JP2000024960A - Trigger switch circuit for power tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit particularly for reducing contact point abrasion of a power source switch and a short-circuit switch in a trigger switch circuit mounted on a power tool. SOLUTION: Four members of a power source switch SW1 in a trigger switch circuit, a speed setting first sliding piece sliding on a variable resistor RG, a voltage control second sliding piece connected to a gate of a switching element FET and a short-circuit switch SW2 are constituted so as to be operated by interlocking with an operation lever. Thus, the power source switch SW1 is turned on and off when the first sliding piece exists in a position dislocated from the variable resitor RG, and the short-circuit switch SW2 is turned on and off when the second sliding piece is put in a floating state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trigger switch circuit mounted on a power tool such as an electric drill, and more particularly, to a method for reducing the contact wear of a power switch and a short-circuit switch in the trigger switch circuit. The present invention relates to a circuit configuration that is reduced.

[0002]

2. Description of the Related Art A conventional power tool trigger switch circuit comprises a control circuit section 10 provided at both ends of a DC power supply E, a DC motor M and a switching element FET at both ends of the DC power supply E, as shown in FIG. Are connected in series, and a series circuit in which a power switch SW1, a diode D, and a short-circuit switch SW2 are connected in series.

The control circuit 10 comprises two first and second comparators IC1 and IC2 and capacitors C1 to C5.
, Resistors R1 to R5, a speed setting variable resistor R6, resistors R7 to R16, diodes D1 and D2, and a Zener diode ZD. The connection state is as follows.

First, a DC motor M and a switching element F
ET and a resistor R in parallel with the switching element FET
8 and a capacitor C1 are connected in series. A series circuit including resistors R1 and R2 is connected in parallel to the capacitor C1. The resistor C2 is connected in parallel with the resistor R2.

The capacitor C1 is charged via the DC motor M and the resistor R8 when the switching element FET is off, and is charged when the switching element FET is on.
And discharge through the switching element FET.

A capacitor C2 is connected in parallel to both ends of the DC power supply E via a resistor R11.
Are connected in parallel with resistors R3, R4, R5 of a series circuit. A speed setting variable resistor R6 is connected in parallel to the resistor R4. The speed setting sliding member 11 is provided around the speed setting variable resistor R6. These structures will be described later.

The positive input terminal of the first comparator IC1 is connected between the resistors R1 and R2, and the negative input terminal is connected to the slider of the variable resistor R6 via a resistor R7 and via a capacitor C3. Connected to the negative side of the DC power supply E.

An output terminal of the first comparator IC1 is connected to a second comparator IC2 via a diode D1.
Is connected to the plus side input terminal. The positive input terminal of the second comparator IC2 is connected between the resistors R13 and R14 among the resistors R12, R13 and R14 connected in series to both ends of the DC power supply E.

The negative input terminal of the second comparator IC2 is connected to an intermediate position of a series circuit of a resistor R10 and a capacitor C4 connected to both ends of a DC power supply E via a resistor R11. A diode D2 and a resistor R16 are provided between the resistor R10 and the capacitor C4.
Are connected. This capacitor C
4 is a resistor R10 when the switching element FET is on.
, And is discharged via the diode D2 and the resistor R16 when the switching element FET is turned off.

The output terminal of the second comparator IC2 is connected to the gate of the switching element FET via a resistor R15. Further, the connection between the resistor R15 and the switching element FET is connected to the minus side of the DC power supply E via a Zener diode ZD.

As shown in FIG. 11, the speed setting sliding portion 11 includes, in parallel with a variable resistor R6 formed in a belt shape, a sliding member 12 which is a non-resistor having the same length, and a variable resistor R6 having the same length.
6 and a slider 13 provided so as to straddle the sliding body 12.

The slider 13 is slidably moved while being in contact with the variable resistor R6 and the slider 12 in conjunction with the pulling of an operation lever (not shown).

Next, of the operation of the trigger switch circuit having such a connection state and configuration, particularly the operation of the speed setting sliding portion 11 will be described with reference to the drawings.

First, FIG. 12 shows an equivalent circuit when the slider 13 in the speed setting sliding portion 11 moves in conjunction with the operation lever, and shows a voltage e supplied to the minus terminal of the first comparator. Is e = Ia.R5 + Ib.VR. Here, the resistance VR is a resistance corresponding to the movement of the variable resistor R6.

Therefore, as shown in FIG. 13, the relationship between the voltage e and the resistance VR is such that the resistance value of the resistance VR decreases in accordance with the stroke of the operating lever, and is linear in proportion to the resistance value of the resistance VR. The voltage e decreases.

