Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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REVERSIBLE ROTARY TO LINE~R MOTION CONVERTII~G D~VICE : -
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l~a( kground of thc Invc?nlioll
I\/lany pI~ior ar t devices in the general class c f thC? sub,ject
invention are l;nown uncler ~arious descriptiorls such as roller nut
assemblies, ball-screw c]evices, and Jack-screw devices. In those
prior art devices, various nuts and screw memi)ers are combinc?d
with rollers or ball bearings wilich in combination permit such
devices to be used as reversible rotary to linear motion converting
devices generally with a minimum of frictional losses in the operation
of the devices. One common problem with such prior art devices is
that they are not inherently capable of absorbing or converting relatively
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- large forces in action or reaction. The problem is a result of point
loading through balls or high loading on necessarily small roller sha~ts '
and bearings.
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Summary oi the Invention
In contradistinction to lknown prior art devices, the subject
invention inherently provides a device capable of absorbing and trans- ~ -
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~- mitting relatively large forces in action and reaction. That unique
- advantage of the subject invention over the known devices of the prior
art results from a construction where no inherently weak part is
required to absorb large forces in action or reaction.
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In one embodiment of the invention the foregoing is accomplished
by a construction which comprises: a screw member having multiple-
-, lead threads, a plurality of roller members equal in number to the ~`
' 10 number of thread starts on the screw member, and an annular nut
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member. The roller members have a plurality of annular teeth of sub- `
stantially equal pitch to the teeth of the screw member and a substantially ~-
matching configuration to the shape of the teeth of the screw member~
The roller members are mounted about the screw member in rolling
contact with the threads of the screw member. The annular nut member
has a plurality of internal annular grooves which are of substantially :
equal pitch and complementary shape to the annular teeth of the roller ;
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members. Essential to the invention is that the number of annular
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grooves in the nut member be substantially equal to the number of -
20 annular teeth on each of the roller members. The nut member is
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mounted about the roller members with the teeth of the roller members
; in rolling contact with the grooves of the nut member. In that arrange-
ment, the total action ancl reaction forces on each of the roller members
will be substantially equal and opposite when, for example, the nut
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member is constrained against rotation but permitted to axially translate,
and the screw ~nember is rotated.
Those skilled in the art will appreciate from the detailed descrip-
tion hereinafter following that in operation the roller members will orbit
and will equalize in their orbits under load. Further, it will be appre- ;
ciated that the locating collars as shown and described relative to certain ;~
- embodiments of the invention carry substantially no load, and function
merel~r as locating means, and as such locating means are primarily
important in the initial assembly of the device. Because the total action
and reactlon forces on each roller member are substantially equal and
Z opposite to each other, the locating collars may be omitted or removed `
in the use and operation of the device. Of course, those skilled in the ~ ~ -
' art will appreciate that under conditions of manufacture where the manu-
facturing tolerances are wide, it is advisable to leave the locating collars
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in the device to maintain the roller members properly circumferentially ;
spaced-apart about the screw member and within the nut member, In
` one embodiment of the invention, the locating collars are secured to-
gether in the form of a cage, and with the use of such a cage in the device
rather wide manufacturing tolerances can be accommodated in the device
and yet with the device still being in substantial balance in regard to the
total action and reaction forces applied to each of the roller members.
The primary object of the present invention is to provide a re-
versible rotary to linear motion converting device of a simple construc-
tion that will convert rotary rnotion to linear motion, or the opposite,
through ~ubstantially pure rolling contact between the parts of the device
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thus producing a device of minimum ~rictional losses in operation
and which is inherently capable of transmitting substantial power
therethrou~h and of absorbiny relatlvely larye loads in operation.
