GB2502367A - A ball screw and a screw drive device - Google Patents

A ball screw and a screw drive device Download PDF

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Publication number
GB2502367A
GB2502367A GB1209336.5A GB201209336A GB2502367A GB 2502367 A GB2502367 A GB 2502367A GB 201209336 A GB201209336 A GB 201209336A GB 2502367 A GB2502367 A GB 2502367A
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GB
United Kingdom
Prior art keywords
nut
screw shaft
ball screw
balls
inner thread
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB1209336.5A
Other versions
GB201209336D0 (en
GB2502367B (en
Inventor
Graham Dodds
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Group Ltd
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Airbus Group Ltd
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Filing date
Publication date
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Priority to GB1209336.5A priority Critical patent/GB2502367B/en
Publication of GB201209336D0 publication Critical patent/GB201209336D0/en
Publication of GB2502367A publication Critical patent/GB2502367A/en
Application granted granted Critical
Publication of GB2502367B publication Critical patent/GB2502367B/en
Expired - Fee Related legal-status Critical Current
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
    • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
    • F16H25/20—Screw mechanisms
    • F16H25/22—Screw mechanisms with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
    • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
    • F16H25/20—Screw mechanisms
    • F16H25/24—Elements essential to such mechanisms, e.g. screws, nuts
    • F16H25/2472—Safety nuts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
    • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
    • F16H25/20—Screw mechanisms
    • F16H25/22—Screw mechanisms with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members
    • F16H25/2204—Screw mechanisms with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members with balls

Abstract

A ball screw is provided. The ball screw comprises: an elongated screw shaft 1 having an outer thread 1a, 1b on its surface; a first and at least one second nut 2, 2' each having an inner thread 2a, 2b each of which first and second ends, the first and second ends being separated In the axial direction of the screw shaft 1; and a number of balls 3 which are retained between the outer thread 1a, 1b of the screw shaft 1 and the inner thread 2a, 2b of the first and the second nut 2, 2', respectively. The first nut (2) is comprised of at least two separable parts (21, 22; 23, 24, 25) which are displaceable between a first, engaged position in which they provide for the transfer of load between the balls 3 and the outer thread 1a of the screw shaft 1 and the inner thread 2a of the first nut 2, and a second, disengaged position in which no load is transferred between the balls 3 and the outer thread 1a of the screw shaft 1 and the inner thread 2a of the first nut 2, and a similar arrangement with regard to the second nut 2. A screw drive device including a ball screw as detailed above is also disclosed.

Description

BALL SCREW AND BALL SCREW DRIVE DEVICE
FIELD OF THE INVENTION
The invention relates to a ball screw and a ball screw drive device.
A ball screw generally comprises an elongated screw shaft which has at least one outer thread on its surface, and a nut which has an inner thread with a first end io and a second end, the first and second ends being separated in the axial direction of the screw shaft, and a number of balls which are retained between the outer thread of the screw shaft and the inner thread of the first and second nut, respec-tively.
is BACKGROUNDOFTHE INVENTION
Figure 5 is a simplified 2-D section through a common ball screw. The ball screw C comprises a screw shaft 1, with a raised thread 1 a that supports a number of balls 3. The nut 2, with a thread 2a engages with the balls 3. So, in 3-D, the screw shaft -20 has a raised helix, and the nut 2 has a recessed helix which engages with the helix on the screw via the balls 3. The return path 5 for the balls 3 is shown in a mere schematically way.
There are two possible modes of operation of a ball screw, namely i) the nut is ro- tated and the screw shaft moves linearly inside the nut, H) the screw shaft is ro-tated and the nut moves linearly along the screw. The balls act to carry the load in a low friction manner and are able to circulate through a return path to achieve this.
Ball screws may have a "jamming" failure mode, where the whole mechanism will lock and fail to move because of a jam between the nut, the balls and the screw shaft. The most common jam which may occur in a ball screw is caused when a ball is stuck at the entrance to the return path. A way of releasing the jam, and therefore removing that driving load path, could allow the screw to be actuated by another nut, without the original nut preventing movement.
US 7 190 096 B2 discloses an electrical actuator which comprises two or more electrical motors to drive a threaded screw, and which has an armature that drives a threaded roller screw that is engaged to the threaded screw. Each armature of each motor is independently engageable and/or dis-engageable with the screw by way of threaded roller screws, the ends of which are tapered to enable them to be lifted away from or lowered into engagement with the threaded screw.
