Abstract:
An actuator for controlling joint movement of a robot includes a first deceleration module and a second deceleration module, which receives and outputs driving force by being in gear with the first deceleration module. The first deceleration module includes a driving motor, a first print circuit board for controlling the driving motor by feeding back the output of the second deceleration module, at least one first reduction gear which is rotated by a driving motor, and a housing on which the driving motor, the first print circuit board, and the first reduction gear are mounted. The second deceleration module includes at least one other reduction gear, which rotates by being in gear with the first reduction gear, and a case on which the second reduction gear is mounted and which is connected to the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     This patent application is a National Phase application under 35 U.S.C. §371 of International Application No. PCT/KR2012/008902, filed Oct. 26, 2012, which claims priority to Korean Patent Application No. 10-2011-0110070 filed Oct. 26, 2011, entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an actuator for controlling motion. 
     2. Description of the Related Art 
     Robots, from industrial robots to humanoid robots, are widely used and can perform flexible articulated motions through actuators having a deceleration function. 
     In particular, within the robotics industry, which has rapidly developed in recent times, robotics mechanisms that have only been used in specific industrial fields are also being applied to broader industrial fields leading to a convergence of technologies. For example, home cleaning robots, programmable education robots, robot toys, entertainment robots, and so on, are being further developed and produced. 
     An actuator related to driving within robot technology is a very important part. Further, a major component that constitutes the actuator may be a decelerator. Various kinds of decelerators such as a gear-type decelerator, a rolling ball-type decelerator, a cycloid decelerator, and so on, may be used as the decelerator. 
     Here, the gear-type decelerator, which is a widely used general decelerator, is a decelerator using an involute tooth form; the rolling ball-type decelerator is a decelerator in which a ball rolls in a guide groove having an epicycloid curve and a hypocycloid curve facing each other to perform deceleration rotation; a harmonic drive decelerator is a decelerator in which, when an oval wave generator assembly is rotated, an elliptically moving portion is transmitted to a flexspline by an elliptically revolving bearing and the flexspline is slowly rotated while skipping the outermost ring gear to induce deceleration; and the cycloid decelerator is a decelerator in which a trochoid gear serving as a planetary gear is eccentrically rotated while fixing a pin, and only the trochoid gear is rotated by a pinhole and the pin disposed in a trochoid at the same angular interval to obtain deceleration rotation. 
     Among these, in particular, since the cycloid decelerator can implement various deceleration ratios and is advantageous for high precision and high deceleration, the cycloid decelerator is widely used in fields that require precise control. Related technologies of the decelerator are disclosed in Korean Utility Model Registration No. 0325018 and Korean Patent Laid-open Publication Nos. 2010-0038146 and 2011-0068500. 
     However, considering the various decelerators including the above-mentioned related technologies, since the deceleration gear is installed in one housing, the size of the decelerator is increased and a user cannot easily set the deceleration ratio. In addition, the user cannot flexibly select his/her requirements (e.g., a center distance, a gear-type, a gear ratio, and the like). 
     SUMMARY 
     In one embodiment, provided is a separable actuator module capable of being modularized as a primary deceleration module and a secondary deceleration module to enable flexible selection. 
     In another embodiment, provided is a separable actuator module capable of providing various applications according to the needs of a user through a high degree of freedom, expandability, and compatibility. 
     In yet another embodiment, provided is a separable actuator configured to control an articulated motion of a robot, including a primary deceleration module, and a secondary deceleration module meshed with the primary deceleration module to receive and output power, wherein the primary deceleration module includes a first printed circuit board configured to feed back output of a driving motor and the secondary deceleration module to control the driving motor, one or more primary deceleration gears rotated by the driving motor, and a housing in which the driving motor, the first printed circuit board, and the primary deceleration gears are mounted, and the secondary deceleration module includes one or more secondary deceleration gears meshed and rotated with the primary deceleration gears, and wherein the secondary deceleration gears are mounted and connected to the housing. 
     The primary deceleration gears may include a driving gear fixed to a rotary shaft of the driving motor; a driven gear meshed with the driving gear; and a transmission gear installed on the same shaft of the driven gear to be rotated with the driven gear and meshed with the secondary deceleration gears. 
     The secondary deceleration module may be any one of a gear-type decelerator having an involute tooth form, a rolling ball-type decelerator, a harmonic drive decelerator, and a cycloid decelerator. 
     The secondary deceleration module may further include a position detector configured to detect the output and convert the output into an electrical signal and transmit the electrical signal, and the position detector may be any one of a magnetic absolute encoder, a potentiometer, and an optical rotary absolute encoder. 
