JPH0113868Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a reaction torque absorbing device in a drive mechanism of an electric screwdriver equipped with a speed reduction device using a planetary gear mechanism.

[Conventional technology and its problems]

2. Description of the Related Art Conventionally, it has been known to employ a planetary gear mechanism shown in FIG. 1 as a speed reduction device that reduces the rotational driving force of an electric motor or the like to increase its torque, or as a speed increase device that increases the speed. That is, this planetary gear mechanism has a planetary gear supported on a rotating disk 16 between a sun gear 12 fixed to a drive shaft 10 of an electric motor, etc., and an internal ring gear 14 having annular internal teeth. meshing the gears 18;
By fixing the ring gear 14 to a casing or the like, reduced rotational force in the same direction as the drive shaft 10 is transmitted to the driven shaft connected to the rotating disk 16. This type of planetary gear mechanism has a driving shaft and a driven shaft aligned on the same axis, and can be constructed relatively compactly, so it can be used in small devices such as electric screwdrivers and wire wrapping machines that connect wires without soldering. Suitable for use in electric rotating tools.

By the way, if we consider the case of tightening a screw using an electric screwdriver equipped with this planetary gear mechanism, the threading process of the screw is such that the tip of the screw touches the screw hole and then the screw head reaches the hole. It consists of a screw-in process, in which the screw rotates while encountering slight resistance until reaching the opening, and a final tightening process, in which the screw is firmly tightened by overcoming strong resistance. However,
The final tightening of the screw is performed by releasing at once the sum of the rotational torque specific to the electric motor and the inertia torque accumulated in the driver shaft as it rotates. If the tightening torque for this screw is too strong, the screw may break or the threads may be destroyed, and if the torque is too weak, the screw may loosen over time. It was difficult to stop tightening at the required torque. In addition, when the screw is finally tightened, the driver shaft encounters rapidly increasing mechanical resistance and stops suddenly, which applies stress to the meshing part of the planetary gear mechanism, causing damage and causing an unpleasant recoil shock to the driver operator. This increases fatigue, reduces work efficiency, and shortens tool life.

The applicant developed an electric motor built into the screwdriver grip in order to reduce the impact received on the grip during the final tightening of the screw and to dampen excessive torque on the screw in the screw tightening operation using an electric screwdriver. An electric screwdriver in which the speed reducer connected to the drive shaft of the motor is not directly fixed to the grip, but the speed reducer and the grip are elastically connected via a coil torsion spring wrapped around the outer periphery of the speed reducer. developed and filed a patent application (Japanese Unexamined Patent Publication 1973-
143198). In the electric screwdriver configured in this way, when the driver shaft suddenly encounters a high resistance force during a screw tightening operation, the high inertia force on the motor drive shaft side is absorbed by the coil torsion spring, and the inertia is This prevents force from being transmitted to the driver shaft, and also prevents reactionary impact on the gripping portion.

However, the above-mentioned electric screwdriver is not related to the internal mechanism of the reduction gear, and its outer casing is elastically held between the screwdriver gripping part via a coil torsion spring, and therefore, for example, a planetary gear mechanism is not connected to the electric screwdriver. In a structure in which the driver shaft is interposed between the drive shaft and the driven shaft, if the driver shaft encounters rapidly increasing mechanical resistance and suddenly stops during final tightening of the screw, the meshing part of the planetary gear mechanism The disadvantage is that it is not possible to avoid the stress applied to the That is, in the conventional electric screwdriver, elastic action acts between the screwdriver grip and the device casing in a state where stress is applied to the meshing part of the planetary gear mechanism, so that the meshing part of the planetary gear mechanism The problem is that there is no protection at all.

Therefore, the purpose of the present invention is to provide a drive mechanism for an electric screwdriver that combines a planetary gear mechanism so that the driven shaft can absorb external mechanical loads in response to the rotational torque transmitted from the drive shaft to the driven shaft via the planetary gear mechanism. To provide a reaction torque absorbing device capable of effectively absorbing and protecting a meshing part of a planetary gear mechanism from the harmful reaction torque released when a momentary stop occurs.

