JP2533560B2 - Electric tool - Google Patents

Description

Detailed Description of the Invention 【Technical field】

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric tool powered by a motor, and more particularly to an electric tool such as a wrench or a screwdriver for tightening work.

[Background Art]

In the case of tightening work such as an electric wrench or an electric screwdriver, it is necessary to make the tightening torque variable in order to improve its workability and to prevent the object to be tightened from being destroyed, and also the number of rotations. It is a condition that good workability can be obtained by making it variable so that the rotation speed can be kept low at the start of the tightening work. Among the power tools that perform tightening, the rotary inertia of the hammer strikes the anvil to generate a rotary impact, which allows bolts and screws to be tightened. The tightening force is adjusted by increasing or decreasing the rotational inertia of the hammer. FIG. 12 shows a conventional circuit for controlling the rotation speed of the motor M. The motor M is connected to the power supply V via the rotation direction changeover switch SW ₂ , the switching element S, and the power supply switch SW ₁ , and the switching element S is connected to the control circuit C. The control circuit C controls the ON time of the switching element S according to the resistance value set by the variable resistor VR to change the amount of electricity to the motor M, thereby making the rotation speed of the motor M variable. . In the figure, D is a flywheel diode. Here, the power switch SW ₁ is normally turned on and off by operating the trigger lever, but if the resistance value of the variable resistor VR is made variable by an operation means different from this trigger lever, the trigger lever is operated to turn it on. At this point, the rotation of the motor M rises up to the set number of rotations at once, so there is a problem that the wood screw falls over during a work that requires a slow rotation at the beginning, such as when tightening a long wood screw. , The usability becomes poor. For this purpose, pull the trigger lever to turn on the power switch SW.
Not only ₁ is turned on, but the resistance value of the variable resistor VR is also changed according to the operation amount of the trigger lever. With this device, if the trigger lever is pulled a little, the power switch SW ₁ is turned on, the motor M starts up at a low rotation speed, and if the pulling amount of the trigger lever is increased, the rotation speed of the motor M is accordingly increased. Since it becomes higher, it is preferable in terms of usability. However, even this one has the following problems. That is, in the impact type, as described above, the change in the rotation speed of the motor M directly changes the tightening force and, in addition, the variable resistor according to the pulling amount of the trigger lever.
Since the resistance value of VR changes and the rotation speed of the motor M changes, when the tightening force is desired to be small, such as when tightening a small screw, due to the stroke of the trigger lever, You must keep the trigger lever slightly pulled. However, it is difficult to adjust the pulling force of the trigger lever to maintain the state where only such a slight operation is performed, sometimes pulling the trigger lever too much, the tightening force becomes excessive, and the screw is broken. There is.

[Object of the invention]

The present invention has been made in view of the above points, and its purpose is to perform tightening work with good usability, from a small tightening force to one requiring a large tightening force. It is to provide a power tool that can do.

