GB1575941A - Roller-cage for gripping a gear to be machined - Google Patents

Description

(54) ROLLER-CAGE FOR GRIPPING A GEAR TO BE MACHINED (71) We, VOUMARD MACHINES Co.

S.A. of rue Jardiniere 158 in La Chaux-de Fonds, canton of Neuchltel, Switzerland, a company limited by shares duly organized under the laws of Switzerland, 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 : This invention relates to roller-cages for gripping gears to be machined on a machine tool, especially on a grinding machine, as well as to a method of manufacturing such rollercages. More particularly, this invention relates to roller-cages of the type comprising a ring having apertures or groups of apertures regularly spaced around its circumference and rollers disposed in these apertures, each roller being mounted on a spindle extending at an angle corresponding to that of the teeth of the gear to be machined.

In the known roller-cages of this type, the apertures are circular or oval and are easily produced by drilling or by milling. The spindles are usually metal wires of the piano-wire type, about 0.8 mm. in diameter, which are bent back into holes drilled on each side of the apertures. When the jaws of the grinding-machine chuck clamp the rollers so that the latter, in turn, will grip the gear, these jaws effect a movement which also has an axial component; depending upon the position which the rollers happen to occupy prior to clamping, they move axially to a greater or lesser extent since they are not adequately held by the rounded edges of the apertures. The gear is then gripped irregularly, especially when the teeth thereof have a cross-section which varies along the length of the tooth, e.g., in the case of "corrected" teeth which swell in the middle, or in the case of slightly conical teeth. This irregularity in the axial disposition of the clamped rollers impairs the geometry of their grip, which is no longer exerted uniformly around the gear. This may have a very unfavourable influence upon the quality of the grinding when the inside of the bore of a gear is supposed to be trued exactly concentrically with the cut gear.

It will also be noted that many different models of such roller-cages must be produced-for various diameters and for various modules, even on the same diameter--with only a few units of each model being manufactured. This explains why it must be practical to produce this type of roller-cage in very small runs and by what might almost be called craft methods, to the exclusion of expensive tooling which must be readapted each time another roller-cage model is to be manufactured.

Thus there is a need for a roller-cage which makes it possible to eliminate the drawbacks previously mentioned while answering the nonprohibitive manufacturing requirements indicated above.

According to the present invention, there is provided a roller-cage for gripping a gear to be machined on a grinding machine or other machine-tool, comprising a cylindrical ring formed with apertures uniformly spaced around or in at least three groups regularly distributed around, the circumference of the ring, a plurality of rollers each mounted, with radial play, in one of the apertures on a spindle disposed at an angle to a transverse plane passing through the axis of said ring, wherein each of the rollers has a specific axial dimension between two plane end faces thereof extending at right angles to the associated spindle, and wherein the apertures are identical to one another, are all identically positioned in the ring with respect to the side edges of the ring, and each has two opposed straight edges at right angles to the associated spindle and separated by a distance which is sufficient to prevent jamming, but not great enough to allow axial displacement of the associated roller.

Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal section, taken on the line I-I of Figure 2, through the chuck of a machine-tool, typically an internal grinding machine, in which a gear is gripped by a roller-cage according to the invention, Figure 2 is an end-on view of the assernbly shown in Figure 1, Figure 3 is a section along the same plane as Figure 1, showing a detail of the roller-cage on a larger scale, and Figures 4 and 5 are partial views of rings forming part of two further embodiments of the roller-cage according to the invention.

Figure 1 shows a chuck (fixed in a manner not shown to the spindle of a grinding machine, for example) comprising concentric parts 1 and 2 and three jaws 2a. With the aid of a roller cage 4, the chuck grips a gear B, the inner bore of which is to be ground. An axial stop sleeve 3, fast with the spindle or with the chuck, holds the gear B axially. It should be noted that, as a variation, the sleeve 3 might be larger in dia meter so as to rest against the roller-cage 4 rather than against the part to be ground. In that case the roller-cage would have to be in serted in the chuck the other way around so that the outer surface of a rim 6a thereof (Figure 3) would face towards the inside in order to rest against an axial stop sleeve analogous to the sleeve 3, but somewhat larger in diameter. This variation in the mounting of the roller-cage is advantageous in cases where the end face of the gear B against which the sleeve 3 is to rest is not precisely machined.

