Tajnafoi, Jozsef (Karoly, HU)
Gellert, Karoly (Miskolc, HU)
Hidasi, Karoly (Miskolc, HU)
Gribovszki (Miskolc, HU)
Vekony, Sandor (Miskolc, HU)

05/459378

06/03/1975

04/09/1974

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Nehezipari, Muszaki Egyetem (Miskolc-Egyetemvaros, HU)

451/251

451/228, 451/919

B23Q27/00; B24B5/14; B24B19/08; F16H35/00; B24B5/00; B24B19/00; B24B5/16

51/32,33W,5R,90,95WH,97R,97NC,15R,15EC,287R,DIG.32 82/18

Kelly, Donald G.

Ramsey K. J.

Young & Thompson

We claim

1. A grinding machine comprising a grinding tool, means for rotating said grinding tool about a fixed axis, means for rotating a polygonal workpiece about its own axis in contact with said driving tool, means for rotating said axis of said workpiece about an eccentric axis at a speed of rotation equal to the speed of rotation of said workpiece about its own axis multiplied by the number of sides of said polygonal workpiece, and a correcting mechanism for changing the angular velocity of rotation of the workpiece about said eccentric axis in those sections of that motion which are associated with the grinding of the sides of the polygon while maintaining constant the speeds of rotation of said grinding tool about said fixed axis and of said workpiece about its own axis.

2. A grinding machine comprising a grinding tool, means for rotating said grinding tool about a fixed axis, means for rotating a polygonal workpiece about its own axis in contact with said grinding tool, a driven first tubular shaft surrounding and coaxial with a second shaft that rotates said axis of said workpiece about an eccentric axis at a speed of rotation equal to the speed of rotation of said workpiece about its own axis multiplied by the number of sides of said polygonal workpiece, and a correcting mechanism for changing the angular velocity of rotation of the workpiece about said eccentric axis in those sections of that motion which are associated with the grinding of the sides of the polygon, said correcting mechanism comprising a nonrotatable radially deformable ring concentric with said first and second shafts, means for selectively effecting the radial deformation of the ring, an arm carried by said first shaft for rocking about an axis parallel to but spaced from the common axis of said first and second shafts, said arm being biassed against said deformable ring thereby to rock the arm according to the deformation of the ring upon rotation of said first shaft, and means to transmit the rotary and rocking movement of said arm to said second shaft thereby to rotate said second shaft at a variable angular velocity.

3. A grinding machine as claimed in claim 2, said means for radially deforming the ring comprising shoes that bear against the deformable ring, and a rigid ring in which said shoes are screw-threadedly adjustable in radial directions to adjust the deformation of the ring.

4. A grinding machine as claimed in claim 2, and spring means urging said arm into contact with said deformable ring.

5. A grinding machine as claimed in claim 2, and a disc carried by said second shaft, a stop carried by said disc and engageable with a portion of said arm for transmitting said rotation and rocking movement of said arm to said disc, and means mounted on said disc for adjusting the position of said stop relative to said arm.

The invention concerns a grinding machine whereby diverse polygonal workpiece may be ground in a manner similar to convention roll grinding and internal grinding.

In the field of manufacture of machines, vehicles and mass production the demand arises ever more frequently to form workpieces for performing certain tasks in a polygonal shape. Polygonally shaped workpieces are particularly suitable e.g. for connecting shafts and components coupled thereto, for performing shape-determining tasks of mass production, tools, stamping tools and the like and for control tasks etc. Although their use affords great technical and economic advantages, their general reduction to practice has so far in many cases run into obstacles.

The major part of the obstacles has hitherto been the absence of a process and apparatus enabling the efficient, sufficiently accurate and economic production of a polygonal workpiece ground both externally and internally in a way similar to e.g. a shaft produced on a traditional machine tool.

A further obstacle to the rapid growth of use has also been the fact that the shapes and dimensions of polygonal workpieces required in industry may vary widely and in the hitherto known processes and apparatuses the change-over from one shape and one set of dimensions to another has meant a lot of time and considerable assembly work.