US 2009/0193915 Al describes a separable ball screw which comprises a threaded screw shaft, a transfer ring, a plurality of balls and a separable nut being sequentially engaged to the screw shaft, wherein the balls are distributed in holes in the annular surface of the transfer ring as a power transfer medium between the is transfer ring and the screw shaft, and a separable nut having a hollow centre, en- 1-closing around the transfer ring, wherein an inner annular surface of the separable nut has one or more grooves, the inner annular surface and the groove serving for C limiting positions of the balls. The positions of the balls are limited by the opera- tions of the inner annular surface or the groove of the separable nut so as to con- y-20 trol the initial positions for rotation operation as a ball screw operation or linear op-eration between the screw shaft and the transfer ring as a sliding track.
SUMMARY OF THE INVENTION
The object of the invention is to provide for an improved ball screw and an im-proved ball screw drive device.
According to one aspect of the invention the object is achieved by a ball screw comprising an elongated screw shaft having at least one outer thread on its sur-face, a first and at least one second nut each having an inner thread which each has a first end and a second end, the first and second ends being separated in the axial direction of the screw shaft, and a number of balls which are retained be- tween the outer thread of the screw shaft and the inner thread of the first and sec-ond nut, respectively, wherein the first nut is comprised of at least two separable parts which are displaceable between a first, engaged position in which they pro-vide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut, and a second, disengaged posi-tion in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut is released, and wherein the at least one second nut is comprised of at least two separable parts which are dis- placeable between a first, engaged position in which they provide for a load carry-ing contact between the balls and the outer thread of the screw shaft and the inner io thread of the second nut, and a second, disengaged position in which the load car- rying contact between the balls and the outer thread of the screw shaft and the in-ner thread of the second nut is released.
According to another aspect of the invention the object is achieved by a ball screw is drive device with a ball screw comprising an elongated screw shaft having at least one outer thread on its surface, a first and at least one second nut each having an inner thread which each has a first end and a second end, the first and second C ends being separated in the axial direction of the screw shaft, and a number of balls which are retained between the outer thread of the screw shaft and the inner -20 thread of the first and second nut, respectively, wherein the first nut is comprised of at least two separable parts which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut, and a second, disengaged position in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut is released, and wherein the at least one second nut is comprised of at least two separable parts which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the second nut, and a second, disengaged position in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the second nut is released, and comprising a motor which is rotationally coupled to one of the screw shaft and the nut of the ball screw for driving the same, and a driven element which is coupled to the other of the screw shaft and the nut of the ball screw to be translationally driven by the same.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the present invention shall be described with reference to the ac-companying drawings, in which Fig. 1 is a schematic longitudinal cross section through a ball screw according to io one embodiment of the invention; Fig. 2a) and b) is a schematic transversal cross section through a ball screw ac-cording to one embodiment of the invention; is Fig. 3a) and b) is a schematic transversal cross section through a ball screw ac-cording to another embodiment of the invention;
N-
C Fig. 4a) -c) is a schematic diagram of different ball screw drive devices according to embodiments of the invention; and r 20 Fig. 5 is a schematic longitudinal cross section through a ball screw according to
the prior art.
DETAILED DESCRIPTION OF EMBODIEMENTS
Before beginning a detailed description of the embodiments, a general description of embodiments will follow.
A ball screw as described here in general comprises an elongated screw shaft which has at least one outer thread on its surface, and a first and at least one sec-ond nut which each have an inner thread each having a first end and a second end, the first and second ends being separated in the axial direction of the screw shaft, and further a number of balls which are retained between the outer thread of the screw shaft and the inner thread of the first and the at least one second nut, respectively. The first nut, in general, is comprised of at least two separable parts which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut, and a second, disengaged position in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut is released. Also the at least one second nut is comprised of at least two separable parts which are displaceable between a first, engaged position in which they provide for a load carrying contact between the io balls and the outer thread of the screw shaft and the inner thread of the second nut, and a second, disengaged position in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the sec-ond nut is released.
is This arrangement allows a jam to be removed by splitting the nut, and retains the balls to prevent loose debris. The nut is still engaged with the screw, but cannot carry any load. Accordingly, the disconnectable or disengageable nut has two or C more separable parts that remain engaged with each other and the screw after disconnection, but are unable to carry a load. r 20
In general, the two nuts would use different threads on the screw shaft to ensure that damage to a thread by the failure of one nut would not affect the ability of the other nut to continue to operate.
