Strain wave generator for harmonic reducer

Proposed is a strain wave generator for a harmonic reducer, the strain wave generator including: a cam formed with a plurality of segmented cams on a long-diameter side and the same number of segmented cams on a short-diameter side alternately abutted along a circumferential direction, wherein each of the segmented cams on a long-diameter side has an outer circumference surface of a certain cylindrical surface of a small radius, each of the segmented cams on a short-diameter side has an outer circumference surface of a certain cylindrical surface of a large radius, and the cylindrical surface of each of the segmented cams on a long-diameter side and the cylindrical surface of each of the segmented cams on a short-diameter side, abutted each other, have a common tangent line at a meeting point thereof.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a strain wave generator, which is a component of a harmonic reducer mainly applied to a joint of an industrial robot and, more particularly, to a strain wave generator improved to allow a phenomenon of occurrence of backlash or a decrease in frictional torque to be prevented.

DESCRIPTION OF THE RELATED ART

In general, a harmonic reducer10applied to an industrial robot transmits high-speed rotation of a servomotor to an output shaft at a high reduction ratio of 1:30 to 1:320. As shown inFIG.1, as an elliptical strain wave generator11rotates, points, at which a flexspline12surrounding the elliptical strain wave generator11meshes with an outer circular spline13, move along a circumferential direction, and a key point to establishing speed reduction is in allowing such points to be rotated in an opposite direction by a difference of the number of teeth.

However, according to the harmonic reducer of the same principle, there is a problem in that backlash occurs due to a space between teeth due to a design and processing error of the teeth and wear of parts such as bearings.

In particular, the strain wave generator11has an elliptical shape cam, so there are problems that precise processing of the outer shape is quite difficult, mass production is difficult, and the production cost is also high. In addition, there is a problem that fairly expensive equipment is required for precise measurement of the cam shape of the strain wave generator11. Furthermore, the flexspline12has to be assembled with the strain wave generator11in an elastically deformed state, so there are problems that assembly skill is required, and productivity is low.

On the other hand, in order to solve the above problems, the applicant has proposed Korean Patent No. 10-2303050 (issue date: Sep. 16, 2021) and Korean Patent No. 10-2345641 (issue date: Dec. 31, 2021) and the disclosure disclosed in Korean Patent Publication No. 10-2021-0155587 (publication date: 2021 Dec. 23).

A key point of the above patents and disclosure is to solve a tooth design and a backlash problem resulting therefrom by converting a coupling between the flexspline22and the circular spline23into a face-to-face friction structure as shown inFIG.2.

However, even in such a case, there still exists a difficulty of machining a cam-type strain wave generator21. In particular, when the vertical surface pressure V by the strain wave generator21is not sufficiently transmitted to the flexspline22side due to machining error, friction surface wear, bearing wear, and the like, frictional force f with the circular spline23is lowered, so that sufficient friction torque is not generated, so the performance as a reducer may not be guaranteed.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure has been made keeping in mind the above problems occurring in the related art, and a first objective of the present disclosure is to provide an improved strain wave generator to facilitate shape processing.

A second objective of the present disclosure is to provide a strain wave generator capable of preventing backlash from occurring in the case of a toothed speed reducer and preventing transmitted vertical surface pressure from decreasing in the case of a toothless speed reducer.

In order to achieve the above objective, there may be provided a strain wave generator for a harmonic reducer, the strain wave generator including: a cam formed with a plurality of segmented cams on a long-diameter side and the same number of segmented cams on a short-diameter side alternately abutted along a circumferential direction, wherein each of the segmented cams on a long-diameter side has an outer circumference surface of a certain cylindrical surface of a small radius, each of the segmented cams on a short-diameter side has an outer circumference surface of a certain cylindrical surface of a large radius, and the cylindrical surface of each of the segmented cams on a long-diameter side and the cylindrical surface of each of the segmented cams on a short-diameter side, abutted each other, have a common tangent line at a meeting point thereof.

Here, on the cylindrical surfaces of the segmented cams on a long-diameter side and the segmented cams on a short-diameter side, V grooves may be formed to be connected to each other in the circumferential direction to form a single track, and a plurality of balls may be seated along the track.

Alternatively, on the cylindrical surfaces of the segmented cams on a long-diameter side and the segmented cams on a short-diameter side, a plurality of rollers may be in rolling contact with the cylindrical surfaces.

At this time, at opposite sides on the cylindrical surface of the segmented cams on a long-diameter side and the segmented cams on a short-diameter side, barrier ribs configured to guide the rollers not to deviate from the track may be formed to be connected to each other in the circumferential direction to form a single track, and the plurality of rollers may be seated along the track.