The wider use of polygonal workpieces has also been hindered by the fact that the hitherto known machines and devices used for their production had not been rigid enough to resist the rotational movements and translational circular movements (planetary movements) and elliptical movements giving rise to relatively large force effects without change of shape or wear; and after a relatively long operational life they could not ensure the specified dimensional accuracy, or alternatively in order to achieve the necessary rigidity, it has been necessary to build very robust and expensive machines and to limit the speeds of the movement which had an unfavourable effect on productivity.

To machine the exterior and interior surfaces of polygonal workpieces in a manner akin to turning there is already known a process and apparatus which can produce workpieces at a quality of grade IT 8, dimensionally accurately and true to the desired shape (Hungarian Patent Specification No. 156,607). To produce greater dimensional accuracy, better trueness of shape and higher surface quality one must employ grinding-type machining; however, between the tools of turning and grinding there are such differences in shapes, sizes and drive mechanisms that it is not possible to produce polygonal workpieces machined on the external and internal surfaces by copying a process and machine employed in turning.

In the hitherto known processes for grinding the external surfaces of polygonal workpieces great problems have arisen.

In many known processes a difficulty is caused by the fact that the movement of the large-mass grinding wheel, spindle, sheaves, headstock etc., caused by a lever mechanism generated considerable dynamic forces; in addition the headstock must move in synchronism with the movement of the workpiece which is difficult to achieve and which from the points of view of accuracy of working, wear and service life of the machine causes difficulties.

In one known process a difficulty is caused also by the use of elliptical motion in place of planetary motion in order to eliminate errors stemming from changes in diameter of the grinding disc. The motion is obtained by the superposition of two mutally perpendicular linear components 0f movement. This motion may be generated e.g. by means of an eccentric, wherein the horizontal component of the eccentric movement is transmitted to the rotary shaft of the grinding disc by a push rod and the vertical component by a two-armed lever. The lever arm ratio of the two-armed lever is adjustable, which makes it possible to change the circular motion into a movement along an elliptical path. The transmission to the grinding disc of the two components of movement set the requirement on the grinding disc that it should be journalled in a complicated system of positive constraints made up of the following parts:

The grinding shaft is journalled in main bearings. The main bearings are displaceable in vertical, linear guides. The linear guides are carried by a body which is displaceable in horizontal guides.

The horizontal guides are formed in a grinding slide which can be regarded as rigid enough.

Thus in this known system, the large-mass grinding disc rotating at about 3000 r.p.m. moves in a serially connected, weak constraint system, with a period corresponding to the number of sides of the polygon, for each rotation of the workpiece. This circumstance leads to the creation of large dynamic forces.

It occurs in the course of using polygonal workpieces that for an already existing workpiece machined on its external or internal surface, a suitable pair of workpieces is required to be made, and the already existing and the new workpieces have to be interfitted in accordance with the given requirements. This means in essence that one must be able to grind polygonal profiles, characterised by the given polygonal number and by the maximum and minimum radii, along differently profiled curves.

Some of the known processes and grinding machines also suffer from the fault that wear of the grinding disc greatly influences the trueness of shape and dimensional accuracy of the workpiece produce, and neither the auxiliary movements in the directions of feed and rotation, nor the main machining movement always be set to the optimum value.

The invention seeks to provide a grinding machine for the machining of polygonal workpieces by means of which both the external and the internal surfaces of workpieces can be finish-machined with a dimensional accuracy equal to that of traditional grinding processes; the workpieces belonging together and pushed into each other have external and internal surfaces which fit togehter along practically the whole of their circumference, during machining the generated dynamic forces are smaller by an order of magnitude than those in known solutions, the change-over from one polygonal shape to another of different dimensions and configuration can be effected quickly and easily, wear of the grinding disc has practically no influence on the trueness of shape and on dimensional accuracy, the auxiliary movements in the directions of feed and cut, as well as main machining movement may be optimised for the machining requirements at all times, furthermore the machine or construction used for grinding has few components, is not liable to breakdown, is rigid, and in addition affords the possibility of fitting ground workpieces to workpieces of a given polygonal shape fabricated by another process, by virtue of the fact that a polygonal profile characterised by a given polygon number and by maximum and minimum radii can be ground with differently profiled curves.

