SCREW ASSEMBLY AND TRANSPORT APPARATUS INCLUDING SAME

The present invention relates to a screw assembly and to a transport apparatus including the same. The present invention includes a screw, a bearing shaft into which a portion of the screw is inserted, and a filling member that is positioned between a threaded rod of the screw and an inner circumferential surface of the bearing shaft. The filling member is formed to have an outer circumferential surface diameter that is larger than the outer circumferential surface diameter of the screw and is equal to or larger than the inner circumferential surface diameter of the bearing shaft.

TECHNICAL FIELD

The present invention relates to a screw assembly and a transport apparatus including the same.

BACKGROUND

A ball screw is an apparatus which changes a direction of motion and is connected to a motor of automated facilities so as to be used for position control. The ball screw includes a screw of long rod shape having a thread at an exterior circumference thereof and a ball nut coupled to the screw. A plurality of steel balls contacting with the thread of the screw are disposed at the ball nut.

The ball nut is coupled to an object that will be transported, and both ends of the screw is rotatably connected to another object. One end of the screw is connected to the motor so as to be rotated, and thereby the ball nut moves along a length direction of the screw.

One end portion of the screw is supported by a bearing. According to conventional arts, an end of the screw has a coupling end, a diameter of which is smaller than that of a middle portion of the screw, and the bearing is mounted at the coupling end. The coupling end passing through the bearing is coupled to one end portion of the coupling. The other end portion of the coupling is coupled to the motor and power of the motor is transmitted to the screw through the coupling.

The screws may be classified according to manufacturing method into screws manufactured through thread rolling and screws manufacturing through grinding.

Since the thread and the coupling end is manufactured by cutting a cylindrical raw material according to the grinding, the screw may be manufactured precisely. However, production cost is high according to the grinding.

The thread rolling is suitable to mass production and has low cost compared with the grinding, but has difficulties in controlling tolerance of an exterior diameter of the thread. That is, it is very frequent according to the thread rolling that a center of a circle formed by the threaded rod and a shaft center of the coupling end are misaligned. Therefore, vibration occurs when the screw works.

CONTENTS OF THE INVENTION

Technical Object

The present invention has been made in an effort to provide a screw assembly and a transport apparatus including the same having advantages of easily and precisely aligning a shaft center, being strong with load, and facilitating assembling and disassembling.

Means for Achieving the Object

A screw assembly according to an exemplary embodiment of the present invention may include a screw, a bearing shaft into which a portion of the screw is inserted, and a filling member positioned between a threaded rod of the screw and an inner circumferential surface of the bearing shaft, wherein a diameter of an outer circumferential surface of the filling member is larger than that of an outer circumferential surface of the screw and is equal to or larger than that of the inner circumferential surface of the bearing shaft.

The filling member may be a spring, the spring may have a straight portion including a straight cross-sectional portion substantially, and the straight portion of the spring may contact with the inner circumferential surface of the bearing shaft.

The bearing shaft may include a clamping portion, and the clamping portion may tighten up the filling member and the screw.

The screw assembly may further include a housing in which the bearing shaft is positioned, a bearing mounted in the housing and supporting the bearing shaft, and a connecting member mounted in the housing and having a side portion coupled to the bearing shaft.

The screw assembly may further include a motor having at least a portion thereof being inserted into the housing, wherein a shaft of the motor is coupled to the other side portion of the connecting member.

A side surface of the connecting member may push and support the bearing.

The screw assembly may further include a fixing member positioned between the connecting member and the bearing, and pushes and supports the bearing.

A screw assembly according to another exemplary embodiment of the present invention may include a screw, a bearing shaft into which a portion of the screw is inserted, a filling member positioned between a threaded rod of the screw and an inner circumferential surface of the bearing shaft, and a fixing bolt penetrating through the bearing shaft and engaged to the screw.

A transport apparatus according to an exemplary embodiment of the present invention may include the screw assembly that is described above, a frame which is connected to the housing and at which the screw is rotatably mounted, and a table connected to the screw so as to move linearly.

