JPH01164292A - Controlling circuit with battery driving of motor-operated tool - Google Patents

Abstract

PURPOSE:To obtain a controlling circuit with the battery driving of a motor- operated tool excellent in the characteristic of a torque limiter, by stopping the oscillation of the chopping wave generator of a pulse width modulation circuit, when current detecting signal comes to a value according to the set torque output of a previously set motor. CONSTITUTION:By a voltage comparing circuit 21, the chopping wave signal Ea of output generated from a chopping wave generator 20, and the output signal of a variable resistor VR1 are compared with each other, and the pulse of a duty according to the compared result is applied to a MOSFET transistor Tr 2. In the meantime, by an integrator 24, motor current signal Ec detected by a current detecting resistor R1 is integrated. Besides, by a voltage comparing circuit 25, the oscillation of the chopping wave generator 20 is stopped, when the output signal Ee of the integrator 24 comes to a value according to the set torque of a motor set by a variable resistor VR2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to torque and rotational speed control of a power tool powered by a battery.

(Prior art) Conventionally, the torque-rotation speed characteristic of a DC motor is as shown in Fig. 11. When a battery-powered power tool is an electric screwdriver, for example, when a screw is tightened at the rotation speed of N1 in Fig. 11, it is tightened. When the motor is locked at the end of the process, a locking torque of T1 is generated, and this locking torque may cause the screw to break. Therefore, in such cases, install a mechanical torque limiter clutch on the motor axis. The motor is made to idle at Tlo in FIG.

On the other hand, a mechanical torque limiter has a short lifespan due to wear of the limiter rock, requiring parts to be replaced in a short period of time. A triangular wave is generated by connecting a motor 3, a power MO3FET 4, and a current detection resistor 5 in series, and using a battery 1 as a power source.
! ! a comparator 7 that converts the output from 6 into a pulse with an arbitrary duty ratio and inputs it to the gate of MO8FEr4;
A duty ratio 1IIIJ111 circuit 8 that controls the duty ratio of the pulses output from the comparator 7 in proportion to the output from the current detection resistor 5, and settings of the motor 3 in which the output from the current detection resistor 5 is preset. An electronic torque limiter device consisting of a torque limiter circuit 9 that controls the gate voltage of the MOS FET 4 to stop the supply of power to the motor 3 when corresponding to the torque is considered, and this circuit shown in FIG. 3 is controlled by the torque-rotational speed characteristic shown in FIG.

In the case of such an electronic torque limiter device, as shown in FIG. 9, a current detection resistor 5 is used between the source terminal S and 0, and the voltage drop across the resistor can be regarded as the load current. In that case, the value of the current detection resistor 5 is usually 10 to 20 m.
Ω, but since more than IOA flows as a current, the current detection resistor 5 is P=I R=10 X(20x10')=2w
t, a resistance of P=2 watt or more is required. In order to achieve such a low resistance value and high power resistance, for example, an insulated lead wire of 0.75xts2 is required to have a length of 0.5 to 1 m.
Although it is used by winding it into a coil, the current detection resistor 5 generates heat corresponding to the wattage, so it was very difficult to mount the current detection resistor 5, especially considering the motor characteristics. If sufficient heat dissipation is taken into account, the shape of the power tool becomes too large, which has the disadvantage of impeding workability and portability using the power tool.

(Problems to be Solved by the Invention) The present invention provides a battery-powered power tool (for example, an electric screwdriver) that does not shorten the life of a battery-driven power tool (for example, an electric screwdriver) and that reduces the external shape of the power tool. The goal is to provide a battery-powered control circuit for power tools with excellent torque limiter characteristics without increasing the size.

(Means for solving the problem) What is the invention? MO with motor and current sense terminal on f source battery
Connect each of the 8FETs and the current detection resistor in series,
a comparator that converts the output from the triangular wave generator powered by the battery into pulses with an arbitrary duty ratio and inputs the pulses to the gate of the MO8FET with a current sense terminal; and a motor whose output from the current detection resistor is set in advance. and a torque limiter circuit that stops the oscillation of the triangular wave generator and stops the supply of power to the motor when the set torque output corresponds to the set torque output.

(Function) In the battery-driven control circuit for the power tool configured as described above, when the power switch is turned on, the MO8FET with a current sense terminal connected in series with the battery-driven motor
A pulse from a circuit that combines a triangular wave generator and a comparator circuit is input to the gate terminal of the motor, and the motor rotates at a speed corresponding to the duty ratio of pulse energization, greatly reducing power loss in the drive transistor and dissipating heat. The board can be made smaller and the electrical circuit can be easily mounted.Furthermore, although a current corresponding to the rotational torque of the motor flows through the current detection resistor connected to the current sense terminal of the MO8FET with a current sense terminal, the load current does not flow, allowing the use of a low-power current sensing resistor, but when the output from the current sensing resistor exceeds a preset value, an output is generated from the torque limiter circuit and causes the triangular wave generator to oscillate. Stop it, MOS
By cutting off the FET, the power supply to the motor is stopped, which allows the electronic circuit to have a torque limiter function by omitting the torque limiter of the mechanical clutch, and also prevents triangular waves from being generated when the torque limiter is activated. By stopping the oscillation of the device, battery power consumption is significantly reduced, and battery-powered power tools (
For example, when using an electric screwdriver), there is no reduction in service life like when using a mechanical torque limiter, and
It is possible to obtain a control circuit for battery-powered power tools with excellent torque limiter characteristics without increasing the external shape of the shell.

