The present invention relates to an apparatus for translating rotary movement to rectilinear movement, using members with helical grooves or threads and profiled rolling bodies co-acting and engaging there¬ with. Amongst such apparatus ball nuts and screws, for example, are known in the prior art, and these have small friction but also the disadvantage that the gear reduction is small, i.e. there is a large linear displacement for each revolution of the rotary movement. Devices with screws and nuts are also known, and these devices can be given a large gear reduction, i.e. a small linear displacement for each revolution of the rotary movement. However, these devices have the disadvantage that they have large friction. Apparatus of the kind described are also often expensive.

The translating apparatus in accordance with, the invention combines the best properties of the described known apparatus. The apparatus thus has low friction, i.e. good efficiency,at the same time enabling a.large gear reduction.

The advantages stated are achieved in that a tubular outer cylinder, comprising an outer casing at one end having a transverse portion and at the other an end wall opening, surrounds an inner cylinder arranged therein, axially displaceable through the end wall opening of the outer cylinder but unrotatable in relation thereto, said inner cylinder comprising an inner casing with a cylindrical inner surface having a helicalthread or helical groove, the outer cylinder having, preferably at the transverse portion thereof, a rotatably mounted but axially undiεplacable driving means comprising a drive shaft extending axially concentric with the helical groove in the inner casing, and at its end opposite to the transverse portion of the outer cylinder . having at least one eccentrically disposed cylindrical journal rigid- lyponnected to said drive shaft, said journal carrying at least one rotatably mounted but axially undiεplaceable cylindrical rolling body, a profiledrolling body, the outer cylindrical surface of which has annular ridges in a plane normal to said journal, e.g. with a thread profile, formed for complementary engagement with the helix grooves in the inner casing, the object being that when the drive shaft is

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rotated, the ridges on the axially undisplaceable profiled rolling bodies engage with the helix groove of the unrotatable inner casing and displace the inner cylinder axially and linearly, in relation to the outer cylinder .a distance and direction depending on the pitch and direction of the helical groove.

Further advantages are obtained if the eccentric journal consists of an eccentric sleeve rigidly and undistortably attached to the drive shaft, and having a hole for accomodating the drive shaft, eccentric ally disposed in relation to the journalling surface.

It is also advantageous to make the profiled rolling body as a roll¬ ing bearing, the outer surface fo its outer ring having complementar ridges coacting and engaging with the helix groove.

It is even advantageous to make the apparatus so that the outer ring of the rolling bearing carries a separate sleeve, the outer peripher of which has the complementary ridges, or that the driving means comprises several profiled rolling bodies evenly distributed around the centre line of the drive shaft.

Other valuable advantages are obtained by the profiled rolling bodie being arranged for axial and radial adjustment on the eccentric jour als, for the purpose of allowing said bodies to be tightened against each other for eliminating axial play between said bodies of the dri ing system and the helical groove or thread of the inner cylinder.

The invention will now be described in connection with an embodiment and while referring to the accompanying drawing where Figure 1 is a longitudinal cross section of a complete unit, Figure 2 is a view of a section along the line II - II in Figure 1, Figure 3 illustrates a portion of the apparatus according to an alternative preferred embod ment, Figure ^■ ) is a view of a section of an apparatus with three profiled rolling bodies, seen in the direction IV - IV in Figure 3» and Figure 5 illustrates an alternative embodiment of a profiled rolling body.

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The apparatus according to the invention consists of three main parts, an outer cylinder, an inner cylinder and a driving unit.

From Figure 1 it is apparent that the outer cylinder 1 consists of an outer casing or tube 2 with an opening 3 at one end. The opening 3» either in an end piece or in the tube itself, is not formed circu¬ larly. The inner tube 11 is thus taken through the opening 3 linear¬ ly but non-rotatably glidably. The outer casing 2 has, at its other end portion, a transverse portion 5 with front and back side surfaces 6 and 7 and a cylindrical bearing surface 8.

The inner cylinder 10 consists of an inner casing or tube 11, the inner surface of which is cylindrical and has helix grooves, preferab¬ ly with a thread profile, along the major portion of its length. The tube 11 slides in and is guided by the opening 3 in the outer casing. As mentioned, the inner tube is glidably but unrotatably taken through the opening 3. This can be achieved by the opening being formed as a polygon, by the outer surface of the inner casing being provided with a long key coacting with a keyway in the end wall piece ^■■ +, or in some other known mode.

