Abstract:
Disclosed is a power transmission device. A power transmission device according to one embodiment of the present invention includes: a rack having a plurality of rack tooth profiles; a plurality of pin gears, which have a plurality of power transmission pins that rotate relative to the rack tooth profiles for power transmission, and are provided at a distance from each other along the lengthwise direction of the rack; and input gears which are disposed between the pin gears and rotatively connect the plurality of pin gears such that the pin gears rotate at the same speed as each other.

Description:
TECHNICAL FIELD 
     The present invention relates to a transmission device for converting a torque, and more particularly, to a transmission device for converting a torque which is capable of driving a single or a plurality of pin gears with only a single driving device so that not only an increased nominal load capacity is provided compared to a conventional technology but also a desired level of a deceleration rate is obtained without a complex deceleration device while using a rack of a limited size, thereby enabling all rolling motions including a rotational motion by an input gear and a linear motion by a rack and improving efficiency in power transmission. 
     BACKGROUND ART 
     A transmission device for converting a torque is classified into a rack and pinion for converting a rotational motion to a linear motion or vice versa, and a gear train for converting a rotational speed and a torque while transmitting a rotational motion only. In most cases, a power transmission system of a transmission device for converting a torque mainly adopts a tooth profile according to an involute curve principle. However, a tooth profile according to a cycloid curve principle is used in rare cases. 
     Such a transmission device for converting a torque is widely used for a variety of industrial machines including semiconductor devices and flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), organic light-emitting display (OLED), etc. In a transmission device for converting a torque that is applied to various industrial machines or is being prepared for application thereto, the transmission device is mostly operated as one pinion is gear-engaged with one rack, and desired power is transmitted as the pinion moves with respect to the rack or the rack moves with respect to the pinion. 
     However, contrary to the above typical case, when there is a limit in the size of a rack while nominal load capacity is large, a plurality of pinions or pinch gears and driving devices according thereto are required with respect to one rack. In this regard, it is difficult to match synchronization speeds of driving devices. In addition, since embodiment of a deceleration rate appropriate for high speed transmission is difficult, the application of the transmission device for converting a torque is practically delayed and thus improvement of the structure thereof is demanded. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
     The present invention provides a transmission device for converting a torque which is capable of driving a single or a plurality of pin gears with only a single driving device so that not only an increased nominal load capacity is provided compared to a conventional technology but also a desired level of a deceleration rate is obtained without a complex deceleration device while using a rack of a limited size, thereby enabling all rolling motions including a rotational motion by an input gear and a linear motion by a rack and improving efficiency in power transmission. 
     Description of the Drawings 
     According to the present invention, since a single or a plurality of pin gears can be driven with only a single driving device, not only an increased nominal load capacity is provided compared to a conventional technology but also a desired level of a deceleration rate is obtained without a complex deceleration device while using a rack of a limited size and thus all rolling motions including a rotational motion by an input gear and a linear motion by a rack may be possible and efficiency in power transmission may be improved. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a use state of a transmission device for converting a torque according to an embodiment of the present invention. 
         FIG. 2  is an enlarged perspective view of major portions in  FIG. 1 . 
         FIG. 3  is an enlarged perspective view of an input gear. 
         FIG. 4  is an exploded perspective view of a pinch gear. 
         FIG. 5  illustrates an internal structure of the power transmission pin of  FIG. 4 . 
     
    
    
     BEST MODE 
     According to an aspect of the present invention, there is provided a transmission device for converting a torque which includes a rack having a plurality of rack tooth profiles, a plurality of pin gears provided separated from each other in a lengthwise direction of the rack, each pin gear having a plurality of power transmission pins relatively rotating along the plurality of rack tooth profiles for power transmission, and an input gear arranged between the pin gears and connecting the plurality of pin gears to be capable of rotating to allow the plurality of pin gears to rotate at the same speed. 
     Each of the plurality of pin gears includes a body for rotatably supporting the plurality of power transmission pins, and a rotation support bearing unit coupled to a center area of the body and supporting a rotational motion of the body. 
     The body may be provided by a pair of bodies that are arranged separated from each other and parallel to each other to be are connected to opposite end portions of each of the plurality of power transmission pins. 
     The rotation support bearing unit may be arranged at each of the pair of bodies to be symmetrically so that a radial load generated in the power transmission with the input gear is offset and an external force added to the rotation support bearing unit is reduced. 
