Wiper ring and ball screw provided with wiper ring

A wiper ring to be applied to a nut of a ball screw having a screw shaft comprises a plurality of segments each constituted as independent element having a seal portion to be contacted to the screw shaft, support pins extending in an axial direction of the screw shaft so as to correspond to the segments, respectively, the segments being arranged in a circumferential direction of the screw shaft to be rotatable about the pins, the pins being connected to each other through support members so as to limit the relative movement of the respective pins, and a spring member for urging the segments arranged circumferential direction of the screw shaft so as to be directed towards radially central side of the screw shaft.

BACKGROUND OF THE INVENTION

The present invention relates to a wiper ring to be mounted to an end portion of a nut of a ball screw and also relates to a ball screw provided with such wiper ring.

Japanese Utility Model Laid-open Publication No. HEI 6-6795 disclosed such a wiper ring, in which one end side portion or entire portion of a wiper ring is divided into a plurality of segments or blocks in a circumferential direction thereof, and each of the segments is pressed towards radially center side by means of spring to thereby improve tightness between an inner peripheral portion of the wiper ring and a screw shaft disposed inside therein.

In such known art, in the structure in which only the one end side portion of the wiper ring is divided into a plurality of segments or blocks, there is usually formed a cutout portion, called “bias-cut”, at one portion of the wiper ring in its circumferential direction for separating the same. However, in an arrangement in which such wiper ring is mounted to a screw shaft, the bias-cut portion is widened (opened) and the inner peripheral portion of the wiper ring is deformed unwillingly in form of non-circular shape, and for this reason, at a portion opposite to the bias-cut forming portion of the wiper ring, the segment is closely contacted to the screw shaft. However, on the side of the bias-cut forming portion, the tightness of the segment to the screw shaft is made worse. As a result, sealing performance of the ball screw may be made different at various portions, thus being inconvenient.

On the other hand, the case where the entire portion of the wiper ring is divided into a plurality of segments or blocks will cause the following defective.

In such structure, when a gap is formed between adjacent two segments in the circumferential direction thereof, the gap may be widened when the segments are shifted. In such occasion, foreign material or like may easily invade and lubricant may easily leak through the widened gap. On the contrary, when the segments are contacted to each other in order to eliminate such gap, the movement of the respective segment towards the radially central portion of the segment due to such mutual contacting will be limited, which results in degradation of tightness between the segments and the screw shaft and deterioration of the sealing performance. Furthermore, in a case where any foreign material is clogged between the segment and the screw shaft, the segment is displaced towards the radially outer peripheral side against the force of the spring pressing the segment, and hence, the inner peripheral portion of the segment is separated from the screw shaft, thus deteriorating the sealing performance and hence being defective.

SUMMARY OF THE INVENTION

An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a wiper ring and a ball screw provided with the wiper ring, by which sealing performance of a screw shaft with respect to segments of the wiper ring can be enhanced.

The above and other objects can be achieved according to the present invention by providing, in one aspect, a wiper ring to be applied to a screw unit having a shaft member comprising:

a plurality of segments each constituted as independent element having a seal portion to be contacted to the shaft member;

support shafts extending in an axial direction of the shaft member so as to correspond to the segments, respectively, the segments being arranged in a circumferential direction of the shaft member to be rotatable about the support shafts, the support shafts being connected to each other through support members so as to limit relative movement of the respective support shafts; and

a spring member for urging the segments arranged circumferential direction of the shaft member so as to be directed towards radially central side of the shaft member.

According to the wiper ring of this aspect, the respective segments are deformed in their attitudes so as to closely contact the shaft member such as screw shaft of the ball screw unit while being pressed towards the central side of the screw member by means of spring and rotating about the support shafts such as pins. Accordingly, the respective segments can be well contacted to the shaft member, and the improved sealing performance can be realized at any circumferential position.

Further, the support shafts of the respective segments are mutually connected to thereby limit or restrict the relative movement of the support shafts, so that the movement of the segments in the circumferential and radial directions can be properly limited. Therefore, the biting of foreign material in a widened gap between the segments in the circumferential direction can be prevented, the leakage of lubricant can be also prevented, and the degradation of the sealing performance due to the movement of the segments in the radially outer peripheral direction can be further prevented.