DISCLOSURE OF THE INVENTION

Therefore, the present invention is provided with the first variable resistor and the second variable resistor, and the number of rotations of the motor is made variable according to the resistance value of both variable resistors. The variable resistor changes the resistance value according to the operation amount of the power switch trigger lever, and the second variable resistor changes the resistance value by an operation means different from the trigger lever. Characterized in that the rotation speed of the motor is changed according to the operation amount of the trigger lever, and the motor corresponding to the operation amount of the trigger lever is set according to the setting of the resistance value of the second resistor. The change range of the rotation speed of is changed. Hereinafter, the present invention will be described in detail based on the illustrated embodiments. First
The electric tool shown in the figure is an impact type electric screwdriver, and the structural points and the operation thereof will be described first. In a casing 6 having a grip portion 7 to which a storage battery pack 5 as a power source V is attached, As a drive mechanism, a motor M, a spindle 1, a hammer 2, and an anvil 3 are incorporated. A sun gear 41 is fixed to the output shaft of the motor M fixed to the casing 6 via a mounting base 60, and the spindle 1 whose rear end is supported by the mounting base 60 via a bearing 61 has the above-mentioned structure. A plurality of planet gears 42 that mesh with the sun gear 41 are attached. Since the planet gears 42 are also meshed with the mounting base 60 and the internal gear 43 fixed to the gear case 62 which is a part of the casing 6, the spindle 1 has the spindle 1 and the planet gear 42 and the internal gear. It rotates by the deceleration output of the planetary mechanism composed of 43. The hammer 2 has a ring shape surrounding the spindle 1,
It is slidable in the axial direction with respect to the spindle 1, and is biased axially forward by a spring 52. Further, a plurality of axial grooves 20 are provided on the inner peripheral surface of the hammer 2, and a striking portion which engages with the anvil 3 supported by the casing 6 via the bearing 64 is provided on the tip end surface.
21 is projected. On the other hand, a cam groove 10 inclined with respect to the axial direction is cut on the outer peripheral surface of the spindle 1, and the cam groove 10 and the groove 20
A spindle 1 and a hammer 2 are connected for rotation about an axis by a ball 4 that fits in and. As shown in FIG. 6, the holder 30 at the tip of the anvil 3 is arranged in the insertion hole 31 that opens to the tip surface of the anvil 3, the sleeve 32 that covers the anvil 3, and the hole formed in the anvil 3. A ball 33 and a spring 34 for urging the sleeve 32.The sleeve is inserted into the annular groove 16 formed at the base of the driver bit 15.
By holding the ball 33 with the pressing portion 36 provided on the inner surface 32, the driver bit 15 is held. In this holder 30, the balls 33 are installed at two different positions in the axial direction, and as shown in FIGS. 10 and 11, they project from the retaining ring 37 provided on the anvil 3. Locking groove 39 that can lock the protrusion 38
Is formed on the inner peripheral portion of the rear end of the sleeve 32,
As shown in FIGS. 7 and 8, it is possible to accommodate two types of driver bits 15 having different lengths from the rear end to the groove 16. Inserting the driver bit 15 into the insertion hole 31
As shown in FIG. 7, the pressing portion 36 is retracted so as to come to a position between the above two kinds of balls 33, and the driver bit 15 having a short length from the rear end to the groove 16 is used. Is further retracted the sleeve 32 to guide the projection 38 into a locking groove 39 that opens at the rear end surface at one end in the circumferential direction, and then rotate the sleeve 32 to lock the projection 38 in the depth of the locking groove 39. For the driver bit 15 having a long length from the rear end to the groove 16, the driver bit 15 is inserted as described above, and then the sleeve 32 is returned by the spring 34. Then, the driver bit 15 attached to the holder 30
When the motor M is rotated by applying the to the object to be tightened, the hammer 2 connected to the spindle 1 via the balls 4 also rotates as the spindle 1 rotates by the deceleration output of the motor M. At this time, if the rotational torque of the hammer 2 is smaller than the load torque for rotating the object to be tightened, the hammer 2 retracts along the cam groove 10 while compressing the spring 25, and the striking portion 21 moves toward the anvil 3. When disengaged from the hammer 2, the hammer 2 is urged by the spring 25 and the cam groove 10
When the striking portion 21 receives the guide by the, the striking portion 21 gives a rotational impact to the anvil 3. The tightening force generated by this rotational impact tightens the screws and bolts. It should be noted that the cam groove 10 is formed by connecting two grooves having opposite inclination directions in a V-shape so that the rotation direction of the motor M can be reversed and the screw can be loosened. It has become. Here, this electric tool is provided with a trigger lever 8 at the base of the grip 7 and a dial 9 on the side surface of the rear end of the casing 6. As shown in FIG. 2, a power switch SW ₁ , a switching element S, and a rotation direction changeover switch SW ₂ are connected between the power source V and the motor M, and a control circuit C for controlling the switching element S is connected. A series circuit of two variable resistors VR ₁ and VR ₂ is connected to. The variable resistor VR ₁ is operated by the trigger lever 8 in the same manner as the power switch SW ₁ to change the resistance value according to the operation amount of the trigger lever 8, and the variable resistor VR ₂ is operated by the dial 9 as described above. It changes the resistance value. In addition, changeover switch SW
₂ is a switching lever 8 provided adjacent to the trigger lever 8
Switched by 0. The control circuit C, the power switch SW ₁ and the variable resistor VR ₁ are arranged in the switch box 18 as shown in FIG. ₁ , and the switching element S is provided on the casing 6 via the heat sink 19. It is arranged in the rear end portion. Now, assuming that the total resistance values of the variable resistors VR ₁ and VR ₂ are R ₁ and R ₂ , respectively, and the adjustment resistance values are αR ₁ and βR ₂ (0 ≦ α, β ≦ 1), the resistance values shown in the figure are shown. R _a, the ratio R _a / R _B of R _B is a _{= R a / R B (αR} 1 + βR 2) / (R 1 + βR 2) = (αK + β) / (K + β) ( However, K = R ₁ / R ₂ ). For this reason, if K = 1, the variable resistor VR is operated by operating the trigger lever 8.
_When the resistance value αR ₁ of ₁ is changed, the change pattern of the ratio R _A / R _B changes as shown in FIG. 3 according to the setting of the resistance value βR ₁ of the variable resistor VR ₂ . The control circuit C, which controls the amount of electricity to the motor M through the switching element S in proportion to the change in the ratio R _A / R _B , changes the change range of the rotation speed of the motor M. Therefore, if the resistance ratio K of both the variable resistors VR ₁ and VR ₂ is set appropriately, the trigger lever can be adjusted by adjusting the resistance value βR ₂ of the variable resistor VR _{2 by} operating the dial 9. When changing the rotation speed of the motor M according to the operation amount of 8, it is possible to obtain a rotation speed change pattern suitable for the work target. For example, for tightening a small screw, β is set to about 0.2. However, for those requiring a large tightening force such as bolts, if β = 1 is set, appropriate workability can be obtained. Both variable resistors VR ₁ and VR ₂ may be connected in parallel as shown in FIG. Further, as shown in FIG. 5, if an adjustment resistor R ₃ is further added to the parallel circuit of both variable resistors VR ₁ and VR ₂ ,
For example, for a drilling screw or the like that requires a high-speed rotation start, the rotation start immediately after the operation of the trigger lever 8 can be accelerated.

