JP3704432B2 - Trigger switch circuit for electric tools - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a trigger switch circuit mounted on an electric tool such as an electric drill, and more specifically, a circuit configuration in which contact wear of a power switch and a short-circuit switch in the trigger switch circuit is reduced. About.
[0002]
[Prior art]
As shown in FIG. 6, the trigger switch circuit for a power tool in the prior art has a control circuit unit 10 provided at both ends of a DC power supply E, and a DC motor M and a switching element FET connected in series to both ends of the DC power supply E. The power supply switch SW1, a diode D, and a short circuit switch SW2 are connected in series.
[0003]
The control circuit unit 10 includes two first and second comparators IC1 and IC2, capacitors C1 to C5, resistors R1 to R5, a speed setting variable resistor R6, resistors R7 to R16, and diodes D1 and D2. And a Zener diode ZD, the connection state of which is as follows.
[0004]
First, a series circuit including a resistor R8 and a capacitor C1 is connected in parallel with the switching element FET between the DC motor M and the switching element FET.
A series circuit composed of resistors R1 and R2 is connected in parallel to the capacitor C1. The resistor R2 is connected to the capacitor C5 in parallel.
[0005]
The capacitor C1 is charged via the DC motor M and the resistor R8 when the switching element FET is off, and is discharged via the resistor R8 and the switching element FET when the switching element FET is on.
[0006]
A capacitor C2 is connected in parallel to both ends of the DC power supply E via a resistor R11, and series circuit resistors R3, R4, and R5 are connected in parallel with the capacitor C2. A speed setting variable resistor R6 is connected in parallel to the resistor R4. The speed setting sliding portion 11 is provided around the speed setting variable resistor R6. These structures will be described later.
[0007]
The positive side input terminal of the first comparator IC1 is connected between the resistors R1 and R2, the negative side input terminal is connected to the slider of the variable resistor R6 via the resistor R7, and the DC power source via the capacitor C3. It is connected to the negative side of E.
[0008]
The output side terminal of the first comparator IC1 is connected to the plus side input terminal of the second comparator IC2 via the diode D1. 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.
[0009]
The negative side input terminal of the second comparator IC2 is connected to an intermediate position of the series circuit of the resistor R10 and the capacitor C4 that are connected to both ends of the DC power source E via the resistor R11. 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 on, and is discharged via the diode D2 and the resistor R16 when the switching element FET is off.
[0010]
The output terminal of the second comparator IC2 is connected to the gate side of the switching element FET via a resistor R15. Further, the resistor R15 and the switching element FET are connected to the negative side of the DC power source E through a Zener diode ZD.
[0011]
As shown in FIG. 7, the speed setting sliding portion 11 includes a sliding body 12 which is a non-resistance body having the same length in parallel with the variable resistor R6 formed in a strip shape, and these variable resistance body R6 and the sliding body. 12 and a slider 13 provided so as to straddle 12.
[0012]
The slider 13 is configured to move slidably while contacting the variable resistor R6 and the sliding body 12 in conjunction with the pulling state of an operation lever (not shown).
[0013]
Next, among the operations of the trigger switch circuit having such a connection state and configuration, the operation of the speed setting sliding portion 11 will be described with reference to the drawings.
[0014]
First, FIG. 8 is an equivalent circuit when the slider 13 in the speed setting sliding portion 11 moves in conjunction with the operation lever. The voltage e supplied to the negative terminal of the first comparator is:
e = Ia * R5 + Ib * VR
It is. Here, the resistance VR is a resistance corresponding to the movement of the variable resistor R6.
[0015]
Therefore, as shown in FIG. 9, the relationship between the voltage e and the resistance VR is such that the resistance value of the resistance VR decreases according to the stroke of the operation lever, and linearly proportional to the resistance value of the resistance VR. Decrease.
[0016]
Next, the relationship between the voltage between motors and the stroke by the speed setting sliding portion 11 having such characteristics will be described with reference to FIG.
[0017]
First, the slider 13 that moves in conjunction with the operation lever is in a state where power is not supplied to the DC motor.
(1) When the operating lever is pulled in (the slider 13 slides on the variable resistor R6 and interlocked with the operating lever), the power switch SW1 (see FIG. 6) is turned on.