With the invention the task set is solved by rotating the workpiece to be ground about its own axis which is parallel with the axis of a grinding disc or ring which has either a stationary axis or an alternatingly moving axis, and at the same time the axis of the workpiece is rotated along the periphery of a cylinder of rotation with an axis parallel with axis of the workpiece, the number of revolutions being equal to the number of revolutions of the workpiece about its own axis multiplied by the number of sides of polygon, and the ratio of angular velocities of the former fundamental motions is periodically changed.

A further characteristic is that in the course of machining the internal surfaces, the shaft of the stone carrying out the machining and rotating about its own axis is displaced together with an arm performing an angular or linear movement about the axis of the grinding disc or ring carrying out the machining of the external surfaces, and the distance between the stationary shaft of the grinding disc or ring operating on the outer mantle and the point on the periphery of the stone farthest or nearest to the shaft is kept equal to the radius of the grinding disc or ring operating on the outer surface.

A further characteristic of the invention is that in the course of machining both half-sections of each side of the polygonal workpiece, from the starting point of a half-section the angular velocity of the planetary movement of the workpiece is continuously changed to a maximum value, then by changing the sign of the change of angular velocity the change in angular displacement stemming from the change in angular velocity is continuously reduced to the end of the half-section.

Another characteristic of the the invention is that during machining the workpiece is rotated about its own axis and the shaft of the workpiece is rotated in the same or in the opposite direction along the periphery of the cylinder of rotation.

The grinding machine according to the invention is characterized in that it has: a main spindle rotating about an axis parallel with the axis of a tool, e.g. a grinding disc or ring, rotating about a stationary axis, an axially adjustable tailstock spindle parallel and rotating synchronously with the main spindle, a respective centre in the main spindle and in the tailstock spindle, which centres are either of constant eccentricity and exchangeable or are of adjustable eccentricity, a driving device for the workpiece mounted between the centres, further, it has between the driving device and the main spindle a transmission for effecting a positive rotational coupling, with a transmission ratio equal to the number of the polygon, i.e. the number of sides of the workpiece, and in the kinematic chain of the gear mechanism, in the sections of the translational circular movement belonging with the polygonal sides, there is a correcting mechanism which periodically changes the angular velocity.

A further characteristic of the grinding machine according to the invention is that it has an arm angularly displaceable about the axis of the tool e.g. a grinding disc or ring for machining the outer surface of the workpiece which arm forms part of the mechanism for keeping the rotating tool, e.g. the bore stone, for machining the internal surfaces in oscillating motion along a predetermined circular arc, a slide on the arm freely displaceable along the length of the arm, and a second arm which can be rotated about one of its ends that is at the axis of the cylinder of rotation described by the axis of the workpiece, while the other end is secured to the slide so as to be rotatable about the centre point of the latter.

A further characteristic of the grinding machine according to the invention is that it has an arm displaceable perpendicularly to the axis of the workpiece and parallel with the plane covered by the tool, e.g. pottery stone, grinding disc or grinding ring, for machining the outer surface of the workpiece, which arm forms part of the mechanism for keeping the tool, e.g. the bore stone which rotates about its own axis, and which is for machining the internal surfaces, in oscillating motion about a predetermined linear path; and it has on said arm a slide supporting a further arm, the slide being freely displaceable along the length of the first arm, the further arm beng pivotable about the centre point of the slide, and the second arm is rotatable about its other end falling on the axis of rotation described by the axis of the workpiece.

A further characteristic of the grinding machine according to the invention is that it has two forks secured in parallel on the shaft of the tool for machining the outer surfaces, the forks forming part of the mechanism for maintaining the bore stone for machining the internal surfaces in oscillation along a predetermined circular arc, and it has a mandrel projecting into the recess of one of the forks and secured eccentrically on the tail spindle, and further it has a spindle displaceable in the recess of the other fork and holding the bore stone for machining the internal surfaces of the workpiece.

A further characteristic of the grinding machine according to the invention is that is has a tapped spindle for moving the spindle holding the bore stone along the length of the recess of the fork, and a tapped profile coupled to the tapped spindle, and it has a dog clutch for interrupting the positive coupling in the transmission for effecting the rotational positive coupling between the driving device and the eccentric centre.