     The housing and the case may have a plurality of bolt holes formed at preset intervals, and the bolt holes may form a rectangular shape to form a unit lattice. 
     The separable actuator may further include one or more positioning pins inserted into the bolt hole to fasten the housing and the case. 
     The secondary deceleration gears may include a plurality of pin gears protruding from an inner circumferential surface of a mounting space of the case to be formed along the inner circumferential surface; an input gear meshed and rotated with the primary deceleration gears; a first and a second eccentric shafts, eccentric from a rotational center of the input gear and sequentially protruding from the input gear; and a first and a second plate gears installed on the first and second eccentric shafts and configured to come in contact with the pin gears to be rotated therewith according to rotation of the first and second eccentric shafts, respectively, and the separable actuator may further include an output member fixed to the plate gear and rotated with the plate gear. 
     The separable actuator may further include a position detector configured to detect rotation of the output member and convert the detected result into an electrical signal to transmit the electrical signal, wherein the position detector is any one of a magnetic absolute encoder, a potentiometer, and an optical rotary absolute encoder. 
     The position detector may include a rotary rod sequentially passing through the input gear, the first and second eccentric shafts, and the first and second plate gears, and having one end fixed to an output shaft installed at a center of the output member to be rotated with the output shaft; a magnet fixed to the other end of the rotary rod; and a second printed circuit board spaced apart from the magnet and in which a magnetic encoder configured to detect rotation of the magnet is mounted. 
     The position detector may further include a rod housing installed at a center of an input side of the case; and a bearing inserted into the rod housing to support the rotary rod. 
     The position detector may include a rotary rod sequentially passing through the input gear, the first and second eccentric shafts, and the first and second plate gears, and having one end fixed to an output shaft installed at a center of the output member and rotated with the output shaft; a printed circuit board spaced apart from the rotary rod; and an encoder mounted in the printed circuit board and coupled to a lower end of the rotary rod, and configured to detect rotation of the rotary rod. 
     The first and second eccentric shafts may be eccentric in opposite directions. 
     The number of teeth of the pin gears may be larger than that of the first and second plate gears. 
     The case may further have a bearing groove recessed along the inner circumferential surface and disposed at an output side of the pin gears, and the secondary deceleration module may further include a bearing inserted into the bearing groove to support the output member. 
     According to the embodiments above, the separable actuator module is modularized into the primary deceleration module and the secondary deceleration module to enable flexible selection by a user. In addition, various applications are possible according to the needs of the user via a high degree of freedom, expandability, and compatibility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a separable actuator according to an embodiment of the present invention; 
         FIG. 2  is a view schematically showing a primary deceleration module shown in  FIG. 1 ; 
         FIG. 3  is a view showing assembly of the separable actuator shown in  FIG. 1 ; 
         FIG. 4  is a view showing assembly of a separable actuator according to another embodiment of the present invention; 
         FIG. 5  is a cut-away perspective schematically showing the secondary deceleration module shown in  FIG. 1 ; 
         FIG. 6  is an exploded perspective view of a secondary deceleration module shown in  FIG. 5 ; 
         FIG. 7  is an exploded perspective view showing a cross-section of the secondary deceleration module shown in  FIG. 5 ; 
         FIG. 8  is an exploded perspective view showing the secondary deceleration module and a position detector shown in  FIG. 5 ; 
         FIG. 9  is an exploded perspective view showing a rotary rod, a magnet, and a rod bearing shown in  FIG. 8 ; and 
         FIG. 10  is a perspective view schematically showing a position detector according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, an exemplary embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . The embodiment of the present invention may be modified in various types, and the scope of the present invention should not be limited to the embodiments to be described below. The embodiments are provided to describe the present invention to those skilled in the art in detail. Accordingly, shapes of elements shown in the drawings may be exaggerated to emphasize clearer description thereof. 
     As shown in  FIG. 1 , a separable actuator according to the present invention includes a primary deceleration module  100  and a secondary deceleration module  200 . 
     Here, the primary deceleration module  100  may be commonly used and the plurality of secondary deceleration modules  200  are configured to provide various deceleration ratios in order to implement the various deceleration ratios and degrees of freedom. Further, when the plurality of primary deceleration modules  100  are provided, the number of sets is exponentially increased such that the deceleration ratio and the degrees of freedom can be extensively varied. 