(Example) Next, the configuration of an example of the present invention will be described with reference to FIGS. 1 to 7.

Next, FIG. 1 shows a structural diagram of a battery driver. The battery driver 11 is located at the bottom of the main body 12! ! The battery bag 14 is inserted into the insertion IL13, the main switch SW1 is connected to the attached battery terminal, and the upper part of the motor M is connected to the electric
There are a 1111 circuit 15, a variable resistor VRI adjusted by a dial 16, and a variable resistor VR2 adjusted by a dial 17, R1 is used for shifting, VR2 is used for torque limiter adjustment, and the motor M has a gear. A chuck 19 is connected via the row 18.

Next, FIG. 2 is a block circuit diagram of this embodiment, and FIG. 3 is an electric circuit diagram thereof. In FIG. 2, Ea to E-, h are the voltages when the motor M is without fLAi. As a result, when the operation shown in FIG. 4 is performed and the load increases, Eh changes as shown in FIG. 5.

The power supply battery B includes a power switch SW1, a DC motor M for driving electric tools, etc., and a power MO8FET transistor for power control of the motor M, which has a lower on-resistance than a bipolar transistor, allowing the size of the heat sink to be made smaller, and any number of transistors can be connected in parallel. A MOSFET transistor Tr2 with a current sense terminal that can reduce the power loss by half by connecting two in parallel, for example, compared to the case of one, and a resistor of about 20 to 300 for detecting the motor MW current. R1 and each are connected in series, MOS FET
A comparator I is connected to the gate terminal of the transistor Tr2.
CI, resistors R2 to R6, R15, and capacitors CI, C2
A triangular wave generator consisting of C1 and R, respectively.
3 sets the oscillation frequency, and resistors R2 to R6, RIs
The output from the triangular wave generator 20 whose amplitude is determined by is a voltage comparison circuit 21 consisting of a comparator IC2, resistors R7 to R1G, and VRl, and a pulse generating circuit that changes the duty ratio by a change in the comparison voltage caused by a change in VRl. 22, the output from the current detection resistor R1 is input to the transistor Trl after being converted into a pulse with an arbitrary duty ratio. IC3 and resistor R1 (i~R19 and capacitor C5
A non-inverting amplifier 23 consisting of a resistor R2G, a capacitor C3, and a diode D2.
an integrating circuit 24 that converts the output pulse from the output pulse into a level voltage;
Comparator IC4, resistors R21 to R25, and variable resistor V
A voltage comparison circuit 25 consisting of R2 and a transistor Tr
4 and resistors R26 to R28, and is input to the gate terminal of 5CR1 forming a stop circuit 27.

Next, the operation of this embodiment will be explained.

First, as a means for changing the no-load rotation speed of the DC motor M, the control circuit of this embodiment changes the average voltage applied to the t-taper M by controlling the duty ratio of pulses.
Vt=Ea+Ia-Rat-Ea Therefore, la=□ holds between the voltage of motor M, vt1, armature reaction Ea1, armature resistance Ra, and motor current 1a.

Ea As a result, when the torque increases and the rotational speed decreases, the armature reaction Ea becomes smaller, so the motor current 1a increases, and this increases the motor current la, that is, the amplitude of the drive pulse current. become.

Therefore, the amplitude of this drive pulse current is fixed by R1 of low resistance.
After converting the voltage into a voltage and amplifying it, the integrating circuit 24 converts it into a level voltage and inputs it to the voltage comparator circuit 25 to perform a limiter operation.

Next, variable speed of the motor M is performed as follows.

That is, FIG. 4 shows the motor no-load operating characteristics when the comparison voltage EO of the comparator IC2 is changed as EOI, EO2, and EO3 using the variable resistor VR1, and therefore,
By changing the comparison voltage EO of the comparator IC2 as EOI, EO2, and EO3 using the variable resistor VRI, the duty ratio of the pulse from the pulse generating voltage comparison circuit 25 can be changed to 11/lo-, -t3/lo. The rotational speed of the motor M can be changed from low speed to high speed.