According to one embodiment, the at least two separable parts of each of the first and the at least one second nut are housed in a common rigid frame in which they are radially displaceable between the first, engaged position and the second, dis-engaged position, and in which common rigid frame the at least two separable parts of each of the first and the at least one second nut are arranged fixedly against rotational displacement.
The first and the at least one second nut may be arranged to provide for parallel or alternate load paths of the ball screw, wherein, for parallel load paths, the at least two separable parts of the first and the at least one second nut are in the first, en-gaged position, and, for providing alternate load paths, the at least two separable parts of one of the first and the at least one second nut are in the first, engaged position, and the at least two separable parts of other one of the first and the at s least one second nut are in the second, disengaged position.
In general, two such disconnectable nuts would be used within a common rigid frame to drive the screw, so that if one nut jams, it can be disconnected, and the other nut continues to drive the load on the screw. This provides a ball screw with single failure tolerance against jamming.
According to one embodiment the nut is comprised of two separable parts which essentially are separated in a plane including the longitudinal axis of the screw shaft and which are displaceable in opposite directions between a first, engaged is position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the nut, and a second, dis-engaged position in which the load carrying contact between the balls and the o outer thread of the screw shaft and the inner thread of the nut is released. The two separable parts of the nut essentially each may have a cross section of a half cir-cle.
According to an alternative embodiment the nut is comprised of three or more separable parts which essentially are separated in a number of planes including the longitudinal axis of the screw shaft and which are displaceable in radial direc-tions with reference to including the longitudinal axis of the screw shaft between a first, engaged position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the nut, and a second, disengaged position in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the nut is re-leased. The three or more separable parts of the nut essentially each may have a cross section of a part of a circle.
In all embodiments a return path may be located within the nut radially outward of the inner thread and connecting the first and second ends of the inner thread for returning the balls between the first and second ends of the inner thread.
Further, a ball screw drive device which is described here comprises a ball screw with an elongated screw shaft having at least one outer thread on its surface, and a first and at least one second nut each having an inner thread which each has a first end and a second end, the first and second ends being separated in the axial direction of the screw shaft, and further a number of balls which are retained io between the outer thread of the screw shaft and the inner thread of the first and the at least one second nut, respectively. The first nut is comprised of at least two separable parts which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut, and a second, disengaged po-is sition in which the load carrying contact between the balls and the outer thread of the screw shaft and the inner thread of the first nut is released. Also the at least one second nut is comprised of at least two separable parts which are displace-C able between a first, engaged position in which they provide for a load carrying contact between the balls and the outer thread of the screw shaft and the inner -20 thread of the second nut, and a second, disengaged position in which the load car- rying contact between the balls and the outer thread of the screw shaft and the in- ner thread of the second nut is released. Further, the ball screw drive device com-prises at least one motor which is rotationally coupled to one of the screw shaft and the entity of the first and the at least one second nut of the ball screw for driv-ing the same, and a driven element which is coupled to the other of the screw shaft and the entity of the first and the at least one second nut of the ball screw to be translationally driven by the same.
According to one embodiment of the ball screw drive device the motor is rotation- ally coupled to the screw shaft for driving the same and the driven element is cou- pled to the first and the at least one second nut of the ball screw to be translation-ally driven by the same.
According to another embodiment of the ball screw drive device the at least one motor is rotationally coupled to the first and the at least one second nut of the ball screw for driving the same and the driven element is coupled to the screw shaft of the ball screw to be translationally driven by the same.
According to another embodiment of the ball screw drive device, the at least two separable parts of each of the first and the at least one second nut are housed in a common rigid frame in which they are radially displaceable between the first, en-gaged position and the second, disengaged position, and in which common rigid io frame the at least two separable parts of each of the first and the at least one sec-ond nut are arranged fixedly against rotational displacement, and wherein the at least one motor is rotationally coupled to the common rigid frame.
According to still another embodiment of the ball screw drive device the at least is two separable pads of each of the first and the at least one second nut are housed in a common rigid frame in which they are radially displaceable between the first, engaged position and the second, disengaged position, and in which common rigid C frame the at least two separable pads of each of the first and the at least one sec-ond nut are arranged fixedly against rotational displacement, and wherein the y-20 driven element is rotationally coupled to the common rigid frame.
