String length adjusting device

1. A string length adjustment device comprising:

a fixed housing including a drum rotation axis formed in a central region thereof;

a rotation housing rotatably coupled with respect to the fixed housing;

a winding drum inserted into the fixed housing and the rotation housing and including a winding part around/from which a string is wound or unwound; and

a coupling unit guide shaft coupling the fixed housing to the rotation housing, the coupling unit guide shaft guiding up/down operations of the rotation housing for operations of winding or unwinding the string,

wherein the coupling unit guide shaft includes elastic ribs and protrusions, the elastic ribs being elastically biased in an outward radial direction and the protrusions being formed on the elastic ribs, and

wherein the rotation housing includes protrusion supports formed on walls of a shaft insertion hole of the rotation housing to support the protrusions.

2. The string length adjustment device according to claim 1 , wherein unidirectional sawteeth are disposed in any one of the fixed housing and the rotation housing in the direction in which the fixed housing and the rotation housing are coupled with each other, latches interacting with the unidirectional sawteeth by being selectively engaged with the unidirectional sawteeth so as to allow the string to be wound around or unwound from the winding drum are disposed in the other of fixed housing and the rotation housing in which the unidirectional sawteeth are not formed, housing coupling sawteeth are disposed in an annular shape in a lower region of the rotation housing, and drum coupling sawteeth interacting with the housing coupling sawteeth by being engaged with the housing coupling sawteeth are disposed in an annular shape in an upper region of the winding drum.

3. The string length adjustment device according to claim 2 , wherein the housing coupling sawteeth and the drum coupling sawteeth are provided in the form of right triangle or obtuse triangle, and the housing coupling sawteeth and the drum coupling sawteeth are engaged with each other such that oblique sides are in contact with the respective corresponding sides and sides forming heights are in contact with the respective corresponding sides forming heights.

4. The string length adjustment device according to claim 3 , wherein each of the coupling sawteeth has a flexibility allowing the coupling sawtooth to be elastically moved when an external force is applied to the coupling sawtooth.

5. The string length adjustment device according to claim 2 , wherein when the rotation housing is pressed downward to allow the string to be wound, the latches are engaged with the unidirectional sawteeth, the rotation housing is rotated only in one direction, the housing coupling sawteeth of the rotation housing and the coupling sawteeth of the winding drum are firmly in close contact with each other to cause the winding drum to be integrally rotated when the rotation housing is rotated, and when the rotation housing is pulled upward to allow the string to be unwound, the latches are engaged with or spaced apart from the unidirectional sawteeth, the rotation housing is rotated in one direction or is rotated in a forward or reverse direction, and the housing coupling sawteeth of the rotation housing and the coupling sawteeth of the winding drum are completely spaced from each other so that an interference state is removed.

6. The string length adjustment device according to claim 2 , wherein the drum coupling sawteeth comprise:

first drum coupling sawteeth shaped to allow the housing coupling sawteeth of the rotation housing to be rotated in either forward or reverse direction; and

second drum coupling sawteeth disposed in lower regions of the first drum coupling sawteeth and shaped to be engaged with the housing coupling sawteeth so as to allow the rotation housing and the winding drum to be integrally rotated.

7. The string length adjustment device according to claim 2 , wherein the unidirectional sawteeth are formed along an inner peripheral surface, an outer peripheral surface, or the top surface, and are shaped to allow the latches to be rotated in one direction.

8. The string length adjustment device according to claim 2 , wherein free ends of the latches are shaped to be hooks that are elastically moved toward the inside of the radial direction or upward out of the top surface.

9. The string length adjustment device according to claim 1 , wherein elastic restoration reinforcing portions for reinforcing elastic restoration of the elastic ribs are further provided in the elastic ribs.

10. The string length adjustment device according to claim 1 , wherein the protrusions of the coupling unit guide shaft are disposed above the protrusion supports when the rotation housing is pressed toward the fixed housing so as to wind the string, and are disposed under the protrusion supports when the rotation housing is pulled upward so as to unwind the string.

11. The string length adjustment device according to claim 1 , wherein two circular plates for maintaining the string position are disposed to be spaced from each other in the winding drum.

12. The string length adjustment device according to claim 1 , wherein the coupling unit guide shaft includes a shaft and a screw, wherein the shaft is inserted from the rotation housing side and into the rotation axis of the fixed housing to prevent up/down movements of the winding drum, and the screw enables the rotation axis of the fixed housing and the shaft to be coupled and fixed to each other.

13. The string length adjustment device according to claim 1 , wherein the rotation housing further includes a number of individual latches and latch guides for guiding the individual latches, wherein the individual latches are separately made to be engaged with the sawteeth of the fixed housing side and are coupled to the rotation housing side.

14. The string length adjustment device according to claim 13 , wherein each of the individual latches includes a first latch interacting with the sawtooth of the fixed housing side by being engaged with the sawtooth, and a second latch that is integrally formed with the first latch, formed to have a smaller thickness than the first latch at one side of the first latch for providing the first latch with elastic restoration, and supported by the latch guide.

15. The string length adjustment device according to claim 14 , wherein an individual latch deviation blocking portion is further formed on an inner wall of the latch guide and is disposed between the first latch and the second latch to prevent the individual latches from being deviated.