JPS5810195B2 - electric screwdriver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric screwdriver configured to hold a driver bit in a bit holder rotated by a motor.

In a conventional electric screwdriver, for example, as shown in FIG. 1, a bit holder 13 is attached via a bearing 12 to the tip of a housing 11 that is held in the hand of an operator.
The rotational force of a motor 14 built into the bit holder 1 is transmitted to the bit holder 13 via a speed reduction mechanism 15 using planetary gears, thereby making it possible to rotate the bit holder 13.

By attaching a separate driver bit (not shown) to the bit holder 13, screw tightening and loosening operations can be performed.

However, the reduction mechanism 15 of the electric screwdriver shown in FIG.
A first stage planetary gear 153 is meshed between a first stage pinion gear 151 connected to the output shaft of the motor 14 and an internal gear 152 fixed to the housing 11, and this first stage planetary gear 153 is The second rotatably held
The second stage planetary gear 155 is meshed between the stage pinion gear 154 and the internal gear 152, and the second stage planetary gear 155 is rotatably held in the bit holder 13. Although it can always rotate at a predetermined reduction ratio, the bit holder 13 is suddenly stopped when tightening the screw, so in addition to the torque of the motor 14, an impact torque is generated due to the inertia of the moving parts, and the reaction force due to that torque is generated. There is a problem in that the impact torque is transmitted to the operator's hand via the housing 11, making the operator feel extremely uncomfortable, and furthermore, the impact torque also reduces the tightening accuracy.

It is also possible to interpose a torsion coil spring between the motor and the bit holder to alleviate this impact torque, but even then, the only way to obtain the desired tightening strength is through experience, so it requires skill. However, there is a limit to the improvement of the tightening accuracy.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electric screwdriver that can reduce the discomfort conveyed to the operator when tightening screws, and can also achieve high tightening accuracy without requiring any skill.

The present invention will be described below using examples with reference to FIG. 2 and subsequent figures.

First, FIG. 2 shows an improved type of the conventional electric screwdriver shown in FIG. 1 as an embodiment of the electric screwdriver according to the present invention.

In that case, a bit holder 13 holding a driver bit 16 has a tightening ring 1 screwed into the housing 11.
7 via a bearing 12 so as to be rotatable.

Further, an internal gear 152 of the reduction mechanism 15 interposed between the bit holder 13 and the motor 14 has one end supported by the housing 11 via a bearing 18 and the other end supported by the tightening ring 17 via a bearing 19. It is built in such a way that it can be rotated by being supported.

Therefore, this reduction mechanism 15 as a whole has a configuration substantially equivalent to a differential gear.

That is, the first stage pinion gear 151 of the speed reduction mechanism 15 constitutes the input shaft of the differential device, and the portion where the second stage planetary gear 155 is held by the bit holder 13 constitutes one output shaft of the differential device, Internal gear 152 constitutes the other output shaft of the differential.

Furthermore, with reference to FIG.
On the other hand, on the inner surface of the portion 111 of the housing 11 that faces the outer peripheral surface of the internal gear 152 at intervals, coil devices (yokes) of the same number as the permanent magnets 21 are installed at multiple locations forming angles with each other. 22 is fixed.

In this way, the permanent magnet 21 and the coil device 22 constitute a generator, and when the internal gear 152 rotates, an alternating current voltage proportional to the rotation speed is induced in the coil device 22.

Moreover, as shown in Fig. 4, a series resistance R is applied to this generated voltage.
When the current I is turned on, a current I flows and a torque proportional to this current is generated, and this torque acts on the internal gear 152.

Here, the permanent magnet 21 constitutes the rotor of the generator, while
It goes without saying that the coil device 22 constitutes a stator of the generator.

To tighten a screw using the electric screwdriver having the above-described structure, the tip of the driver bit 16 is pressed against the screw head of a screw that has been slightly screwed in beforehand, and the power switch 23 is turned on.

Then, the motor 14 is driven and the first stage pinion gear 15
Rotate 1.

Since the internal gear 152 has a braking force similar to a dynamic brake, it rotates only slowly.
Therefore, the first stage planetary gear 153 is the internal gear 15.
2 and rotate the second stage pinion gear 154 accordingly.

Furthermore, the second stage planetary gear 155 is also an internal gear 152.
The bit holder 13 is rotated at a reduced speed accordingly.

As a result, the screw is tightened by the driver bit 16.