According to a further embodiment of the ball screw drive device a first motor is rotationally coupled to the first nut of the ball screw and at least one second motor is rotationally coupled to the at least one second nut of the ball screw for driving the same, and the driven element is coupled to the screw shaft of the ball screw to be translationally driven by the same. The first motor and the at least one second motor may be mechanically or electrically coupled to each other.
The main advantage is a fault tolerant ball screw drive and ball screw drive which e.g. may be useful for deployment of aero surfaces, landing gear and other similar actuation mechanisms which need high reliability.
Now, referring to the figures, a detailed description of embodiments of the ball screw and the ball screw drive will follow.
Fig. 1, Fig. 2a) and b) and Fig. 3a) and b) show schematically a ball screw accord-ing to embodiments of the invention.
The ball screw comprises an elongated screw shaft 1 which has at least one outer thread 1 a, lb on its surface, and a first and a second nut 2, 2' which each has an inner thread 2a, 2b each having a first end and a second end, the first and second io ends being separated in the axial direction of the screw shaft 1. A number of balls 3 are retained between the outer thread 1 a, lb of the screw shaft 1 and the inner thread 2a, 2b of the first and the second nut 2, 2', respectively.
The first nut 2, generally, is comprised of at least two separable parts 21, 22; 23, is 24, 25 which are displaceable between a first, engaged position in which they pro-vide for a load carrying contact between the balls 3 and the outer thread la of the screw shaft 1 and the inner thread 2a of the first nut 2, and a second, disengaged C position in which the load carrying contact between the balls 3 and the outer thread la of the screw shaft 1 and the inner thread 2a of the first nut 2 is released. r 20
Also the second nut 2' is comprised of at least two separable parts 21, 22; 23, 24, which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls 3 and the outer thread lb of the screw shaft 1 and the inner thread 2b of the second nut 2', and a second, disen-gaged position in which the load carrying contact between the balls 3 and the outer thread lb of the screw shaft 1 and the inner thread 2b of the second nut 2' is released.
The at least two separable parts 21, 22; 23, 24, 25 of each of the first and the sec- ond nut 2, 2' are housed in a common rigid frame 4 in which they are radially dis- placeable between the first, engaged position and the second, disengaged posi-tion, and in which common rigid frame 4 the at least two separable parts 21, 22; 23, 24, 25 of each of the first and the second nut 2, 2' are arranged fixedly against rotational displacement.
The dotted line along the centre of the nut 2, 2' is the "break line", so that if the two halves, i.e. parts 21, 22 of the nut 2, 2' separate by a small amount along this line, the balls 3 can no longer transmit the load, and no balls 3 are lost from the nut 2, 2'. It may seem that the mechanism would still jam because the "broken" nut and the screw shaft would interfere when the ball screw rotates. However, in the pre-sent embodiment, the complete redundant ball screw contains two of these nuts 2, 2' in a rigid frame 4, such that a nut can successfully "break" after a jam, and the other nut can continue to carry the load via the frame, with the frame 4 preventing contact between the "broken" nut and the screw shaft 1, so a low friction sliding contact will be needed between each nut 2, 2' and the frame 4 in this direction perpendicular to the screw axis. c'115
The first and the second nut 2, 2' provide for parallel or alternate load paths of the ball screw, wherein, for parallel load paths, the at least two separable parts 21, 22; 0 23, 24, 25 of the first and the second nut 2, 2' are in the first, engaged position, and, for alternate load paths, the at least two separable parts 21, 22; 23, 24, 25 of y-20 one of the first and the second nut 2, 2' are in the first, engaged position, and the at least two separable parts 21, 22; 23, 24, 25 of other one of the first and the sec-ond nut 2, 2' are in the second, disengaged position.
In general, the two nuts 2, 2' would use different threads la, lb on the screw shaft 1 to ensure that damage to one of the threads 1 a, lb by the failure of one of the nuts 2, 2' would not affect the ability of the other nut to continue to operate. Fault tolerance is improved if the second of the nuts 2, 2' is on a separate helix or thread on the screw shaft (a so-called two start screw), so that damage to one thread does affect the operation of the other nut.