In accordance with the principal object, the invention
contemplates a motion converting device which comprises a screw
member having multiple-lead threads, a plurality of roller mem-
bers equal in number to the number oE thread starts on the screw
member, with each of the roller members haviny a plurality of
annular teeth of substantially equal axial pitch to the threads
of the screw member and a substa~tially matching configuration
to the shape of the threads of the screw member. The roller mem-
bers are mounted in substantially equally spaced-apart positions
about the screw member with the armular teeth thereof in rolling ~--
contact with the threads of the screw member. An annular nut mem-
ber is provided having a plurality of internal annular grooves ofsubstantially equal pitch and complementary shape to the annular
teeth of the roller members, with the number of annular grooves
of the nut member being substantially equal to the number of ;~
annular teeth on each of the roller members. The nut member is
mounted about the roller members with the teeth of the roller-
members in rolling contact with the grooves of the nut member. -
The ends of the roller members are devoid of any mechanical
connection with the nut member which will prevent the roller
members from moving under load circumferentia].ly about the screw
member and within the nut member without rotating to thereby per-
mit the roller members to float relative to each other while
remaining substantially equally-spaced circumferentially about
the screw r"ember and within tne nut member, whereby any rotational
force applied to the screw member with the nut member constrained
against rotation results in an aY~ial translation of the nut member
relative to the screw member with the total action and reaction
forces on each of the roller mcmbers being substantially equal.
Other objects and features of the invention will be
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apparent upon a perusal of the hereinafter following specifi-
cation read in conjunction with the drawings.
: In The Drawin~s
FIG. 1 is a side elevational view partially in cross section
of one embodiment of a device constructed according to the invention;
FIG, 2 is a complete end elevational vicw of the structure
shown in FIG, l;
FIG. 3iS a view similar to FIG, 2, but showing one end of the
~` device having a locating collar and retaining cap for the collar;
-~ 10 FIG. 4 shows an isometric view of the locating collars of FIG,
3 constructed as a rigid cage;
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FIG, 5is an end elevational view of the device as shown in :
FIG, 3, but with the locating collar cage of FIG. 4 assembled therein;
FIG, 6is a diagrammatic view showing the developed lead for ~:
the threads of the screw member of a device of the invention having
three roller members;
FIG, 7iS an enlarged fragmentary side elevational view of another
embodiment of the invention including dirt seals which prevent the interior
of the dev.ice from being contaminated by dirt;
FIG, û is a side elevational view of another embodiment of the~
invention having six roller members and with the device shown in sub-
stantially cross section; and
FIG, 9is an end elevational view of the device shown in FIG, 8,
, 25 but shown substantially circum~erentially complete.
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Detailed I~escription oî the Yreferrecl Embocliments
In a preferred embodiment of the invention, three subassemblies
in assembled form consti-tute a device for converting rotary power into
linear power with minimum friction losses. The three subassemblies
or main operating parts of the device are a screw, an outer body or nut
member, and a æet of roller members.
` The screw may be of a conventional thread form with multiple ~
thread starts. In the preferred forms a screw with three or more thread `; ~ ?
starts is used. Further, in the preferred forms a screw is used which ~ -
has a profile of a 90 degree included angle between the sides of each
lû tooth on the thread profile. -
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The outer body or nut member is provided with a plurality of -~
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annular grooves internally thereof. The annular grooves are comple- -
mentary in shape to the teeth of the screw member. The annular grooves
of the nut member further have substantially the same axial pitch as that
of the threads of the screw member. ,;
The set of roller members are equal in number to the number ~ ~
of thread starts on the screw member. Each of the roller members ~ ~;
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have a plurality of armular teeth which are of substantially equal pitch
and complementary shape to the annular grooves of the nut member. ;~
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The screw memberJ the nut member, and the roller members ~ -
are relatively si~ed so that the roller members may be assembled within
~, the nut member with the annular teeth of the roller members in rolling ~
contact with the annular grooves of the nut member and with the screw ~ ;
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member threacled between the roller member s with the he~lical threads
of the screw member in rolling contact with the annular teeth of the
roller members, such as shown in the drawlngs.
