JPH02174582A - Switch circuit for power tool - Google Patents

Abstract

PURPOSE:To increase a motor torque by detecting the increase of a motor load through a current value at the time of the low-speed rotation of a motor and by applying a feedback to the motor load. CONSTITUTION:Normally when a switch 15 is opened and a low-speed control circuit 13 is in an operating state and a motor M is not loaded, a triangular- wave oscillator circuit 16 produces a triangular wave, which is set as a basis, to operate a switching circuit 17 to operate an output element 14 and to rotation-control the motor M. When a load is applied to the motor M and electric current is increased, the increased current is detected by a motor current sensing circuit 20 composed of a resistance 21 and an amplifier circuit 22 to send a signal to the triangular-wave oscillator circuit 16 to increase the load current of the motor.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a switch circuit for a power tool that controls the drive of a motor of various power tools such as, for example, an electric screwdriver and an electric drill.

(b) Prior Art Usually, the switch of this type of power tool is constructed of the circuit shown in Section 3.

That is, the motor M is connected to the power source E through a main circuit 50, and a forward rotation control switch section 51 and a reverse rotation control switch section 52 are interposed in the main circuit 50, which connect the motor M by reversing its polarity. However, these switch sections 51, . 52, when one of them is turned on, the power is turned on and the rotation is controlled in a predetermined direction at the same time.

Further, an output element 53 and a short-circuit switch part 54 are connected in parallel to the above-mentioned main circuit 50, and the output element 53 controls the rotation speed of the motor M by controlling switching of this, and also controls the rotation speed of the motor M. When the switch unit 54 is turned on, the motor M is directly connected to the power source E and driven at high output 6. The diode 55.5 in the forward direction from both ends of the motor M
A triangular wave oscillator circuit 57 connected through a triangular wave oscillating circuit 57 outputs a triangular wave control signal a as shown in FIG. The rotation control signal C is output when the level of the triangular wave control signal a is high by comparing the setting signal A, and the rotation control signal C is used to control the switching of the output element 53 via the switching circuit 60, thereby controlling the motor. Controls the rotation of M.

Further, by changing the setting of the variable resistor 59 described above, rotation control signals cl, c2. The time widths tl and t of c3, respectively.
2. Different signals of t3 can be obtained, and the rotational speed of the motor M can be varied steplessly using these signals.

Therefore, the power tool switch is
The motor will be equipped with a forward/reverse selector switch which also serves as a forward/reverse switch, and a slide switch to steplessly vary the rotation of the motor M (see Japanese Patent Application No. 62-288229).

(c) Problems to be solved by the invention In the case of the switch circuit configured as described above, it is easy to control the power, so it is easy to use. The problem is that the components such as the switch mechanism, variable resistor, and high output control element are expensive, which increases the cost.

In order to solve this problem, for example, if the motor output control is configured to control the output in two stages, high and low, the switch mechanism will have a 2-position switching mechanism, eliminating the need for a variable resistor, and reducing costs. However, since the motor power control is in two stages, it is difficult to use.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a switch circuit for a power tool, which has a simple switch circuit configuration and can provide motor power control equivalent to stepless speed change.

(d) Means for Solving Problems The first aspect of the present invention provides a switch circuit for switching the output of a motor between high speed and low speed, and a control current set to low speed when the switch circuit is at low speed. and a motor current detection circuit that detects the current flowing through the motor when the motor is controlled at low speed, and the motor current detection circuit detects an increase in current. The switch circuit for a power tool is characterized in that the output of the motor current detection circuit is fed back to the low speed control circuit so as to increase the control current of the low speed control circuit when the motor current detection circuit detects In the second aspect of the invention, the low-speed control circuit oscillates a triangular wave based on ON time and OFF time, and
A triangular wave oscillation circuit that generates a control output when the time is reached;
A switching circuit performs switching operation using the above control output, and the motor main circuit is turned on by the operation of the above switching circuit.
The motor current detection circuit is composed of an output element that controls the supply current of the motor by FF/ON control, and the motor current detection circuit includes a resistor interposed between the output element and the power supply, and a motor current detecting circuit that detects the motor current from both ends of this resistor. The switch circuit for the power tool according to the first aspect of the invention is characterized in that the switch circuit includes an amplifier circuit that extracts a detection signal and feeds it back to the triangular wave oscillation circuit.

(E) Function The switch circuit of the power tool of the present invention detects the current flowing through the motor current detection circuit when the switch circuit is at low speed, and at the same time detects the current flowing through the motor when the switch circuit is at low speed, and when this detection is an increase in current, that is, when the switch circuit is at low speed, When the load becomes large, this detection output is used to increase the control current of the low-speed control circuit that drives and controls the motor by increasing the control current of the low-speed control circuit that drives and controls the motor. increase.

(/\) Effects of the Invention As a result of the above, according to the present invention, when the motor load increases during low-speed rotation control, the motor control current is automatically increased and the motor torque is increased. '', a control state equivalent to a continuously variable speed can be obtained.

As a result, rotational control equivalent to continuously variable speed can be obtained even though the speed is changed in two stages (high and low), making it easy to use, simplifying the circuit configuration, and reducing costs.

(1-) Examples Embodiments of this invention will be described in detail below with reference to the drawings.