【The invention's effect】

As described above, in the present invention, the first variable resistor that changes the resistance value according to the operation amount of the trigger lever is provided, and the second variable resistor that changes the resistance value by the operation of other operation means is provided. Since the rotation speed of the motor is controlled according to the resistance values of the both variable resistors, it has an excellent property in terms of usability that the rotation speed of the motor increases as the operation amount of the trigger lever increases. In addition, since the rising speed of the motor at the beginning of operating the trigger lever can be adjusted by the second variable resistor, from the one that requires a small tightening force to the one that requires a large tightening force, It is possible to demonstrate the ease of use.

[Brief description of drawings]

FIG. 1 is a cutaway side view of an embodiment of the present invention, FIG. 2 is a circuit diagram of the same as above, FIG. 3 is a characteristic diagram showing the action of the same, FIG. 4 is a circuit diagram of another example, and FIG. Circuit diagrams of other examples, FIGS. 6 to 9 are vertical sectional views of the above holder, and FIGS. 10 and 11 are sectional views taken along the line AA in FIG. 6 and B- in FIG. 8, respectively. 12 is a circuit diagram of a conventional example, where M is a motor,
VR ₁ and VR ₂ are variable resistors, and 8 is a trigger lever.

Claims (1)

(57) [Claims] 1. A first variable resistor comprising a first variable resistor and a second variable resistor, wherein the number of rotations of a motor is variable according to the resistance value of both variable resistors. The resistor is for changing the resistance value according to the operation amount of the power switch trigger lever, and the second variable resistor is for changing the resistance value by an operation means different from the trigger lever. Characteristic power tool.