Effect of the Invention

According to an exemplary embodiment of the present invention, the thread of the screw does not contact with the bearing shaft, and a spring having a center being the same as that of a virtual circle formed by the threaded rod contacts with the bearing shaft. Therefore, centers thereof and the center of the bearing shaft are the same. Since the bearing shaft, the spring and the screw rotate about the center formed by the threaded rod of the screw, vibration of the screw due to misaligning may be prevented and a position of the ball nut may be precisely controlled.

Since the straight portion of the spring other than a circular portion thereof contacts with the inner circumferential surface of the bearing shaft according to an exemplary embodiment of the present invention, a contact area is maximized so as to increase frictional force. In addition, the clamping portion is tightened up by a bolt and the spring is pressed toward the threaded rod of the screw. Therefore, the screw may be firmly fixed to the bearing shaft.

According to an exemplary embodiment of the present invention, machining an end of the screw is unnecessary so as to couple the screw to the bearing shaft and the screw is coupled to the bearing shaft in a state that the spring is coupled to the screw. Therefore, machining time of the end of the screw may be eliminated.

According to an exemplary embodiment of the present invention, the screw to which the spring is coupled is coupled to the bearing shaft, and the bearing shaft is coupled to the bearing mounted at the housing. That is, since the coupling end of the screw in prior arts is not formed according to an exemplary embodiment of the present invention, the bearing having larger interior diameter may be used. Therefore, supporting force of the screw may be improved.

Since the motor shaft and the bearing shaft are tightened up by control of the clamping portion of the connecting member according to an exemplary embodiment of the present invention, assembling and disassembling of the motor shaft and the screw is easy.

Since protrusions and depressions formed at a surface of an anti-rotation portion is stuck in an end portion of the screw and protrusions and depressions formed at the other surface of the anti-rotation portion is stuck in the inner circumferential surface of the bearing shaft when the fixing bolt is engaged with the end portion of the screw, the screw and the bearing shaft are prevented from moving separately according to an exemplary embodiment of the present invention.

DETAILS FOR EXECUTING THE INVENTION

A screw assembly and a transport apparatus including the same according to an exemplary embodiment of the present invention will be described referring toFIG. 1toFIG. 4. A screw assembly according to an exemplary embodiment of the present invention can be applied to a transport apparatus according to an exemplary embodiment of the present invention. Therefore, the transport apparatus to which the screw assembly is applied will be mainly described.

FIG. 1is a perspective view of a transport apparatus according to an exemplary embodiment of the present invention,FIG. 2is a perspective view of a screw assembly shown inFIG. 1,FIG. 3is a partial exploded perspective view of a screw assembly shown inFIG. 2, andFIG. 4is a cross-sectional view of a screw assembly shown inFIG. 2.

Referring toFIG. 1toFIG. 4, a transport apparatus1according to the present exemplary embodiment includes a screw assembly2, a frame60and a table50. The screw assembly2includes a screw10, filling members21and31, bearing shafts22and32, a connecting member40and a motor M.

A size of the frame60is determined according to an object that will be transported. The frame60may be fixed to a ground or a machining device (not shown), and a body of the machining device may functions as the frame as the case may be.

The screw assembly2and the table50are mounted on the frame60.

The table50is connected to the frame60through a guide61and is connected to the screw10through a ball nut50a. The table50moves linearly by operation of the screw10. Connection between the table50and the guide61may be different from that shown inFIG. 1. A transport object (not shown) may be laid on the table50or a part of the machining device may be coupled to the table50.

A fixing end portion20is mounted at a side portion of the frame60and a supporting end portion30is mounted at the other side portion of the frame60. The screw10is rotatably mounted between the fixing end portion20and the supporting end portion30.

The fixing end portion20includes a housing26, the motor M mounted at the housing26, the bearing shaft22, a spring21, a bearing B, the connecting member40and an outer ring pushing plate27. The screw10is inserted into and fixed to the bearing shaft22.

The screw10receives power from the motor M and is rotated. A threaded rod12is formed on an outer circumferential surface of the screw10and the ball nut50amoves along the threaded rod12. A steel ball (not shown) of the ball nut50ais disposed on the threaded rod12.

A screw thread11and the threaded rod12formed on the screw10may be manufactured through thread rolling. A center axis of the screw10with respect to the screw thread11may be misaligned from that with respect to the threaded rod12due to characteristics of thread rolling. In order to align the axis of the threaded rod12with a center of a shaft of the motor M, the filling members are coupled to portions of both edges of the screw10.