Next, in FIG. 5, the duty ratio of the pulse is set to a no-load ratio of 172 so that about 50% voltage is applied to the motor M in a no-load state with the comparison voltage EO of the comparator IC2 constant. In the case of increasing the load on motor M, if the load on motor M increases now, motor M
As the rotation speed decreases and the motor current 1a increases, the amplitude of the pulse voltage EC from both ends of the current detection resistor R1 also increases, and the output voltage of the integrating circuit 24 also changes from Eel to Eel.
increases to

Furthermore, when the torque is excessive, such as when the screw tightening is completed, the motor M current 1a increases significantly, and the output voltage Ee3 of the integrating circuit 24 and the like increases to the reference voltage Eg set by the variable resistor VR2 in accordance with the screw tightening torque, etc. If it exceeds the voltage comparator circuit 25
The output of transistors Tr4 and 5CR1 is turned on.
turns on, the oscillation of the triangular wave generator 20 stops, one terminal of the comparator ICI becomes Ov, the output voltage of the comparator IC2 also becomes OV, and the transistor Tr1 also becomes Ov.
The FF becomes the MOS FET transistor Tr2.
The gate voltage of Tr3 becomes Ov, and the transistor Tr2
．． Along with Tr3, the motor M is turned off.

When the motor M/fi is turned off, the voltages FC and Eh also become OV, but 5CR1 remains conductive as long as the anode current flows, so the oscillation of the triangular wave generator 20 continues to stop, and the motor current is subsequently interrupted.

In this way, for example, with an electric screwdriver, the screw will not be cut due to over-tightening, and burnout of the motor M during overload can be reliably prevented.Furthermore, when the limiter is activated, the motor M is in a state where a constant torque is applied. Since the system is reliably stopped when the power supply is stopped, it is possible to reduce unnecessary power consumption of the battery, and to prevent additional tightening that would occur if the constant torque application state continues after the limiter is activated. It is also possible to prevent the phenomenon of thread breakage caused by.

In addition, in Fig. 3, in order to increase the drive current of the motor, MOS
MOS FET Tr3 in parallel with FET Tr2
The operation in this case is shown in FIG.

(Effects of the Invention) The present invention provides a power supply battery with a motor and a current sense terminal.
Each of the SFET and the current detection resistor is connected in series,
a comparator that converts the output from the triangular wave generator powered by the battery into pulses with an arbitrary duty ratio and inputs the pulses to the gate of the MOSFET with a current sense terminal, and the output from the current detection resistor is set in advance. A battery-driven control circuit for a power tool includes a torque limiter circuit that stops oscillation of the triangular wave generator and stops supplying power to the motor when the torque output corresponds to a set torque output of the motor.

This greatly reduces the power loss of the drive transistor, making the heat sink smaller and making it easier to mount the electric circuit.Furthermore, if the power tool is an electric screwdriver, for example, it reliably prevents the screw from being cut due to over-tightening. In addition, burnout of the motor during overload can be reliably prevented.Furthermore, since the motor is reliably stopped when the power supply is stopped, unnecessary power consumption of the battery can be reduced. This has the effect of preventing the phenomenon of screw breakage due to additional tightening that occurs when a constant torque application state continues.

[Brief explanation of the drawing]

Figure 1 is a broken side view of a battery driver according to an embodiment of the present invention, Figure 2 is a block diagram of its control circuit, and Figure 3 is a block diagram of its control circuit.
4 to 6 are its operation diagrams, FIG. 7 is a connection diagram of the MOSFET, FIG. 8 is an electrical control circuit diagram of the conventional example, and FIG. 9 is the conventional example. MOS
FET connection diagram, FIG. 10 is a torque-rotational speed characteristic diagram of the DC motor in the electric control circuit of FIG. 8, and FIGS. 11 and 12 are torque-rotational speed characteristic diagrams of the DC motor in the conventional embodiment. . B...Power supply battery M...DC motor Tr2
...MOS FET transistor R1...Resistor for motor current detection 20...Triangular wave generator 21...Voltage comparison circuit 2
2... Pulse generation circuit 25... Voltage comparison circuit 27
... Stop circuit applicant Mari Denki Seisakusho Co., Ltd. Agent Patent attorney Oka 1) Hidehiko (2 others) 14 ・ Figure 1 Figure ■ fJ Figure 12 Eh 1
・Figure 4, Figure 6, Figure 10, Figure 91! I 7WJ Figure 8

Claims (1)

[Claims] A motor, a MOSFET with a current sense terminal, and a current detection resistor are each connected in series to a power supply battery, and the output from a triangular wave generator using the battery as a power supply is converted into pulses with an arbitrary duty ratio, and the current sense terminal is connected to the current sense terminal. With MOSFE
a comparator input to the gate of T; and a torque limiter circuit that stops oscillation of the triangular wave generator and stops supplying power to the motor when the output from the current detection resistor corresponds to a preset torque output of the motor. A battery-powered control circuit for a power tool, characterized by comprising each of the following.