The roller-cage 4 chiefly comprises rollers 5 and a ring 6. The ring 6 includes rectangular (possibly square) apertures 7 in which the rollers 5 are disposed substantially without axial play, as shown in Figure 3. Each roller 5 is mounted on a spindle 8 with sufficient radial play to allow the roller 5 to move radially in order to transmit the gripping effect. Figure 4 illustrates the manner in which the apertures 7 are disposed in the ring 6 in the case of a roller cage intended to grip a gear having straight teeth, whereas Figure 5 shows the way in which the apertures 7 are to be disposed in the case of a rollercage intended to grip a helical gear. In the embodiments illustrated, each spindle 8 is held by two studs 9 riveted to the ring 6. When the gear B is clamped in the chuck, the rollers 5 are used to transmit the gripping effect of the jaws 2a so that the rollers 5 press against the opposing flanks of two adjacent teeth of the gear B. Each jaw 2a may grip by means of as many rollers 5 as the width of the bearing surface of the jaw 2a will permit. Thus the apertures 7 and the rollers 5 may be grouped accordingly in the ring 6, as shown in Figure 2.

However, when the roller-cage is used on a machine-tool--typically an internal grinding machine--which is designed to load the workpieces automatically or semi-automatically, the rollers 5 will preferably be situated all around the circumference of the ring 6. In this case, the gear B, mounted in advance in the roller-cage 4, can be placed in the chuck in any rotary position since, regardless of this position, there will always be a sufficient number of rollers 5 situated in the regions where the clamping action of the chuck jaws 2a is applied.

Particularly when the teeth of the gear have a cross-section which varies along the length of the tooth, e.g., in the case of "corrected" teeth which swell very slightly in the middle, or in the case of slightly conical teeth, it is preferable to use rollers 5 having a cylindrical outer bearing surface only in a small middle portion thereof, the two portions near the axial extremities of the roller 5 being slightly conical, as shown in Figures 1 and 3.

When the roller-cage is to be used in this way, particularly to grip a gear having teeth with slightly bulging flanks, it is important for all the rollers 5 to act in the same transverse plane through the axis of the gear to be ground if it is desired to achieve very high-accuracy performance (about one micron) as concerns the concentricity of the inner bore with respect to the gear. In this case, it is absolutely essential to avoid any axial play of the rollers 5 on their spindles 8 and to ensure that all the rollers 5 are precisely aligned in said transverse plane. It is for this reason that the rollers 5 are disposed in the apertures 7 without any axial play except to the minimal extent necessary for preventing jamming. To this end, the rollers 5 must have parallel end faces which are at right angles to the axes of the rollers, and the edges of the apertures 7 adjacent to the end faces of the rollers must be straight and at right angles to the axes of the rollers. Each aperture 7 must also be precisely positioned, all the homologous points of each of the apertures having to be situated in the same transverse plane through the axes of the ring 6. In this way, the rollers 5 are positioned exactly as desired in that their end faces rest against the straight edges of the apertures, with the result that excellent grinding precision is achieved.

As regards the manufacture of the ring 6, and particularly the placement of the apertures 7 with the desired accuracy, it must be recalled that a great variety of cages may be necessary since each time the roller-cage must fit the diameter and the number of teeth of the gear.

On the other hand, only a relatively limited number of roller-cages of a single model will be needed each time, so that in order to manufacture a large variety of different rings with very high accuracy, it will be of advantage to employ a method of manufacture which not only is very flexible but also makes it possible to produce rectangular or square apertures in a sleeve with the required accuracy. For that purpose, a milling process, which produces rounded edges at least at certain portions, will not be very suitable; a method of machining by electroerosion, on the other hand, gives completely satisfactory results for making the apertures 7 in the rings 6. A single machine for machining by electroerosion, equipped with electrode-tools of various dimensions, makes it possible to manufacture a large variety of rings for roller-cages with the desired accuracy, in small quantities, and at no great expense.

In the embodiment illustrated, it will be seen that the ring 6 includes an inner radial rim 6a which serves two purposes, viz., to give the ring 6 greater rigidity and to provide a support surface for a marginal zone of an end face of the gear (e.g., B) to be internally ground.

In a variation (not shown) which is especially suitable for a roller-cage intended to grip gears of very small modules, but which would also be suitable for larger modules, it would be possible to fix the spindle 8, not in studs 9, but rather in bores made at the proper locations in the rim 6a and in a second rim, analogous to the rim 6a, but disposed on the other side of the ring 6, this second rim having notches, between the portions comprising the bores receiving the spindle 8, through which the teeth of the gear may pass when the gear is inserted in the roller-cage.

WHAT WE CLAIM IS: 1. A roller-cage for gripping a gear to be machined on a grinding machine or other machine tool, comprising a cylindrical ring formed with apertures uniformly spaced around or in at least three groups regularly distributed around, the circumference of the ring and a plurality of rollers each mounted, with radial play, in one of the apertures on a spindle disposed at an angle to a transverse plane passing through the axis of said ring, wherein each of the rollers has a specific axial dimension between two plane end faces thereof extending at right angles to the associated spindle, and wherein the apertures are identical with one another, are all identically positioned in the ring with respect to the side edges of the ring, and each has two opposed straight edges at right angles to the associated spindle and separated by a distance which, with respect to the axial dimension of the associated roller, is sufficient to prevent jamming but not great enough to allow axial displacement of said roller.