     In addition, as the secondary deceleration module  200 , a gear-type decelerator using an involute tooth form; a rolling ball-type decelerator in which a ball rolls in a guide groove having an epicycloid curve and a hypocycloid curve facing each other to perform deceleration rotation; a harmonic drive decelerator in which, when an oval wave generator assembly is rotated, an elliptically moving portion is transmitted to a flexspline by an elliptically revolving bearing and the flexspline is slowly rotated while skipping the outermost ring gear to induce deceleration; and a cycloid decelerator in which a trochoid gear serving as a planetary gear is eccentrically rotated while fixing a pin, and only the trochoid gear is rotated by a pinhole and the pin disposed in a trochoid at the same angle interval to obtain deceleration rotation, may be used. In addition, decelerators assembled by combining, without limitation, the above-mentioned decelerators may also be used. 
     In particular, as shown in  FIGS. 1 and 2 , the primary deceleration module  100  is configured to primarily decelerate power of a driving motor  120 , which is input from the primary deceleration module  100 , according to a gear ratio. 
     For this, the primary deceleration module  100  includes a module housing  110 , the driving motor  120  installed in the module housing  110 , a main printed circuit board (PCB)  130  configured to control power supply and cutoff, and communication with the primary deceleration module  100 , a sub-PCB  140  configured to receive feedback of a position of an output shaft and control driving of the driving motor  120 , a driving gear  150  fixed to a rotary shaft of the driving motor  120 , a driven gear  160  meshed with the driving gear  150  to induce primary deceleration, and a transmission gear  170  integrally formed with the driven gear  160  and configured to transmit power to the secondary deceleration module  200 . 
     In one embodiment, the driving gear  150  and the driven gear  160  that constitute a deceleration unit may be a spur gear-type, a harmonic gear, or a combination thereof. The spur gear-type is a conventional spur gear-type, and the harmonic gear is known to have reduced backlash than other gear-types, and may be applied to a robot that requires precise control. 
     In addition, since an output shaft of the primary deceleration module  100  is meshed with an input shaft of the secondary deceleration module  200 , through spur gear engagement, and a deceleration function (i.e., spur gear engagement) at a connecting section between the primary deceleration module  100  and the secondary deceleration module  200 , i.e., intermediate deceleration, is further performed in addition to a primary deceleration function by a primary decelerator (i.e., a driving gear+a driven gear), installed at the primary deceleration module  100 , and a secondary deceleration function by a secondary decelerator, installed at the secondary deceleration module  200 , deceleration efficiency is further increased. 
     Moreover, while not shown, a position detector such as a magnetic absolute encoder, a potentiometer, an optical rotary absolute encoder, or the like, configured to detect a position of the secondary output shaft to feed the detected position back to the PCB, is further installed at the secondary deceleration module  200 . 
     As shown in  FIG. 1 , the actuator deceleration module has four coupling holes  180  with tabs formed at a coupling surface of the primary deceleration module  100 , that may be in a rectangular shape, and a plurality of coupling apertures  210  with tabs formed at a coupling surface of the secondary deceleration module  200  to couple the primary deceleration module  100  and the secondary deceleration module  200 . 
     Moreover, a plurality of unit lattice-type bolt holes  182  are formed in at least one surface of the primary and secondary deceleration modules  100  and  200  by a multitude of unit lattices to increase expandability. The unit lattice-type bolt holes  182  are constituted by at least four bolt holes disposed to form a substantially rectangular shape at predetermined intervals to define a basic lattice as a unit lattice, and a plurality of other bolt holes are formed based on the unit lattice by a multitude of unit lattices. 
     In other words, the bolt holes have a structure in which a plurality of unit lattices are repeated, and thus a plurality of primary deceleration modules having different sizes may be connected to increase the volume thereof, i.e., increase expandability. Accordingly, the size (i.e., volume) of the actuator module can be increased or decreased in proportion to the unit lattice according to the needs of a user. 
     The present invention allows a user to arbitrarily vary the volume because the modules are modularized by a multitude of unit lattices. In particular, as shown in  FIG. 1 , when a positioning pin  190  is further installed at an arbitrary position of the coupling surfaces of the first and secondary modules  100  and  200 , the assembly can be performed rapidly, smoothly, and more precisely in shorter time periods. 
     Moreover, an output member  220  installed at the secondary deceleration module  200  is a member configured to output decelerated power, which is formed of a conventional shaft. Since the output member  220  should be assembled to a shaft by a coupling or a key engagement to use the decelerated power, the assembly is very inconvenient. However, in the present invention, since the decelerated power can be used when the member is exchanged with a flange, and a plurality of bolt holes (reference numerals are omitted) are formed within the flange surface, so that the decelerated power can be used when the bolt is simply fastened, whereby this embodiment enhances the convenience of use. 
     The actuator module as shown in  FIG. 3  can be implemented based on the above-mentioned concept. For example,  FIG. 3  shows a general instance wherein the input shaft and the output shaft configured to apply power are maintained in parallel when the primary deceleration module  100  and the secondary deceleration module  200  are assembled. 