At its rear end, the inner tube has a sliding bush 16. Sliding surfac¬ es can alternatively be formed on the inner tube 11 itself. Conical disk springs 17 _> 18 can be mounted on the sliding bush to advantage, as buffers for the end positions of the inner cylinder. At the inner¬ most position, the buffer 18 will come into contact with the trans¬ verse portion 5 a at the outmost position the buffer 17 will come into contact with an eccentric plate 25» described in detail below.

At its outer end, the inner casing has a transverse portion 13 to which are attached two lugs Λh with holes 15« The driven member, e.g. a lever or arm, can be connected to the hole 15 b means of a pin (not shown).

The driving means or driving system 20 comprises a shaft 23• _> rotatab¬ ly mounted in the transverse portion 5 of the outer casing 2. A washer 22 bears against each side surface 6 and 7 of said transverse portion

5, said bearing washers being attached to the shaft ?3 and thus pre¬ vent the drive shaft 23 from moving axially. Outside the transverse portion 5, one end of the drive shaft 23 is formed into a neck 21 for connecting to the rotary power movement.

The eccentric plate 25 is attached to the other end of the drive shaft 23, and carries a journal 28 disposed eccentrically in relatio to the shaft 23. The eccentricity between the centre line 2h of the shaft 23 and the centre line of the journal 28 is denoted by e in th Figure. A profiled rolling body 33 is mounted on the journal 28, its outer surface having ridges 33 running perpendicular to the journal 28 and being complementary to the helical groove or threads 12 of th inner cylinder 10.

The diameter of the profiled rolling body y\ is selected such that its ridges 33 engage with the grooves 12 of the inner casing 11- A double eccentric plate 26 is attached to the outer end of the journa 28., said plate carrying a second journal 29 diametrically opposite the first journal 28, and at the same distance e from the centre" lin 2h _t said journal 29 carrying a second profiled rolling body 2 which is similar to the body 1. A stop washer 27 is attached to the outer end of the journal 29» so that the rolling body 32 is axially retain ed between it and the double eccentric plate 26.

The profiled roller 32 engages with the helical groove 12 of the inner casing 11 in a position diametrically opposite the engaging position of the roller ^~~ 1, The dimensions of the parts described are selected such that the profiled rollers >1 and 3 ² engage with a suit able .force in the grooves 12 of the inner casing 11.

When the drive shaft 23 rotates, the profiled rollers 31 and 32 will follow or roll in the grooves of the inner casing 11 such that when the shaft 23 has turned one revolution in relation to the casing 11 the rollers have displaced the inner casing a distance corresponding to one pitch of the helical groove 12. During this displacement, the inner cylinder 10 an<_ _j khe outer cylinder 1 have also been displaced a

pitch xially and linearly in relation to each other but- ithout any mutual turning or rotation.

The described embodiment ^• allows the selection of a very small pitch for the groove 12, down to one mm or less per revolution, and thus allows a very large gear reduction between the rotary movement and linear movement. This means, for example, that the neck 21 can normals ly be connected directly to the rotary driving power source.

By pretenεioning the rollers 31 and 3 axially and/or radially in re¬ lation to each other, by means of adjusting washers or sprung resili¬ ent elements, any play in the translating apparatus can be completely removed and very great positional accuracy obtained, which is necess¬ ary, e.g. for positioning movements in machine tools.

Figure 2 is a cross section along the line II-II in Figure 1, illustra¬ ting the outer casing 2 and inner casing 11 with its helical groove 12. Also illustrated are the drive shaft 23 with attached eccentric plate 2 and journal 28, as well as the profiled roller 1- rotatably mounted but axially fixed on journal 28. Finally, the double eccentric plate 26 connecting journals 28 and 29, with the profiled roller on the journal 29 carriec y the plate 26 are also illustrated. The eccentrici¬ ty e between the centre line 2k of the drive shaft and the centre lines of the journals 28 and 29 is given to the left in the Figure. The figure also illustrates how engagement between the grooves 12 and the ridges 33 of the profiled rollers >1 and 3 occurs along approximately segment-shaped surfaces, defined by circular lines with radii co.rres- ponding to the least diameter of the groove 12 and the greatest dia¬ meter of the profiled rollers Jl and 32.

As is apparent from the above, the ridges or threads 33 °f the profil¬ ed rollers 31 and 32 are perpendicular to the journals 28 and 29, and therefore also perpendicular to the inner cylindrical surface and centre line of the inner casing 11. The grooves 12, engaged by the ridges 33 of the rollers 31, 32, form an angle to the centre line of the inner casing 11, this angle depending on the pitch of the helical groo