2. A roller-cage in accordance with claim 1 intended particularly for gripping a gear with teeth having a cross-section which varies along the length of the tooth, wherein the circumferential surface of each roller has a central cylindrical portion flanked by conical portions.

3. A roller-cage in accordance with claim 1 or 2, wherein each spindle is mounted adjacent to the cylindrical inner surface of the ring, in two studs riveted to the ring on each side of an aperture substantially in line with the middle of the straight edges of said aperture.

4. A roller cage in accordance with any preceeding claim, wherein the ring has an integral rim directed radially towards the centre and intended to support the gear axially.

5. A roller-cage in accordance with claim 4 intended particularly for a gear of very small module, wherein the spindles are fixed at one end in said rim and at the other end in a second rim likewise projecting radially inward from the ring circumference and having notches for the passage of the tips of the teeth of the gear wher the latter is placed in or removed from the roller-cage.

6. A rollercage in accordance with any preceeding claim intended particularly for a grinding machine having automatic or semi-automatic loading, wherein the ring is formed with said apertures containing rollers around its entire circumference.

7. A roller-cage in accordance with any preceeding claim, wherein the apertures are rectangular or square.

8. A method of manufacturing the rollercage defined in any preceeding claim, wherein the apertures are cut by electro-erosion out of the ring, which is made of metal.

9. A roller-cage for gripping a gear to be machined on a machine-tool, especially on a grinding machine, substantially as hereinbefore described with reference to the accompanying drawings.

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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. not be very suitable; a method of machining by electroerosion, on the other hand, gives completely satisfactory results for making the apertures 7 in the rings 6. A single machine for machining by electroerosion, equipped with electrode-tools of various dimensions, makes it possible to manufacture a large variety of rings for roller-cages with the desired accuracy, in small quantities, and at no great expense. In the embodiment illustrated, it will be seen that the ring 6 includes an inner radial rim 6a which serves two purposes, viz., to give the ring 6 greater rigidity and to provide a support surface for a marginal zone of an end face of the gear (e.g., B) to be internally ground. In a variation (not shown) which is especially suitable for a roller-cage intended to grip gears of very small modules, but which would also be suitable for larger modules, it would be possible to fix the spindle 8, not in studs 9, but rather in bores made at the proper locations in the rim 6a and in a second rim, analogous to the rim 6a, but disposed on the other side of the ring 6, this second rim having notches, between the portions comprising the bores receiving the spindle 8, through which the teeth of the gear may pass when the gear is inserted in the roller-cage. WHAT WE CLAIM IS:

1. A roller-cage for gripping a gear to be machined on a grinding machine or other machine tool, comprising a cylindrical ring formed with apertures uniformly spaced around or in at least three groups regularly distributed around, the circumference of the ring and a plurality of rollers each mounted, with radial play, in one of the apertures on a spindle disposed at an angle to a transverse plane passing through the axis of said ring, wherein each of the rollers has a specific axial dimension between two plane end faces thereof extending at right angles to the associated spindle, and wherein the apertures are identical with one another, are all identically positioned in the ring with respect to the side edges of the ring, and each has two opposed straight edges at right angles to the associated spindle and separated by a distance which, with respect to the axial dimension of the associated roller, is sufficient to prevent jamming but not great enough to allow axial displacement of said roller.

2. A roller-cage in accordance with claim 1 intended particularly for gripping a gear with teeth having a cross-section which varies along the length of the tooth, wherein the circumferential surface of each roller has a central cylindrical portion flanked by conical portions.

3. A roller-cage in accordance with claim 1 or 2, wherein each spindle is mounted adjacent to the cylindrical inner surface of the ring, in two studs riveted to the ring on each side of an aperture substantially in line with the middle of the straight edges of said aperture.

4. A roller cage in accordance with any preceeding claim, wherein the ring has an integral rim directed radially towards the centre and intended to support the gear axially.

5. A roller-cage in accordance with claim 4 intended particularly for a gear of very small module, wherein the spindles are fixed at one end in said rim and at the other end in a second rim likewise projecting radially inward from the ring circumference and having notches for the passage of the tips of the teeth of the gear wher the latter is placed in or removed from the roller-cage.

6. A rollercage in accordance with any preceeding claim intended particularly for a grinding machine having automatic or semi-automatic loading, wherein the ring is formed with said apertures containing rollers around its entire circumference.

7. A roller-cage in accordance with any preceeding claim, wherein the apertures are rectangular or square.

8. A method of manufacturing the rollercage defined in any preceeding claim, wherein the apertures are cut by electro-erosion out of the ring, which is made of metal.

9. A roller-cage for gripping a gear to be machined on a machine-tool, especially on a grinding machine, substantially as hereinbefore described with reference to the accompanying drawings.