Abstract:
The present invention relates to a transmission internally meshing a planetary gear structure; more particularly, to a reducer that makes it possible to maintain the precision and continuity of power transmission reliably and also to be miniaturized, comprising a frame body provided with a toothed gear internally meshed thereto; a first shaft provided with a sun gear; a plurality of planetary gears operably coupled to the sun gear; a number of crank structures mechanically coupled to corresponding planetary gears; a planetary gear structure mechanically coupled to the crank structures and operably engaged with the toothed gear of the frame body; and a second shaft mechanically coupled to the crank structures.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a transmission internally meshing a planetary gear structure used as a reducer for controlling an automated and precision control machine such as a numerical controlled apparatus. 
     In general, automated and precision control machines equipped with reduction gears to reduce high rotary speed conveyed through a motive axis of power source such as an electric-powered motor or a servomotor. The reducer gears are required to move precisely and to be miniaturized, in order to reduce a size of an automated and a precision control machines and to increase precision of automated and precision control machines. 
     BACKGROUND OF THE INVENTION 
     One of the conventional reducers is an RV series of Vigo Drive™ developed and marketed by Teijin Seiki. The RV series of Teijin Seiki has been endowed with a plurality of pinch differences and a plurality of first-step reduction gears at an output end for securing an insertion space for a motive axis of power source inside an input shaft, thus conveying deceleration movement. 
     The RV series of Teijin Seiki, however, have the following problems: 
     (1) Since a plurality of pinch differences is used, a deceleration ration is frequently calculated as non-terminating decimals when calculating the deceleration ratio. Therefore, errors are accumulated when the reducer is frequently used and it leads to a decrease in the precision of deceleration movement. 
     (2) The RV series of Teijin Seiki can be comfortably applied to high-reduction gear ratio, as the diameter of an output end of the input shaft is made small in order to place a first-step reduction gear at the output end. However, extra parts are required when it is applied to low-reduction gear ratio, thus making the reducer bigger. 
     (3) Since first-stage reduction gears are located at an output end, extra parts for oil-sealing are required in order to prevent oil leakage such as grease from the circumferential portion of the first-step reduction gears. Therefore, the manufacturing cost and weight are increased. 
     (4) Since a first-step reduction gear is located at an output end, the length of an insertion space in an input shaft is ensured for the insertion of a motive axis of power source. However, the caliber of the insertion space is limited exceedingly due to the use of pinch differences. 
     (5) When installing a first-step reduction gear at an input end to address the above problems, the diameter of the insertion space for the motive axis insertion of power source gets very small due to the first-step reduction gear in a body with a prescribed diameter and the deceleration range gets limited exceedingly. 
     (6) Because pinch differences are adopted, the number of pins accommodated in a predetermined body gets limited due to the diameter of a pin—about 2 mm, thus making the deceleration range limited exceedingly. 
     Another reducer with an internal planetary gear is described in detail in commonly owned Korean Patent No. 242207, which is incorporated herein by reference as if fully set forth herein. The reducer comprises a main crank structure that is combined with a motive axis of power source in an Oldham coupling method. The reducer receives the conveyed rotary power from the power source, a plurality of planetary gears. The plurality of planetary gears conducts deceleration movement translating and rotating according to the rotation of supplementary crank structures and a plurality of supplementary crank structures that execute translation and rotation movement engaged with the planetary gears. 
     The reducer of the Korean Patent No. 242207, however, has cases where the rotary movement of the main crank structure and the supplementary axes are not perfectly aligned with each other. For example, the perfect alignment may not be achieved due to reasons of processing, assembling and deformation, as the supplementary crank structures are connected to the planetary gear that translate and rotate at the same time. In other words, the rotation of the supplementary crank structures is not regulated. Here, when the supplementary crank structures move, or when load is added from outside, a problem arises in that the supplementary crank structures vibrate periodically to the rotating direction, thereby dropping the qualities of precision and continuity of power transmission. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a transmission internally meshing a planetary gear structure that can maintain the precision and continuity of power transmission reliably and also can be miniaturized. In this manner, problems of the conventional technologies mentioned above can be addressed. 
     It is another object of the present invention to provide a transmission internally meshing a planetary gear structure which is easy to oil-seal, and applicable to both high-reduction gear ratio and low-reduction gear ratio, thus making the reducer inexpensive and small. 