In the embodiment shown in Fig. 2a) and b) the nut 2, 2' is comprised of two sepa- rable parts 21, 22 which essentially are separated in a plane including the longitu- dinal axis of the screw shaft 1 and which are, as illustrated by the arrows, dis-placeable in opposite directions between a first, engaged position in which they provide for a load carrying contact between the balls 3 and the outer thread 1 a, lb of the screw shaft 1 and the inner thread 2a, 2b of the nut 2, 2', which is shown in Fig. 2a), and a second, disengaged position in which the load carrying contact be-tween the balls 3 and the outer thread 1 a, lb of the screw shaft 1 and the inner thread 2a, 2b of the nut 2, 2' is released, as shown in Fig. 2b). In the shown em-bodiment, the two separable parts 21, 22 of the nut 2, 2' essentially each have a cross section of a half circle.
io In the embodiment shown in Fig. 3a) and b) the nut 2, 2' is comprised of three (or more) separable parts 23, 24, 25 which essentially are separated in a number of planes including the longitudinal axis of the screw shaft 1. The separable parts 23, 24, 25 are displaceable, as shown by the arrows, in radial directions with refer-ence to the longitudinal axis of the screw shaft 1 between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread 1 a, lb of the screw shaft 1 and the inner thread 2a, 2b of the nut 2, 2', as shown in Fig. 3a) and a second, disengaged position in which the load carrying C contact between the balls 3 and the outer thread 18, lb of the screw shaft 1 and the inner thread 2a, 2b of the nut 2, 2' is released, as shown in Fig. 3b). The three y-20 or more separable parts 23, 24, 25 of the nut 2, 2' essentially each have a cross section of a part of a circle.
In the ball screw a return path, as schematically shown at 5 in Fig. 5 for the prior art ball screw, may be located within the nut 2, 2' radially outward of the inner thread 2a, 2b and connecting the first and second ends of the inner thread 2a, 2b for returning the balls between the first and second ends of the inner thread 2a, 2b in a closed circle.
Fig. 4a) -c) shows schematic diagrams of different ball screw drive devices ac-cording to embodiments of the invention.
The ball screw drive device comprises a ball screw 10 as described above with reference to Figs. 1 to 3. The ball screw drive device comprises further at least one motor 11, 12, 13 which is rotationally coupled to one of the screw shaft 1 and the entity of the first and the at least one second nut 2, 2' of the ball screw for driv-ing the same, and a driven element 14 which is coupled to the other of the screw shaft 1 and the entity of the first and the at least one second nut 2, 2' of the ball screw 10 to be translationally driven by the same.
In the embodiment shown in Fig. 4a) the motor 11 is rotationally coupled to the screw shaft 1 for driving the same, and the driven element 14 is coupled to the first and the second nut 2, 2' of the ball screw 10 to be translationally driven by the same. The at least two separable parts 21, 22; 23, 24, 25 of each of the first and the second nut 2, 2' are housed in a common rigid frame 4 in which they are ra- dially displaceable between the first, engaged position and the second, disen-gaged position, and in which common rigid frame 4 the at least two separable parts 21, 22; 23, 24, 25 of each of the first and the second nut 2, 2' are arranged fixedly against rotational displacement. The driven element 14 is rotationally cou-pled to the first and the second nut 2, 2' by the common rigid frame 4.
N-
C In the embodiment shown in Fig. 4b) the motor 11 is rotationally coupled to the first and the second nut 2, 2' of the ball screw 10 for driving the same and the y-20 driven element 14 is coupled to the screw shaft 1 of the ball screw 10 to be trans-lationally driven by the same. As described above with reference to Figs. 1-3, the at least two separable parts 21, 22; 23, 24, 25 of each of the first and the second nut 2, 2' are housed in a common rigid frame 4 in which they are radially displace-able between the first, engaged position and the second, disengaged position, and in which common rigid frame 4 the at least two separable parts 21, 22; 23, 24, 25 of each of the first and the second nut 2, 2' are arranged fixedly against rotational displacement. The motor 11 is rotationally coupled to the first and the second nut 2, 2' by the common rigid frame 4.
In the embodiment shown in Fig. 4c) a first motor 12 is rotationally coupled to the first nut 2 of the ball screw 10 and at least one second motor is rotationally cou-pled to the at least one second nut 2' of the ball screw 10 for driving the same, and the driven element 14 is coupled to the screw shaft 1 of the ball screw 10 to be translationally driven by the same. In the shown embodiment, the first motor 12 and the second motor 13 are mechanically or electrically coupled -at 15 -to each other.