A further characteristic of the grinding machine according to the invention is that it has, in the transmission which brings about the positive rotational coupling between the drive mechanism and the eccentric centre, a correcting device which has an eccentric journalled in a disc; further, the eccentric has an end projecting into a recess in a disc secured for rotation with a shaft which transmits rotation, via gear wheels, to the main spindle supporting the centre; at the other end of the eccentric there is an arm which is always in contact with the surface of the correcting body; and further, the machine has a threaded spindle for displacing the correcting body along the length of the tubular shaft rotatable in an internal thread in the correcting body and by virtue of that rotation capable of carrying the disc in which the eccentric is journalled.

A further characteristic of the grinding machine according to the invention is that it has in the correcting mechanism, a ring radially deformable by shoes which can be set by screws in any desired angular position relative to a rigid ring which is concentric with a shaft having the same r.p.m. as the main spindle carrying the eccentric centre; in the bore of the deformable ring a disc is secured for rotation with a tubular shaft; an arm rotatable about a pin journalled in the disc; on one end of the arm there is a feeler urged into permanent contact with the surface of the bore of the ring by a spring; further, it has an arm portion which bears against a stop which projects from the other end of the arm and is adjustable by means of a tapped spindle on the disc rotating with the shaft.

A further characteristic of the grinding machine according to the invention is that it has in the correcting mechanism, a helical gear wheel which is mounted displaceably on and for rotation with the shaft for transmitting rotation to the main spindle carrying the eccentric centre, the gear wheel being biased in one direction by a spring; another helical, driving gear wheel meshing with the first gear wheel; a push rod guided in the casting of the main spindle housing and supported by a thrust bearing on the side of the axially displaceable gear which is opposite to the spring; and a ring which is rigidly secured to two diametrically opposite points of the disc secured on and for rotation with, the shaft, the remaining point of the ring being axially deformable by shoes which can be adjusted by screws in any angular position relative to the disc, the ring being in permanent contact with a roller mounted in the push rod and serving as a track for the movement of the roller.

A further characteristic of the grinding machine according to the invention is that it has epicyclic gearing in the correcting mechanism within the transmission bringing about the positive rotational coupling between the main spindle supporting the eccentric centre and the workpiece-driving mechanism, the epicyclic gearing being between the shaft rotating at the r.p.m. of the main spindle and a tubular shaft concentric with the first shaft and being tiltable about the shaft; and it has a roller rotatable on a shaft projecting from the casing of the epicylcic gearing; further, it has an arm of variable rotational axis one end of which is supported by the roller while the other end bears against the correcting body which is secured on the shaft for rotation therewith.

A further characteristic of the grinding machine according to the invention is that it has, in addition, an oblique bore formed in a body secured to the end of the main spindle, a centre with a cylindrical shaft journalled in the bore, and a push rod which is coupled to the internal end of the shank of the centre and which is displaceable along the axial direction of the main spindle.

The invention is described in detail with reference to the preferred embodiments of the grinding machine illustrated in the drawings.

FIG. 2 shows an embodiment of the grinding machine similar to that of FIG. 1, but with the difference that the axis of the workpiece rotates along the cylinder of rotation oppositely to the workpiece.

FIG. 3 is an exemplary scheme of a grinding machine according to the invention wherein machining of the external surface of the workpiece is carried out by a grinding ring, and the workpiece and its axis rotate in the same direction.

FIG. 4 shows an embodiment similar to that of FIG. 3, with the difference that here the workpiece axis and the workpiece rotate in opposite directions.

FIG. 5 is a view parly in elevation and partly in section of an exemplary mechanism for use in practising the scheme shown in FIGS. 1 and 2.

FIG. 6 is a view from another direction of the mechanism shown in FIG. 5.

FIG. 7 is a view of one of the forks of the mechanism shown in FIG. 5.

FIG. 8 is a view of the other form of the mechanism shown in FIG. 5.

FIG. 9 is a schematic view of a centre of continuously adjustable eccentricity.

FIG. 10 is a part-elevation, part-section of a driving mechanism of a construction different from that shown in FIG. 9 and being of a slotted link or fork type.

