GB2111635A

GB2111635A - A device for converting a rotary motion to a linear movement

Info

Publication number: GB2111635A
Application number: GB08235891A
Authority: GB
Inventors: Bo Granbom
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-12-16
Filing date: 1982-12-16
Publication date: 1983-07-06
Also published as: ZA829135B; ES518230A0; DD209237A5; JPS58109758A; IL67427A0; DE3245119A1; IT1155379B; NL8204861A; NO824223L; FI824315A0; FI824315L; BR8207315A; KR840002963A; DK554782A; FR2518208A1; SE8107545L; IT8224754A0; IT8224754A1; AU9134582A; BE895370A

Abstract

The device comprises a first elongate body (1, 19) provided with screw threads (2) extending along the body, and a second body coaxially rotatable relative to the first body, which second body (3, 8, 24, 25) has at two rolls (4) provided with cams (5) engaging with the screw threads in the first body. Upon rotation of the bodies in relation to each other one body is moved linearly relative to the other body. The first body in the region of the threads (2) also is provided with cogs (11), which run transversely to the threads and in one direction of movement and provided over substantially the entire length of the body. Each roll (4) includes cogs (12) running transversely to the cams (5) thereof and in the direction of movement, which cogs (12) correspond to the cogs of the first body and are provided over substantially the entire length of the roll (4). <IMAGE>

Description

SPECIFICATION A device for converting a rotary motion to a linear movement This invention relates to a device for converting a rotary motion into a linear movement and more particularly concerns such a device which comprises a first elongate body provided with screw threads extending along the body, and a second bodycoaxi- ally rotatable relative to said first body and having at least two rolls (or wheels) provided with cams (or threads) engaging with the screw threads of said first body, whereby upon rotation of the bodies relative to each other one body is moved linearly relative to the other.

Known devices of the aforesaid kind apply the screw-nut principle or are designed with a ball nut screw. The first-mentioned device is restricted as to its use because of the high friction and the heat development involved therewith. The latter device implies, owing to its structural design, that the linear movement is relatively large in relation to the rotary motion, i.e. the possibility of varying the gear ratio is limited.

In order to avaid these problems, it is known to use freely rotatable wheels or rolls, which are supported in one of the members movable relative to each other and by means of parallel ribs or cams co-operate with threads of the second member. By rotating, for example, the threaded member, the wheels roll and their cams engage with the threads whereby the member provided with the wheels is moved. Due to the fact that the cams follow closed circles, i.e. each cam is located in a plane of its own, it is necessary that the axle of the respective wheel is inclined through an angle corresponding to the pitch angle of the thread or, when the wheel axles are arranged in parallel with the axle of the threaded member, that the wheels are located axially offset relative to each other.This implies complications at the manufacture to meet the already high requirements on close tolerances, so that the device will operate satisfactorily.

At other known devices the wheels or rolls are provided with threads corresponding to the threads on the threaded member. At these devices, however, the problem also involved with the devices described above still remains, that the wheels must be guided and driven accurately bythethreaded member and all the time must abutthethreads thereof and engage with the same. As soon as there occurs an obliquity between the wheels and the threaded portion, or a wheel disengages therefrom and thereby gives rise to different wheel speeds, the device unavoidably will jamb.

For being able to increase the forces transferred between the members, and thereby to meet the increased wheel bearing forces, it is known to surround the wheels or rolls with a nut, which along the inside is provided with threads engaging with the wheels, which threads have the same pitch angle as the threads of the wheels in order to prevent the wheels from migrating in the nut. At this type of device one has succeeded to synchronize the rotation of the wheels relative to each other by providing one end of the respective wheel with a gear ring, which meshes with a corresponding gear ring of the nut. Even this design involves serious disadvantages, because due to the relatively locked configuration the wheels must co-operate with the threaded member, the screw and the threaded nut, and because a relative movement between the screw and wheels cannot be prevented.It is, therefore, very difficult to effect self-braking of the device, i.e. that the device even at maximum load will be standing still without a separate brake. Due to the possibility of a relative movement between the screw and wheels, it is necessary, when the device has been moved to a stop in an extreme position, to dismantle the entire device for restoring it to working order.

The invention provides a device for converting a rotary motion into a linear movement, comprising a first elongate body provided with screw threads extending along the body, and a second body coaxially rotatable relative to said first body and having at least two rolls (or wheels) provided with cams (or threads) engaging with the screw threads of said first body, whereby upon rotation of the bodies relative to each other one body is moved linearly relative to the other, wherein the first body in the region of the threads has cogs extending transversely to the threads and generally in the direction of the movement and provided over or substantially over the entire body, and the respective roll also has cogs extending transversely to the cams thereof and generally in the direction of the movement, which cogs correspond to the cogs of the first body and are provided over or substantially over the entire roll.

