this way, it is possible to alleviate the decrease in the rotational speed of the motor and obtain the desired torque/rotation speed characteristics shown in FIG. Since it uses voltage fluctuations across the switching element due to fluctuations in the back electromotive force of the motor, it is possible to detect the locked state of the motor without wasting battery energy, which is most important in battery-powered power tools. This has the effect of effectively cutting off the power supply to the motor.

[Brief explanation of drawings]

Figures 1 and 3 are characteristic diagrams of the conventional embodiment;
The figure is a waveform diagram showing the duty ratio control.
The figure is a cutaway side view of an electric drill 4 according to an embodiment of the present invention, FIG. 5 is an electric circuit diagram thereof, FIG. 6 is a torque/rotation speed characteristic diagram of the motor M1, and FIG. 7 is a diagram showing its operating state. FIG. 4: Electric drill, 7: Electric control circuit, 8: Triangular wave generator, 9, 12: Comparator, 10: Reference voltage generator, 11: Lock detector, FET1:
MOS FET transistor, Tr1: transistor.

Claims (1)

[Claims] 1. In a power tool that controls the duty ratio of a switching element connected to a battery via a tool drive motor in response to load fluctuations on the motor, the motor reverses when the motor becomes locked or close to lock. A lock detector changes the output voltage due to an increase in the voltage across the switching element due to a decrease in electromotive force, and a lock is established by comparing the output voltage from the lock detector with a reference voltage set in advance corresponding to the motor lock. and a motor lock detection comparator that changes the output when the output voltage from the detector exceeds the reference voltage. A power tool characterized in that the switching element is held in an OFF state by a change in the output of the motor lock detection comparator.