For ~ set of three roller members, a screw member of three
thread starts is used and FIG, 6 in diagrammatic form shows the devel-
oped lead for the three thread starts of the screw member ~or the three ~;
roller members. ~
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Althou~h different arrangements may be provided for assembling
the device as described, a convenient asserably method involves forrning
each of the roller members with short stub shafts at each end thereof,
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such as shown in the drawings, and further providing two locating r,~
,~ collars, The locating collars are merely flat ringS having an internal
's~ diameter greater than the crest diameter of the scFew member and con- ;
veniently an outer diameter less than the crest diameter of the annular
teeth defined by the adjacent annular grooves in the nut member. Each
of the locatlng collars is further formed -with holes of a diameter sub~
stantially equal to the diameter of the stub shaft on the ends of the roller
members. The small holes in the locating collars are equally spaced
circumferentially thereabout and equal in r~umber to the number of
roller members. l~ssernbly of the device is then a simple matter of -
inserting the roller mernbers within the nut member with the annular
teeth of the roller members in rolling contact with the annular grooves
of the nut me~nber, circumferentially spacing the roller members and
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applying the locatlng collars on each end of the roller members with the
stub shafts extending into the small holes in the locating collars, The
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scre~v member may then be thrcaclecl ;nto the central opening defined
by the roller rnembers. ~t`ter assemhly the locating collars can be
remove~, if desired, since those collars carry sub.stantially no load
in the operation of the device. ~However, where the parts are made
with relativeLy wkle manufacturing tolerances, it may be preferred to
leave the locating collars mounted on the roller mernbers to ensure
that each of the roller members will begin its orbital motion at the
proper position in the operation of the device. Once the roller members
are under load they are self balancing.
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It should be emphasized that the number of annular grooves in
the nut member must be substantially equal to the number of annular
teeth on the roller members. That key feature of the invention results
in a device wherein all of the forces in the operation of the device are in~
ternally balanced in a stable arrangement. If the nut member is con-
strained against rotation but allowed to axially translate, and if the `
screw member is then rotated, the roller members will transmit forces
with almost pure rolling action between the threads of the screw and the
annular grooves of the nut member. There is substantially the same - ~ `
amount of rolling contact resisting both the action and reaction forces,
and those forces are equal and substantially colinear, resulting in a low
friction, stable and strong rotary to linear motion converting device.
From the foregoing, it may be seen that the locating collars are not anti-
friction bearings or load carrying members. Those noted features of the
subject invention point out the significant difference between devices of the -
subject invention and many of the prior art devices having similar roller
members. The prior anti-frlction bearings, which must necessarily be ;
made quite sma]l and are considerably more expensive and weaker than
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the ar~arlgerrle~nt ot the subiect invention, can not carrY the reation
loads to the clegrec that the r()ller n~emt~er an(l screw teeth can be
loadedO
In devices of the present invention, furt}ler economies in manu-
5 facture and a substantially stronger device can l~e achieved hy making
the teeth of the screw member and the roller me:mbers, and the grooves
of the nut member to have a tooth profile of a 90 degree included angleO
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From the drawings and from the foregoing description, it may be
seen that as the screw turns and the nut member is rotatively constrained
: 10 but permitted linear translation, the rollers are caused to roll and trans-
. late in a planetary motion. Thus, the effective lead of the device, which
is the ratio of linear output to angular input9 is less that the lead of the -~. screw. The following formula may be used to calc~late the effective lead ;
for any particularly sized device of the invention~
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( D+ S ) ' '
Where: ~
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L' - the effective lead of the device,
L ~ the actual lead of the screw member,
. D ~ the rolling pitch diameter of the nut member or the mean .
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diameter of the teeth engagement between the roller
members and the nut member, and .~ -
S ~ the pitch diameter of the screw member or the mean
diameter of tooth and thread engagement between the
roller mernbers and the screw member.