The drawing shows a switch circuit of a power tool. In FIG. 1, a motor M is connected to a power source E through a main circuit 10. In this main circuit 10, there is a forward rotation control switch that reverses the polarity of the motor M and connects it. A rotation control switch section 11 and a reverse rotation control switch section 12 are installed, and when one of these switch sections 11, 12 is turned on, the power is turned on and the rotation is controlled in a predetermined direction at the same time.

Furthermore, an output element 14 forming part of the low-speed control circuit 13 and a short-circuit switch section 15 forming the high-speed control circuit are connected in parallel to the main circuit 10 described above.
By controlling this by switching, the torque of the motor M is controlled, and when the short-circuit switch section 15 is turned on, the motor M is directly connected to the power source E and the motor M is controlled to rotate at high speed.

The aforementioned low-speed control circuit 13 is composed of a triangular wave oscillation circuit 16, a switching circuit 17, and the aforementioned output element 14. The circuit 16 is configured with a resistor, a capacitor, and an amplifier, and generates a triangular wave (see the triangular wave in FIG. 4) based on ON time and OFF time, and also generates a second
As shown in the figure, a control signal a is output during ON time (signal charging).

The above-described switching circuit 17 performs a switching operation on the output element 14 in response to the above-mentioned control signal to drive and control the motor M.

A resistor 21 constituting a part of a motor current detection circuit 20 that detects the current flowing through the motor M is interposed between the output cable 14 and the power supply E, and this motor current detection time 1% 20 is The circuit is configured by the above-mentioned resistor 21 and an amplifier circuit 22, and the amplifier circuit 22 amplifies both ends of the resistor 21.
outputs a detection signal corresponding to an increase or decrease in the current flowing through the motor M, feeds this detection output back to the triangular wave oscillation circuit, and in response to an increase in the current flowing through the motor M, the control signal a of the triangular wave oscillation circuit 6 increases. As a result, the control current of the motor M is increased.

To explain the operation of the switch circuit of the power tool configured in this way, normally the short circuit switch section 15 is open, so the low speed control circuit 13 is in the operating state, and the forward rotation control switch section 11 or the reverse rotation control switch is in the operating state. By turning on the section 12, the motor M is controlled to rotate at a low speed in a set direction.

When there is no load on the motor M, the triangular wave oscillation circuit 16 oscillates a triangular wave, which is basically set, and the switching circuit 17 is operated with the control signal a whose ON time width is 1゛1, and the output element 14 is operated to control the rotation of motor M.

When a load is applied to the motor M, the current flowing through the motor M increases, and the motor current detection circuit 20 formed by the resistor 21 and the amplifier circuit 22 detects this increased current and outputs the triangular wave oscillation circuit. The ON time of the triangular wave oscillated by the triangular wave oscillation circuit 16 is increased correspondingly to the increase, and as a result, the time width of the control signal a from the triangular wave oscillation circuit 16 is T2,
T3 becomes longer, the ON time of the output element 14 becomes longer, and the torque of the motor M increases.

As a result of the above, when controlling the rotation at low speed, the motor M
When the load on the motor M is increased, the control current of the motor M is automatically increased and the motor torque is increased, so that a control state equivalent to a continuously variable speed is obtained.

Next, when switching to high speed, by turning on the short circuit switch section 15, the motor M is directly rotationally controlled by the power source E, so that high speed rotation control is achieved.

At this time, since switching is performed with the motor torque being high, there is extremely little shock during switching, allowing for smooth work.

As a result, even though the speed is changed in two stages (high and low), it is possible to obtain rotation control equivalent to continuously variable speed, which simplifies the circuit configuration with ease of use, and reduces costs.

Note that the configuration of the present invention is not limited to the configuration of the above-described embodiment.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, Fig. 1 is a switch circuit diagram of a power tool, Fig. 2 is a signal waveform diagram of the main part, Fig. 3 is a switch circuit diagram of the prior art, and Fig. 4 is its main part. FIG. 10... Main circuit 13... Low speed control circuit 1
4... Output element 16... Triangular wave oscillation circuit 1
7...Switching circuit 20...Motor current detection circuit

Claims (2)

[Claims] (1) a switch circuit that switches the motor output between high speed and low speed; a low speed control circuit that drives and controls the motor with a control current set to low speed when the switch circuit is low speed; a motor current detection circuit that detects a current flowing through the motor when the motor is being controlled; and when the motor current detection circuit detects an increase in current, the control current of the low speed control circuit is increased; A switch circuit for a power tool characterized in that the output of a motor current detection circuit is fed back to a low speed control circuit. (2) The low-speed control circuit includes a triangular wave oscillation circuit that oscillates a triangular wave based on ON time and OFF time, and generates a control output during the ON time, and a switching circuit that performs a switching operation using the control output; The motor current detection circuit includes an output element that controls the motor main circuit by turning the motor main circuit OFF-ON through the operation of a switching circuit, and the motor current detection circuit includes a resistor interposed between the output element and a power source. 2. The switch circuit for a power tool according to claim 1, further comprising: an amplifier circuit which extracts a motor current detection signal from both ends of the resistor and feeds it back to the triangular wave oscillation circuit.