FIG. 11 is a diagram illustrating the possible profile changes in the case of a triangular shape.

FIG. 12 is qualitative diagram illustrating, for a triangular shape, the changes in the maximum difference t m in the normal direction between the profiles produced with a tool of infinite radius and with a tool of finite radius R _k .

FIG. 13 shows an exemplary embodiment of a grinding machine according to the invention wherein the arm carrying the spindle of the bore stone -- in the case of R k = ∞ -- performes linear harmonic motion, and the direction of rotation of the workpiece is the same as the direction of rotation of the workpiece axis along the cylinder of rotation.

FIG. 14 shows an embodiment similar to that of FIG. 13, with the difference that the direction of rotation of the workpiece is opposite to the direction of rotation of the workpiece axis along the cylinder of rotation.

FIG. 15 shows a scheme for an exemplary embodiment of the mechanism suitable for guiding the arm supporting the bore stone.

FIG. 16 shows a schematic variant of the mechanism of FIG. 15, using forks.

FIG. 17 is a scheme usable for grinding conical bores and is similar to the mechanism shown in FIG. 5.

FIG. 18 is a scheme of an exemplary embodiment of an insert usable in the mechansim shown in FIG. 17 and enabling the setting of any relative angular position between the oscillating and the rotating components.

FIG. 19 is a diagram illustrating the grinding conditions of points on the profile of minimum and maximum radii, for a rectangular workpiece.

FIG. 20 is a diagram illustrating the grinding conditions of a transitional profile section, between points on the profile of minimum and maximum radii, for a rectangular workpiece.

FIG. 21 is a diagram illustrating a family of curves obtained as a result of grinding with a disc of different diameters.

FIG. 22 is a diagram of an exemplary embodiment of the basic system of a grinding machine according to the invention.

FIG. 23 is a diagram for determining the nature of the auxiliary movements arising in the grinding machine according to the invention, and illustrating the grinding conditions of points of minimum and maximum radii on the profile.

FIG. 24 is a diagram for determining the nature of the auxiliary movements, and illustrating the grinding conditions of a transitional section between points of minimum and maximum radii on the profile.

FIG. 25 is a diagram similar to FIG. 21, but showing a family of curves producible on one whole side of a rectangular shape.

FIG. 26 is a diagram of an exemplary embodiment of a connecting mechanism usable in the case of a basic system to that shown in FIG. 22.

FIG. 27 is a diagram showing another location and construction of a correcting mechanism.

FIG. 28 is a side view of the correcting mechanism shown in FIG. 27.

FIG. 29 is a front view of the correcting mechanism shown in FIG. 28.

FIG. 30 is a schematic diagram of another exemplary embodiment of a correcting mechanism.

FIG. 31 is a more detailed view, on an enlarged scale, of the correcting mechanism of FIG. 30.

FIG. 32 is a schematic diagram of another examplary embodiment of a correcting mechanism.

FIG. 33 is a schematic diagram of an exemplary embodiment of an eccentric centre for clamping a workpiece.

During grinding the outer surface the axis of the grinding disc 4 is stationary, only the workpiece 1 rotates with an angular velocity ω _md around its axis 2 which rotates with an angular velocity ω _e around axis 3. During grinding the inner surface the workpiece 1 rotates as in the previous case, while the bore stone 5 is journalled in a link drive mechanism. The link mechanism moving the spindle of the bore stone has the following characteristics: the length of the arm 6 rotating about the axis 3, designated in the drawings by E, is E = (N--1)e. The centre point 7 of the link at the end of the arm 6 is opposite the axis 2, i.e. turned by 180°. The axis of oscillation 8 of the oscillating arm 8 coincides with the axis of the grinding disc 4.

The spindle of the bore stone 5 is displaceably secured on the swinging arm 8, and in such a manner that the point of the bore stone 5 nearest to the axis 9 is spaced from the axis 9 by a distance equal to the radius R _k of the grinding disc 4, and can deviate from this in the ± direction only by a small differential value. If the diameter of the bore stone is smaller than the diameter of the smallest osculating circle of the profile curve, then it does not influence the shape of the profile.