N-aD r

Claims (15)

  1. CLAIMS1. A ball screw comprising -an elongated screw shaft (1) having at least one outer thread (1 a, 1 b) on its sur-face, -a first and at least one second nut (2, 2') each having an inner thread (2a, 2b) io which each has a first end and a second end, the first and second ends being separated in the axial direction of the screw shaft (1), and -a number of balls (3) which are retained between the outer thread (1 a, 1 b) of the screw shaft (1) and the inner thread (2a, 2b) of the first and the at least one sec-is ond nut (2, 2'), respectively, N-wherein -the first nut (2) is comprised of at least two separable parts (21, 22; 23, 24, 25) -20 which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread (1 a) of the screw shaft (1) and the inner thread (2a) of the first nut (2), and a second, disen-gaged position in which the load carrying contact between the balls (3) and the outer thread (1 a) of the screw shaft (1) and the inner thread (2a) of the first nut (2) is released, and -the at least one second nut (2') is comprised of at least two separable parts (21, 22; 23, 24, 25) which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread (1 b) of the screw shaft (1) and the inner thread (2b) of the second nut (2'), and a second, disengaged position in which the load carrying contact between the balls (3) and the outer thread (1 b) of the screw shaft (1) and the inner thread (2b) of the second nut (2') is released.
  2. 2. The ball screw of claim 1, wherein the at least two separable parts (21, 22; 23, 24, 25) of each of the first and the at least one second nut (2, 2') are housed in a common rigid frame (4) in which they are radially displaceable between the first, engaged position and the second, disengaged position, and in which common rigid frame (4) the at least two separable parts (21, 22; 23, 24, 25) of each of the first and the at least one second nut (2, 2') are arranged fixedly against rotational dis-placement.
  3. 3. The ball screw of claim 1 or 2, wherein the first and the at least one second nut (2, 2') provide for parallel or alternate load paths of the ball screw, wherein, for parallel load paths, the at least two separable parts (21, 22; 23, 24, 25) of the first and the at least one second nut (2, 2') are in the first, engaged position, and, for alternate load paths, the at least two separable parts (21, 22; 23, 24, 25) of one of is the first and the at least one second nut (2, 2') are in the first, engaged position, and the at least two separable parts (21, 22; 23, 24, 25) of other one of the first and the at least one second nut (2, 2') are in the second, disengaged position.
  4. 4. The ball screw of claim 1, 2 or 3, wherein the nut(2, 2') is comprised of two y-20 separable parts (21, 22) which essentially are separated in a plane including the longitudinal axis of the screw shaft (1) and which are displaceable in opposite di-rections between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread (1 a, 1 b) of the screw shaft (1) and the inner thread (2a, 2b) of the nut (2, 2'), and a second, disengaged position in which the load carrying contact between the balls (3) and the outer thread (la, 1 b) of the screw shaft (1) and the inner thread (2a, 2b) of the nut (2, 2') is re-leased.
  5. 5. The ball screw of claim 4, wherein the two separable parts (21, 22) of the nut (2, 2') essentially each have a cross section of a half circle.
  6. 6. The ball screw of claim 1, 2 or 3, wherein the nut (2, 2') is comprised of three or more separable parts (23, 24, 25) which essentially are separated in a number of planes including the longitudinal axis of the screw shaft (1) and which are dis-placeable in radial directions with reference to including the longitudinal axis of the screw shaft (1) between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread (1 a, 1 b) of the screw shaft (1) and the inner thread (2a, 2b) of the nut (2, 2'), and a second, disengaged position in which the load carrying contact between the balls (3) and the outer thread (1 a, 1 b) of the screw shaft (1) and the inner thread (2a, 2b) of the nut (2, 2') is released.
  7. 7. The ball screw of claim 6, wherein the three or more separable parts (21, 22) of the nut (2, 2') essentially each have a cross section of a part of a circle.