Next, the relationship between the inter-motor voltage and the stroke by the speed setting sliding portion 11 having such characteristics will be described with reference to FIG.

First, a slider 1 that moves in conjunction with an operation lever
3 indicates that when the power is not supplied to the DC motor, the operation lever is pulled in (when the slider 13 is
The power switch SW1 (see FIG. 10) which slides on the drive lever 6 and is linked to the operation lever is turned on.

Further, when the operating lever is depressed and the variable resistance R
When the slider 13 comes into contact with 6, the voltage between the DC motors M starts to rise.

When the operating lever is further pulled in, the slider 13 for speed setting moves while sliding on the variable resistor R6, and the voltage between the motors M varies linearly according to the amount of stroke (stroke) of the operating lever. To rise.

When the operating lever is further pulled in, the slider 1
3 goes to the end of the variable resistor R6, and the maximum controllable voltage is supplied to the motor M.

If the operating lever is further pulled in this state, the short-circuit switch SW2 linked to the operating lever is turned on, and the maximum voltage having a duty ratio of 100% is supplied to the DC motor M without passing through the switching element FET. You.

In this way, the operation lever
Power switch SW1, slider 13 and short-circuit switch S
The rotation of DC motor M can be controlled by the operation with W2.

[0023]

However, the trigger switch circuit for a power tool according to the prior art described above includes a power switch SW1 and a short-circuit switch SW2.
Is turned on / off, the switching element FET is always in a controllable state. Therefore, when the power switch SW1 or the short-circuit switch SW2 is turned on / off, the switching element FET is on / off controlled, so that a potential difference occurs between the contact points of the switches, and a spark is generated when the switch is turned on / off. This spark causes a problem that contact wear increases due to this spark, and that a long life cannot be expected.

Therefore, there is a problem to be solved by a circuit configuration for reducing the contact wear of the power switch and the short-circuit switch.

[0025]

In order to solve the above-mentioned problems, a trigger switch circuit for a power tool according to the present invention comprises:
A power switch provided between the DC power supply and the motor; a switching element connected in series with the motor; a short-circuit switch connected in parallel to the switching element; and a switching element connected to the switching element in accordance with the amount of operation of the operation lever. Control means for controlling the on-duty, wherein the control means comprises a speed setting sliding portion having a first slider sliding on a variable resistor; A voltage control sliding portion connected to the gate of the element and having a second slider that slides on a non-resistive sliding body, wherein the power switch, the first and second switches are provided. The slider and the short-circuit switch are configured to operate in conjunction with the operation lever, and the second slider is connected to the DC power supply minus side (GND) when the second slider is connected to the DC power supply negative side (GND). Switch The second switch is turned on and off, and the short-circuit switch is turned on and off when the second slider is disengaged from the non-resistance slide and is in a float state.

In the variable resistor, resistors are connected in parallel.

As described above, the power switch, the short-circuit switch, and the first and second sliders are linked to the operation lever so that the power switch and the short-circuit switch are turned on and off. The switching element connected in series with the DC motor is controlled so as to be 100% cut off or conductive. By controlling in this way, the switch can be turned on / off with the potential difference between the contacts of the power supply and short-circuit switches eliminated, and the occurrence of sparks and the like generated between the contacts of the switch can be reduced. it can.

Also, since the voltage applied to the motor rises and falls in a downwardly curved shape instead of linearly by connecting a resistor in parallel with the variable resistor, a slow rotation rise time is particularly required at low speed rotation. You will be able to take a lot.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a trigger switch circuit for a power tool according to the present invention will be described with reference to the drawings. The same components as those in the prior art will be described with the same reference numerals for easy understanding.

FIG. 1 shows a trigger switch circuit for an electric tool.
As shown in the figure, the control circuit unit 2 provided at both ends of the DC power source E
0, a series circuit in which a DC motor M and a switching element FET are connected in series at both ends of a DC power supply E, and a series circuit in which a power switch SW1, a diode D, and a short-circuit switch SW2 are connected in series. .

The control circuit unit 20 includes two first and second comparators IC1 and IC2 and capacitors C1 to C5.
, Resistors R1 to R5, a speed setting variable resistor R6, resistors R7 to R17, diodes D1 and D2, and a Zener diode ZD. The connection state is as follows.

First, the DC motor M and the switching element F
ET and a resistor R in parallel with the switching element FET
8 and a capacitor C1 are connected in series. A series circuit including resistors R1 and R2 is connected in parallel to the capacitor C1. A capacitor C5 is connected in parallel with the resistor R2.