     A transmission internally meshing a planetary gear structure comprises: a body wherein an internal gear is formed on an outer circumferential surface; an input shaft wherein formed are serration on the outer circumferential surface and an insertion space inside for power source connection; a plurality of first planetary gears wherein formed are serrations that fit with those of the input shaft, thereby moving engaged with the input shaft; a plurality of crank structures which are equipped with both a number of coaxial lines having the identical axis and a number of eccentric components that is, located between the coaxial lines, having a predetermined eccentric amount but with phase differences to each other, and which rotate by the rotary movement of the first planetary gears; second planetary gears wherein the planetary gears are formed along the outer circumferential surface and engaged with the internal gears of the body, also formed is a central hole that the input shaft penetrates in the center and the eccentric components of the crank structures pass through a circumferential portion and conduct translation and rotation movement to the rotary movement of the crank structures; a precession prevention plate wherein a central hole penetrated by the input shaft is formed in the center, the coaxial lines at the back end of the crank structures penetrate the circumferential portion so that they are connected, and the generation of the precession is blocked when the crank structures rotate; and an output shaft plate wherein a central hole that the input shaft penetrates in the center, of which the circumferential portion is combined to the coaxial lines of the fore end of the crank structures and conveys the rotary power of the crank structures. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a disassembled schematic view illustrating a transmission internally meshing a planetary gear structure in accordance with the present invention; 
     FIG. 2 shows an assembled schematic view depicting a transmission internally meshing a planetary gear structure in accordance with the present invention; 
     FIG. 3 represents a cross-section showing a transmission internally meshing a planetary gear structure in accordance with the present invention; 
     FIG. 4 depicts a cross-section view illustrating an input shaft of a transmission internally meshing a planetary gear structure in accordance with the present invention; 
     FIG. 5 presents a side view showing crank structures of the transmission shown in FIG. 3; and 
     FIG. 6 is a plan view representing the transmission internally meshing a planetary gear structure in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying FIGS. 1 to  6 , a transmission internally meshing a planetary gear structure of a preferred embodiment of the present invention will be described in detail hereinafter. 
     As shown in FIGS. 1 to  3 , a transmission internally meshing a planetary gear structure of the present invention is connected to a power source such as servo motor, and includes an input shaft  110  formed with a tooth-shaped surface  112  at the outer circumferential surface of the back end; a plurality of primary planetary gears  210  engaged with the tooth-shaped surface  112  at the input shaft  110  of the back end; and a plurality of crank structures  310  fixed at each of the primary planetary gears  210 . 
     In the preferred embodiment, the number of primary planetary gears  210  and the number of crank structures  310  are 3, respectively. 
     As shown in FIG. 4, the input shaft  110  is a hollow cylinder that has an insertion space  114  formed inside for connecting a motive axis of power source thereto and a number of screw holes  116  formed at a predetermined interval for connecting bolts to join the front end of the input shaft  110  to a fixing plate which will be described later. The input shaft  110  rotates by power transmitted from the power source through the motive axis of the input shaft. The input shaft  110  and the primary planetary gears  210  are supported and constrained by multiple bearing around the crank structure  310 . 
     As shown in FIG. 5, each of the crank structures  310  includes a disk  312  with predetermined thickness, eccentric components  314 A and  314 B formed at both sides of the disk  312 , respectively; and a couple of coaxial lines  316 A and  316 B formed at the ends of the eccentric components  314 A and  314 B. Here, the disks  312 , the eccentric components  314  and the coaxial lines  316  are integrated into a body. The eccentric components  314 A and  314 B at both sides of the disk  312  are located eccentrically to the central axis of the disk  312 . An eccentric component  314 A at one side of the disk  312  and an eccentric component  314 B at the other side of the disk  312  have a phase difference of 180° to each other. Also, the central axis of the two coaxial lines  316 A,  316 B is perfectly aligned with that of the disk  312 . The coaxial lines  316 A,  316 B at the back end of the disk  312  are connected to the center of the primary planetary gears  210 , therefore, the rotary movement of the input shaft  110  is conveyed to the crank structures  310  through the primary planetary gear  210  when the input shaft  110  rotates. Here, the crank structure  310  rotates and revolves on its own axes. 
     The eccentric components  314 A,  314 B at both sides of the crank structure  310  support each of the two planetary gears  320 A,  320 B so that the planetary gears  320 A,  320 B can be moved. The two planetary gears  320 A,  320 B perform cycloid motion by the eccentric amount of the two eccentric components  314 A,  314 B when the crank structure  310  rotates. Bearings  330  installed between the eccentric components  314 A,  314 B and the planetary gears  320 A,  320 B help the crank structures  310  rotate smoothly. Here, the two planetary gears  320 A,  320 B are positioned closely to each other at both sides of the disks  312  with a gap just less than the thickness of the disks  312  between them. Therefore, when conducting rotation and translation movement, the two planetary gears  320 A,  320 B are prevented from contacting each other and generating frictional heat and abrasion. 
     Each of the two planetary gears  320 A,  320 B has a shape of a disk and a number of pass-through holes are formed in predetermined intervals. Also, a gear is formed on the surface. In the present embodiment of the present invention, the pass-through holes of both planetary gears  320 A,  320 B are classified into three holes for the crank structures  310  and six holes for consolidating pins  340 . The consolidating pins  340  are hollow cylinders tapped on the inner circumferential surface. The consolidating pins  340  tie firmly an anti-gyration plate  510  and an output shaft  610 . Also, the consolidating pins  340  distribute load evenly and easily adjust preload amount on main bearings  520 ,  620 . By keeping a predetermined distance between the main bearings  520 ,  620 , they can ensure the moment load for outside load caused by the main bearings  520 ,  620 , thus the moment rigidity of the reducer is maintained. In this case, the pass-through holes for crank structures  322  are positioned at an interval of 120° , and between two adjacent pass-through holes for crank structures  322 , two holes for consolidating pins  324  are arranged with predetermined intervals. 