Alternatively, on the cylindrical surface of the plurality of segmented cams on a long-diameter side and on the cylindrical surface of the plurality of segmented cams on a short-diameter side, one flexible bearing inner ring may be coupled, and a plurality of balls or rollers may be seated on the flexible bearing inner ring.

At this time, on the plurality of balls or rollers, one flexible bearing outer ring may be coupled.

On the other hand, at an inner side of the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side, a central shaft may be installed, between an inner circumference surface of the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side and an outer circumference surface of the central shaft, tapered grooves inclined in an axial direction may be formed to extend in a circumferential direction, a plurality of balls may be inserted into the tapered grooves, respectively, and by pressing the plurality of balls in the axial direction through a lock nut coupled to an outer circumference surface of the central shaft, positions of the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side may be finely adjusted outward.

At this time, each of the segmented cams on a long-diameter side may have a long hole formed to extend in a circumferential direction adjacent to the cylindrical surface thereof and may exert pressing force in a radial direction through an elastic deformation in which a width of the long hole may be narrowed by the plurality of balls pressed in the axial direction.

Alternatively, at an inner side of the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side, a central shaft is installed, tapered grooves inclined in an axial direction may be formed on inner circumference surfaces of the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side, respectively, a ball may be inserted into each of the tapered grooves, and by pressing the plurality of balls in the axial direction through a lock nut coupled to an outer circumference surface of the central shaft, positions of the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side may be finely adjusted outward.

At this time, a flange, configured to support the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side in the axial direction, may be formed to extend in a radial direction from one end of the central shaft, and the flange may be elastically deformed in the axial direction by the plurality of segmented cams on a long-diameter side and segmented cams on a short-diameter side pressed by the balls, thereby preventing excessive force from being transmitted in the radial direction through the plurality of segmented cams on a long-diameter side and segmented cams on a short diameter side.

As described above, according to a strain wave generator according to the present disclosure, each of outer circumference surfaces of segmented cams on a long-diameter side and segmented cams on a short-diameter side has a cylindrical surface of a certain radius, so there is an advantage that the outer circumference surface of the segmented cam can be easily, quickly, and accurately machined by lathing or grinding by simple rotation.

DETAILED DESCRIPTION OF THE INVENTION

As shown inFIG.3, a strain wave generator100according to an embodiment of the present disclosure includes a cam110formed by two segmented cams111on a long-diameter side and two segmented cams112on a short-diameter side112alternately abutted in a circumferential direction.

The segmented cams111on a long-diameter side and the segmented cams112on a short-diameter side112each have cylindrical surfaces111aand112aof a constant radius, that is, a cylindrical surface of a regular circle, wherein each of the segmented cams111on a long-diameter side has a cylindrical surface111aof a small radius r1, and each of the segmented cams112on a short-diameter side112has a cylindrical surface112aof a large radius r2.

At this time, the segmented cams111on a long diameter side and the segmented cams112on a short diameter side have centers O1and O2, respectively, different from each other and are configured to have a common tangent line L at a point P where the cylindrical surfaces111aand112ameet with each other, whereby the cylindrical surface111aand cylindrical surface112aare allowed to be smoothly connected. In this way, it is possible to implement one outer circumference surface of the cam consisting of four segmented cams111and112.

A cam using a combination of segmented cams may be implemented by a combination of six segmented cams as shown inFIG.4, that is, three segmented cams111on a long-diameter side′ and three segmented cams112′ on a short-diameter side. In addition, the same principle may be applied to eight segmented cams and the like.

In addition, in the combination of all the segmented cams, each of the cylindrical surfaces111aand111a′ of the segmented cams111on a long-diameter side and111′, respectively, becomes an acting surface with respect to the outer flexspline (see12inFIG.1) or the circular spline13.

A plurality of balls120is configured to be in rolling contact along the cylindrical surfaces111aand112aof the segmented cams111the long diameter side and the segmented cams112on a short diameter side, respectively. To this end, V grooves111band112bare formed to be connected in a circumferential direction as shown inFIG.5so that the balls120may be seated along the track.

Alternatively, as shown inFIG.6, a configuration, in which a flexible bearing inner ring130is coupled on the cylindrical surfaces111aand112aso that the balls120are seated thereon, may be used, or as shown inFIG.7, a configuration, in which a flexible bearing outer ring140is additionally coupled on the balls, may be used. Meanwhile, the balls120and the flexible bearing inner and outer rings130and140inFIGS.6and7may be replaced with rollers (not shown) and flexible bearing inner and outer rings (not shown) corresponding to the rollers.