The capacitor C1 charges through the DC motor M and the resistor R8 when the switching element FET is off, and discharges through the resistor R8 and the switching element FET when the switching element FET is on.

A capacitor C2 is connected in parallel to both ends of the DC power supply E via a resistor R11.
And resistors R3, R4 and R5 connected in series in parallel. A speed setting variable resistor R6 is connected in parallel to the resistor R4. Also, an intermediate point between the temperature setting variable resistor R6 and the resistor R5 (second sliding body Z) and an intermediate point between the speed setting variable resistor R6 and the resistor R7 (third sliding body X).
Is connected to a resistor R17. The speed setting sliding portion 21 is formed around the speed setting variable resistor R6, and the first slider 23 (see FIG. 3A) that slides on the variable resistor R6 will be described later. The second part of the voltage control sliding part 22
3 (see FIG. 3B). Here, the speed setting sliding portion 21 and the voltage controlling sliding portion 22 constitute a control means, and the control means switches the switching element F in accordance with the operation pull-in amount of the operation lever.
It has a structure for controlling the so-called on-duty, which controls the gate-side potential of the ET. These structures will be described later.

The positive input terminal of the first comparator IC1 is connected between the resistors R1 and R2, and the negative input terminal is connected to the third sliding member X via a resistor R7 and via a capacitor C3. It is connected to the negative side of DC power supply E.

The output terminal of the first comparator IC1 is connected to the second comparator IC2 via a diode D1.
Is connected to the plus side input terminal. The positive input terminal of the second comparator IC2 is connected between the resistors R13 and R14 among the resistors R12, R13 and R14 connected in series to both ends of the DC power supply E.

The negative input terminal of the second comparator IC2 is connected to an intermediate position of a series circuit of a resistor R10 and a capacitor C4 connected to both ends of the DC power supply E. A series circuit including a diode D2 and a resistor R16 is connected to an intermediate position between the resistor R10 and the capacitor C4. The capacitor C4 is charged via the resistor R10 when the switching element FET is turned on, and is discharged via the diode D2 and the resistor R16 when the switching element FET is turned off.

The output terminal of the second comparator IC2 is connected to the gate side of the switching element FET via the voltage control sliding portion 22 and the resistor R15. or,
The power supply E is connected to the negative side of the DC power supply E via a Zener diode ZD from between the resistor R15 and the switching element FET.

As shown in FIG. 2, the speed setting sliding section 21 is a non-resistive element having the same width and a predetermined length at the beginning and end sides of the variable resistor R6 formed in a belt shape. 1
And the second sliding bodies Y and Z are formed on the same extension as the first and second sliding bodies Y and Z and at the same length as the variable resistor R6 at predetermined intervals. And a third sliding body X.

Then, as shown in FIG. 3A, the first sliding body Y, the variable resistor R6, and the second sliding body Z
And the first slider 23 formed of a conductive member is slidably contacted so as to straddle the third slider X.

The first slider 23 is, as shown in FIG.
Notches are provided at both ends to form a forked shape, the forked portion is bent in the same direction, and free ends at both ends are further bent in the opposite direction to provide a contact 25 formed. I have.

As shown in FIG. 2, the voltage control sliding portion 22 includes a fourth sliding body C which is a non-resistive body formed in a belt shape,
A non-resistive fifth sliding body B formed on the same extension line as the fourth sliding body C and having a predetermined length at a predetermined interval.
And the fifth sliding member B and a sixth non-resistive sliding member A formed with a key-shaped gap.

The length of the fifth and sixth sliding members B and A is shorter than the length of the third sliding member X of the speed setting sliding portion.

Then, as shown in FIG. 3B, a conductive member is formed so as to straddle the fourth sliding member C, the variable resistor R6, the fifth sliding member B, and the sixth sliding member A. The second
Are slidably contacted with each other.

The second slider 24 used for the voltage control sliding section 22 has the same shape as the first slider 23 used for the speed setting sliding section 21. I have. That is, as shown in FIG. 4, the contact structure has a bifurcated shape at both ends.

The voltage control sliding portion 22 having the above-described structure floats the second slider 24 when the operation lever is retracted and the second slider 24 is in a full stroke state (FIG. 3B).
24A), the on-duty of the switching element FET, that is, the voltage of the gate is set to the continuous High state, and the switching element FET is made 100% conductive.

Next, among the operations of the trigger switch circuit having such a connection state and configuration, the operation of the speed setting sliding portion 21 and the operation of the voltage control sliding portion 22 which functions in conjunction therewith will be described. This will be described with reference to FIG.