[Means for solving problems]

The recoil torque absorption device in the drive mechanism of an electric screwdriver according to the present invention connects a sun gear to the drive shaft of an electric motor, supports a plurality of planetary gears that mesh with the sun gear on a rotating disk, and supports the rotating disk. In the drive mechanism of an electric screwdriver, a driven shaft serving as a working axis of the driver is connected to the center of the drive shaft, and a planetary gear mechanism is coupled with an internal ring gear that provides rotational motion to the planetary gear. A casing is provided that supports the driven shaft and has a stepped portion at the other end to accommodate a rotating disk connected to the driven shaft, and a plurality of planetary gears supported by the rotating disk are provided within the casing. A ring gear is housed so as to be freely rotatable in mesh with the casing, and a coil spring is inserted between the stepped portion of the ring gear and the rotating disk within the casing, and the coil spring is configured to rotate in the direction in which the driven shaft is tightened with the screw. One end of the ring gear is locked to the inner circumferential edge of the end of the ring gear in order to maintain torsional elasticity in the opposite direction, and the other end is locked to the stepped portion of the casing, so that when the driven shaft completes screw tightening, the driven shaft reaches a predetermined position. The ring gear meshing with the planetary gear and the rotating disk of the driven shaft are reversed by the elasticity of the coil spring to absorb reaction torque when a momentary stop occurs due to an opposite load.

[Effect]

According to the reaction torque absorbing device according to the present invention, the planetary gear group rotationally driven by the sun gear directly connected to the drive shaft meshes with the ring gear fixed to the casing and revolves around the planet while rotating. At this time, if the driven shaft connected to the rotating disk that supports the planetary gear group momentarily stops due to an external mechanical load, the planetary gear group also stops instantaneously, and the motor that is transmitted via the sun gear The inertial force is transmitted to the ring gear via the planetary gear group, but this inertial force becomes a reaction torque on the driven shaft and is transmitted to the coil spring, and the ring gear rotates slightly while resisting the spring elasticity. It can absorb and soften the impact.

〔Example〕

Next, an embodiment of the reaction torque absorbing device in the drive mechanism of an electric screwdriver according to the present invention will be described in detail below with reference to the accompanying drawings.

FIGS. 2 and 3 show the disassembled state of the drive mechanism of an electric screwdriver employing the reaction torque absorbing device according to the present invention. For convenience of explanation, the same components as those shown in FIG. 1 will be described with the same reference numerals. That is, in this embodiment, the drive mechanism is the drive shaft 10 of the electric motor 22.
A sun gear 12 is fixed to a sun gear 12, three planetary gears 18 are rotatably supported on a rotating disk 16 directly connected to a driven shaft 20, and the planetary gears 18 are rotatably supported through the driven shaft 20. It basically consists of a casing 24 having a stepped portion that accommodates an internal ring gear 14 that meshes with the internal ring gear 14 to impart a revolution motion. Generally, the ring gear 14 is fixedly fitted into the casing 24 to transmit power to the driven shaft 20, but in the present invention, the ring gear 1
The outer diameter of the ring gear 4 is set to be slightly smaller than the inner diameter of the casing 24 so that the ring gear 14 can freely rotate against the casing 24 in a sliding manner. A spiral coil spring 26 is inserted in series between the ring gear 14 and the casing 24 to elastically lock the ring gear 14 to the casing 24 in the rotational direction. In this case, the spiral coil spring 26 is
One end of the ring gear 14 is inserted into a locking hole 28 formed on the inner circumferential surface of the end portion of the ring gear 14, and the other end thereof is inserted into a locking hole 29 formed on the inner surface of the stepped portion of the casing 24 for fixation. Moreover, this spiral coil spring 26 is
Drive shaft 10 of electric motor 22, ie sun gear 1
Use one that is wound in a direction that provides winding resistance with respect to the rotation direction of No. 2. Each component shown in FIGS. 2 and 3 is housed in the casing 24,
The structure of the drive mechanism is shown in FIG. That is, since the ring gear 14 is elastically locked to the casing 24 in the rotational direction, the rotation of the planetary gear 18 as a normal planetary gear mechanism occurs below the torque limit required for bending and winding the coil spring 26. However, if an excessive torque of more than a predetermined value is applied to the ring gear 14, the ring gear 14 is moved by the coil spring 2.
It will be understood that the flexural winding of 6 is carried out to cause a slight rotation with respect to the casing 24 in an elastic manner.

