Planetary gear reduction device with torque limiter function

Details Planetary gear reduction device with torque limiter function Planetary gear reduction device with torque limiter function

2001-11-29

2004-01-27

Pang, Roger (Department: 3681)

Planetary gear transmission systems or components

Condition responsive control

Overload release

C192S056560

Reexamination Certificate

active

06682454

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a simple-structured, compact planetary gear reduction device with a torque limiter function.
2. Description of the Prior Art
As a reduction device for reducing a rotation speed of a motor or the like, a planetary gear reduction device is generally known conventionally. The planetary gear reduction device can obtain a large reduction ratio and can be made compact, so it works effectively for various types of apparatuses to which it is attached.
FIGS. 1A and 1B
are a plan view and a partially cutaway side view, respectively, showing the structure of one of conventional planetary gear reduction devices.
In this conventional planetary gear reduction device, as shown in
FIGS. 1A and 1B
, a stationary ring gear
46
is fixedly attached to a lower portion of a housing
43
, and a motor
45
is mounted to a lower portion of the ring gear
46
.
A sun gear
44
is fixedly mounted to a motor output shaft
45
a
rotatably supported at the center of the lower portion of the housing
43
and serving as an input shaft of the planetary gear reduction device. A planetary gear
47
meshes with the sun gear
44
through respective teeth formed on their respective outer circumferential surfaces, and meshes with the ring gear
46
through teeth formed on an inner circumferential surface of the ring gear
46
. The planetary gear
47
is coaxially, integrally overlaid with another planetary gear
48
. Three planetary gear pairs each constituted by the planetary gear
47
and the planetary gear
48
and rotatably attached to a carrier
51
and a carrier
52
provided on their lower and upper sides, respectively, are disposed around the sun gear
44
.
FIG. 1B
shows one of the three planetary gear pairs.
An output shaft
41
is rotatably mounted at the center of an upper portion of the housing
43
through a stop ring
42
such that an axially down movement of the output shaft
41
is stopped. A flange gear
49
is fixed to the output shaft
41
in a press fit manner, and inner teeth
49
a
formed on the lower portion of the inner circumferential surface of the flange gear
49
mesh with teeth
48
a
formed on an outer circumferential surface of the planetary gear
48
(although not shown, the flange gear
49
meshes similarly with two other planetary gears
48
at different positions).
In the conventional planetary gear reduction device, when the motor
45
is driven to rotate the motor output shaft
45
a
, the sun gear
44
and then the planetary gear
47
are rotated. As the planetary gear
47
meshes with the ring gear
46
which is stationary, it moves around the sun gear
44
while rotating. As a result, the flange gear
49
is rotated through the planetary gear
48
. Rotation speed of the motor output shaft
45
a
is reduced to that of the output shaft
41
in this manner.
The conventional planetary gear reduction device has the following problems.
When, for some reasons, an overload acts on an apparatus in which the planetary gear reduction device is equipped, power transmission must be disconnected to protect the motor and the planetary gear reduction device themselves. Also, when an overload acts on the apparatus due to, e.g., a human body touching with the apparatus, power transmission must be disconnected to assure safety.
However, the planetary gear reduction device according to the prior art does not have a torque limiter function. Therefore, a torque limiting mechanism for disconnecting power transmission depending on the frictional state of a clutch disk must be added to the output shaft of the planetary gear reduction device, which inevitably makes the structure become large. Even when a reduction device formed by combining gear trains without using a planetary gear reduction device is adopted and a torque limiting mechanism is mounted in it, the structure is complicated, thereby inevitably becoming large also.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above circumstances in the prior art, and has as its object to provide a simple-structured, compact planetary gear reduction device with a built-in torque limiting mechanism, which can reliably disconnect power transmission when an overload acts on it.
In order to achieve the above object, according to the first aspect of the present invention, a planetary gear reduction device with a torque limiter function, comprises: a housing; an input shaft commonly served by an output shaft of a power source, rotatably supported by one of end of the housing, located at a radially central and axially lower portion of the housing and adapted to take in a torque from the power source; an output shaft rotatably supported by the other end of the housing, located at a radially central and axially upper portion of the housing adapted to take out the torque transmitted from the power source; a reduction gear train provided between the input shaft and the output shaft and comprising a plurality of gears meshing with one another; and a built-in torque limiting mechanism constituted in said reduction gear train, whereby when an excessive torque is generated in the output shaft, torque transmission from the input shaft to the output shaft is disconnected by an action of said torque limiting mechanism.
According to the second aspect of the present invention, the torque limiting mechanism of the first aspect comprises: a planetary bevel gear which is one gear of the reduction gear train; a flange gear mounted to the output shaft freely in an axial direction and fixedly in a circumferential direction and meshing with the planetary bevel gear through inner teeth formed on a bevelled lower end surface thereof; a compression means provided between an upper surface of the flange gear and a lower surface of an upper lid of the housing and adapted to constantly press the flange gear toward the planetary bevel gear, whereby when an excessive torque is generated in the output shaft, the planetary bevel gear and the flange gear are disengaged from each other by a reaction force generated between respective teeth of those gears meshing with each other so as to disconnect torque transmission from the input shaft to the output shaft.
According to the third aspect of the present invention, the torque limiting mechanism of the first aspect comprises: a flange gear mounted to the output shaft fixedly in an axial direction and freely in a circumferential direction; an internal gear formed on an upper surface of the flange gear; a declutch gear mounted to the output shaft freely in the axial direction and fixedly in the circumferential direction and adapted to mesh with the internal gear; and a compression means provided between an upper surface of the declutch gear and a lower surface of an upper lid of the housing and adapted to constantly press the declutch gear toward the internal gear, whereby when an excessive torque is generated in the output shaft, the declutch gear and the internal gear are disengaged from each other by a reaction force generated between respective teeth of those gears meshing with each other so as to disconnect torque transmission from the input shaft to the output shaft.
According to the fourth aspect of the present invention, the torque limiting mechanism of the first aspect comprises: a flange gear mounted to the output shaft fixedly in an axial direction and freely in a circumferential direction; a friction surface portion formed on an upper surface of the flange gear; a clutch disk mounted to the output shaft freely in the axial direction and fixedly in the circumferential direction and adapted to come in frictional contact with the friction surface portion; and a compression means provided between an upper surface of the clutch disk and a lower surface of an upper lid of the housing and adapted to constantly press the clutch disk toward the friction surface portion, whereby when an excessive torque is generated in the output shaft, the clutch disk and the friction surface portion are disengaged from each other by a

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