First, FIG. 5 shows an equivalent circuit when the first slider 23 of the speed setting sliding portion 21 moves in conjunction with the operation lever. The equivalent circuit is connected to the minus input terminal of the first comparator IC1. The supplied voltage e is e = Ia · R5 + Ib · R. Here, the resistance R is a combined resistance of the variable resistance VR and the resistance R17, and R = 1 / ((1 / VR) + (1 / R17)).

Therefore, e = Ia.R5 + Ib / ((1 / VR) + (1 / R1
7))

Here, by setting the resistances R17 ≦ R6, the relationship between the voltage e supplied to the minus input terminal of the first comparator IC1 and the variable resistance VR becomes as shown in FIG. As the value of increases,
The voltage e increases in a curved upward curve.

On the contrary, as shown in FIG.
The relationship between the voltage e supplied to the negative input terminal of the comparator IC1 and the trigger stroke by the operation lever is such that when the first slider 23 that moves in conjunction with the operation lever pulls the operation lever, the variable resistor VR Since the value moves in the decreasing direction, the voltage e supplied to the minus input terminal of the first comparator IC1 decreases in a upward curve as the trigger stroke increases.

Further, as shown in FIG. 8, the relationship between the GS voltage of the switching element FET and the trigger stroke is such that the voltage e supplied to the minus input terminal of the first comparator IC1 has an upward curve. Because of the influence (see FIG. 7), the voltage of the output terminal of the second comparator IC2, that is, the voltage between the GS of the switching element FET and the voltage of the switching element FET rises along a downward curve.

The relationship between the motor-to-motor voltage and the stroke by the speed setting sliding portion 21 and the voltage controlling sliding portion 22 having the above-described characteristics between the trigger stroke and the GS voltage is described. , FIG. 1, FIG. 2 to FIG. 4, and FIG.

First, when the power is not supplied to the DC motor M, the first and second sliders 23 and 24, which move in conjunction with the operation lever, are connected to the first slider 21 of the speed setting sliding portion 21. Is located in the region of the first sliding member Y which is a non-resistance conductor, the second slider 24 of the voltage control sliding portion 22 is located in the region of the fifth sliding member B, Since the power supply voltage is short-circuited to the ground side, the on-duty of the switching element FET is cut off by 100%. In this state, no potential is applied between the DC motors M and the power switch SW1
No potential difference occurs between them. In such a state, the power switch SW1 interlocked with the operation lever
(See FIG. 1) can be turned on and off.

When the power switch SW1 is turned on, power is supplied to each circuit, and the first and second comparator ICs are turned on.
1. A power supply voltage is also supplied to the IC 2 to establish a controllable system. At this time, the second slider 24 of the voltage control
Is fitted in a key-like position between the fifth sliding body B and the sixth sliding body A, is short-circuited to the ground side of the power supply voltage, and the on-duty of the switching element FET is cut off 100%. It is in a state.

When the operating lever is further retracted, the first slider 23 of the speed setting sliding portion 21 comes to the starting end of the first sliding body Y and the variable resistor R6. At the same time, the second slider 24 of the voltage control sliding portion 22 contacts only the sixth sliding member A, and the controllable minimum voltage is supplied to the motor M.

When the operating lever is further pulled in, the first slider 23 of the speed setting sliding portion 21 moves while sliding on the variable resistor R6. At this time, as shown in FIG. 8, the voltage (on-duty) between the switching element FET and GS rises as a downward curve. Therefore, the voltage between the motors M increases slowly as compared with the amount of pulling in of the operation lever, so that the rotation of the motor M is not a sudden rotation but a gradual increase. This has the advantage that a large amount of low-speed rotation can be obtained, and positioning during drilling and adjustment of the degree of tightening at the time of screw tightening become easy.

When the operating lever is further pulled in, the first slider 23 of the speed setting sliding portion 21 comes off the terminal end of the variable resistor R6, comes into contact with the non-resistance second sliding member Z, and the motor M Is supplied with the maximum voltage that can be controlled.

In this state, if the operating lever is further pulled in, the first slider 23 of the speed setting sliding portion 21 slides on the non-resistive second sliding member Z, and the voltage control slide. The second slider 24 of the part 22 is disengaged from the sixth slider A, and is in a floating state, and the on-duty of the switching element FET is in a state of 100% conduction. 100
The potential difference hardly occurs between the drain and the source of the switching element FET in the% conduction state.

In such a state, the short-circuit switch SW2 can be turned on, and if it is further retracted, it cannot be further retracted, so-called full stroke. When the short-circuit switch SW2 is turned on, the switching element FE
The maximum voltage is supplied without passing through T, and the DC motor M rotates at full speed.

