Machine element or mechanism – Mechanical movements – Rotary to rotary
Reexamination Certificate
2001-02-16
2003-09-23
Joyce, William C (Department: 3682)
Machine element or mechanism
Mechanical movements
Rotary to rotary
C074S409000, C242S397000
Reexamination Certificate
active
06622580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to backlash-free speed reducing devices and, more particularly, to a backlash-free speed reducing device designed to allow all the rotatable cylinders of a rotary unit and a power output unit to be linearly movable along their shafts in opposite directions when the cylinders are rotated by power transmission cables operated in conjunction with the drive shaft of a drive motor, thus maintaining desired tension of the transmission cables during an operation of the speed reducing device for achieving a high speed reduction ratio and preventing a backlash of the cables during such operation.
2. Description of the Prior Art
FIG. 1
is a perspective view of a conventional speed reducing device. As shown in the drawing, the conventional speed reducing device comprises a longitudinal drive shaft
120
axially extending from a drive motor
140
. A first power transmission cable
180
is fixed to the external surfaces of two first cylinders
220
of a rotary unit
200
at its opposite ends. This first transmission cable
180
is also wound around the drive shaft
120
of a drive motor
140
several times at its middle portion. Therefore, the cable
180
can be wound around or unwound from the two first cylinders
220
while rotating the cylinders
220
in response to a rotation of the drive shaft
120
.
A rotating shaft
240
is axially fixed to the center of one end of each first cylinder
220
. A second power transmission cable
160
is fixed to the external surfaces of the rotating shafts
240
of the two first cylinders
220
at its opposite ends. This second transmission cable
160
is also wound around the second cylinder
320
of a power output unit
300
several times at it middle portion. The second transmission cable
160
can be thus wound around or unwound from the rotating shafts
240
of the two first cylinders
220
while rotating the second cylinder
320
of the power output unit
300
in accordance with a rotation of the two first cylinders
220
. Therefore, the rotating force of the drive motor
140
is transmitted to the power output unit
300
through the drive shaft
120
, the first transmission cable
180
, the rotary unit
200
, and the second transmission cable
160
.
In the conventional speed reducing device, the first cable
180
is fixed to one of the two first cylinders
220
at one end thereof, and extends from the first cylinder
220
to be wound around the drive shaft
120
several times prior to being fixed to the other first cylinder
220
at the other end thereof.
When the drive shaft
120
is rotated in a direction by the rotating force of the motor
140
, the first cable
180
is unwound from one of the two first cylinders
220
, and is wound around the other first cylinder
220
, thus finally rotating the power output shaft
340
of the power output unit
300
. In such a case, the first transmission cable
180
is moved in either direction in accordance with a rotating direction of the drive shaft
120
.
However, the conventional speed reducing device has the following problems. That is, when the first transmission cable
180
is wound around or unwound from the two first cylinders
220
in accordance with a rotation of the drive shaft
120
, it is almost impossible to maintain a desired tension of the first cable
180
at portions between the drive motor
120
and the two first cylinders
220
during the rotation of the drive shaft
120
. That is, the first transmission cable
180
is undesirably loosened to lose its desired tension when the speed reducing device is operated to achieve a high speed reduction ratio. In such a case, the speed reducing device creates a backlash of the first cable
180
.
Due to such a backlash created by the uneven tension of the first transmission cable
180
, it is almost impossible to appropriately transmit the rotating force of the first cylinders
220
to the power output unit
300
through the second transmission cable
160
. Such a backlash also prevents the speed reducing device from achieving a desired high speed reduction ratio.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a backlash-free speed reducing device, which is designed to allow all the rotatable cylinders of a rotary unit and a power output unit to be linearly movable along their shafts in opposite directions when the cylinders are rotated by power transmission cables operated in conjunction with the drive shaft of a drive motor, thus maintaining desired tension of the transmission cables during an operation of the speed reducing device for achieving a high speed reduction ratio and preventing a backlash of the cables during such operation.
In order to accomplish the above object, the present invention provides a backlash-free speed reducing device, comprising a drive unit consisting of a drive motor, with a drive shaft axially extending from the drive motor; a first power transmission cable wound around the drive shaft a predetermined number of times; a rotary unit having a least one first rotatable cylinder, with the first transmission cable fixed to the external surface of the first rotatable cylinder at an end thereof and wound around or unwound from the first rotatable cylinder in response to a rotation of the drive shaft, the first rotatable cylinder being concentrically fitted over a rotating shaft such that the first rotatable cylinder is linearly movable along the rotating shaft in opposite directions; a second power transmission cable fixed to the external surface of the rotating shaft of the rotary unit at one end thereof and wound around the rotating shaft a predetermined number of times; and a power output unit having a second rotatable cylinder, with the second transmission cable wound around the second rotatable cylinder, the second rotatable cylinder being concentrically fitted over a power output shaft.
In the backlash-free speed reducing device, the rotary unit preferably has two first rotatable cylinders concentrically fitted over two rotating shafts, respectively, such that the two first rotatable cylinders are linearly movable along the two rotating shafts.
The first transmission cable is fixed to the external surfaces of the two first rotatable cylinders at opposite ends thereof, and is wound around or unwound from the first rotatable cylinders in response to a rotation of the drive shaft.
The first rotatable cylinder is linearly movable along the rotating shaft in opposite directions.
In addition, the second rotatable cylinder is linearly movable along the power output shaft in opposite directions.
In the backlash-free speed reducing device, a first fixing hole is formed on the external surface of the first rotatable cylinder so as to fix the end of the first transmission cable on the first rotatable cylinder.
In the backlash-free speed reducing device, a second fixing hole is formed on the external surface of the rotating shaft of the first rotatable cylinder so as to fix the end of the first transmission cable on the rotating shaft.
REFERENCES:
patent: 903997 (1908-11-01), Martinson
patent: 1854555 (1932-04-01), Mendola
patent: 2212823 (1940-08-01), Bulk
patent: 2430523 (1947-11-01), Meyer
patent: 2868504 (1959-01-01), Minty
patent: 5022619 (1991-06-01), Mamada
patent: 5105672 (1992-04-01), Carson et al.
patent: 5207114 (1993-05-01), Salisbury, Jr. et al.
patent: 5388480 (1995-02-01), Townsend
Chang Pyung Hun
Jeon Bo Kyoung
Jung Je Hyung
Park Hyung Soon
Park Ju Yi
Joyce William C
Korea Advanced Institute of Science and Technology
Rothwell Figg Ernest & Manbeck
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