Circulating member for a ball screw

A circulating member for a ball screw is disposed on a nut, the nut is formed with Gothic type threads, and the circulating member of the ball screw is formed with return path for enabling the balls to circulate. The connecting ports at both ends of the return path for connecting the threads of the nut are shaped in Gothic style, thus eliminating the level difference and consequently preventing the balls from being struck and jammed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a component for a ball screw, and more particularly to a circulating member for a ball screw, which can eliminate the conjunction level difference and prevent the balls from being struck.

2. Description of the Prior Art

Nowadays, ball screw is used more and more widely in modern industries. As a linear transmission means, the ball screw not only has high precision but also has the advantages of low frictional loss, high energy conversion ratio, low noise and high rigidity. Hence, it is self-evident that the ball screw is very important to various industrial mechanisms.

In order for the balls between the screw and the nut to circulate smoothly and for eliminating the circulating impact force caused therebetween, the nut is usually provided at both ends thereof with a circulating member (for example, circulating cap). And the circulating member is a key member for enabling the balls circulation from the screw and the nut. Therefore, how to develop an improved and competitive circulating cap is the common goal that the manufactures are striving for.

The conventional circulating members are shown inFIGS. 1,2and3.

FIGS. 2 and 3show an ordinary conventional circulating structure, andFIG. 1shows a circulating member disclosed in U.S. Pat. No. 2,618,166, wherein the conventional ball screw comprises: a nut10, a screw11, a plurality of balls12, and a circulating member13installed radially from outside into inside of the ball screw. The circulating member13is inserted in the nut10via the hole101and serves to cooperate with the Gothic type (Gothic type or Gothic shape is a pointed arch) thread102to guide the balls12. The balls12climb over the ridge of the threads of the screw11and move from one thread102to the other neighboring thread102through the return path131of the circulating member13connected between two neighboring threads102. The two neighboring inner threads102of the nut10are connected with the return path131of the circulating member13to form an enclosed circulating path for enabling the balls to circulate endlessly. The structures shown inFIGS. 2 and 3are the same in design, therefore, they are designated with the same reference numbers. These conventional circulating structures have the disadvantages as follows:

When the balls12move into the return path131of the circulating member13, since the inner threads102of the nut10are of Gothic type, but the return path131of the circulating member13is a circular arc-shaped passage. Inevitably, at the conjunction between the return path131of the circulating member13and the inner threads102of the nut10appears a non-continuous level difference X and consequently the balls12are likely to be struck or jammed by the level difference X when moving in and out of the circulating member13, and consequently, the balls12can't move smoothly.

The aforementioned circulating member13generally refers to a cap piece, an engaging piece, or the like, used to connect the thread for enabling the balls to circulate. The circulating path131is circular arc-shaped and constant in cross section. Since the circulating path131can't flushly abut the inner threads102of the nut10, inevitably, there will exist a level difference X, and consequently, the balls will strike the level difference X.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a circulating member for a ball screw which won't have a severe conjunction level difference.

To obtain the abovementioned objective, the circulating member for a ball screw in accordance with the present invention is disposed on a nut with Gothic type threads and is formed with a return path to be connected to the threads of the nut for enabling balls to circulate. At either end of the return path of the circulating member is formed a connecting port for connecting the threads of the nut, and the connecting port is shaped in Gothic style.

By such arrangements, level difference at the conjunction between the circulating member and the nut disappears, thus preventing the balls from being struck and jammed, reducing the operation noise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be more clear from the following description when viewed together with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiment in accordance with the present invention.

Referring toFIGS. 4 and 5, an embodiment of the circulating member for ball screw in accordance with the present invention is a circulating cap20, but the present invention is not limited to the circulating cap, all circulating members installed in the nut of the ball screw are considered to be within the scope of the present invention.

The circulating cap20is radially disposed in a through hole41of a nut40, in the nut40are formed Gothic type threads42through which the nut40is threaded to a screw30. The circulating cap20is formed with a return path21for connecting the threads42of the nut40. The structural improvements of the present invention are described as follows:

At either end of the return path21of the circulating cap20are formed a connecting port211for connecting the threads42of the nut40, and the connecting ports211are shaped in Gothic style for cooperating with the Gothic type threads42of the nut40.

By such arrangements, level difference at the conjunction between the circulating member and the nut disappears, thus preventing the balls from being struck and jammed, and reducing the operation noise.

It is to be noted that, as shown inFIGS. 6 and 7, the return path21of the circulating member in accordance with the present invention is circular arc-shaped and inconstant in cross section (gradually changed in cross section), between the two connecting ports211is a circular arc-shaped path212that is gradually changed toward both sides to form the Gothic type connecting port211.

Therefore, the aforementioned connecting port is Gothic type and is constant in cross section, and the part221of the circulating path where the balls move upward (as shown inFIG. 7) is gradually changed into a circular arc-shaped path212with an inconstant cross section, and then is turned into a circular arc-shaped path212with a constant cross section when passing through the thread ridge. Such an embodiment enables the balls to roll more smoothly.

Finally,FIG. 8shows the data comparison between the drive torque of a ball screw with the conventional circular arc-shaped connecting port and the drive torque of a ball screw with the Gothic connecting port of the present invention. As far as the circular arc-shaped connecting port is concerned, the drive torque of the ball screw is unstable, and its average drive torque is relatively large as compared with the Gothic type connecting port. These test data show that the structural design of the circulating path of the present invention can prevent the balls from being struck and jammed.

To summarize, the present invention is disposed on a nut, the nut is formed with Gothic type threads, and the circulating member of the ball screw is formed with return path for enabling the balls to circulate. The connecting ports at both ends of the return path for connecting the threads of the nut are shaped in Gothic style, thus eliminating the level difference and consequently preventing the balls from being struck and jammed.