Since the contact of the short-circuit switch SW2 can be turned on without any potential difference, the occurrence of spark or the like can be reduced. The short-circuit switch S
W2 is turned off under the same conditions as when it is turned on.

As described above, when the power switch SW1 and the short-circuit switch SW2 are turned on and off, they are turned on and off while eliminating the potential difference between the contacts. Wear can be reduced. When the contact wear can be reduced in this way, inexpensive contact materials can be used,
The contact material such as silver and silver alloy is not required for the contact, and the switch itself can be downsized.

In addition, since the rotation control of the DC motor is controlled by raising and lowering the voltage with a downwardly curved voltage, the rotation can be gently increased particularly at low speed rotation, and the screw tightening adjustment can be performed. Easier to do.

[0064]

As described above, the trigger switch circuit of the electric power tool according to the present invention can be used in both the power supply switch which is a part of the circuit configuration and the short-circuit switch connected in parallel with the switching element. Since the switch is turned on and off with the potential difference between the contacts eliminated, the spark etc. generated from the contacts of both switches can be extremely reduced, the service life of the contacts can be extended, and the material of the switch Has the effect of being able to be cheap.

Further, since the voltage applied to the motor rises and falls in a downward curved shape instead of linearly by connecting the resistor in parallel with the variable resistor, a slow rotation rise time is particularly required at low speed rotation. There is an effect that it is easy to adjust the screw tightening, etc.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a trigger switch for a power tool according to the present invention.

FIG. 2 is a plan view showing a pattern of a sliding body of a sliding portion for speed setting and a sliding portion for voltage control.

FIG. 3A is a schematic sectional view of a speed setting sliding portion, and FIG. 3B is a schematic sectional view of a voltage control sliding portion.

FIG. 4 is a plan view of the slider.

FIG. 5 is an equivalent circuit diagram of a circuit of the speed setting sliding section.

FIG. 6 is a schematic graph showing a relationship between a voltage e supplied to a negative input terminal of the first comparator and a resistance value of a variable resistor VR.

FIG. 7 is a schematic graph showing a relationship between a voltage e supplied to a negative input terminal of the first comparator and a trigger stroke.

FIG. 8 is a schematic graph showing a relationship between a GS voltage and a trigger stroke of the switching element FET.

FIG. 9 is a graph showing a relationship between a motor-to-motor voltage and a stroke.

FIG. 10 is a circuit diagram of a trigger switch for a power tool according to the related art.

FIG. 11 is an explanatory view showing a pattern of a sliding body of a speed setting sliding portion in the prior art.

FIG. 12 is an equivalent circuit diagram of a speed setting sliding portion according to the related art.

FIG. 13 is a graph showing a relationship between a trigger stroke and a voltage of a variable resistor according to the related art.

FIG. 14 is a graph showing a relationship between a motor-to-motor voltage and a stroke of an operation lever in the related art.

[Explanation of symbols]

Reference numeral 20: control circuit section, 21; speed setting sliding section, 22; voltage control sliding section, 23; first slider, 24; second slider, 25; contact point, SW1, power supply Switch, SW2;
Short-circuit switch, SW3; Control switch, R1 to R
5; resistance, R6; variable resistance, R7 to R15; resistance, C1
To C4; capacitor, FET; switching element, M;
DC motor, D1 to D3; diode, E; DC power supply,
IC1; first comparator, IC2; second comparator

Continued on the front page (72) Inventor Isao Inagaki 7-7-3 Kikuna, Kohoku-ku, Yokohama-shi, Kanagawa F-term in Satori Electric Co., Ltd. 3C036 EE19 EE20

Claims (2)

[Claims] 1. A power supply switch provided between a DC power supply and a motor, a switching element connected in series with the motor, a short-circuit switch connected in parallel to the switching element, and a switch for operating the operating lever. Control means for controlling the on-duty of the switching element, and the trigger switch circuit, wherein the control means,
A speed setting sliding portion including a first slider that slides on the variable resistor, and connected to a gate of the switching element;
And a voltage control sliding portion provided with a second slider that slides on a non-resistance sliding body, wherein the power switch;
The first and second sliders and the short-circuit switch are configured to operate in conjunction with the operation lever, and the second slider is connected to a negative DC power source (GND). The power switch is turned on and off when the switch is turned off, and the short-circuit switch is turned on and off when the second slider is detached from the non-resistance slide and floats.
A trigger switch circuit for a power tool, wherein the trigger switch circuit is turned off. 2. The trigger switch circuit for an electric tool according to claim 1, wherein the variable resistor has a resistor connected in parallel.