Further, in the present invention, the state, that the support shafts as rotational centers of the respective segments are connected to each other, means that the support shafts are connected to each other through members different from the segments or through the segments themselves to thereby restrict the relative movement therebetween. The support shafts may be constituted independently from the segment, or segment itself is utilized as support shaft.

In a preferred embodiment of this aspect, the support member is a support ring formed as a member independent from the segments and the support shafts are connected to each other through the support ring.

In this example, the respective segments are supported by the support ring to be rotatable about the support shafts such as pins. The support ring may be separated at one portion in its circumferential direction, and in such case, since the cut portion corresponding to the bias-cut in the conventional structure of the wiper ring is formed on the support ring, the wiper ring can be entirely deformed and the segments can be surely urged against the shaft member by the spring member.

Furthermore, according to this aspect, (N-2) segments in the plural segments (N: total number thereof) are formed with the support shafts and hole portions for receiving the support shafts in an arrangement shifted in the circumferential direction of the shaft member, either one of remaining two (2) segments is provided with the support shaft and another one of the remaining two segments being formed with the hole portion, the segments being connected to each other by fitting the support shafts to the hole portions of the adjacent two segments in the circumferential direction in a manner that the remaining two segments are unconnected.

According to this example, the respective adjacent segments can be supported to be rotatable about the support shafts and the respective support shafts can be connected through the segments. Therefore, no connection is made between two segments, so that the cut (separated) portion, corresponding to the conventional bias-cut, is formed and the wiper ring can be entirely deformed. Thus, the segments can be surely urged against the shaft member by the spring member.

Furthermore, it may be possible that each of the segments comprises a segment body having the seal portion and a support plate arranged in a manner shifted in the circumferential direction with respect to the segment body, either one of the support plate and the segment body is formed with the support shaft and another one thereof is formed with the hole portion.

In this example, since the support plate extends behind a slit formed between the segment bodies, so that the inside and outside portions of the wiper ring are not communicated through the slit, and hence, the invasion of foreign material can be prevented as well as leakage of the lubricant.

In another aspect of the present invention, there is also provided a wiper ring to be applied to a screw unit having a shaft member comprising:

a support ring;

a plurality of segments each having a seal portion to be contacted to the shaft member, the segments being arranged on one side of the support ring in a circumferential direction of the support ring and connected to each other to be rotatable about a predetermined support shaft with respect to the support ring; and

a spring member for urging the segments arranged in the circumferential direction of the support ring towards radially central side of the support ring.

According to the wiper ring of this aspect, substantially the identical advantageous effects to those mentioned above will be achieved. That is, since the respective segments can be supported by the support ring to be rotatable about the support shafts such as pins, the respective segments are deformed in their attitudes so as to closely contact the shaft member such as screw shaft of the ball screw unit while being pressed towards the central side of the screw member by means of spring and rotating about the support shafts such as pins. Accordingly, the respective segments can be well contacted to the shaft member, and the improved sealing performance can be realized at any circumferential position.

Further, the support shafts of the respective segments are mutually connected through the support ring to thereby limit or restrict the relative movement of the support shafts, so that the movement of the segments in the circumferential and radial directions can be properly limited. Therefore, the biting of foreign material in a widened gap between the segments in the circumferential direction can be prevented, the leakage of lubricant can be also prevented, and the degradation of the sealing performance due to the movement of the segments in the radially outer peripheral direction can be further prevented.

The support ring may be separated at its one portion in the circumferential direction, and in such case, the cut (separated) portion, corresponding to the conventional bias-cut, is formed on the support ring, so that the wiper ring can be entirely deformed. Thus, the segments can be surely urged against the shaft member by the spring member.

In this aspect, a slit may be formed between adjacent segments when the segments are connected to the support ring.

In a further aspect, there is provided a wiper ring to be applied to a screw unit having a shaft member comprising:

a plurality of segments each having a seal portion to be contacted to the shaft member, the segments being arranged in a circumferential direction of the shaft member; and

a spring member for urging the segments arranged in the circumferential direction of the shaft member in the radially central direction of the shaft member,

wherein (N-2) segments in the plural segments (N: total number thereof) are formed with support shafts extending in an axial direction of the shaft member and hole portions for receiving the support shafts in an arrangement shifted in the circumferential direction of the shaft member, either one of remaining two segments is provided with the support shaft and another one of the remaining two segments being formed with the hole portion, the segments being connected to each other by fitting the support shafts to the hole portions of the adjacent two segments in the circumferential direction in a manner that the remaining two segments are unconnected.

