GB1578476A

GB1578476A - Reversible rotary to linear motion converting devices

Info

Publication number: GB1578476A
Application number: GB1798577A
Authority: GB
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 1976-05-03
Filing date: 1977-04-29
Publication date: 1980-11-05
Also published as: AU2471077A; FR2350519A1; CA1058909A; DE2718888C2; FR2350519B1; SE7705047L; NL186338B; NL7704792A; IT1086289B; BR7702733A; BE854192A; JPS52133471A; DE2718888A1; AU512598B2; ES458412A1; CH615258A5; NL186338C; SE436920B; AR213955A1

Description

(54) REVERSIBLE ROTARY TO LINEAR MOTION CONVERTING DEVICES (71) We, ILLINOIS TOOL WORKS INC., a corporation organised under the laws of the State of Delaware, United States of America, of 8501 West Higgins Road, Chicago, Illinois 60631, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to motion converting devices of simple construction that convert rotary motion to linear motion, or the opposite, through substantially pure rolling contact between the parts of the devices, which not only have minimum frictional losses but are also inherently capable of transmitting substantial power therethrough and of absorbing relatively large loads in operation.

A motion converting device in accordance with the present invention comprises a rod provided with a series of grooves; a sleeve of larger internal diameter than the external diameter of the rod and provided with a series of internal grooves, the grooves on either the rod or the sleeve defining a plurality of continuous helical threads; and a plurality of roller members equal in number to the number of threads provided on either the rod or the sleeve, each roller member having a series of annular teeth of substantially equal axial pitch to the aforementioned grooves and of substantially matching configuration to the shape of said grooves; said roller members being interposed between said rod and said sleeve in positions, at least prior to use, which are substantially equally spaced-apart circumferentially, with each of the teeth of the roller members being in rolling contact with the grooves in both the rod and the sleeve to couple the rod and the sleeve relatively to one another, and with the roller members being free during use to shift circumferentially relatively to one another substantially to equalise the total action and reaction forces on the roller members; the arrangement being such that, upon application of rotational force to either the rod or the sleeve, the other moves linearly relatively thereto when constrained against rotation.

Preferably, the rod is formed as a screw member having multiple-lead threads, and the sleeve is formed with a series of internal annular grooves equal in number to the number of teeth on each of the roller members, whereby any rotational force applied to the screw member, with the sleeve constrained against rotation, results in an axial translation of the sleeve relatively to the screw member. The reverse arrangement is also possible, however, in which the sleeve is formed as a nut member with multiple-lead threads, and the rod is formed with a series of external annular grooves equal in number to the number of teeth on each of the roller members. For convenience, throughout the remaining description (but not the claims) the rod will always to referred to as a screw member, and the sleeve will always be referred to as a nut member, regardless of which of those members is in fact formed with a plurality of multiple-lead threads.

Although different arrangements may be provided for assembling the abovementioned preferred device, a convenient assembly method involves forming each of the roller members with short stub shafts at each end thereof and further providing two locating collars. The locating collars are merely flat rings having an internal diameter greater than the crest diameter of the screw member, and conveniently an outer diameter less than the crest diameter of the annular teeth where they contact the adjacent annular grooves in the nut member. Each of the locating collars is further formed with openings, such as radially extending slots, whose circumferential width are substantially equal to the diameters of the stub shafts on the ends of the roller members. The openings in the locating collars are equally spaced circumferentially thereabout and are equal in number to the number of roller members. Assembly of the device is then a simple matter of inserting the roller members within the nut member, with the annular teeth of the roller members in rolling contact with the annular grooves of the number member, circumferentially spacing the roller members and applying the locating collars to each end of the roller members with the stub shafts extending into the openings in the locating collars. The screw member may then be threaded into the central opening defined by the roller members. After assembly the locating collars are removed. However, where the parts are made with relatively wide manufacturing tolerances, it may be preferred to leave the locating collars mounted on the roller members, until immediately before use, 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 selfbalancing i.e. they can shift circumferentially relatively to one another.

The above-noted key feature of the invention results in a device wherein all of the forces in the operation of the device are internally balanced in a stable arrangement.