[0018]
(2) Further, when the operating lever is pushed and the slider 13 comes into contact with the variable resistor R6, the voltage between the DC motors M starts to rise.
[0019]
(3) When the operating lever is further pulled, the speed setting slider 13 moves while sliding on the variable resistor R6, and the voltage between the motors M is linear according to the pulling amount (stroke) of the operating lever. To rise.
[0020]
(4) When the operating lever is further pulled, the slider 13 goes to the end of the variable resistor R6, and the maximum voltage that can be controlled is supplied to the motor M.
[0021]
(5) If the operating lever is further pulled in this state, the shorting switch SW2 linked to the operating lever is turned on, and the maximum voltage with a duty ratio of 100% is supplied to the DC motor M without passing through the switching element FET. The
[0022]
In this way, the rotation control of the DC motor M can be performed by the operations of the power switch SW1, the slider 13, and the short-circuit switch SW2 that are linked to the operation lever.
[0023]
[Problems to be solved by the invention]
However, in the trigger switch circuit for a power tool in the prior art described above, the switching element FET is always in a controllable state when the power switch SW1 and the short-circuit switch SW2 are turned on / off. Therefore, when the power switch SW1 or the short circuit switch SW2 is turned on / off, the switching element FET is turned on / off, so that a potential difference occurs between the contact points of the switch, and a spark is generated when the switch is turned on / off. There is a problem that contact wear increases due to this spark, and life cannot be improved.
[0024]
Therefore, there is a problem that must be solved in a circuit configuration that reduces contact wear of the power switch and the shorting switch.
[0025]
[Means for Solving the Problems]
In order to solve the above-described problems, a trigger switch circuit for an electric tool according to the present invention includes a power switch provided between a DC power supply and a motor, a switching element connected in series with the motor, and in parallel with the switching element. a trigger switch circuit comprising a shorting switch connected, and control means for controlling the on-duty of the switching element in accordance with the operation retraction amount of the operating lever, wherein the control means is connected to a power supply side First and second sliding bodies composed of a non-resistance body, a variable resistance body, and a non-resistance body connected to the ground side, and a third sliding body composed of a non-resistance body connected to the input side of the comparison control means. A speed setting sliding portion comprising a first slider that is in contact with and slides on the first and second sliding bodies including the variable resistor and the third sliding body, The switch A non-resistance fourth sliding body connected to the gate side of the switching element, a non-resistance fifth sliding body connected to the ground side, and an output side of the comparison control means; And a non-resistive sixth sliding body formed to be shorter than the third sliding body. The fourth sliding body and the fifth and sixth sliding bodies A voltage control sliding portion including a second slider that slides in contact with the sliding body, the power switch, the first and second sliders, and the short circuit. The four switches and the switch are configured to operate in conjunction with the operation lever, and the second slider contacts the fifth slider and supplies the ground potential to the gate of the switching element. Sometimes the power switch is turned on and off,
The short circuit switch is turned on / off when the second slider is detached from the sixth sliding body and is in a floating state when the on-duty of the switching element is 100% conductive.
[0026]
In this way, the power switch, the shorting switch, and the first and second sliders are linked to the operating lever in the operating lever, and when the power switch and the shorting switch are turned on / off, The switching elements connected in series are controlled so as to be cut off or conducted 100%. By controlling in this way, the switch can be turned on / off with no potential difference between the contacts of the power supply and the short-circuit switch, and the occurrence of sparks or the like generated between the contact points of the switch can be reduced. it can.
[0027]
In addition, by connecting the resistor to the variable resistor in parallel, the voltage applied to the motor rises and falls in a downward curve rather than linearly, so a slow rotation rise time is required especially during low-speed rotation. Will be able to.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a trigger switch circuit for an electric tool according to the present invention will be described with reference to the drawings. In addition, the same number is given and demonstrated to make it easy to understand the same thing as a prior art.
[0029]
As shown in FIG. 1, the trigger switch circuit for an electric tool includes a control circuit unit 20 provided at both ends of the DC power supply E, and a series circuit in which a DC motor M and a switching element FET are connected in series at both ends of the DC power supply E. The power switch SW1, the diode D, and the short circuit switch SW2 are connected in series.