     The rotation support bearing unit may include a plurality of pin support bearings arranged at an equiangular interval along a circumferential direction of the body as many as the number of the plurality of power transmission pins and supporting rotational motions of the plurality of power transmission pins, and a center portion rotation shaft provided at a rotation center portion of the body and forming a center of rotation with respect to the body and a center of revolution with respect to the plurality of power transmission pins. 
     The center portion rotation shaft may be coupled to the body by a plurality of coupling members. 
     The rotation support bearing unit may further include a center portion rotation shaft support bearing that is coaxially arranged with the center portion rotation shaft between the center portion rotation shaft and the body and supporting the center of rotation according to a rotational motion of the body. 
     The rotation support bearing unit may further include a center portion oil seal that is connected to the center portion rotation shaft support bearing and lubricating and hermetically sealing the center portion rotation shaft support bearing. 
     The rotation support bearing unit may further include a plurality of outer oil seals that are provided corresponding to the plurality of pin support bearings one by one and seals a plurality of pin insertion support holes in which the plurality of power transmission pins are inserted and supported are formed in the body. 
     A lubricant flow hole through which a lubricant flows may be provided in each of the plurality of power transmission pins along a lengthwise direction of each of the plurality of power transmission pins. 
     A lubricant inlet and a lubricant outlet, through which the lubricant is input and output, may be provided in a lateral wall of each of the power transmission pins to be connected to the lubricant flow hole. 
     The lubricant input and the lubricant output may be arranged in opposite directions along a radial direction of the plurality of power transmission pins at opposite end portions of the lubricant flow hole. 
     The input gear may include an input gear main body where a plurality of input tooth profiles are formed on an outer surface along a circumferential direction thereof to correspond to the plurality of power transmission pins of the plurality of pin gears and interact with the plurality of power transmission pins, and an input gear shaft protruding from a center area of the input gear main body. 
     The plurality of input tooth profiles may be any one of tooth profiles selected from a trochoid tooth profile, a cycloid tooth profile, and an involute tooth profile. 
     The input gear may be a single input gear and the plurality of pin gears may be provided by a pair with respect to the single input gear arranged between the plurality of pin gears. 
     MODE OF THE INVENTION 
     The attached drawings for illustrating exemplary embodiments of the present invention are referred to in order to gain a sufficient understanding of the present invention, the merits thereof, and the objectives accomplished by the implementation of the present invention. Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. Like reference numerals in the drawings denote like elements. 
       FIG. 1  is a perspective view illustrating a use state of a transmission device for converting a torque according to an embodiment of the present invention.  FIG. 2  is an enlarged perspective view of major portions in  FIG. 1 .  FIG. 3  is an enlarged perspective view of an input gear.  FIG. 4  is an exploded perspective view of a pinch gear.  FIG. 5  illustrates an internal structure of the power transmission pin of  FIG. 4 . 
     First, referring to  FIGS. 1 and 2 , the transmission device for converting a torque according to the present embodiment includes a rack  110  having a plurality of rack tooth profiles  111 , a plurality of pin gears  120  provided separated from each other in a lengthwise direction of the rack  110 , each of the pin gears  120  having a plurality of power transmission pins  140  relatively rotating along the rack tooth profiles  111  for power transmission, and an input gear  180  arranged between the pin gears  120  and connecting the pin gears  120  to be capable of rotating so that the pin gears  120  rotate at the same speed. 
     The rack  110  is a linear rod gear and performs a linear motion in interaction with the pin gears  120 . In the present embodiment, although it will be described later, since the pin gears  120  are connected to the single rack  110  via the input gear  180 , an increased nominal load capacity may be provided compared to a conventional technology while using the rack  110  having a limited size. In other words, not only the number of parts decreases but also foot print of a device decreases as well and thus the capacity may be increased at least twice compared to the conventional technology. 
     The rack tooth profiles  111  are continuously formed in the lengthwise direction of the rack  110  at one side of the rack  110 . The rack tooth profiles  111  may adopt any one of a trochoid tooth profile, a cycloid tooth profile, and an involute tooth profile. 
     While the rack  110  performs a linear motion, the pin gears  120  perform a rotational motion. In the present embodiment, two pin gears  120  having the same structure are provided. Since this structure is a mere example, three or more pin gears  120  may be combined to be used. 
     Since the rack  110  performs a linear motion and the pin gears  120  perform a rotational motion, the transmission device for converting a torque according to the present embodiment may provide appropriate power to a processing apparatus (not shown) while the pin gears  120  move with respect to the rack  110  or the rack  110  moves with respect to the pin gears  120 . 