As another modification, as shown inFIG.8, a configuration, in which a plurality of rollers150is in rolling contact on the cylindrical surfaces111aand112aof the segmented cams111on a long-diameter side and the segmented cams112on a short-diameter side112, respectively, may be used. To this end, barrier ribs111cof a predetermined width are formed to be connected in the circumferential direction on the cylindrical surfaces111aand112afor smooth orbital circulation of the rollers150, whereby the rollers150are allowed also to be seated on the orbit of the cylindrical surfaces111aand112awithout deviating therefrom.

On the other hand, in consideration of a processing error of the strain wave generator100, an installation error of the reducer, an occurrence of wear due to use, and the like, balls170are interposed between the segmented cams111and112and a central axis160of same as shown inFIG.9and configured to be able to fine-tune positions in a radial direction of the segmented cam111or112.

Specifically, an outer circumference surface of the central shaft160foams the inclined tapered surface161so that a tapered groove H is formed between the inner circumference surface111dof the segmented cam111or112and the outer circumference surface of the central shaft160, thereby allowing the ball170to be inserted inward. In addition, a lock nut180may be screwed to the outer circumference surface of the central shaft160to allow the ball170to be pressed into the tapered groove H through a washer181as a medium. Accordingly, a position of the segmented cam111or112may be adjusted to the outside, that is, in the radial direction by the ball170to be inserted into the tapered groove H.

As shown inFIG.10, a tapered groove H may be formed by allowing the outer circumference surface of the central shaft160′ to be a circumference surface of a certain radius and the inner circumference surface111eof the segmented cam111or112to be foamed in a tapered surface.

Alternatively, as shown inFIG.11, a configuration may be used such that tapered grooves111fand112finclined in an axial direction are formed on the inner circumference surfaces of the segmented cams111and112to allow a ball170′ to be inserted into each thereof, whereby the balls may be pressed with a lock nut (see180′ inFIG.10).

On the other hand, as a configuration that may automatically compensate for a case in which vertical surface pressure is lowered or backlash occurs, due to wear of the ball120or the roller and its bearing circulating on the cylindrical surfaces111aand112aof the segmented cams111and112inFIG.3and/or due to wear of the flexspline (see12inFIG.1) or circular spline (see13inFIG.1) coupled to an outer side of the strain wave generator100, a long hole111gformed to extend in a circumferential direction at an inner point adjacent to the cylindrical surface111aof each of the segmented cams111on a long-diameter side may be provided as shown inFIGS.12to14.

InFIG.14, each of the segmented cams111, which receive force outwardly by the balls170pressed by the lock nut180, becomes to exert pressing force on the ball120that is on the circumference surface111athrough elastic deformation in which the width of the long hole111gis narrowed. Accordingly, the ball120becomes to be more closely contacted with the outer flexspline (see12ofFIG.1) and the circular spline13, whereby a decrease in the vertical surface pressure transmitted to the splines or the occurrence of backlash may be prevented.

At this time, a notch162ais formed at a base end of a flange162extending radially from one end of the central shaft160to support the segmented cams111and112, so that when the force pressed by the lock nut180is excessive to the ball170, the flange162may be elastically deformed in the axial direction (left direction inFIG.14), thereby preventing excessive force from being transmitted to the segmented cams111and112as it is.

In the present embodiment, a configuration in which the notch162ais formed for axial elastic deformation of the flange162is used, but the present disclosure is not limited thereto. In other words, various other methods, such as a method to make elastic deformation more easily by reducing the thickness of the flange162and the like, may be applied, thereby replacing the configuration.

In addition, the configuration in which the flange160is elastically deformed in such a way is applicable to a structure as shown inFIG.10in which the long hole111gis not formed in the segmented cams111.

FIG.15is a toothless harmonic reducer200to which the strain wave generator100ofFIGS.3and10is applied. In this case, a flexspline210rotate in reverse according to a diameter difference while being moved in rolling on an inner circumference surface of a circular spline220, thereby rotating a driven shaft230in a large reduction ratio compared to a drive shaft (that is, a central shaft160).

FIG.16is a toothed harmonic reducer300to which the strain wave generator ofFIGS.12and14is applied. In this case, in a state in which a flex spline310is closely meshed with a circular spline320by the pressure of the balls120on the outer side of the segmented cams111and112, meshed points rotate in reverse by a difference of numbers of teeth while being moved in a circumferential direction, thereby rotating a driven shaft330in a large reduction ratio.

On the other hand, the strain wave generator described above is only an embodiment for helping the understanding of the present disclosure, so the scope of the present disclosure defined by the claims to be described below should not be limited by the above description.