     As described above, the actuator module can also continuously perform secondary deceleration through the secondary deceleration module  200 , while performing a primary deceleration function through the primary deceleration module  100 , and thus can be applied to a field that requires more precise and accurate control. Since the actuator module is constituted by standardized modules, the actuator can be freely expanded and reduced, exchanged with a new combination to have a desired deceleration ratio according to the environment of a user, and maximize the degrees of freedom of the user. 
     While the present invention has been described with reference to the exemplary embodiment above in detail, different types of embodiments are also possible. Accordingly, the technical spirit and scope of the claims described below are not limited to the exemplary embodiment. 
     Hereinafter, another exemplary embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . Accordingly, the shapes of the elements shown in the drawings may be exaggerated to emphasize a clearer description thereof. Hereinafter, contents distinguished from the above-mentioned embodiment will be described, and description omitted below will be replaced with the above-mentioned description. 
       FIG. 4  shows an embodiment wherein the input shaft and the output shaft are perpendicularly maintained when the primary deceleration module  100  and the secondary deceleration module  200  are perpendicularly assembled. 
     The secondary deceleration module is a decelerator in which an internal gear having an epitrochoid tooth form is used. A pin gear  110  and a plate gear  300 , to be described below (see  FIG. 6 ), may have an epitrochoid tooth form, but may also have an involute tooth form. 
     As shown in  FIGS. 5 and 6 , a case  100  has a cylindrical mounting space. The pin gear  110  protrudes from an inner circumferential surface of the mounting space to be formed along the inner circumferential surface. The pin gear  110  may be integrally formed with the case  100  upon formation of the case  100 . 
     Conversely, as disclosed in Korean Patent Laid-open Publication No. 2010-0038146, the conventional pin gear  110  employs a roll-shaped pin fitted into the case  100  and fixed thereto one by one. Accordingly, since a processing error as well as assembly tolerance may be generated upon manufacturing due to an alternate production, requirements for high precision and high deceleration cannot be easily realized, thus causing malfunctions. However, according to one embodiment of the present invention, the pin gear  110  corresponding to the plate gear  300 , having the epitrochoid tooth form, is integrally formed with the case  100  during a forming step of the case  100 , and thus assembly errors as well as processing errors can be minimized, and manufacturing costs can be reduced. 
     An input gear  200  may be mounted in the mounting space of the case  100 , and can be connected to a motor through a lower end (or an input side with reference to  FIG. 5 ) of the case  100 . The transmission gear  170 , described above, is engaged with the input gear  200  to transmit power to the input gear  200 . That is, the driving gear and the input gear  200  are meshed with each other in a spur gear-type of a helical gear-type, and the rotary shaft of the driving gear and the rotary shaft of the input gear are disposed in parallel. However, alternatively, the input gear  200  may be directly connected to the rotary shaft of the motor, or may be engaged with the driving gear in a bevel gear-type. 
     First and second eccentric shafts S 1  and S 2  sequentially protrude from the input gear  200  toward the outside, wherein the first eccentric shaft S 1  is disposed closer to the input gear  200  than the second eccentric shaft S 2 . The first and second eccentric shafts are eccentric from a rotational center of the input gear  200 . Eccentric directions thereof are opposite, but eccentric amounts thereof are substantially the same. The first and second eccentric shafts S 1  and S 2  are connected to the input gear  200  through a central shaft  210 . 
     First and second plate gears  302  and  304  have a circular disk shape with the same size, and have the epitrochoid tooth form. The first and second plate gears  302  and  304  are adhered to each other and have a plurality of plate holes  310  formed therearound. As shown in  FIG. 7 , the first and second plate gears  302  and  304  are fastened to each other through a fixing pin  330  inserted into the plate hole  310  to transmit power to an output member  500 . 
     The first plate gear  302  is rotatably installed at the first eccentric shaft S 1 , and the second plate gear  304  is rotatably installed at the second eccentric shaft S 2 . The first and second plate gears  302  and  304  are disposed to be eccentric from each other and rotated according to rotation of the first and second eccentric shafts S 1  and S 2  while coming in contact with the pin gear  110 , but decelerated according to a difference in number of teeth of the first and second plate gears  302  and  304  and the pin gear  110 . 
     Since the pin gear  110  has one more tooth than the plate gear  300 , the plate gear  300  is decelerated at a deceleration ratio of “1/n” (i.e., n=the number of teeth of the plate gear  300 ) of the revolution number of the input gear  200  and rotated. For example, when the number of teeth of the plate gear  300  is 50, the number of teeth of the pin gear  110  is 51, and the plate gear  300  has a deceleration ratio of 1/50. 