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FIGS, 1 ~nd 2 show one embodiment ot the inven-tion in assemble~
form. In that embodiment a screw nlembcr lO having three thread starts
is provicled. ~Further, the teeth of the threads have a profile in an axial
plane of an included angle of substantially 90 degree.s. The roller
members 11 are three in nurnber. Each of the roller members is forrned
with a plurality of annular teeth extending substantially the ~ull length of
each roller member 11, The annular teeth of the roller members 11 are
- of substantially equal axial pitch to the teeth of the screw member 10 and ;
the configuration of the teeth of the roller members 11 substantially
match the shape of the teeth of the screw member 10. The nut member
12 is merely a cylindrical member with a plurality of annular grooves
formed therein and arranged throughout substantially the full length of
the nut member 12. The annular grooves in the nut member 12 are of ;
substantially equal pitch to that of the roller members 11 and have a ~ -
shape complementary to the shape of the annular teeth of the roller
`- members 11. The nut member 12 has substantially as many annular '
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grooves as there are annular teeth on each of the roller members 11. ` ~ ~
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While each of the roller members 11 as shown is provided with
, a short stub shaft 13 at each end thereof, those stub shafts are not
- 20 involved in the operation of the device but are conveniently provided for
' use in locating the roller members 11 in the positions shown in FIG. 2
~ ~' in the initial assembly of the device, Neither the screw member 10
', nor the nut member 12 are shown with any members for either rotating
those parts or constraining one of the parts against rotation while
permitting axial translation thereof. Those skilled in the art will
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appreciate that the device as clescril)ed can hc used in many clifferent
machines where it is desired to convert rotary motion to a linear
mo-tion. 'rhe clevice is, of co-lrse, reversible and can also be used in
applications where, for example, a linear force is applied to the nut
member 12, constrained against rotation, to cause the screw member
10 to rotate.
FIGS. 3 and 5 show essentially the same basic device as des-
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cribed relative to FIGS. 1 and 2, except that FIGS. 3 - 5 show locating
collar constructions that are intended to remain as part of the device
lo during its use and operation. As shown in FIG. 3, a screw member ~ ~;
10 having three thread starts is provided with three roller members ~ '
11 assembled thereabout in rolling contact therewith. Although only
one end of the nut member 14 is shown in FIG. 3, it should be under-
stood that both ends of that nut member are externally threaded at 15,
as shown in FIG. 3, to receive a pair of end caps s~lch as end cap 16
shown in FIG, 3, The end caps 16 are internally threaded for applica-
tion over the ends of the nut member 14. The cap members 16 are pro-
vided with a central opening capable of receiving the screw member 10
therethrough. As shown in FIG. 3, a locating collar 17 is mounted
radially within the nut rnember 14 and circumferentially about the screw
member 10. Three small openings 18 in the locating collar 17 encircle
the stub shafts 13 of the roller member 11. The inner face of the cap
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member 16 holds the locating collar 17 within the device.
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In some contemplated uses and arrangements of devices of the
invention where manufacturing tolerances may be relatively considerably
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wide so that the fit het~veen tlle scre~v mcmber 10, the roller members
11, ancl the n~lt memher 14, is so loose that in use ancl opercltion the ~:
roller .members 11 may skew from their normal axes paral.lel to the
longitudinal axis of the screw member 10, a locating collar eage 20,
such as shown in FIG. 4, may be advantageously used to maintain the
proper axial alignment of the roller members 11. The locating collar
cage 20 as shown in FIG. 4 is shown in Ei'IG. 5 :mounted in a device such . .
as that of FIG. 3 in substitution of the two support locating collars 17, ;~
The locating collar cage 20 is a unitary assembly of a pair of locating
. 10 collars 21 and three struts or support members 22, The support me.mbers ~ :
22 in addition to spacing the locating collars 21 as shown, essentially pre- :
... ', vent relative rotation between the locating collars 21 about the longitudinal . ~.,
axis through the cage 20, For convenient assembly of a device of the .~?' - .
invention with the cage 20, three slots 23 are provided in each locating .. ;~
/ . 15 collar 21. The slots 23 which extend radially inwardly from the outer .~-:
, ,., periphery of the locating collars 21 have a radial depth such that when
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three roller members 11 are placed within the locating collars 21 with the ;
~., stub shafts 13 at the bottom of the slots 23, the cage 20 together with the ;
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three roller members 11 may be axially inserted into the nut member 14
with no interference between the teeth of the nut member 14 and the teeth ~;
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~ of the roller members 11. Upon that axial insertion, the roller members .