Preferred and optional features of the invention are set forth in claims 2 to 10.

It is therefore possible to provide a device which does not jam when it is moved to an end stop, which can be designed to be self-braking, and the gear ratio of which can be altered relatively extensively within the scope of the basic structure of the device.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Fig. lisa schematic longitudinal section through an embodiment of the device according to the invention, Fig. 2 shows the threaded screw comprised in said embodiment and a roll co-operating with the screw, Fig. 3 is a partial section of screw and roll, Fig. 4 is a schematic section of a detail of said embodiment, Fig. 5 is a section along V-V in Fig. 4 of the detail according to Fig. 4, Fig. 6 shows schematically another gear design between screw and roll, Fig. 7 is a schematic section of another embodiment of the invention, and Fig. 8 is a partial section of a further embodiment of the invention.

Fig. 1 shows an embodiment of the invention, which comprises a screw 1 provided with threads 2.

In a bearing housing 3 a plurality of rolls or wheels 4 are located, which are provided with threads 5 run ning opposed to the screw 1 and having the same pitch as the pitch of the screw. The screw 1 is driven by an electric motor 6 rigidly supported in a cylinder 7. The bearing housing 3 is connected to a hollow rod 8, which can receive the screw 1 and is movably supported in bearings 9 at the end of the cylinder 7.

The rod 8 is slidably supported in the cylinder by means of the periphery of the bearing housing. At the free end of the cylinder 7 and rod 8 eyes 10 are located. Upon activation of the screw 1,the rolls 4 roll on the screw 1 and, owing to the engagement of the threads with each other, the bearing sleeve 3 and the rod 8 are moved relative to the cylinder 7.

In order to prevent slip between the threads of the screw and the threads of the rolls, and thereby to prevent the rolls of the bearing housing 3 from jamming when the device is moved against an end stop, the screw 1 is provided over its entire length and on the thread crowns with cogs 11, see particularly Figs.

2 and 3. The respective roll 4 is provided between the threads 5, i.e. in the bases of the troughs between the threads, with corresponding cogs 12. In Figs. 2 and 3 the screw 1 and a roll 4 are shown separated, but in mounted state the rolls and the screw engage with each other with their threads and cogs. This mounted state is schematically apparent from Figs. 4 and 5, where a screw 1 and five rolls 4 engaging therewith are shown (only one roll is shown). As appears from Figs, 2 and 4, the respective roll 4 has at each end an axle journal 13, which is provided with a number of parallel ridges 14 each defining a trapezium. The bearing housing 3 is provided at each end with an inwardly directed flange or thickening 15 with an inward facing bearing surface 16, along the inner periphery of which grooves 17 corresponding to the ridges 14 are located.As should be clearly apparent from Fig. 4, in the mounted state the respective roll with its threaded and cogged periphery engages with and rests against the threaded and cogged outer surface of the screw 1 and with its axle journals 13 rests against the bearing surface 16 of the bearing housing 3, with the ridges 14 running in the grooves 17. Due to the fact that the five rolls are axially locked in a common plane at the bearing housing 3 by means of the ridges 14 and grooves 17, each roll is assigned to a clearly defined position along the periphery of the screw 1 in the embodiment shown to a fifth part of a pitch from each other. No roller bearing holders for maintaining the pitch are required.

As the threads 2 of the screw and the threads 5 of the rolls 4 each define a trapezium, as shown in Figs.

2 and 4, and as the axle journals 13 are provided with the ridges 14 which each define a trapezium engaging with the corresponding grooves 17, it is possible to minimize the radial forces acting during the operation of the device, and instead to render pure the axial forces, thereby preventing great bending moments in the bearing housing 3. By providing the axle journals 13 with a number of ridges 14, a relatively large bearing surface taking up the axial forces is obtained. In combination with the relatively large contact surface obtained between the threads ofthe screw 1 and rolls 4 due to their configuration, it is possible totally to achieve such a static friction that the device will be self-braking.

The arrangement of axle journals 13 rolling freely along the bearing surface 16 of the bearing housing 3 implies, that it is possible expediently to some extent to vary the gear ratio of the device by changing the diameter of the axle journals 13 (and of the bearing surface 16) while maintaining the remaining variables unchanged.The formula for the total gear ratio Utcan be derived to be as follows Ut=S(nR+np-S d2 where n,=nR -- D2 wherein S=pitch (right-hand and left-hand thread of the screw 1 and roll 4 d2=diameter of the axle journal 13 D2=diameter of the bearing surface 16 np=movement distance of the axle journal 13 in relation to the diameter of the bearing surface 13 nR=number of revolutions by roll 4 per screw revolution Fig. 6 shows the cogs of the screw 1 and roll 4 on the thread flanks instead of on the thread crowns and, respectively, on the thread bases. In Fig. 6 the cogs of the screw 1 and the cogs of the roll 4 are designated by 11' and, respectively, 12'.