According to the wiper ring of this aspect, the respective adjacent segments are supported to be rotatable about the support shafts such as pins, so that the respective segments are deformed in their attitudes so as to closely contact the shaft member such as screw shaft of the ball screw unit while being pressed towards the central side of the screw member by means of spring and rotating about the support shafts. Accordingly, the respective segments can be well contacted to the shaft member, and the improved sealing performance can be realized at any circumferential position.

Further, the support shafts of the respective segments are mutually connected to thereby limit or restrict the relative movement of the support shafts, so that the movement of the segments in the circumferential and radial directions can be properly limited. Therefore, the biting of foreign material in a widened gap between the segments in the circumferential direction can be prevented, the leakage of lubricant can be also prevented, and the degradation of the sealing performance due to the movement of the segments in the radially outer peripheral direction can be further prevented.

Furthermore, the connection between the adjacent two segments is interrupted, the cut (separated) portion, corresponding to the conventional bias-cut, is formed on the support ring, so that the wiper ring can be entirely deformed. Thus, the segments can be surely urged against the shaft member by the spring member.

In this aspect, a slit is formed between adjacent segments when the respective segments are connected.

In still further aspects of the present invention, there are provided ball screw or ball screw units each comprising:

a screw shaft;

a number of rolling members to be applied to the screw shaft;

a nut mounted to the screw shaft through the rolling members; and

a wiper ring mounted to at least one axial end portion of the nut, the wiper ring comprising the elements or members mentioned above with respect to first, another and further aspects of the present invention.

According to the ball screw (unit) utilizing the wiper ring of the above aspects, the wiper ring is mounted to at least one end portions of the nut, so that the durability of the nut against the foreign material or like can be achieved with the improved sealing performance of the wiper ring.

Further, it is to be noted that the nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

One preferred embodiment of the present invention will be described hereunder with reference to the accompanying drawings.

First, with reference toFIG. 1, a ball screw10generally comprises a screw shaft11, a number of balls12as rolling members and a nut (or nut member)13to be mounted to the screw shaft11through the balls12. The nut13has an inner peripheral surface portion to which a ball rolling groove13ais formed. The balls are rolled along a passage formed by a ball rolling groove11aof the screw shaft11and a ball rolling groove13aof the nut13in accordance with the relative rotation of the screw shaft11and the nut13. When the ball12reaches one end portion of the ball rolling groove13a,the ball12is returned to the opposite side portion of the ball rolling groove13athrough a return tube14fixed to the nut13.

The nut is provided, at its both ends, with recessed portions13b,13bfor mounting a wiper. Further, it is to be noted that, in the illustration ofFIG. 1, although only the one end side of the nut13, the other end side has substantially the same structure as that of the illustrated side.

A wiper ring20is mounted to each of the recessed portions13bso as not to come off therefrom by means of stopper ring15. The purpose of mounting the wiper ring20is to prevent foreign material adhering to the screw shaft11from invading into the nut13and to prevent lubrication agent(lubricant) such as grease from leaking outside.

FIGS. 2 to 4show detail structure or arrangement of such wiper ring20.

Each of the wiper rings20comprises a support ring21, a plurality of segments22A to22H (which, hereunder, may be generally as segment(s)22as shown inFIG. 1) disposed on one side of the support ring21, and a spring member (spring ring)23mounted to the outer peripheral portions of the segments22. The support ring21and the respective segments22will be produced through an injection molding of a synthetic resin material, for example.

The support ring21is formed in shape of plate having one peripheral portion at which a bias-cut21ais formed as shown inFIG. 2. The support ring21is further formed, at its one side portion, with a shallow recessed portion21bhaving a bottom portion acting as a mounting surface of the segment22. Further, the spring ring23is formed by connecting both ends of a coil spring so as to provide a ring shape.

The support ring21has an inner peripheral surface21dwhich is formed to be equal to a contour shape on the axially perpendicular sectional surface of the outer periphery of the screw shaft11so as to be closely contacted to the screw shaft11. Further, in a case where the inner peripheral surface21dof the support ring21is formed to have an inclination so as to cross at an acute angle with respect to the mounting surface21aof the support ring21, the tightness of the support ring21to the screw shaft11will be enhanced. Moreover, in a case where the inner peripheral surface21dof the support ring21can be manufactured with high performance to thereby highly ensure the tightness to the screw shaft11, it may be not necessary to form the bias-cut21amentioned before, and the support ring21may be formed in the endless ring shape.