Now, just before the end of tightening the screw, the screw head is seated, so the rotational speed of the driver bit 16 is rapidly reduced to an extremely low speed.

For this reason, the internal gear 152 overcomes the braking action such as a dynamic brake and starts high-speed rotation.

Therefore, even if the motor 14 continues to rotate as before, the impactful reverse torque acting on the driver bit 16 is suppressed to an extremely low level, and is almost never transmitted to the housing 11. It will not be tightened more than necessary.

At the moment the screw head is seated, the internal gear 152
Since the rotation speed is extremely low or zero, no torque is generated due to the above-mentioned power generation effect, and therefore no shock due to this is transmitted to the housing 11.

By the way, when the internal gear 152 rotates at high speed in this way, the current I flows as described above, and a torque proportional to this current I is generated, and this torque is transmitted to the driver bit 16 via the second stage planetary gear 153. ,
The screws are securely tightened.

That is, the final tightening force of the screw is determined by the internal gear 152.
is determined by the torque generated as a result of the rotation of the

When the screw tightening is completed, the rotation of the driver bit 16 is always stopped, so the rotational speed of the internal gear 152 is constant, and a constant voltage is generated. Therefore, by determining the resistance value of the resistor R, the current I can also be adjusted. The current I becomes constant, and the torque generated in proportion to this current I also becomes constant.

Therefore, there is no variation in the final tightening force, and the screw is always tightened with a constant tightening force.

Furthermore, this tightening force can be adjusted by changing the resistance value of the resistor R7.

That is, when the resistance R is increased, the current I decreases inversely proportional to it, and the generated torque also decreases, so the tightening force becomes smaller.
On the other hand, when the resistance R is decreased, the tightening force increases due to the completely opposite phenomenon.

In view of this point, it is preferable to use a variable resistor as the resistor R so that the tightening force can be adjusted to an arbitrary value.

Furthermore, the voltage caused by the current I when the tightening is completed is detected and compared with the reference voltage as shown in FIG. It is also possible to automatically stop the drive of 14.

According to this, by appropriately changing and selecting the reference voltage E, the motor 14 is stopped when the desired tightening force is obtained,
This makes it possible to obtain a constant tightening force and to prevent wasteful power consumption of the motor 14.

The above description has been about tightening the screws, but in order to also loosen the screws, the internal gear 152
It will be understood that it is sufficient to use bearings 18 and 19 that rotatably support the bearings 18 and 19, which allow rotation in only one direction and prevent rotation in the other direction.

As explained above using the embodiments, in the electric screwdriver according to the present invention, when a stopping force is applied to the output shaft connected to the bit holder of the differential, the other output shaft of the differential rotates at high speed. As a result, the impact torque that is generated when tightening screws is suppressed to a small level, which stabilizes the tightening accuracy and reduces the shock that is transmitted to the hands of the operator when he or she grips the screws while working. The final tightening force is generated by the action of a generator that utilizes the rotation of the other output shaft, so it is easy to generate a constant tightening force without controlling the motor itself. Even if the operator changes, the same tightening force can be obtained, and the part that generates this tightening force has almost no wear parts, so it has excellent durability.

Although the above-mentioned embodiment uses a differential device that is an improved deceleration mechanism of a conventional electric screwdriver, it is possible to obtain the same effect by using a differential device with other configurations. Of course.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view of an example of a conventional electric screwdriver, showing the internal mechanism. FIG. 2 is a partial cross-sectional view of an example of an electric screwdriver according to the present invention, also showing the internal mechanism.
FIG. 3 is a cross-sectional view taken along the line ■--■ in FIG. 2, and FIG. 4 is a schematic circuit diagram showing an example of application of current by a generator. DESCRIPTION OF SYMBOLS 11...Housing, 13...Bit holder, 14...Motor, 15...Deceleration mechanism, 16...Driver bit, 21...・・・
... Permanent magnet, 22 ... Coil device, 23.
...Power switch, 152...Internal gear.

Claims (1)

[Claims] 1. An electric driver that rotates a bit holder with a motor, including a differential device interposed between the motor and the bit holder, an input shaft of the differential device being connected to the motor, and one of the differential devices the output shaft of the differential gear is connected to the bit holder, a permanent magnet is fixed to the other output shaft of the differential device, and a coil device is attached to the opposing surface of the fixed part facing the other output shaft with a space therebetween. An electric screwdriver characterized in that the coil device and the permanent magnet constitute a generator.