Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
1999-11-15
2001-09-11
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S424860, C074S424870
Reexamination Certificate
active
06286383
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ball screw unit in which a screw shaft meshes with a nut member via a plurality of balls so as to convert a rotating motion of a motor to a linear motion in a slide portion of a machine tool or an industrial robot and transmit that linear motion thereto, and more particularly to improvement of the ball screw unit in which a ball arranging member for arranging a plurality of balls at a predetermined interval is incorporated in a ball infinite circulation path of the nut member.
DESCRIPTION OF THE RELATED ART
The ball screw unit is used in a number of linear slide portions and the like of an industrial robot, mainly to give a linear traveling amount corresponding to a rotation amount of the motor to a movable body such as a table or the like. Generally, the ball screw unit comprises a screw shaft in which a spiral ball rolling groove is formed on an outer peripheral face thereof and a nut member which meshes with the screw shaft via a plurality of balls, and contains an infinite circulation path in which the balls circulate. When the screw shaft connected to a motor is rotated, a plurality of the balls interposed between the screw shaft and nut member circulate in the infinite circulation path provided in the nut member, so that the nut member moves linearly gently in an axial direction of the screw shaft correspondingly.
On the other hand, in such a conventional ball screw unit, individual balls circulating in the ball infinite circulation path make contact with balls located back and forth, so that smooth circulation of the balls is hampered and further, a contact sound produced between adjacent balls when the screw shaft is rotated at a high speed grates on the ears. Japanese Utility Model Application Laid-Open No.HEI5-27408 has disclosed a ball screw unit for solving such problems.
In the ball screw unit disclosed therein, a belt-like ball arranging member having a flexibility is provided in the ball infinite circulation path so that it is capable of circulating. Such an arranging member has ball pockets each for accommodating the ball disposed at a predetermined interval. Therefore, the balls are accommodated in the ball infinite circulation path of the nut member such that they are arranged in the belt-like arranging member at the predetermined interval and consequently, in this ball screw unit, a contact between the balls circulating in the infinite circulation path is prevented.
Further, in the ball screw unit, the ball infinite path is formed by mounting a ball circulation pipe on the nut member and a pair of guide grooves for guiding both edge portions of the ball arranging member are formed in an inner peripheral face of the ball circulation pipe. Therefore, a fluttering of a belt-like retainer in the ball circulation pipe is prevented by such a guide groove thereby ensuring smooth circulation of the balls in the ball infinite path.
However, in the conventional ball screw unit, although circulation of the arranging member is guided by the guide grooves in the ball circulation pipe as described above, in a region in which the balls roll between the screw shaft and nut member, that is, in load region, only the arranging member is inserted in a slight gap formed between an outer peripheral face of the screw shaft and an inner peripheral face of the nut member. Thus, if the belt-like arranging member deflects even slightly with a circulation of the balls, the arranging member which moves relatively in an opposite direction makes a contact with the outer peripheral face of the screw shaft, so that the arranging member is worn early. Further, a large resistance is applied to circulation of the arranging member and circulation of the balls, so that smooth motion of the nut member with respect to the screw shaft is hampered.
If the guide grooves for the belt-like arranging member are formed in only the ball circulation pipe, unless the arranging member is formed endlessly, an end portion of the arranging member is caught by an entrance of the ball circulation pipe when it invades therein from the load region, so that smooth circulation of the arranging member is also obstructed.
SUMMARY OF THE INVENTION
The present invention has been accomplished in views of such problems, and therefore, an object of the invention is to provide a ball screw unit which prevents an arranging member built in an infinite circulation path of a nut member from making contact with a screw shaft, and prevents such an arranging member from being caught in the infinite circulation path during circulation, thereby ensuring smoothness in ball circulation and a motion of the nut member with respect to the screw shaft and preventing wear in the arranging member.
To achieve the above object, the present invention provides a ball screw unit comprising a plurality of balls, a screw shaft in which a spiral ball rolling groove is formed on an outer peripheral face thereof, a nut member having a spiral load rolling groove opposing the ball rolling groove of the screw shaft, provided on an inner peripheral face thereof, the nut member meshing with the screw shaft via the balls, and a circulation path forming member for connecting both ends of the load rolling groove of the nut member so as to form an infinite circulation path for the balls, wherein a ball arranging member which arranges the balls at a predetermined interval and circulates in the infinite circulation path with the ball is provided in the infinite circulation path, a guide piece which is projected to both sides in an arrangement direction of the ball with respect to a diameter of the ball is formed in the ball arranging member, a pair of guide grooves for accommodating the guide piece of the ball arranging member is formed in an inner circumference of the circulation forming member in a ball rolling direction, and a pair of introducing grooves which accommodates the guide piece of the ball arranging member and are continuous with the guide groove are formed on both sides of the load rolling groove of the nut member.
According to such a technological means, guide pieces extending on both sides of the ball arranging member in the direction of the ball arrangement from a diameter of the ball are formed on the ball arranging member circulating in the infinite circulation path with the balls, and an introducing groove for accommodating the guide piece of the ball arranging member is formed on both sides of the load rolling groove of the nut member. Thus, when the balls roll between the load rolling groove of the nut member and ball rolling groove of the screw shaft, that is, the load region, the ball arranging member is guided by the introducing groove along an inner peripheral face of the nut member. Therefore, in such a load region, the ball arranging member which moves with rolling of the balls never flutters thereby making it possible to prevent a contact between the ball arranging member and screw shaft.
Because the introducing groove formed on both sides of the load rolling groove of the nut member is continuous with the guide groove formed in an inner circumference of the circulation path forming member, even if the ball arranging member is not formed endlessly, an end portion of the ball arranging member invading into the circulation path forming member from the load region is not caught at an entrance of the circulation path forming member and a plurality of the ball arranging members can be built in series in the infinite circulation path provided in the nut member.
Here, the aforementioned ball arranging member may be of any type as long as a plurality of balls can be arranged at a predetermined interval and for example, a belt-like retainer as disclosed in the above-mentioned Japanese Utility Model application Laid-Open No.HEI5-27408, in which ball accommodating holes having a slightly larger diameter than the ball diameter are formed in a flexible belt of synthetic resin at a predetermined interval. However, from viewpoint of preventing the balls from rolling out of the load rolling
Ebina Shigeru
Michioka Hidekazu
Shirai Takeki
Takeda Ryuji
Arent Fox Kintner Plotkin & Kahn
Fenstermacher David
THK Co. Ltd.
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