If the nut member is constrained against rotation but allowed to translate axially, 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 member 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 for installation purposes only.

This is a significant difference from many of the prior art devices having similar roller members and permanent locating collars which prevent the roller members from shifting during use circumferentially relatively to one another.

Making the number of annular grooves in the nut member equal in number to the number of teeth on the roller members leads to devices which can absorb relatively large loads during use.

In devices of the present invention, further economies in manufacture and a substantially stronger device can be achieved by making the teeth of the screw member and the roller members, and the grooves of the nut member to have a tooth profile of a 90 degree included angle.

It may be seen that as the screw turns and the nut member is rotatively constrained but permitted linear translation, the rollers are caused to roll and translate in a planetary motion. Thus, the effective lead of the device, which is the ratio of linear output to angular input, is less than the lead of the screw. The following formula may be used to calculate the effective lead for any particularly sized device of the invention: D L'=Lf D+S Where: 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 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 members and the screw member.

Several devices in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevational view partially in cross-section of one embodiment of a device constructed according to the invention; Figure 2 is a complete end elevational view of the structure shown in Figure 1; Figure 3 is a view similar to Figure 1, but showing one end of a device having a locating collar and retaining cap for the collar; Figure 4 is a diagrammatic view showing the developed lead for the threads of the screw member of a device of the invention having three roller members; Figure 5 is a fragmentary side elevational view of another embodiment of the invention including dirt seals which prevent the interior of the device from being contaminated by dirt; Figure 6 is a side elevational view of another embodiment of the invention having six roller members, the device being partially shown in cross-section; and Figure 7 is an end elevational view of the device shown in Figure 6 but shown substantially circumferentially complete.

Figures I and 2 show one embodiment of the invention in assembled form and ready for immediate use. In that embodiment a screw member 10 having three thread starts is provided. Further, the teeth of the threads have a profile in an axial plane of an included angle of substantially 90 degrees.

There are three roller members 11. Each of the roller members is formed with a plurality of annular teeth extending substantially the full 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 matches the shape of the teeth of the screw member 10.

A 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, 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 grooves as there are annular teeth on each of the roller members 11.

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 involved in the operation of the device but are conveniently provided for use in locating the roller members 11 in the positions shown in Figure 2 in the initial assembly of the device. Neither the screw member 10 nor the nut member 12 is 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 appreciate that the device as described can be used in many different machines where it is desired to convert rotary motion to linear motion. The device is, of course, 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.

The manner in which the stub shafts 13 are used in locating the roller members 11 will now be described. As shown in Figure 3, a screw member 10 have three thread starts is provided with three roller members 11 assembled thereabout in rolling contact therewith. Although only one end of nut member 14 is shown in Figure 3, it should be understood that both ends of that nut member are externally threaded at 15, as shown in Figure 3, to receive a pair of end caps such as end cap 16. The end caps 16 are internally threaded for application over the ends of the nut member 14. The end caps 16 are provided with a central opening capable of receiving the screw member 10 therethrough. As shown in Figure 3, a locating collar 17 is mounted radially within the nut member 14 and circumferentially about the screw member 10. Three small openings 18 in the locating collar 17 closely encircle the stub shafts 13 of the roller members 11. The inner faces of the end caps 16 hold the pair of locating collars 17 within the device, the locating collars 17 being removed before use of the device to permit the roller members 11 to shift circumferentially relatively to one another.

For a set of three roller members, a screw member of three thread starts is used and Figure 4 shows, in diagrammatic form, the developed lead for the three thread starts of the screw member for the three roller members.

Figure 5 shows a dirt seal arrangement that can advantageously be used with and as part of devices of the subject invention. A screw member 10, a roller member 11, and a nut member 19 are shown in Figure 5 in a fragmentary view. Each end of the nut member 19 is provided with an annular cavity 26 to receive a 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 19. The radially inner side 27d of the seal 27 is threaded 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 cover 28 is threaded over the end of the nut member 19 to retain the seal 27 beyond the end of the roller member 11 and within the cavity 26.

