News Column

Patent Application Titled "Ball Screw Bearing Device" Published Online

July 3, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventor Nagai, Yutaka (Fujisawa-shi, JP), filed on July 20, 2012, was made available online on June 19, 2014.

The assignee for this patent application is NSK Ltd.

Reporters obtained the following quote from the background information supplied by the inventors: "Ball screws include a nut having a spiral groove formed in an inner peripheral surface, a screw shaft having a spiral groove formed in an outer peripheral surface, and balls arranged between raceway grooves formed by the spiral groove of the nut and the spiral groove of the screw shaft.

"If ball screws used as precision feed mechanisms, such as machine tools, injection molding machines, and semiconductor device manufacturing apparatuses, are used with high speed and high cycle, the ball screws have high temperature and heat deformation occurs in the screw shaft or the nut (the screw shaft elongates due to thermal expansion). Along with this, load distribution abnormality of the balls or deterioration of operability occurs, and the positional accuracy of the feed mechanisms is worsened. Therefore, in the ball screws that require high positional accuracy, measures for cooling the screw shaft, the nut, and the bearing device arranged at an end portion of the screw shaft are taken.

"Patent Document 1 describes that a nut and a rolling bearing are cooled by providing gaps between a housing to which an outer ring of the rolling bearing that rotatably supports an end portion of a screw shaft is internally fitted and a body frame fixed to the housing via a heat insulating material and between the nut and a movable body fixed to the nut via a heat insulating material and by feeding cooling air into the respective gaps. Additionally, Patent Document 2 describes a ball screw having a cooling mechanism in a nut."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventor's summary information for this patent application: "Problem to be Solved

"However, in the technique described in Patent Document 1, there is room for improvement in terms of the cooling efficiency of the rolling bearing. Specifically, since an outer peripheral portion of the housing is cooled and the bearing device that is a heat generation source and its vicinity are not cooled, efficient cooling is not performed.

"Thus, the invention has been made paying attention to the above problems and an object thereof is to provide a ball screw bearing device capable of efficiently cooling the vicinity of a rolling bearing that rotatably supports an end portion of a screw shaft of a ball screw, and the vicinity of a bearing device.

"Solution to the Problem

"In order to achieve the above object, there is provided a ball screw bearing device including an inner ring that fits to an end portion of a screw shaft of a ball screw and rotates integrally with the screw shaft; an outer ring that rotatably supports the inner ring via a plurality of rolling elements arranged on an outer peripheral surface of the inner ring; and a housing that has an inner peripheral surface that abuts against an outer peripheral surface of the outer ring and rotatably supports the screw shaft. A plurality of through-holes for cooling that pass through both ends of the housing and cause a cooling medium to pass therethrough are formed in an axial direction of the housing.

"Additionally, in the above ball screw bearing device, a groove portion that communicates with the through-holes for cooling is formed in an end surface of the housing.

"Additionally, it is possible to adopt a configuration in which the through-holes for cooling are coupled together by pipes via joint members outside the housing.

"Additionally, the through-holes for cooling may be equally arranged along the circumferential direction of the housing.

"By arranging the above through-holes for cooling in this way, it is possible to cool uniformly in the circumferential direction of the housing by using the through-holes for cooling provided inside the housing closer the rolling bearing than the outside of the housing. Therefore, the rolling bearing that rotatably supports the end portion of the screw shaft of the ball screw is able to be cooled more efficiently than the method of Patent Document 1 that cools the outside of the housing with air.

"Additionally, three to six of the through-holes for cooling may be formed.

"Although a cooling effect is able to be enhanced as the number of the through-holes for cooling is larger, the mechanical strength of the housing decreases and machining costs also increase. Additionally, when the number of the through-holes for cooling is two, even if the through-holes for cooling are arranged at an equal interval in the circumferential direction, a temperature gradient occurs and the housing is easily thermally deformed in an elliptical shape because the arrangement interval of the through-holes for cooling is large. Hence, the through-holes for cooling are preferably arranged within a range of three or more and six or less.

"Additionally, the through-holes for cooling are preferably arranged on an end portion side of the screw shaft or on a flange side.

"Advantageous Effects of the Invention

"According to the ball screw bearing device of the embodiment of the invention, the vicinity of the rolling bearing that rotatably supports the end portion of the screw shaft of the ball screw or the vicinity of the bearing device is able to be efficiently cooled.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a front view illustrating a first embodiment of a ball screw bearing device.

"FIG. 2 is a view when the bearing device of FIG. 1 is viewed from arrow a.

"FIG. 3 is a view when the bearing device of FIG. 1 is viewed from arrow b.

"FIG. 4 is a cross-sectional view taken along IV-IV of FIG. 3.

"FIG. 5 is a plan view illustrating a retaining lid that constitutes the bearing device of FIG. 1.

"FIG. 6 is a front view illustrating a configuration in a second embodiment of the ball screw bearing device.

"FIG. 7 is a right side view illustrating the configuration in the second embodiment of the ball screw bearing device.

"FIG. 8 is a left side view illustrating the configuration in the second embodiment of the ball screw bearing device.

"FIG. 9 is a cross-sectional view along an axial direction, illustrating the configuration in the second embodiment of the ball screw bearing device."

For more information, see this patent application: Nagai, Yutaka. Ball Screw Bearing Device. Filed July 20, 2012 and posted June 19, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3871&p=78&f=G&l=50&d=PG01&S1=20140612.PD.&OS=PD/20140612&RS=PD/20140612

Keywords for this news article include: NSK Ltd.

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Source: Politics & Government Week


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