According to the present exemplary embodiment, the spring21is used as the filling member. The spring21is disposed along the threaded rod12of the screw10. As shown in a cross-sectional view of the spring21, A straight portion211(please seeFIGS. 5 and 7) is formed on an outer circumferential surface of the spring21. The straight portion211of the spring21may be formed by grinding. The outer circumferential surface of the spring21corresponding to the straight portion211contacts with an inner circumferential surface of the bearing shaft22that will be described below. However, there is not straight portion211on the spring21.

A diameter d1of the outer circumferential surface of the spring21mounted on the screw10is larger than that d2of a virtual circle formed by the highest screw thread11(please refer toFIG. 5).

One end of the screw10where the spring21is mounted is inserted in the bearing shaft22. The diameter d1of the outer circumferential surface of the spring21is equal to or larger than that of the inner circumferential surface of the bearing shaft22. Therefore, the outer circumferential surface of the spring21contacts with the inner circumferential surface of the bearing shaft22, and the screw thread11of the screw10does not contact with the inner circumferential surface of the bearing shaft22.

Since the straight portion211of the spring21other than a circular portion thereof contacts with the inner circumferential surface of the bearing shaft22, a contact area may be maximized so as to increase frictional force. Therefore, the spring21may be firmly fixed to the bearing shaft22.

Since the screw thread11having irregular height does not contact with the bearing shaft22and the spring21having the center that is the same as the center of the virtual circle formed by the threaded rod12contacts with the bearing shaft22if the screw10is formed by thread rolling, the centers corresponds to the center of the bearing shaft22. Since the bearing shaft22, the spring21and the screw10rotate about the center of the virtual circle formed by the threaded rod12of the screw10, vibration of the screw due to misalignment may be prevented. Therefore, the screw manufactured by rolling thread having low manufacturing cost may perform as the screw manufactured by grinding according to the present invention.

The bearing shaft22is mounted in the housing26and includes a first coupling portion227, a second coupling portion228and a clamping portion229. A first insert hole223and a second insert hole225are formed in the first coupling portion227, the second coupling portion228and the clamping portion229. A male thread2271(please refer toFIG. 6) is formed at the first coupling portion227.

The shaft of the motor M is inserted in the first insert hole223and the screw10is inserted in the second insert hole225. Since a cross-section of the second insert hole225is larger than that of the first insert hole223, a stepped portion226is formed between the second insert hole225and the first insert hole223. Therefore, the screw10is inserted until contacting with the stepped portion226and is fixed.

Both ends of the clamping portion229are spaced from each other and are tightened up by a bolt. The clamping portion229presses the outer circumferential surface of the spring21and fixes the screw10firmly. Therefore, the screw10does not run idle in the bearing shaft22and receives torque of the bearing shaft22. In addition, since the clamping portion229presses the entire outer circumferential surface of the spring21simultaneously, the screw10is not biased in any one direction.

The second coupling portion228is connected to the clamping portion229, but a part of a boundary portion228aof the second coupling portion228and the clamping portion229is disconnected from the clamping portion229such that the clamping portion229can be tightened up.

The bearing B is coupled to the second coupling portion228. One or more bearings B may be mounted and a side of the bearing B is supported by a step262in the housing26. A size of an inner ring of the bearing B may be determined according to that of the second coupling portion228.

The outer ring pushing plate27is coupled in the housing26and contacts with an outer ring of the bearing B. Therefore, the outer ring pushing plate27fixes the bearing B.

The first coupling portion227is coupled to the connecting member40.

The connecting member40is disposed in the housing26, and includes a body41and first and second engaging portions42and43connected respectively to both sides of the body41. A third insert hole403and a fourth insert hole404are formed in the connecting member40(please refer toFIG. 8).

A cross-section of the third insert hole403is larger than that of the fourth insert hole404. A female thread405is formed on the third insert hole403. Shapes of the first and second engaging portions42and43are substantially similar to a shape of the clamping portion229of the bearing shaft22. However, the shapes of the first and second engaging portions42and43may be variously changed according to design.