The cover 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 not constrained against rotation by the nut member 19 and the cover 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 Figure 5, the nut member 19 may be viewed as being linearly translated in the direction of the arrow 30.

Because the nut member 19 is being linearly translated in that direction to a degree less than would be the case if the seal 27 could be translated as a nut in threaded engagement with the screw member 10, the seal 27 is urged at its side 27a against the cover 28 as shown with one side of the teeth of the seal 27 loaded against one side of the teeth of the screw member 10 as shown. The material of the seal 27 may be selected from known elastomeric materials suitable for such uses, such as the material sold under the Registered Trade Mark Teflon.

From the foregoing, those skilled in the art will appreciate the uniquely simple and efficient characteristics of the described sealing arrangement.

Figures 6 and 7 show a further embodiment of the invention in which the screw member 31 has six thread starts. The roller members 32 are six in number, and the nut member 33 is of substantially the same construction as previously described nut member 12. In all other respects the screw member 31, the roller members 32, and the nut member 33 are constructed and arranged similarly to the corresponding parts of the previously described embodiments and operate in a substantially similar manner in the complete device.

Obviously, there are a total of twice as many rolling contact lines for the six roller member arrangement of Figures 6 and 7 than would be the case for the three roller design of Figure 1 if the roller members of both embodiments had the same number of annular teeth.

From the foregoing detailed description, those skilled in the art will understand that alternatively the nut member 33 may be the element provided with the multiple-lead threads and the screw member may then be provided with a plurality of annular grooves equal in number to the number of annular teeth on the roller members. Of course, to provide any substantial degree of permitted linear translation, the nut member would expectedly be of substantially greater length than the nut members previously described with the annular grooves.

WHAT WE CLAIM IS: I. A motion converting device comprising a rod provided with a series of grooves; a sleeve of larger internal diameter than the external diameter of the rod and provided with a series of internal grooves, the grooves on either the rod or the sleeve defining a plurality of continuous helical threads; and a plurality of roller members equal in number to the number of threads provided on either the rod or the sleeve, each roller member having a series of annular teeth of substantially equal axial pitch to the aforementioned grooves and of substantially matching configuration to the shape of said grooves; said roller members being interposed between said rod and said sleeve in positions, at least prior to use, which are substantially equally spaced-apart circumferentially, with each of the teeth of the roller members being in rolling contact with the grooves in both the rod and the sleeve to couple the rod and the sleeve relatively to one another, and with the roller members being free during use to shift circumferentially relatively to one another substantially to equalise the total action and reaction forces on the roller members; the arrangement being such that, upon application of a rotational force to either the rod or the sleeve, the other moves linearly relatively thereto when constrained against rotation.

2. A motion converting device according to claim 1, in which the rod is formed as a screw member having multiple-lead threads, and the sleeve is formed with a series of internal annular grooves equal in number to the number of teeth on each of the roller members, whereby any rotational force applied to the screw member, with the sleeve constrained against rotation, results in an axial translation of the sleeve relatively to the screw member.

3. A motion converting device according to claim 1, in which the sleeve is formed as a nut member having multiple-lead threads, and the rod is formed with a series of external annular grooves equal in number to the number of teeth on each of the roller members, whereby any rotational force applied to the nut member, with the rod constrained against rotation, results in an axial translation of the rod relatively to the nut member.

4. A motion converting device according to claim 2 or claim 3, in which there are at least three multiple-lead threads on either the screw member or the nut member.

5. A motion converting device according to any preceding claim, in which each of the roller members has a stub shaft extending axially from each end thereof, and prior to use each of the stub shafts extends into a respective opening formed in a pair of locating collars positioned around the rod, the locating collars subsequently being removed to permit the roller members said freedom during use to shift circumferentially relatively to one another.

6. A motion converting device according to claim 5, in which each of the openings is formed as a radially extending slot.

7. A motion converting device according to claim 5 or claim 6, in which prior to use each of the locating collars is held in association with the adjacent stub shafts by a respective cap which is threadingly engaged with the sleeve.