[0030]
The control circuit unit 20 includes two first and second comparators IC1 and IC2, capacitors C1 to C5, resistors R1 to R5, a speed setting variable resistor R6, resistors R7 to R17, a diode D1, It is composed of D2 and a Zener diode ZD, and its connection state is as follows. Here, the first and second comparators IC1 and IC2 constitute a comparison control means.
[0031]
First, a series circuit including a resistor R8 and a capacitor C1 is connected in parallel with the switching element FET between the DC motor M and the switching element FET.
A series circuit composed of resistors R1 and R2 is connected in parallel to the capacitor C1. A capacitor C5 is connected in parallel to the resistor R2.
[0032]
The capacitor C1 is charged via the DC motor M and the resistor R8 when the switching element FET is off, and is discharged via the resistor R8 and the switching element FET when the switching element FET is on.
[0033]
A capacitor C2 is connected in parallel via a resistor R11 to both ends of the DC power supply E, and resistors R3, R4, and R5 connected in series with the capacitor C2 are connected. A speed setting variable resistor R6 is connected in parallel to the resistor R4. Further, the intermediate point between the temperature setting variable resistor R6 and the resistors R3 and R4 (first sliding member Y) and the intermediate point between the speed setting variable resistor R6 and the resistor R7 (third sliding member X). A resistor R17 is connected between them. The speed setting sliding portion 21 is formed around the speed setting variable resistor R6, and a first slider 23 (see FIG. 3A) that slides on the variable resistor R6 will be described later. It has a structure that moves in conjunction with the second slider 24 (see FIG. 3B) of the voltage control sliding portion 22. Here, the speed setting sliding portion 21 and the voltage control sliding portion 22 constitute a control means, and this control means controls the gate side potential of the switching element FET according to the operation pull-in amount of the operation lever. It has a structure for controlling so-called on-duty. These structures will be described later.
[0034]
The positive side input terminal of the first comparator IC1 is connected between the resistors R1 and R2, the negative side input terminal is connected to the third sliding body X via the resistor R7, and the DC power source E is connected via the capacitor C3. It is connected to the negative side.
[0035]
The output side terminal of the first comparator IC1 is connected to the plus side input terminal of the second comparator IC2 via the diode D1. 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.
[0036]
The negative side input terminal of the second comparator IC2 is connected to an intermediate position of the series circuit of the resistor R10 and the 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 on, and is discharged via the diode D2 and the resistor R16 when the switching element FET is off.
[0037]
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. Further, the resistor R15 and the switching element FET are connected to the negative side of the DC power source E through the Zener diode ZD.
[0038]
As shown in FIG. 2, the speed setting sliding portion 21 is connected to the power source side which is a non-resistive body having the same width and a predetermined length on each of the start end side and the end end side of the variable resistor R6 formed in a band shape The first sliding body Y and the second sliding body Z connected to the ground side are on the same extension line, with a predetermined interval, and the first and second sliding bodies Y and Z and the variable resistor R6. And a non-resistive third sliding body X which is formed in the same length as that of the first and second terminals and is connected to the input side of the comparison control means .
[0039]
Then, as shown in FIG. 3A, a conductive member is used so as to straddle the first sliding body Y, the variable resistor R6, the second sliding body Z, and the third sliding body X. The formed first slider 23 is slidably contacted.
[0040]
As shown in FIG. 4, the first slider 23 is formed in a bifurcated shape by providing notches on both ends, and the bifurcated portion is bent in the same direction, and the free end portions at both ends are further formed. The contact 25 is formed by bending in the opposite direction.
[0041]
As shown in FIG. 2, the voltage control sliding portion 22 is connected to the gate side of the switching element, and a fourth sliding body C which is a non-resistance body formed in a strip shape, and the fourth sliding body C A non-resistive fifth sliding body B formed on the same extension line with a predetermined interval and having a predetermined length and connected to the ground side, and a fifth sliding body connected to the output side of the comparison control means A non-resistive sixth sliding body A formed by providing a length of B that is shorter than the third sliding body X and having a key-like gap with the fifth sliding body B ; It is composed of
[0042]
The length composed of the fifth and sixth sliding bodies B and A is formed shorter than the length of the third sliding body X of the speed setting sliding portion 21 .
[0043]
Then, as shown in FIG. 3B, the second slide formed of the conductive member so as to straddle the fourth slide body C, the fifth slide body B, and the sixth slide body A. The child 24 is slidably contacted.