  8. 8. The ball screw of one of claims 1 through 7, wherein a return path (5) is lo- cated within the nut (2, 2') radially outward of the inner thread (2a, 2b) and con-is necting the first and second ends of the inner thread (2a, 2b) for returning the balls between the first and second ends of the inner thread (2a, 2b).N-0
  9. 9. A ball screw drive device comprising a ball screw (10) with y-20 -an elongated screw shaft (1) having at least one outer thread (1 a, 1 b) on its sur-face, -a first and at least one second nut (2, 2') each having an inner thread (2a, 2b) which each has a first end and a second end, the first and second ends being separated in the axial direction of the screw shaft (1), and -a number of balls (3) which are retained between the outer thread (1 a, 1 b) of the screw shaft (1) and the inner thread (2a, 2b) of the first and the at least one sec-ond nut (2, 2'), respectively, wherein -the first nut (2) is comprised of at least two separable parts (21, 22; 23, 24, 25) which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread (1 a) of the screw shaft (1) and the inner thread (2a) of the first nut (2), and a second, disen-gaged position in which the load carrying contact between the balls (3) and the outer thread (1 a) of the screw shaft (1) and the inner thread (2a) of the first nut (2) is released, and -the at least one second nut (2') is comprised of at least two separable parts (21, 22; 23, 24, 25) which are displaceable between a first, engaged position in which they provide for a load carrying contact between the balls (3) and the outer thread (1 b) of the screw shaft (1) and the inner thread (2b) of the second nut (2'), and a second, disengaged position in which the load carrying contact between the balls (3) and the outer thread (1 b) of the screw shaft (1) and the inner thread (2b) of the is second nut (2') is released, and comprising at least one motor (11, 12, 13) which is rotationally coupled to one C of the screw shaft (1) and the entity of the first and the at least one second nut (2, 2') of the ball screw for driving the same, and a driven element (14) which is cou- -20 pled to the other of the screw shaft (1) and the entity of the first and the at least one second nut (2, 2') of the ball screw (10) to be translationally driven by the same.
  10. 10. The ball screw drive device of claim 9, wherein the motor (11) is rotationally coupled to the screw shaft (1) ) for driving the same and the driven element (14) is coupled to the first and the at least one second nut (2, 2') of the ball screw (10)to be translationally driven by the same.
  11. 11. The ball screw drive device of claim 9, wherein the motor (11) is rotationally coupled to the first and the at least one second nut (2, 2') of the ball screw (10) for driving the same and the driven element (14) is coupled to the screw shaft (1) of the ball screw (10)to be translationally driven by the same.
  12. 12. The ball screw drive device of claim 11, wherein the at least two separable parts (21, 22; 23, 24, 25) of each of the first and the at least one second nut (2, 2') are housed in a common rigid frame (4) in which they are radially displaceable be-tween the first, engaged position and the second, disengaged position, and in which common rigid frame (4) the at least two separable parts (21, 22; 23, 24, 25) of each of the first and the at least one second nut (2, 2') are arranged fixedly against rotational displacement, and wherein the motor (11) is rotationally coupled to the common rigid frame (4).
  13. 13. The ball screw drive device of claim 10, wherein the at least two separable parts (21, 22; 23, 24, 25) of each of the first and the at least one second nut (2, 2') are housed in a common rigid frame (4) in which they are radially displaceable be-tween the first, engaged position and the second, disengaged position, and in which common rigid frame (4) the at least two separable parts (21, 22; 23, 24, 25) is of each of the first and the at least one second nut (2, 2') are arranged fixedly against rotational displacement, and wherein the driven element (14) is rotationally coupled to the common rigid frame (4).
  14. 14. The ball screw drive device of claim 11, wherein a first motor (12) is rotation-y-20 ally coupled to the first nut (2) of the ball screw (10) and at least one second motor (13) is rotationally coupled to the at least one second nut (2') of the ball screw (10) for driving the same, and the driven element (14) is coupled to the screw shaft (1) of the ball screw (10) to be translationally driven by the same.
  15. 15. The ball screw drive device of claim 14, wherein the first motor (12) and the at least one second motor (13) are mechanically or electrically coupled (15) to each other.
GB1209336.5A 2012-05-24 2012-05-24 Ball screw and ball screw drive device Expired - Fee Related GB2502367B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
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GB2502367A true GB2502367A (en) 2013-11-27
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3847033A (en) * 1972-07-13 1974-11-12 Csepeli Szerszamgepgyar Method and construction for increasing the service life of rolling screw mechanism with double-nut prestress
US20100122597A1 (en) * 2008-11-17 2010-05-20 Jhe-Kun Liou Ball screw
US20100242651A1 (en) * 2009-03-31 2010-09-30 Thk Co., Ltd. Rolling-element screw device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3847033A (en) * 1972-07-13 1974-11-12 Csepeli Szerszamgepgyar Method and construction for increasing the service life of rolling screw mechanism with double-nut prestress
US20100122597A1 (en) * 2008-11-17 2010-05-20 Jhe-Kun Liou Ball screw
US20100242651A1 (en) * 2009-03-31 2010-09-30 Thk Co., Ltd. Rolling-element screw device

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GB2502367B (en) 2018-08-01

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