The respective segments22(22A to22H) are formed independently and assembled to be separable. The segment22has a rear (back) surface22afacing the support ring21, and a pin22b,as a support shaft member, is located to each of the segments22so as to extend towards the screw shaft11. Further, hole portions (holes)21eare also formed on the support ring21so as to penetrate the same at a portion corresponding to the location of the pin22b.It is, however, not always necessary to form the hole21bto penetrate the support ring21, and it is permitted for the hole21bto be opened to the mounting surface21copposing to the segment22.

The respective segments22can be attached onto the mounting surface21cof the support ring21to be turnable about the pins22bby fitting the pins22binto the holes21e,respectively. According to such fitting, the respective segments22are arranged side by side along the peripheral direction of the support ring21with slits24between adjacent end faces22dand22ein the peripheral direction, and all the pins22bare interconnected respectively through the support ring21. Further, with reference toFIG. 2or3, in order to scoop and then discharge foreign material in the ball rolling groove11aoutside the nut13, the end faces22dand22eof the respective segments22mentioned above are obliquely inclined with respect to the radial and axial direction of the screw shaft, respectively. In the illustrated embodiment, although the slit24is described with a constant width, it may be formed so as to be widened on the outer peripheral side thereof.

Furthermore, each of the segments22is formed, at its inner peripheral surface22f,with a protrusion22gin form of string, as shown inFIG. 4, which is fitted to the ball rolling groove11aof the screw shaft11. Further, each of the segments22is formed, at its outer peripheral portion, with a groove22halong the circumferential direction thereof. When the segments22are assembled with the support ring21by fitting the pins22bof the respective segments22into the holes21eof the support ring, the outer peripheral grooves22hof the respective segments22become continuous to thereby provide one annular groove into which the spring ring23is fitted in an expanded state. According to the restoring force of the spring ring23, the respective segments22are pressed on the radially central side of the screw shaft11(i.e., the radially central side of the support ring21). Thus, the inner peripheral portions22fof the respective segments22function as sealing means in close contact to the screw shaft11. Further, in order to prevent the segments22from coming off from the support ring21, it is desirable to form the pins22bby coming-off prevention means such as press-fitting method, calking method (i.e., a method in which the front end of the pin22bprojecting over the hole21eis fused to be secured) or like method. However, it is necessary to fit the pin22bto be rotatable (turnable) into the hole21e.

The protrusion22gin shape of string is twisted in a spiral shape along the ball rolling groove11aof the screw shaft11, and the shape thereof may differ in accordance with the attachment positions of the segments22A to22H. Accordingly, the respective segments22A to22hhave different shapes from each other in their inner peripheral portions22f. Thus, it is difficult to produce the respective segments by one common mold. On the other hand, since the protrusions22gare fitted into the one continuous ball rolling groove11a, it is required for the protrusions22gof the respective segments22to be continuous to describe one spiral string along the ball rolling groove11a. In order to satisfy such requirement, it would be necessary to form cavities corresponding to the respective segments22A to22H in one set of mold halves to thereby form the segments at once. In such method, it is possible to prescribe, by the mold, the dimensional performance of the respective segments22A to22H and the relative positional relationship therebetween, so that the respective segments22A to22H can be produced more precisely in comparison with the case that the respective segments are produced independently. Moreover, in the integral structure of the support ring21and the segments22, the shape of the mold is made complicated so as to withdraw a core forming the spirally twisted protrusions22g. However, in the case of the present embodiment in which the respective segments22A to22H are formed integrally from each other, since the respective segments are not restricted or affected from each other, so that it is possible to easily withdraw the core forming the inner peripheral portions of the segments22, thus simplifying the structure of the mold.

The wiper ring20thus formed is set to the recessed portion13bof the nut13so as to be directed inside the axial direction of the nut. In the state that the wiper ring20is mounted onto the screw shaft11, even if the support ring21is deformed to widen the bias-cut21a, the segments22receiving the force of the spring ring23are rotated in a manner that the inner peripheral portions22fof the respective segments22are rotated about the pins22bso as to be closely contacted to the screw shaft11. As a result, the respective segments22are equally and tightly contacted to the screw shaft11, and hence, the sealing performance of the wiper ring20can be achieved.