     Each of the pin gears  120 , as illustrated in  FIG. 4 , includes a pair of bodies  130 , the power transmitting pins  140  rotatably supported by the bodies  130  and relatively rotating along the rack tooth profiles  111  of the rack  110  for power transmission, and a rotation support bearing unit  150  coupled to a center area of each of the bodies  130  and supporting a rotational motion of the bodies  130 . 
     The bodies  130  are arranged in a pair separated from each other by the length of each of the power transmission pins  140  or less than the length thereof. The bodies  130  are connected to the opposite end portions of each of the power transmission pins  140  and rotatably support the power transmission pins  140 . 
     A plurality of pin insertion support holes  131  in which the power transmission pins  140  are inserted and supported are provided in the bodies  130  at an equiangular interval along a circumferential direction. The power transmission pins  140  are rotatably supported between the bodies  130  and interact with the rack tooth profiles  111  of the rack  110 . In other words, as the power transmission pins  140  each are engaged with the rack tooth profiles  111  to interact with each other, desired power is transmitted. 
     When the power transmission pins  140  are coupled to the bodies  130 , if the power transmission pins  140  are fixed to the bodies  130  by a press-in method, the power transmission pins  140  of the bodies  130  revolve around the bodies  130 . However, in the present embodiment, the power transmission pins  140  are coupled to the bodies  130  to be simultaneously capable of relatively rotating with respect to the bodies  130  at their positions. In other words, as described below, the power transmission pins  140  may perform rotational motions at their positions by means of a plurality of pin support bearings  152 . 
     As a result, during the rotation of the bodies  130 , the power transmission pins  140  simultaneously rotate and revolve along the bodies  130 . The rotation of the power transmission pins  140  are made only when the power transmission pins  140  interact with the rack tooth profiles  111  of the rack  110  in contact with the rack tooth profiles  111 . 
     To enable the power transmission pins  140  coupled to the bodies  130  to rotate and revolve at the same time, a lubrication structure for maintaining the rotation of the power transmission pins  140  smooth on the bodies  130  is provided. As illustrated in  FIG. 5 , a lubricant flow hole  141  through which a lubricant flows is provided in each of the power transmission pins  140  along the lengthwise direction of each of the power transmission pins  140 . A lubricant outlet  142  and a lubricant inlet  143 , through which the lubricant is input and output through the lubricant flow hole  141 , are provided in a lateral wall of each of the power transmission pins  140  to be connected to the lubricant flow hole  141 . 
     The lubricant outlet  142  and the lubricant inlet  143  may be arranged in the opposite directions along a radial direction of each of the power transmission pins  140  at the opposite end portions of the lubricant flow hole  141 , as illustrated in  FIG. 5 . However, the present invention is not limited thereto and the lubricant outlet  142  and the lubricant inlet  143  may be arranged in the same direction. 
     The rotation support bearing unit  150  is coupled to a center area of each of the bodies  130  to support the rotational motions of the bodies  130 . In the present embodiment, the rotation support bearing unit  150  is symmetrically coupled to the bodies  130 . Accordingly, a radial load generated during the transmission of power with the input gear  180  may be offset and thus an external force added to the rotation support bearing unit  150  may be reduced. As a result, durability of the rotation support bearing unit  150  is improved so that a long term use thereof may be achieved. 
     In addition, as the rotation support bearing unit  150  is symmetrically coupled to the bodies  130 , the rotation support bearing unit  150  may endure a load twice or more compared to a conventional technology based on the same bearing. 
     The rotation support bearing unit  150  includes a plurality of pin support bearings  152 , a center portion rotation shaft  154 , and a center portion rotation shaft support bearing  156 . The pin support bearings  152  are arranged at an equiangular interval along a circumferential direction of the bodies  130  as many as the number of the power transmission pins  140 , to respectively support the rotational motions of the power transmission pins  140 . 
     A variety of roll bearings exhibiting superior strength including ball bearings may be used as the pin support bearings  152 . An outer oil seal  159  is arranged between each of the pin support bearings  152  and each of the power transmission pins  140  to hermetically seal each of the pin insertion support holes  131  in which the power transmission pins  140  are inserted and supported. 
     The center portion rotation shaft  154  is provided at the rotational center portion of each of the bodies  130   a  and forms a rotational center with respect to each of the bodies  130  and a revolving center with respect to the power transmission pins  140 . In other words, the center portion rotation shaft  154  forms a rotational center of each of the pin gears  120 . 