     The two planetary gears  320  are installed in a body  410  with internal gears on the inner circumferential surface thus the two planetary gears  320  are engaged with the body  410 . 
     The coaxial lines  316 A,  316 B at the back end of the crank structures  310  are supported by the anti-gyration plate  510  with mediation of bearings in order to be rotated, while the coaxial lines  316 A,  316 B at the crank structures  310  of the front end are rotating and they also are supported by the output shaft  610  with mediation of bearings. The anti-gyration plate  510  is rotated by the rotary of the crank structures  310  and prevents the gyration of  310  on its own axis while it enhances the output shaft  610 . The output shaft  610  is rotated by the rotary of the crank structures  310  and transmits the rotary power outside. Here, the coaxial lines  316 A,  316 B at the back end of the crank structures  310  pass through the anti-gyration plate  510  and they are connected to the primary planetary gears  210 . 
     On the outer circumferential surface of the anti-gyration plate  510  and the output shaft  610 , a first and second main bearings are installed and they smooth the rotation of the output shaft  610 . Also, bearings are installed between the input shaft  110 , the anti-gyration plate  510  and the output shaft  610  for the smooth rotation of the input shaft  110 . At the circumferential portion corresponding to the pass-though holes of the planetary gears  320  of the anti-gyration plate  510 , a number of screw holes are formed respectively and strength-maintenance bolts are engaged at the screw holes. The strength-maintenance bolts  710  are bound to the consolidating pins  340  inserted into the planetary gears  320  through the screw holes on the anti-gyration plate  510 . 
     The strength-maintenance bolts  710  improve the deflection amount in the radial direction of a reducer by load from outside when a first and a second main bearings  520 ,  620  are pressed. 
     A number of screw holes  612  are formed at predetermined intervals on the circumferential portion of the output shaft  610  and the screw holes  612  are used as charge/discharge for lubricant or grease inside a reducer. Preferably, the number of screw holes  612  is 3. In this embodiment, the screw holes of the output shaft are filled hermetically with bolts engaged therein. The screw holes of bolts  622  are used for preventing the generation of impact in axis-direction on components related to the crank structures  310  by determining and supporting the position of the axis direction of the crank structures  310  when a reducer is assembled wherein crank structures are already assembled and then the planetary gears are fitted in. Also a plurality of holes is formed between two adjacent screw holes at regular intervals to which external apparatuses such as links are equipped. 
     An oil-seal  810  is equipped between the output shaft  610  and the body  410  and the oil-seal  810  prevents the leakage of lubricant such as grease inside a reducer. 
     Meanwhile, in the center of the anti-gyration plate  510 , a central hole is formed by penetrating the two planetary gears  320  and the output shaft  610 . The fore part of the input shaft  110  can be passed through to the fore part of the input shaft  110 . A fixing plate  910  is joined firmly with a number of bolts that constrain the possible axial movement of the input shaft  110 . 
     The operation of a transmission internally meshing a planetary gear structure constituted as mentioned above in accordance with the present invention is explained hereinafter. 
     When an outside power source motivates a motive axis into rotation, an input shaft  110  connected to the motive axis is rotated. In turn, a plurality of primary planetary gears  210  engaged with outer circumferential surface of the input shaft  110  are rotated. 
     Here, rotary power transmitted from each-of the primary planetary gears  210  is passed to the crank structures connected to the primary planetary gears  210  and the crank structures  310  are rotated and revolved. In this case, as rotating and revolving, the crank structures  310  conduct deceleration movement in proportion to a predetermined deceleration ratio, that is, an engagement ratio between the input shaft  110  and the planetary gears  210  joined thereto. The two planetary gears at the eccentric components  312  of the crank structures  310  carry out translation and rotation movement. 
     The deceleration movement of the crank structures  310  is transmitted to the output shaft  610 . The deceleration movement in proportion to the deceleration ratio is transmitted as mentioned above. 
     As mentioned above, various effects of the present invention are described hereinafter. 
     By directly connecting an end of the coaxial lines of the crank structures to the primary planetary gears, which are engaged with the input shaft, the rotary movement of the crank structures is bound by the primary planetary gears, thus vibration generated from the rotation of the crank structures in the conventional technologies is restrained. As a result, the precision and continuity of power transmission can be maintained reliably. 
     By using internal planetary gears, it is easy to control the size of an insertion space inside an input shaft for the insertion of a motive axis of power source and the deceleration movement of precision control machines can be maintained reliably because cases of deceleration ratios calculated in interminating decimals decrease. 
     By using internal planetary gears, gears can be miniaturized with a wide range of speed reduction/increase. 
     Since primary planetary gears located in an input end, oil sealing at an output end is easy to provided, and it&#39;s possible to enlarge primary planetary gears inside a limited body size, thus it allows a reducer to embody high-deceleration ratio and low-deceleration ratio without making the reducer bigger. 
     Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.