     Meanwhile, when the power is transmitted to the output member  500  in a state in which the first and second plate gears  302  and  304  are eccentric in opposite directions, vibrations generated through the first and second plate gears  302  and  304  can be offset, and engagement with the pin gear  110  can be strengthened twofold. In addition, the output member  500  has a fastening hole  520 , and a fastening pin  340  protruding from one side of the plate gear  300  is inserted into the fastening hole  520  to fasten the first and second plate gears  302  and  304  and the output member  500 . 
     As shown in  FIGS. 7 and 8 , the case  100  has a bearing groove  120  recessed along the inner circumferential surface, and the bearing groove  120  is disposed at an output side of the pin gear  110 . A cross roller bearing  400  is installed at an output side of the plate gear  300 , and the output member  500  is installed at an output side of the cross roller bearing  400 . A portion of the cross roller bearing  400  is inserted into the bearing groove  120 , and the remaining portion is inserted into a groove (not shown) recessed from a lower surface (cf.  FIG. 5 ) of the output member  500 . The output member  500  can be smoothly rotated in a state supported by the cross roller bearing  400 . While the embodiment exemplarily describes the cross roller bearing  400 , the cross roller bearing  400  may be replaced with another bearing. 
     In related art, a bearing housing (not shown) including the cross roller bearing  400  is separately fixed to an outer surface of the output side of the case  100 . However, according to one embodiment described herein, an outer wheel of the cross roller bearing  400  may be integrally formed with the case  100 , and thus the cross roller bearing  400  may be integrally formed with the case  100  to minimize assembly errors or processing errors. 
     In particular, since there is no need to separately fix the bearing housing, like the related art, a subsidiary fixing bolt can be omitted to reduce costs, and a precisely performed centering operation can be omitted from assembly to improve precision and productivity. Further, the volume and weight thereof can be minimized to implement a lightweight and compact module. 
     The output member  500  has a circular flange shape, which can be freely and easily connected to output power. The output member  500  has an output shaft  510  installed at a center thereof 
     As shown in  FIGS. 7 and 8 , the secondary deceleration module further includes a position detector  600  configured to detect rotation of the output member  500 . The position detector  600  may be an encoder configured to detect a revolution number in a rotational direction of the output member  500  to detect a position of the output member  500  (or the output shaft  510 ), which may be a magnetic encoder serving as an absolute encoder. However, as described below, the position detector  600  may be replaced with a potentiometer or an optical rotary absolute encoder. The position detector  600  can convert the detected position information into an electrical signal to transmit the signal to a controller (not shown), and the controller can control an input value of the motor through feedback. 
     A rotary rod  610  sequentially passes through centers of the input gear  200 , the first and second eccentric shafts S 1  and S 2 , and the plate gear  300  to be fixed to the output shaft  510 . A magnet  620  is installed at an input side of the rotary rod  610 . A rod housing  640  is installed at a center of the input side of the case  100 , and a rod bearing  630  is inserted into the rod housing  640  to support the rotary rod  610  in which the magnet  620  is installed. 
     A printed circuit board  650  is spaced apart from the magnet  620 , and a position sensor  652  serving as a magnetic encoder is mounted in the printed circuit board  650 . The position sensor  652  is disposed over an opening (not shown) of the rod housing  640  to detect a variation in magnetic flux density upon rotation of the magnet  620  to detect a position of the rotary rod  610 . 
     As described above, the power input through the transmission gear  170  is decelerated at a certain deceleration ratio through the secondary deceleration module to be output through the output member  500 , and the position detector  600  feeds the position information of the output member  500  back to the controller so that the controller can precisely control rotation of the output member  500 . 
     As shown in  FIG. 10 , the encoder includes a mounting section  621  and a rotor  623 , the mounting section  621  is mounted on the printed circuit board  650  and the rotor  623  is rotatably installed at the mounting section  621 . A lower end of the rotary rod  610  is coupled to the rotor  623 , and the encoder detects rotation of the rotary rod  610  to feed the rotation back to the controller. The encoder may be a potentiometer or an optical rotary absolute encoder. 
     The above-mentioned position detector  600  may be applied to another type of secondary deceleration module. That is, the pin gear  110  may be installed in a mounting space separated from the case  100 , and the bearing housing (not shown) including the cross roller bearing  400  may be installed separately from the case  100 . 
     It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments without departing from the spirit or scope of the invention. Thus, it is intended that the disclosure covers all such modifications provided they reside within the scope of the appended claims and their equivalents. 
     The present invention may be applied to various actuators including a robot.