Abrading – Frame or mount – Rotary tool supporter
Reexamination Certificate
1999-10-04
2001-08-21
Eley, Timothy V. (Department: 3723)
Abrading
Frame or mount
Rotary tool supporter
C451S344000
Reexamination Certificate
active
06277013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electric power tools, such as grinders, that transmit rotation of a motor via the motor shaft to a gear disposed coaxially with a spindle. More particularly, the present invention relates to an electric power tool such as described above that includes a mechanism for reducing impact on the tool during operation.
2. Description of the Related Art
A certain type of grinder includes a motor shaft having a gear at its free end and a spindle disposed orthogonally to the motor shaft in a housing. Another gear, such as a bevel gear, is secured to the spindle by suitable means, such as key-groove coupling or press fitting. The bevel gear on the spindle meshes with the gear of the motor shaft so as to transmit torque from the motor to spindle via the bevel gear. The grinding additionally includes a recess in a portion of the bevel gear where the teeth are not formed and a locking device that is biased in the direction away from the recess in the bevel gear. The locking device can be manually pushed into the recess for locking the spindle via the bevel gear in order to facilitate tightening and loosening of a lock nut that attaches, for example, a grinding wheel to the spindle.
When a locking device is used as a brake in a grinder with no electric brake, the tool bit, such as a grinding wheel, continues to rotate due to its own inertia even after the motor is turned off. Thus, if the operator wishes to quickly change the tool bit for a different task, the locking device is used as a brake by bringing the device into contact with the bevel gear. This, however, subjects not only the locking device but also the bevel gear, the spindle, and the housing to severe impact, which may cause deformation or breakage of these elements.
Moreover, as the lock nut tends to be tightened by the rotation of the grinder wheel, when the motor is started, the lock nut is subjected to an impact acting in the direction in which the nut is tightened. When electric brakes (if provided) are applied or the locking device is used as a brake during rotation of the tool bit due to its own inertia, a difference in rotational speed develops between the tool bit, which tends to stay in rotation due to its inertia, and the decelerating bevel gear and spindle. As this difference in speed generates an impact on the lock nut acting in the direction opposite to that in which the lock nut is tightened, the lock nut may be inadvertently loosened.
SUMMARY OF THE INVENTION
In view of the above-identified problems, an important object of the present invention is to provide an electric power tool that lessens impact on a locking device, gears, and other elements of the tool when the locking device is used as a brake.
Another object of the present invention is to provide an electric power tool that realizes a simple and effective structure for reducing clashing between gear teeth at the start of the motor and/or application of brakes.
Still another object of the present invention is to provide an electric power tool that, while reducing clashing between gear teeth, prevents unintended tightening and loosening of a nut, or screw, or bolt used to fasten a tool bit, such as a grinding wheel, to a spindle of the tool during operation.
Still another object of the present invention is to provide an electric power tool that reduces undesirable vibration of the motor shaft and further reduces clashing between gear teeth.
The above objects and other related objects are realized by the invention, which provides an electric power tool including: a motor having a motor shaft; a spindle; a gear disposed coaxially with a spindle for transmitting rotation of the motor shaft to the spindle such that the spindle is freely rotatable relative to the gear; a lock means for preventing rotation of the gear; a first ring-shaped peripheral surface provided in the spindle; a second ring-shaped peripheral surface provided in the gear, the second peripheral surface being coaxial with the first peripheral surface; and a first coil spring disposed in contact with the first and second ring-shaped peripheral surfaces so as to connect the gear and the spindle. In this electric power tool, a difference in speed between the gear and the spindle due to a decrease in the rotational speed of the gear generates a force that causes the first coil spring to change its diameter so as to transmit a braking force applied from the gear to the spindle.
According to one aspect of the present invention, the first ring-shaped peripheral surface is connected to the second ring-shaped peripheral surface such that the two surfaces define a first continuous circular surface. Furthermore, the first and second ring-shaped peripheral surfaces have the same diameter and are coaxial with the spindle and the gear.
According to another aspect of the present invention, the first continuous circular surface is an inwardly circular surface relative to the center thereof. Furthermore, the first coil spring has an outer diameter slightly larger than the diameter of the first continuous circular surface and is fitted in the first continuous circular surface such that the expanding force of the first coil spring connects the gear and the spindle.
According to still another aspect of the present invention, the midpoint of the first coil spring is located at the connection of the first and second ring-shaped peripheral surfaces, such that half the winding of the first coil spring covers the first ring-shaped peripheral surface and the other half of the winding covers the second ring-shaped peripheral surface.
According to yet another aspect of the present invention, the first coil spring may have an approximately square cross section.
In one embodiment, the electric power tool further includes a third ring-shaped peripheral surface provided in the spindle and a fourth ring-shaped peripheral surface provided in the gear. The third peripheral surface is coaxial with the first and second peripheral surfaces and has a diameter differing from that of either the first or second peripheral surface, whereas the fourth peripheral surface is coaxial with the third peripheral surface and has the same diameter as that of the third peripheral surface. The tool additionally includes a second coil spring which is coaxial with the first coil spring and disposed in contact with the third and fourth ring-shaped peripheral surfaces so as to connect the gear and the spindle such that a difference in speed between the gear and the spindle due to an increase in the rotational speed of the gear causes the first coil spring to change its diameter so as to transmit rotation of the gear to the spindle.
In one aspect, the third ring-shaped peripheral surface is connected to the fourth ring-shaped peripheral surface such that the two surfaces define a second continuous circular surface.
In another aspect, the second continuous circular surface is an outwardly circular surface relative to the center thereof, whereas the second coil spring has an inner diameter slightly smaller than the diameter of the second continuous circular surface and is wound around the second continuous circular surface, such that the winding force of the second coil spring connects the gear and the spindle.
In still another aspect, the midpoint of the second coil spring is located at the connection of the third and fourth ring-shaped peripheral surfaces, such that half the winding of the second coil spring covers the third ring-shaped peripheral surface and the other half of the winding covers the fourth ring-shaped peripheral surface.
In yet another aspect, the second coil spring has an approximately square cross section.
According to one aspect, the electric power tool further includes a circular groove which is provided in the gear and the spindle and has inner and outer peripheral surfaces coaxial with the gear and the spindle, with the outer peripheral surface being the first continuous circular surface and the inner peripheral surface being the second continu
Itakura Toru
Sasaki Katsuhiko
Sugiura Shin
Eley Timothy V.
Foley Hoag & Eliot LLP
Makita Corporation
Nguyen Dung Van
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