Fig. 7 shows another embodiment, in which the screw has been replaced by an internally threaded cylinder 19, which is driven by an induction motor, the rotor 20 of which is rigidly connected to the cylinder 19, and the stator with windings 21 of which is attached to a sleeve, which rotatably supports the cylinder 19 in bearings 23. A rod 24 movable relative to the cylinder 19 carries at one end the rotatably mounted rolls 4 between a pair of plate-like holders or carriers 25. In Fig. 7 the rolls are shown supported on axles 26 attached to the carriers. As shown, for example, in Fig. 4 the rolls 4, of course, may have axle journals 13, in which case the carriers have the form of circular discs, which are attached on the rod 24 and have peripheral bearing surfaces provided with grooves, see Fig. 8, in the same manner as the aforementioned bearing surfaces 16 with grooves 17.

By using threads which define a trapezium on the screw (cylinder) and rolls and between axle journals and bearing surfaces it is possible, as mentioned, to minimize the radial forces, at the same time as the radial tolerance will not be critical at the manufacture. It is to be emphasized, however, that it is not necessary according to the invention to use threads of this shape, but also other types, for example V-shaped threads, can be used. The cogs of the screw (cylinder) and rolls are preferably helical, which contributes to quieter running and to an addi tion of force in the axle direction.

As shown with reference to Fig. 7, the rolls 4 can be supported on axles, in which case the end sur faces of the rolls and/or axles shall take up the axial forces. When the inconvenience of having different rolls in one and the same device can be accepted, it also is possible within the scope of the invention to provide the rolls, instead of with threads 5, with parallel cams engaging with the threads 2 of the screw (cylinder). As at the afore-described device, the bases of the troughs between the cams are provided with cogs. In such a device, however, the cams in one roll must be offset in relation to the cams in the other roll, i.e. when five rolls are used at a screw with one thread entrance, the cams of a subsequent roll must be offset a fifth part of the pitch in relation to a preceding roll.

Claims

1. A device for converting a rotary motion into a linear movement, comprising a first elongate body provided with screw threads extending along the body, and a second body coaxially rotatable relative to said first body and having at least two rolls (or wheels) provided with cams (or threads) engaging with the screw threads of said first body, whereby upon rotation of the bodies relative to each other one body is moved linearly relative to the other;; wherein the first body in the region of the threads also has cogs extending transversely to the threads and generally in the direction of the movement and provided over or substantially over the entire body, and the respective roll also has cogs extending transversely to the cams thereof and generally in the direction of the movement, which cogs correspond to the cogs of the first body and are provided over or substantially over the entire roll.

2. A device as claimed in claim 1, wherein the first body is in the form of a screw and the rolls are supported by a bearing housing resting against the ends of the rolls.

3. A device as claimed in claim 2, wherein the bearing housing comprises two peripheral bearing surfaces, which face radially inward, which are axially separated from each other, and which are provided with parallel grooves, and the respective roll is provided at each end with an axle journal, which is formed with ridges corresponding to the grooves of the respective bearing surface.

4. A device as claimed in claim 3, wherein the co-operating grooves and ridges are each shaped to define a trapezium.

5. A device as claimed in any one of claims 14, wherein the cams of the rolls are in the form of threads with a pitch equal to and with rotation opposed to the threads of the first body.

6. A device as claimed in claim 5, wherein the co-operating threads of the first body and rolls are each shaped to define a trapezium.

7. Adevice as claimed in any one of the preceding claims, wherein the cogs of the first body are on the crowns of the thread, and the cogs of the respective roll are in the bases of the troughs between the cams ofthe roll.

8. A device as claimed in any one of the preceding claims, wherein the cogs are helical.

9. A device as claimed in any one of the claims 2-6, wherein the cogs of the first member and the cogs of the respective roll are located on the thread and cam flanks.

10. A device as claimed in claim 1, wherein the first body is in the form of an internally threaded cylinder, and the respective roll at the respective end rests by an axle journal against an outward facing peripheral bearing surface located in a disc-shaped carrier, the respective axle journal and bearing surface are provided with parallel ridges engaging with each other, and the carriers are connected to a rod axially movable in the cylinder.

11. A device for converting a rotary motion into a linear movement, substantially as hereinbefore described with reference to, and as shown in, Figs 1-5, or Figs 1-5 as modified by Fig. 6, or Fig. 7 or Fig.

8 of the accompanying drawings.