The first coupling portion227is inserted in the third insert hole403, and the male thread2271formed at the first coupling portion227and the female thread405formed at the third insert hole403are engaged with each other. However, such engagement may be omitted.

If the first coupling portion227is inserted in the third insert hole403, the first engaging portion42is positioned at the first coupling portion227. At this time, if the first engaging portion42is tightened up by a bolt, the connecting member40and the bearing shaft22can be firmly fixed. In addition, since a side surface of the first engaging portion42contacts with the inner ring of the bearing B and fixes the bearing B, additional means for fixing the inner ring of the bearing B is not necessary.

The shaft of the motor M is inserted in the fourth insert hole404of the connecting member40and is inserted in the first insert hole223of the bearing shaft22, simultaneously. The shaft of the motor M is tightened up by the second engaging portion43.

Therefore, torque of the motor M is transmitted to the screw10through power delivery device such as the shaft of the motor M, the connecting member40, the bearing shaft22and so on. As the shaft of the motor M is fixed to the connecting member40, a center of the shaft of the motor M and a center of the connecting member40coincide with each other. In addition, the centers coincide with the centers of the bearing shaft22and the threaded rod12. Therefore, the screw rotates without shaking when the motor operates and a position of the ball nut can be precisely controlled.

Referring toFIG. 2andFIG. 4, the supporting end portion30, similar to the fixing end portion20, includes a housing26, a bearing shaft22, a spring31, a bearing B and an outer ring pushing plate27. The opposite end portion of the screw10coupled to the fixing end portion20is coupled to the bearing shaft22of the supporting end portion30.

The housing26, the bearing shaft22, the spring31, the bearing B and the outer ring pushing plate27of the supporting end portion30are substantially the same as those of the fixing end portion20, according to the present exemplary embodiment.

Since the supporting end portion30supports an end portion of the screw10, the motor M is not mounted at the supporting end portion30. In addition, the connecting member40for connecting the motor M and the bearing shaft22is removed (please refer toFIG. 8). The screw10positioned at the supporting end portion30may be formed as a free end or a fixed end.

A male thread is not formed at the bearing shaft22of the supporting end portion30because the bearing shaft22does not need to be connected to the connecting member40. Additional means (not shown) for supporting the bearing B instead of the connecting member40may be mounted. Shapes of the housing26, the bearing shaft22, the spring31, the bearing B and the outer ring pushing plate27of the supporting end portion30may be partially changed according to design. For example, a hole corresponding the motor may be removed from the housing26of the supporting end portion30, and the outer ring pushing plate27may be substituted with a snap ring.

A screw assembly according to another exemplary embodiment of the present invention will be described with reference toFIG. 9andFIG. 10.

FIG. 9is an assembled cross-sectional view of a screw assembly according to another exemplary embodiment of the present invention, andFIG. 10is an exploded perspective view of a screw assembly shown inFIG. 9.

Referring toFIG. 9andFIG. 10, a screw assembly1according to the present exemplary embodiment includes a screw10, a fixing end portion20and a supporting end portion (not shown).

The fixing end portion20and the supporting end portion according to the present exemplary embodiment are substantially the same as the fixing end portion20and the supporting end portion30illustrated inFIG. 1toFIG. 8.

However, the fixing end portion20according to the present exemplary embodiment further includes a fixing member70, and shapes of the connecting member40and the bearing shaft22are partially different from those illustrated inFIG. 1toFIG. 8.

The bearing shaft22according to the present exemplary embodiment is connected to a bearing B mounted in a housing26, and includes a first coupling portion227, a second coupling portion228and a clamping portion229. A first insert hole223into which a shaft of a motor M is inserted and a second insert hole225into which the screw10coupled to a spring21is inserted are formed in the bearing shaft22.

According to the present exemplary embodiment, different from an exemplary embodiment illustrated inFIG. 1toFIG. 8, a male thread2281is formed at the second coupling portion228and a male thread is not formed at the first coupling portion227. The bearing B is not positioned at a portion where the male thread2281is formed.

A diameter of the first coupling portion227is different from that of the second coupling portion228. Therefore, a step2278is formed between outer circumferential surfaces of the first coupling portion227and the second coupling portion228. However, the diameter of the first coupling portion227may be equal to that of the second coupling portion228, and in this case, the step2278is not formed.