'!.~'.', 11 may be moved radially outwa:rdly to the positions shown in FIG, 5 and
~: the screw member 10 may then be threaded into the device,
FIG, 7 shows a unique dirt seal arrangment that can advantageously ~:
,'~ 25 be used with and as part of devices of the subject invention. A screw
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member 10, a roller rnernber 11, and ~l nut meml~er 15 are shnwn in
FIG. 7 in a substantially enlarged ~ragmentary vi~w. Each end of
the nut mem~7er 15 is provkled with an annular cclvity 26 to receiv~ a
dirt seal such as dirt seal 27 therein. The dirt seal 27 is formed as
a ring having two substantially flat sides 27a and 27b. The radially
outward side 27c of the seal 27 is preferably cylindrical in shape and
of a smaller diameter than the diameter of the adjacent wall of the
cavity 26 in the nut member 15, The radially inner side 27d of the
seal 27 is threadecl with threads of substantially the pitch of the threads
of the screw member 10 and of substantially complementary shape -to
the shape of the threads of the screw member. A cap member 28 is
;~ threaded over the end of the nut member 15 to retain the seal 27 within
the cavity 26. The cap 28 has a central hole greater than the crest
diameter of the screw member 10, The seal 27 has an axial width
. . .
less than the axial length of the cavity 26. From the foregoing, it may
be seen that the seal 27 is no-t constrained against rotation by the nut ; ~ -
member 15 and the cap 28, Thus, the seal 27 is allowed to rotate
within the cavity 26, Because the effective lead of the device is less
than the lead of the screw member 10, the seal 27 automatically loads
itself in the operation of the device, That automatic loading will
` inherently provide a firm substantially axial sealing arrangement of
the seal 27 on the threads of the screw member 10, In the loaded ;~
position of the seal 27 shown in FIG. 7, the nut member 15 may be ~ -
viewed as being linearly translated in the direction of the arrow 30
shown in FIG. 7, :13ecause the nut member 15 is being linearly trans-
lated in that direction to a degree less than would be the case if the
scal 27 could be translated as a nut in threaded engagement with the
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scre~v l~embcl 10, the seal 27 is ur~c(l at its si(le '27a clgainst the cap
2~ as sllo~ l with one siclc Or the tec~tll of the sc.ll 27 loaclccl a~ainst
onc siclc of th(? teeth of thc screw membcr 10 tlS sllown. ~rhe matcrial
of tlle scal 27 may be selectcd from known elastolneric materials
suitable for S-lCil lSe~::, SUCIl as thc material sokl und(?r the trade mark
TL'FLO~)},i'rom tlle forcgoing, those skillccl in the art will ~Ipprc( i~ltC
the uniquely si-mple and efficient characteristics of the described
sealing arrangement, ',
Ii`lGS. 8 and 9 show a further embodimcnt of the inventioll in ,,~ ' ,'
which the screw member 31 has six tllread starts. The roller members '~
32 are six in nu-mber, and the nut member 33 is of substantially the same
construction as previously described nut member 12. In all other
respects the screw member 31J the roller members 32, and the nut
member 33 are constructed and arranged similarly -to tlle corres,oonding
parts of the previously described embodiments and operate in a substan-
tially similar manner in the complete device. Obviously, therc are a
total of twice as many rolling contact lines for the six roller member
arrangement of FIGS. 8 and 9 than would be the case for the tllree rollcr
desi~gn of FIG. 1 if thc roller members of both cmbodiments had tllc sarme
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number Or annular teeth.
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~;`rom the foregoing detailed description, those skilled in tllC art -~
will understand th~t alternative]y the nut member 33 may bc the elernent
provided with the mllltiple-'leacl threads and thc screw membcr thcll pro-
vided with a plurality of annular groovcs equal in number to thc nurnber
,; 25 of annular teetll on the roller mcmbcrs, O~ courc,e, to providc any
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substantial degl~ee of permittccl linear translation, the llUt membel :
woukl e~pecteclly bc of s-lbstantially greater lengtl-l than ttle nut
members previously lescribed with thc annular grooves.
Having described the invention, it i9 to be unclersltood that
further ernbodiments ot' tile invention may be macde by those skilled
in the art within the spirit and scope of the hereinafter following
claims.
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