[0044]
The second slider 24 used for the voltage control sliding portion 22 has the same shape as the first slider 23 used for the speed setting sliding portion 21. That is, as shown in FIG. 4, the contact structure has a bifurcated shape at both ends.
[0045]
Voltage controlling sliding portion 22 having such a configuration, in the second slider 24 floats state when the state of full stroke pulls the operation lever (state of 24A in to FIG. 3 (B)) The on-duty of the switching element FET is made 100% conductive.
[0046]
Next, among the operations of the trigger switch circuit having such a connection state and configuration, particularly the operations of the speed setting sliding portion 21 and the voltage control sliding portion 22 functioning in conjunction therewith are referred to the drawings. I will explain.
[0047]
First, FIG. 5 is an equivalent circuit when the first slider 23 in the speed setting sliding portion 21 moves in conjunction with the operation lever, and is supplied to the negative input terminal of the first comparator IC1. The voltage e is
e = Ia · R5 + Ib · R
It is. Here, the resistance R is a combined resistance of the variable resistance VR and the resistance R17.
R = 1 / ((1 / VR) + (1 / R17))
It becomes.
[0048]
Therefore,
e = Ia · R5 + Ib / ((1 / VR) + (1 / R17))
It becomes.
[0049]
Next, the relationship between the motor voltage and the stroke by the speed setting sliding portion 21 and the voltage control sliding portion 22 will be described with reference to FIGS. 1, 2 to 4, and 5.
[0050]
First, when the DC motor M is not supplied with power, the first and second sliders 23 and 24 that move in conjunction with the operation lever are the first slides of the speed setting slide 21. The child 23 is in the region of the first sliding body Y, which is a non-resistance conductor, and the second slider 24 of the voltage control sliding portion 22 is in the region of the fifth sliding body B, and the power supply voltage Since it is short-circuited to the ground (ground) side, the ground potential is supplied to the gate of the switching element, and 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 no potential difference is generated between the power switches SW1. In such a state, the power switch SW1 (see FIG. 1) linked to the operation lever can be turned on / off.
[0051]
(1) The power switch SW1 is turned on, power is supplied to each circuit, and a power supply voltage is supplied to the first and second comparators IC1 and IC2 to control them. At this time, the second slider 24 of the voltage control sliding portion 22 is fitted into a key-like position between the fifth sliding body B and the sixth sliding body A, and the power supply voltage is reduced. Shorted to the ground side, the on-duty of the switching element FET is 100% blocked.
[0052]
(2) When the operation lever is further pulled, the first slider 23 of the speed setting sliding portion 21 comes to the starting end portion 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 body A, and the minimum voltage that can be controlled is supplied to the motor M.
[0053]
(3) When the operating lever is further pulled, the first slider 23 of the speed setting sliding portion 21 moves while sliding on the variable resistor R6. At this time, the voltage (on duty) between G and S of the switching element FET rises as a downward curve. Accordingly, since the voltage between the motors M increases slowly compared to the amount of pulling of the operation lever, the rotation of the motor M is not a sudden rotation but a gentle rotation increase. This has the advantage that a large number of low-speed rotation regions can be taken, and positioning at the time of drilling and adjustment of the tightening condition at the time of screw tightening are facilitated.
[0054]
(4) When the operating lever is further pulled, the first slider 23 of the speed setting sliding portion 21 comes off from the terminal end of the variable resistor R6 and contacts the non-resisting second sliding member Z. Is supplied with the maximum controllable voltage.
[0055]
(5) If the operating lever is further retracted in this state, the first slider 23 of the speed setting sliding portion 21 slides on the non-resisting second sliding body Z, and the voltage control slide. The second slider 24 of the portion 22 is detached from the sixth sliding body A and is in a floating state, and the on-duty of the switching element FET is in a state of conducting 100%. There is almost no potential difference between the drain and source of the switching element FET that is 100% conductive.
[0056]
(6) In such a state, the short-circuiting switch SW2 can be turned on, and even if it is further pulled, it is a so-called full stroke that cannot be pulled any further. When the short-circuit switch SW2 is turned on, the maximum voltage that does not pass through the switching element FET is supplied, and the DC motor M is rotated at full speed.