The clamping portion229presses the spring21by a bolt and fixes the screw10to the bearing shaft22. Therefore, the screw10does not run idle in the bearing shaft22and receives torque of the bearing shaft22. In addition, since the clamping portion229presses the entire outer circumferential surface of the spring21simultaneously, the screw10is not biased in any one direction.

The connecting member40includes a first engaging portion42and a second engaging portion43. A third insert hole403into which the first coupling portion227is inserted is formed in the first engaging portion42, and a fourth insert hole404into which the shaft of the motor M is inserted is formed in the second engaging portion43. A diameter of the third insert hole403is larger than that of the fourth insert hole404. Therefore, a raised spot42ais formed between the third insert hole403and the fourth insert hole404.

When the first coupling portion227is inserted into the third insert hole403, the step228acontacts with the first engaging portion42. In addition, if an end of the first coupling portion227contacts with the raised spot42a, the bearing shaft22is not further inserted into the connecting member40.

If the first coupling portion227is inserted into the third insert hole403, the first engaging portion42is positioned at the first coupling portion227. If the first engaging portion42is tightened up at this time, the connecting member40and the bearing shaft22may be fixed more firmly.

The shaft of the motor M is inserted into the fourth insert hole404of the connecting member40and is tightened up by the second engaging portion43.

The fixing member70is positioned between the connecting member40and the bearing B and a female thread71engaged with the male thread2281is formed on an inner circumferential surface of the fixing member70. The fixing member70threaded with the bearing shaft22supports an inner ring of the bearing B. In order to increase coupling force of the bearing shaft22and the fixing member70, a set crew72may be used.

The bolts tightening up the first engaging portion42, the second engaging portion43and the clamping portion229are tightened in the same direction on the same straight line.

If the bolts tightening up the first engaging portion42, the second engaging portion43and the clamping portion229does not lie on the same straight line and are tightened in different directions, a center of the shaft of the motor M may be misaligned from a center of the screw10.

A raised spot262is formed in the housing26and supports an outer ring of the bearing B, and the outer ring pushing plate27is coupled in the housing26and supports the outer ring of the bearing B according to the present exemplary embodiment.

The supporting end portion according to the present exemplary embodiment may be the same as that according to an exemplary embodiment illustrated inFIG. 1toFIG. 8. However, the supporting end portion may be similar to the fixing end portion20according to the present exemplary embodiment.

Constituent elements illustrated inFIG. 1toFIG. 8may be used in the present exemplary embodiment.

A screw assembly according to another exemplary embodiment of the present invention will be described with reference toFIG. 11toFIG. 14. The screw assembly according to the present exemplary embodiment may be mounted at the frame60illustrated inFIG. 1.

FIG. 11is an assembled cross-sectional view of a screw assembly according to another exemplary embodiment of the present invention,FIG. 12is an exploded sectional view of a screw assembly shown inFIG. 11,FIG. 13is an exploded perspective view of a bearing shaft and a motor shown inFIG. 11, andFIG. 14is an enlarged view of A region inFIG. 11.

Referring toFIG. 11toFIG. 14, the screw assembly1according to the present exemplary embodiment includes a screw10, a fixing end portion20and a supporting end portion30.

The screw10according to the present exemplary embodiment is substantially the same as the screw10illustrated inFIG. 1toFIG. 4.

The fixing end portion20transmits torque to and rotatably supports the screw10. The fixing end portion20includes filling members, a bearing shaft22, a housing26, an outer ring pushing plate27, an inner ring pushing plate28and an anti-rotation portion29.

The filling members are coupled to portions of both edges of the screw10. The filling member may be a spring21according to the present exemplary embodiment. The spring21is coupled along a threaded rod12, and a center12C of the threaded rod12coincides with a center21C of the spring21(please refer toFIG. 14). A diameter of an outer circumferential surface of the spring21is larger than an exterior diameter of the screw10and is protruded from an outer circumferential surface of the screw10. The straight portion211, as shown inFIG. 7, may be formed on an outer circumferential surface of the spring21.

The housing26may be coupled to a frame or a machining device of a transport apparatus, and a bearing B is disposed in the housing26. A step262supporting the bearing B is formed in the housing26.