Therefore, the recoil torque absorbing device according to the present invention,
When incorporated into the aforementioned electric screwdriver as a drive mechanism, the inertia force released at the end of the final tightening of the screw is transmitted to the ring gear 14 as a reaction torque. The driven shaft 20 stops instantaneously, and therefore the planetary gear 18 stops its revolving motion with respect to the ring gear 14, but the sun gear 12 connected to the motor 22 still tries to continue rotating, so that the rotational torque inherent in the electric motor and This is because the sum of the inertia torque of the drive shaft 20 accumulated up to the time of instantaneous power failure is transmitted from the sun gear 12 to the ring gear 14 via the planetary gear group 18 that meshes with the sun gear 12). The inertia force overcomes the original shape holding force of the spiral coil spring 26 and bends and coils the spiral coil spring 26.
4 rotates a little with respect to the casing 24 and then stops, in which case the absorption of the harmful reaction torque is achieved. Therefore, the screw tightening work can be performed continuously with an appropriate tightening torque on the belt without causing screw tightening, especially without destroying the thread thread, and the meshing portion of the planetary gear mechanism can be protected.

[Effect of idea]

As is clear from the embodiments described above, according to the present invention, when a mechanical load is applied to the driven shaft and the driven shaft is instantaneously stopped, the inertia force transmitted to the ring gear via the planetary gear mechanism is absorbed by the ring gear itself. By elastically rotating the coil spring, the gear absorbs and buffers smoothly, and accidents such as gear breakage can be prevented. In other words, in the present invention, the ring gear is housed in the casing so as to be freely rotatable, and is connected to the casing in series with the ring gear via a coil spring, so that the driven shaft can be easily rotated. The reaction torque transmitted to the ring gear through the coil spring can be easily absorbed by slightly rotating the ring gear against the spring elasticity of the coil spring.

Therefore, an electric screwdriver incorporating a drive mechanism equipped with a recoil torque absorbing device configured as described above can appropriately and reliably absorb and buffer any recoil torque generated during screw tightening work. The practical advantages of this method are extremely great, such as being able to eliminate all the problems caused to the drive mechanism, especially the planetary gear mechanism, improve work efficiency and extend tool life.

Although the preferred embodiments of the mechanism of the present invention have been described above, the present invention is not limited to these embodiments, and various improvements and changes can be made without departing from the spirit of the invention. be.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the main structure of a general planetary gear mechanism, FIGS. 2 and 3 are exploded explanatory views of a drive mechanism showing an embodiment of the reaction torque absorbing device according to the present invention, and FIG. This figure is a partially sectional side view showing the assembled state of the drive mechanism shown in FIGS. 2 and 3. 10... Drive shaft, 12... Sun gear, 14...
Ring gear, 16... Rotating disk, 18... Planetary gear, 20... Driven shaft, 22... Electric motor, 24
...Casing, 26...Coil spring, 28,2
9...Lock hole.

Claims (1)

[Scope of Claim for Utility Model Registration] A sun gear is connected to the drive shaft of an electric motor, and a plurality of planetary gears meshing with the sun gear are supported by a rotating disk, and the work shaft of the driver is located at the center of the rotating disk. In the drive mechanism of an electric screwdriver, the driven shaft is connected to the driven shaft, and the driven shaft is supported at one end, and the driven shaft is supported at the other end. A casing having a stepped portion is provided at the end to accommodate a rotating disk connected to the driven shaft, and the ring gear is meshed with a plurality of planetary gears supported by the rotating disk within the casing to freely rotate the ring gear. A coil spring is inserted between the stepped portion and the rotating disk within the casing, and the coil spring maintains torsional elasticity in a direction opposite to the direction of rotation of the driven shaft when tightening the screw. One end of the filter is locked to the inner circumferential edge of the end of the ring gear, and the other end is locked to the stepped portion of the casing, and when the screw tightening by the driven shaft is completed, the driven shaft receives a predetermined opposite load and momentarily stops. A reaction torque absorbing device for a drive mechanism of an electric screwdriver, characterized in that a ring gear that meshes with the planetary gear is reversed together with a rotating disk of the driven shaft by the elasticity of a coil spring to absorb reaction torque.