8. A motion converting device according to any preceding claim and including a pair of dirt seals, each of the dirt seals being formed of a resilient elastomeric material in the shape of a flat annular ring, and being held in position beyond respective ends of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

teeth of the screw member 10 as shown. The material of the seal 27 may be selected from known elastomeric materials suitable for such uses, such as the material sold under the Registered Trade Mark Teflon.

From the foregoing, those skilled in the art will appreciate the uniquely simple and efficient characteristics of the described sealing arrangement.

Figures 6 and 7 show a further embodiment of the invention in which the screw member 31 has six thread starts. The roller members 32 are six in number, and the nut member 33 is of substantially the same construction as previously described nut member 12. In all other respects the screw member 31, the roller members 32, and the nut member 33 are constructed and arranged similarly to the corresponding parts of the previously described embodiments and operate in a substantially similar manner in the complete device.

Obviously, there are a total of twice as many rolling contact lines for the six roller member arrangement of Figures 6 and 7 than would be the case for the three roller design of Figure 1 if the roller members of both embodiments had the same number of annular teeth.

From the foregoing detailed description, those skilled in the art will understand that alternatively the nut member 33 may be the element provided with the multiple-lead threads and the screw member may then be provided with a plurality of annular grooves equal in number to the number of annular teeth on the roller members. Of course, to provide any substantial degree of permitted linear translation, the nut member would expectedly be of substantially greater length than the nut members previously described with the annular grooves.

WHAT WE CLAIM IS: I. A motion converting device comprising a rod provided with a series of grooves; a sleeve of larger internal diameter than the external diameter of the rod and provided with a series of internal grooves, the grooves on either the rod or the sleeve defining a plurality of continuous helical threads; and a plurality of roller members equal in number to the number of threads provided on either the rod or the sleeve, each roller member having a series of annular teeth of substantially equal axial pitch to the aforementioned grooves and of substantially matching configuration to the shape of said grooves; said roller members being interposed between said rod and said sleeve in positions, at least prior to use, which are substantially equally spaced-apart circumferentially, with each of the teeth of the roller members being in rolling contact with the grooves in both the rod and the sleeve to couple the rod and the sleeve relatively to one another, and with the roller members being free during use to shift circumferentially relatively to one another substantially to equalise the total action and reaction forces on the roller members; the arrangement being such that, upon application of a rotational force to either the rod or the sleeve, the other moves linearly relatively thereto when constrained against rotation.
2. A motion converting device according to claim 1, in which the rod is formed as a screw member having multiple-lead threads, and the sleeve is formed with a series of internal annular grooves equal in number to the number of teeth on each of the roller members, whereby any rotational force applied to the screw member, with the sleeve constrained against rotation, results in an axial translation of the sleeve relatively to the screw member.
3. A motion converting device according to claim 1, in which the sleeve is formed as a nut member having multiple-lead threads, and the rod is formed with a series of external annular grooves equal in number to the number of teeth on each of the roller members, whereby any rotational force applied to the nut member, with the rod constrained against rotation, results in an axial translation of the rod relatively to the nut member.
4. A motion converting device according to claim 2 or claim 3, in which there are at least three multiple-lead threads on either the screw member or the nut member.
5. A motion converting device according to any preceding claim, in which each of the roller members has a stub shaft extending axially from each end thereof, and prior to use each of the stub shafts extends into a respective opening formed in a pair of locating collars positioned around the rod, the locating collars subsequently being removed to permit the roller members said freedom during use to shift circumferentially relatively to one another.
6. A motion converting device according to claim 5, in which each of the openings is formed as a radially extending slot.
7. A motion converting device according to claim 5 or claim 6, in which prior to use each of the locating collars is held in association with the adjacent stub shafts by a respective cap which is threadingly engaged with the sleeve.
8. A motion converting device according to any preceding claim and including a pair of dirt seals, each of the dirt seals being formed of a resilient elastomeric material in the shape of a flat annular ring, and being held in position beyond respective ends of

the roller members by a pair of annular covers which are secured to the sleeve.
9. A motion converting device according to claim I and substantially as hereinbefore described with reference to Figures 1, 2 and 4, Figure 3, Figure 5, or Figures 6 and 7, of the accompanying drawings.