The bearing shaft22is disposed in the housing26and is supported by the bearing B. A shaft of a motor M is coupled to a side surface of the bearing shaft22, and the bearing shaft22and the shaft of the motor M are coupled by a key K. The key K is fixed to the bearing shaft22by a key cover25.

An end portion of the screw10coupled with the spring21is inserted into the other side surface of the bearing shaft22. An outer circumferential surface of the spring21contacts with an inner circumferential surface of the bearing shaft22.

The center21C of the spring21coincides with the center12C of the threaded rod12. In addition, since the spring21contacts with the inner circumferential surface of the bearing shaft22, the center21C of the spring21coincides with the center22C of the bearing shaft22. Therefore, the center12C of the threaded rod12coincides with the center22C of the bearing shaft22and coincides with a center of the shaft of the motor M.

A partition223ais formed in the bearing shaft22. The screw10is fixed to the bearing shaft22through a fixing bolt24penetrating through the partition223aand the set screw23coupled to the bearing shaft22from the exterior to the interior.

The anti-rotation portion29has an annular shape and is disposed between the partition223aand the screw10. When the fixing bolt24is coupled to the screw10, the anti-rotation portion29tightly contacts with the screw10and the partition223aso as to prevent the screw10from being bent or from running idle in the bearing shaft22.

The outer ring pushing plate27supports an outer ring part of the bearing B and the inner ring pushing plate28supports an inner ring part of the bearing B. The outer ring pushing plate27and the inner ring pushing plate28prevent the bearing B from being departed from the housing26.

A protruding portion M2is formed at the motor M facing the housing26and is inserted into the housing26. Therefore, the motor M can be coupled with the housing26precisely. Since the protruding portion M2is coupled with the housing26, the centers of the shaft of the motor M and the bearing shaft22coincide with each other.

The supporting end portion30supports the opposite end portion of the screw10coupled to the fixing end portion20, and includes a filling member31, a bearing shaft22, a bearing B, a first fixing ring34, a housing26and a second fixing ring35. Since the supporting end portion30supports an end portion of the screw10, the motor is not mounted at the supporting end portion30.

The filling member31and the bearing B of the supporting end portion30are substantially the same as those of the fixing end portion20according to the present exemplary embodiment.

A shape of the housing26of the supporting end portion30is partially different from that of the housing26of the fixing end portion20. For example, the housing26of the supporting end portion30, different from the housing26of the fixing end portion20, does not need to have a space for connecting the motor M.

An outer circumferential surface of the filling member31contacts with an inner circumferential surface of the bearing shaft22of the supporting end portion30. Means for connecting the bearing shaft22with the motor M can be removed from the bearing shaft22of the supporting end portion30.

The first fixing ring34is disposed in the housing26, is coupled to the bearing shaft22, and supports the inner ring of the bearing B. The second fixing ring35is disposed in the housing26and supports the outer ring of the bearing B. The first fixing ring34and the second fixing ring35prevent the bearing B from being departed from the housing26. The first fixing ring34and the second fixing ring35have snap ring shapes that have both end portions spaced from each other and can be contracted or expanded.

Referring toFIG. 15, a screw assembly according to another exemplary embodiment of the present invention includes most of the constituent elements according to the exemplary embodiment illustrated inFIG. 11toFIG. 14. However, the present exemplary embodiment does not include a housing26(please refer toFIG. 11). The bearing B may be fixed to a body of a machining device since the housing is not used.

The bearing shaft22is rotatably coupled to the bearing B, and the screw10coupled with the spring21is connected to the bearing shaft22. The motor M is connected to the bearing shaft22.

A side surface of the bearing B is supported by a step formed at the bearing shaft22and the other side surface of the bearing B is pressed and fixed by the outer ring pushing plate28connected to the bearing shaft22such that the bearing B is not departed from the body. The side surface of the bearing B may be supported by a stepped portion (not shown) formed at the body. Means for preventing the bearing B from being departed from the body may be changed variously. Other constituent elements are the same as those illustrated inFIG. 11toFIG. 14.

The exemplary embodiment illustrated inFIG. 1toFIG. 4does not include the housing26. In this case, the bearing B may be fixed to a body of a machining device.