Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
2001-10-17
2004-03-02
Fenstermacher, David (Department: 3683)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
active
06698301
ABSTRACT:
BACKGROUND OF INVENTION
The invention relates to a screw drive with rolling elements and, more particularly, to a ball screw drive including a screw spindle with a spindle axis and a double nut running on the screw spindle with two separately formed single nuts which are substantially rigidly joined in the direction of the axis of the spindle. In order to set a desired play or bias relative to the screw spindle, the two single nuts can be turned continuously about the axis of the spindle relative to each other and fixed in any relative rotary position corresponding to the desired play or bias.
The Prior Art
Screw drives of the foregoing type are used, for example, for rapid and accurate positioning of tool and work holders and for moving them at defined speeds. Rotary motion of the screw spindle is converted to linear motion of the guided double nut. In order to satisfy the highest possible demands for accuracy in reversing the direction of motion of the double nut, the double nut has to be arranged on the spindle as far as possible without play. For this purpose, when the two nuts are being mounted on the spindle they are turned towards each other far enough to make their facing end surfaces bear against each other. Further turning of the nuts causes the rolling elements to be applied to opposing side surfaces of the raceways of the nuts, which ultimately results in the desired biasing of the two nuts relative to the screw spindle and guidance of the double nut on the spindle substantially without play.
A screw drive of the above type, i.e., a screw drive in which the play or bias of the two single nuts relative to the screw spindle can be infinitely (steplessly) adjusted, is known, for example, from DE-OS 21 35 812. A screw bolt is contained in an intermediate element of the known screw drive which is non-rotatably joined to one of the single nuts, the screw bolt being in screw engagement with a part mounted non-rotatably on the other single nut. The worm drive thus formed allows infinitely variable turning of the two single nuts relative to each other about the axis of the spindle. One disadvantage of this construction is that a relatively large amount of space has to be provided for the worm drive, particularly in a radial direction. Another disadvantage is that, in spite of the self-locking inherent in worm drives, the desired bias set may undesirably re-adjust itself, for example, due to vibrations, causing the screw bolt of the worm drive to turn.
A similarly constructed screw drive is known from DE-OS 23 49 958.
Versions of the generic screw drive are known from DE-OS 23 49 958 and from DE 30 38 774 C2 and the corresponding EP 0 049 903 B1 in which an intermediate element is in frictional engagement with both single nuts in order to prevent relative rotation between them. The frictional forces must therefore be overcome during the assembly, i.e., the relative turning of the two single nuts to set the desired bias or play. This makes exact setting of the play or bias to the desired value considerably more difficult.
Screw drives are further known from DE 24 53 635 C3, DE-OS 25 33 996 and DE 29 40 762 C2 in which the two single nuts can only be turned relative to each other and fixed in predetermined angular steps rather than infinitely variably.
In the screw drive known from German Utility Model 77 08 184, infinitely variable turning of the two single nuts is only possible within a very narrow angular range. In order to set a desired bias or play relative to the screw spindle, it is therefore also necessary to provide spacers between the two nuts, and their thickness must be determined by the desired bias or play. Hence, even with experienced operators it is usually necessary to change the spacers several times during assembly, until the spacer with the right thickness for the desired bias or play has been found. Assembly of the screw drive known from DE-GM 77 08 184 is therefore laborious and time consuming.
In DE 39 00 693 C2, a cavity formed by annular grooves and indentations between the two touching end faces of the single nuts is filled with casting compound to form the intermediate element. The position of relative rotation of the two single nuts corresponding to the desired bias or play must therefore be maintained until the casting compound has completely hardened.
A screw drive where the two single nuts are joined by an intermediate element which yields resiliently in the direction of the axis of the spindle is known from DE 42 08 126 A1. An axially resilient arrangement of this type has the drawback that, when a force exceeding the spring force is exerted on one of the single nuts, the two single nuts may move towards each other, thereby losing the desired bias.
In DE 32 07 566 A1, after the desired bias of the two single nuts has been set, a hole to receive a radial locking bolt is formed in their common contact region, to ensure that the bias obtained is maintained.
SUMMARY OF THE INVENTION
An object of the invention, therefore, is to provide a rolling-body screw drive of the above-mentioned type which, with a straightforward construction and straightforward assembly sequence, readily enables the play or bias of the single nuts relative to the screw spindle to be adjusted and set in a stepless and precise manner to a desired value.
According to the invention, the foregoing object is attained by the provision of a screw drive of the above type, in which either a first of the two single nuts or an intermediate element joined thereto and arranged between the two single nuts has at least one peripheral section pressed into an associated aperture in the second single nut. In accordance with the invention, the non-rotational joining of the first single nut or the intermediate element to the second single nut is the last operation in assembling the screw drive according to the invention. The possibly necessary non-rotational joining of the intermediate element to the first single nut or the formation of the intermediate element on the first single nut may take place in a preceding operation or simultaneously with the non-rotational joining of the intermediate element to the second single nut.
The limit between direct joining of the two single nuts and joining an intermediate element integral with one of them to the other single nut is a fluid transition in practice. It is not always possible to decide which of the two extreme cases applies. Basically any part of the single nut used for joining the other single nut may be considered as an intermediate element, even when that intermediate element is not a separately formed part of the single nut in question.
In order to join the two single nuts or the intermediate element non-rotatably to the second single nut, the latter is first brought into contact with the first single nut or the intermediate element by turning on the screw spindle. The desired play or bias of the two single nuts relative to the screw spindle is then set by further turning of the nuts. The only frictional forces arising between the intermediate element and the nut emanate from the actual bias. When the play or bias has reached the desired value, a peripheral section of the first single nut or of the intermediate element is then pressed into an associated aperture in the second single nut. A secure, non-rotational joint is thus obtained, allowing immediate further processing of the screw drive. Subsequent accidental turning of the two single nuts relative to each other, with resultant re-adjustment of the desired play or bias, is reliably avoided.
In accordance with the invention, the peripheral section may be pressed into the aperture in the second single nut in an axial or/and radial direction. It is then advantageous for the peripheral section which is pressed in to bear on the wall surfaces bounding the aperture only in a peripheral direction. In this way, one can reliably avoid forces acting in either an axial or a radial direction that might influence the bias or play of the two single nuts relative to the screw spindle.
In order to reduce
Blattner Peter
Blaurock Werner
Greubel Roland
Huppman Erich
Och Hugo
Baker & Botts L.L.P.
Fenstermacher David
Rexroth Star GmbH
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