     The center portion rotation shaft  154  is coupled to the rotational center portion of each of the bodies  130  by a plurality of coupling members  161 . A plurality of coupling holes  154   a  to which the coupling members  161  may be coupled are formed in the center portion rotation shaft  154 . 
     The center portion rotation shaft support bearing  156  is coaxially arranged with the center portion rotation shaft  154  between the center portion rotation shaft  154  and each of the bodies  130 , to support the rotation center according to the rotational motions of the bodies  130 . 
     A variety of roll bearings exhibiting superior strength including ball bearings may be used as the center portion rotation shaft support bearing  156 . A center portion oil seal  158  is provided around the center portion rotation shaft support bearing  156 . The center portion oil seal  158  is connected to the center portion rotation shaft support bearing  156  to lubricate and seal the center portion rotation shaft support bearing  156 . 
     The input gear  180  is arranged between the pin gears  120  to rotatably connect the pin gears  120  so that the pin gears  120 , that is, two pin gears in the present embodiment, may be rotated at the same speed. 
     As described above, when the size of the rack  110  is limited while nominal load capacity is large, a plurality of pin gears may be applied to a single rack. However, it is difficult to synchronize the rotations of pin gears in the conventional technology because pinions are simply applied. In the present embodiment, however, the above issue may be solved by applying the pin gears  120  having the above-described structural characteristics and connecting the pin gears  120  by the input gear  180 . 
     The input gear  180 , as illustrated in  FIGS. 1 to 3 , includes an input gear main body  181  where a plurality of input tooth profiles  182  are formed on an outer surface along a circumferential direction thereof to correspond to the power transmission pins  140  of the pin gears  120  and interact with the power transmission pins  140 , and an input gear shaft  183  protruding from a center area of the input gear main body  181 . 
     The input gear main body  181  is provided to be smaller than the size of each of the pin gear  120 . Accordingly, the number of the input tooth profiles  182  formed on the outer surface of the input gear main body  181  is smaller than that of the power transmission pins  140 . As a result, the input gear main body  181  with the pin gears  120  is advantageous in obtaining a deceleration rate. The number of the input tooth profiles  182  may be appropriately designed according to an environment of a process where the power transmission device according to the present embodiment is used. The input tooth profiles  182  may be any one of tooth profiles selected from a trochoid tooth profile, a cycloid tooth profile, and an involute tooth profile. 
     The input gear shaft  183  may be a portion to which a driving apparatus that is not illustrated. When the driving apparatus is connected to the input gear shaft  183 , the initial power is provided through the input gear shaft  183  toward the input gear  180  and then transmitted to the rack  110  via the pin gears  120 . 
     In the present embodiment, since the number of the input tooth profiles  182  is 8 and the number of the power transmission pins  140  is 16, a deceleration rate of 2, accurately, may be obtained. 
     In the above structure, when the driving apparatus is connected to the input gear shaft  183 , as the driving apparatus is operated, the input gear  180  is rotated and thus the pin gears  120  connected to the input gear  180  are rotated. 
     When the pin gears  120  are rotated, the power transmission pins  140  provided in each of the pin gears  120  are engaged with the rack tooth profiles  111  of the rack  110  one by one to interact with each other. In other words, the pin gears  120  perform rotational motions and the rack  110  performs a linear motion. 
     Accordingly, as the pin gears  120  move with respect to the rack  110  and the rack  110  moves with respect to the pin gears  120 , appropriate power may be provided to the processing apparatus. 
     For example, when the pin gears  120  perform rotational motions at their positions, the rack  110  performs a linear motion and thus power according to the linear motion of the rack  110  may be provided to the processing apparatus. Reversely, when the rack  110  is in a fixed state, the pin gears  120  are moved along the rack  110  while rotating and thus the linear motion or the rotational motion may be provided to the processing apparatus. 
     According to the power transmission device according to the present invention having the above structure and operation, since one or a plurality of pin gears are driven with a single driving apparatus, not only an increased nominal load capacity is provided compared to the conventional technology but also a desired level of a deceleration rate is obtained without a complex deceleration device while using the rack of a limited size. Thus, all rolling motions including a rotational motion by the input gear and a linear motion by the rack are available so that efficiency in power transmission may be improved. 
     While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     INDUSTRIAL APPLICABILITY 
     The power transmission device according to the present invention may be used for a variety of machine tools needing a rotational motion or a linear motion and further for industrial mechanical apparatuses, semiconductor or flat panel display manufacturing equipment, and various goods transport equipment.