[0057]
Since it is possible to turn on the contact point of the short-circuit switch SW2 without causing a potential difference, the occurrence of a spark or the like can be reduced. The shorting switch SW2 is turned off under the same conditions as when the shorting switch SW2 is turned on.
[0058]
In this way, when the power switch SW1 and the shorting switch SW2 are turned on / off, they are turned on / off with the potential difference between the contacts eliminated, so that sparks generated between the contacts are suppressed and contact wear is reduced. Will be able to. When contact wear can be reduced in this way, inexpensive contact materials can be used, contact materials such as silver and silver alloys are no longer necessary for the contacts, and the switch itself can be made compact.
[0059]
In addition, the rotation control of the DC motor is controlled by increasing and decreasing with a voltage that draws a downward curve, so that the rotation can be gradually increased especially at low speed rotation, and it is easy to adjust the screw tightening etc. Become.
[0060]
【The invention's effect】
As described above, the trigger switch circuit of the electric power tool according to the present invention has the potential difference between the switch contacts in both the power switch and the short-circuit switch connected in parallel to the switching element. Since the switch is turned on and off in the lost state, sparks generated from the contacts of both switches can be extremely reduced, the life of the contacts can be extended, and the switch material can be made inexpensive. There is an effect that can be done.
[0061]
In addition, by connecting the resistor to the variable resistor in parallel, the voltage applied to the motor rises and falls in a downward curve rather than linearly, so a slow rotation rise time is required especially during low-speed rotation. Thus, there is an effect that the screw tightening can be easily adjusted.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a trigger switch for an electric tool according to the present invention.
FIG. 2 is a plan view showing patterns of sliding bodies of the speed setting sliding portion and the voltage control sliding portion.
3A is a schematic cross-sectional view of a speed setting sliding portion, and FIG. 3B is a schematic cross-sectional view of a voltage control sliding portion.
FIG. 4 is a plan view of the slider.
FIG. 5 is a graph showing the relationship between the motor voltage and stroke.
FIG. 6 is a trigger switch circuit diagram for a power tool in the prior art.
FIG. 7 is an explanatory view showing a pattern of a sliding body of a speed setting sliding portion in the prior art.
FIG. 8 is an equivalent circuit diagram of a speed setting sliding portion in the prior art.
FIG. 9 is a graph showing the relationship between the trigger stroke and the voltage of the variable resistor in the prior art.
FIG. 10 is a graph showing the relationship between the voltage between motors and the stroke of the operating lever in the prior art.
[Explanation of symbols]
20; control circuit portion, 21; speed setting slide portion, 22; voltage control slide portion, 23; first slider, 24; second slider, 25; contact, SW1; Switch, SW2; Short-circuit switch, SW3; Control switch, R1 to R5; Resistor, R6; Variable resistor, R7 to R15; Resistor, C1 to C4; Capacitor, FET; Switching element, M: DC motor, D1 to D3 Diode, E; DC power supply, IC1; first comparator, IC2; second comparator.

Claims (1)

A power switch provided between the DC power source and the motor;
A switching element connected in series with the motor;
A shorting switch connected in parallel to the switching element;
A control means for controlling an on-duty of the switching element according to an operation pull-in amount of an operation lever, and a trigger switch circuit comprising:
The control means includes
First and second sliding bodies comprising a non-resistance body connected to the power supply side, a variable resistance body, and a non-resistance body connected to the ground side, and a non-resistance body connected to the input side of the comparison control means And a first slider that is in contact with and slides on the first and second sliding bodies including the variable resistor and the third sliding body. A sliding part for setting;
A non-resistive fourth sliding body connected to the gate side of the switching element, a non-resisting fifth sliding body connected to the ground side, and an output side of the comparison control means; A length of the fifth sliding body combined with the length of the fifth sliding body is made of a non-resistance sixth sliding body formed shorter than the third sliding body. A voltage control sliding portion provided with a second slider that slides in contact with the sliding body of
The power switch, the first and second sliders, and the shorting switch are configured to operate in conjunction with the operation lever.
So as to turn on and off the power switch when the second slider is supplying a ground potential to the gate of the switching element in contact with the sliding body of the fifth, the second sliding The electric motor characterized in that the short-circuiting switch is turned on / off when the moving element is detached from the sixth sliding body and floats and the on-duty of the switching element is 100% conductive. Trigger switch circuit for tools.

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