FIGS. 5 to 7represent another embodiment of the wiper ring according to the present invention.

With reference toFIGS. 5 to 7, a wiper ring30of this embodiment is provided with a plurality of segments31(31A to31H, eight, in the illustration) and a spring ring32, which is identical structure to that of the wiper ring20of the former embodiment. However, in this embodiment, any support ring, such as that21in the former embodiment, is not provided, and in substitution therefor, the segment31is formed with a segment body33and a support plate34. The respective segments31A to31H are formed independently as separate members to thus be separable, and the segment body33and the support plate34in each segment31are formed of resin material integrally with each other.

The segment body33is not provided with a support shaft member such as pin22bfor the segment22in the former embodiment, and instead, holes33bare formed. Except for this structure, the segment33has substantially identical shape or structure as that of the segment22. Accordingly, constitutional elements of the segment33of this embodiment corresponding to the elements22aand22cto22hof the segment22in the former embodiment are added only with reference numerals33a,33cto33h, respectively, and the descriptions or explanations thereof are omitted herein.

Furthermore, as like in the former embodiment, it is preferred to form the respective segments33A to33H at once by one set of mold halves because of the same reason as that mentioned before with respect to the wiper ring20.

The support plate34serves like the support ring21of the wiper ring20in the former embodiment, and the support plates34are shifted in their phases in the peripheral direction with respect to the segment bodies33and formed, on their surfaces, with pins34aas support shafts, to be fitted to the holes33bformed on the segment bodies33. However, any one of the segments (for example, segment31G) is not provided with such pin34a,and in this connection, the hole33bof the segment31H adjacent to this segment31G may be eliminated.

The segments31A to31H thus constructed are arranged side by side so as to describe a circle and then connected together by fitting each of the pins34ainto the hole33bof each of the adjacent segments. Thereafter, the spring ring32is fitted into the grooves33hformed on the outer periphery of the segment bodies33to thereby complete the wiper ring30of this embodiment. In such wiper ring30, slits35, like the slits24of the wiper ring20of the former embodiment shown inFIG. 2, are formed between the respective bodies33of the connected segments31A to31H. Further, the support plates34of the respective segments31are arranged to be continuous in their peripheral direction and, accordingly, a ring-shaped plate like the support ring21of the wiper ring20is formed. However, as mentioned above, as the segment31G is not provided with the pin34a,the segments31H and31G are not connected. According to the described structure, the wiper ring30is also formed with a cutout portion (separated portion) identical to the bias-cut21aof the wiper ring20ofFIG. 2. Further, it is desired that the connection between the pin34aand the hole33bof the segment31by coming-off prevention methods such as press-fitting method or calking method carried out with reference to the connection between the pin22band the hole21eof the wiper ring20. In such method, however, it is necessary for the pin34ato be fitted to the hole33bin the rotatable manner.

Furthermore, in the wiper ring30of this embodiment, the support plate34is also mounted to the recessed portion13bof the nut so as to be directed axially inward of the nut13. The mounting of the wiper ring30onto the screw shaft11permits to rotate the inner peripheral portions33fof the respective segment bodies33about the pins34aso as to be closely contacted to the screw shaft11while the respective segments31receiving the force of the spring ring32even if the wiper ring30so deformed as that the non-connected segments31G and31H are relatively separated from each other in the circumferential direction. As a result, the respective segments31can be equally and well contacted to the screw shaft11, and hence, the sealing performance due to the wiper ring30can be achieved.

Further, it is to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scopes of the appended claims.

For example, with the wiper ring20ofFIG. 2, the pin22bmay be provided for the support ring21and, on the other hand, the hole21emay be formed on the segment22. With the wiper ring30, also, the arrangement of the hole32band the pin34amay be substituted with each other. Furthermore, the lengths in the circumferential directions of the respective segments22A to22H and31A to31H may be made equal to each other or different from each other, and the number of the segments22and31is not limited to eight (8).

The present application claims priority under 35 U.S.C § 119 to Japanese Patent Application No. 2000-358245 filed Nov. 24, 2000 entitled “WIPER RING AND BALL SCREW PROVIDED WITH WIPER RING”. The contents of that application are incorporated herein by reference in their entirety.