The embodiment shown in FIG. 2 works in principle in the same way as that of FIG. 1, but with the difference that the direction of rotation of the axis 2 of the workpiece about the axis 3 is opposite to that of the rotation of the workpiece about its own axis 2, i.e. ω _e and ω _md are of opposite senses. Compared with the previous embodiments the only deviation is that here the length of the arm 6 is E = (N+1)e, and that the straight line between axes 2 and 3 is on the same half-radius as the arm 6, i.e. they rotate in phase.

In the embodiment shown in FIG. 3 the direction of ω _e agrees with that of ω _md , and the outer surface of the workpiece 1 is machined by means of the tool of superfast grinding, i.e. a ring-shaped stone 10 grinding on its internal surface, which grinding ring 10 surrounds the workpiece 1. The characteristics of the link mechanism for supporting and moving the bore stone 5 are as follows: the length of the arm i.e. E = (N--1)e; the centre point 7 of the link mechanism and the straight line between the axes 2, 3 are mutually opposite, on opposite sides of the axis 3, and the axis of oscillation 9 of the swinging arm 8 coincides with the axis of the grinding ring 10. The spindle of bore stone 5 is secured to the arm 8, and in such a way that the farthest point of the bore stone 5 from the axis 9 is spaced from that axis by a distance equal to the radius of the working surface of the grinding ring 10, from which it can only deviate in the ± direction by a small differential value.

In the scheme shown in FIG. 4 the directions of ω _e and ω _md are mutually opposite. Its characteristics correspond to those described with reference to FIG. 3, with the difference that the length E of the arm 6 is E = (N+1)e, and the centre point 7 of the link mechanism and the straight line between the axes 2, 3 are on the same half-radius, i.e. rotate in phase.

FIGS. 5 - 8 show a practical embodiment corresponding to the schemes shown in FIGS. 1 and 2. The embodiment shown can be used on machines where for machining axle-like polygonal workpieces, between a chuck for holding the workpiece and performing a planetary motion and the centres there is a tailstock, the axis of the centre of the tailstock rotating on a cylinder of rotation with an angular velocity ω _e equal to that of the workpiece axis. The schematic embodiment of a main spindle of this type can be seen in FIG. 9, wherein in an external sleeve 11 there is an axial internal bore of eccentricity e in which an inner sleeve 12 is placed, and a further internal bore is also eccentrically formed in the sleeve 12, and the chuck-holding main spindle 13 is disposed in this further bore. The eccentricity of the bores of the sleeves are determined in such a way that in the angular positions shown in FIG. 9 the axis of the main spindle 13 coincides with that of the outer sleeve 11. Relative to the outer sleeve 11, the inner sleeve 12 is angularly displaceable and in the latter the main spindle 13 is also angularly displaceable. Thus a workpiece held on the main spindle can be brought in a planetary motion within wide limits by rotation of the sleeve 11 about its centre and by appropriately angularly displacing the inner sleeve 12 and the main spindle 13.

To grind outer surface, a tailstock of a construction similar to that shown diagrammatically in FIG. 9 may be used, wherein the outer sleeve of the tailstock rotates in synchronism with the outer sleeve 11 shown in FIG. 9. A detailed description of such a mechanism can be found in Hungarian Patent Specification No. 156,607.

In the embodiment shown in FIGS. 5 - 8, for bore grinding a tailstock centre is not required, and thus the latter can be used as a component rotating about the axis 3 shown in FIGS. 1 and 2. The grinding disc and belt pulley are removed from the spindle of the grinding disc serving to grind the shaft, and in their place forks (slotted links) 14 and 15 are secured such that the planes of symmetry of the forks should coincide (i.e. line d of FIG. 7 should be parallel with the line c of FIG. 8). In place of the circularly moving tailstock centre a mandrel 16 of cylindrical outer surface is secured, and the mandrel is secured without clearance between the limbs of fork 15. The minimum length of the mandrel projecting from the tailstock 17 is determined by the length of the inner surface it is desired to grind and the width of the fork 15.

In the fork 14 a small internal grinder spindle, driven by an air turbine or by high frequency, is secured, which holds a bore stone 5 at its end. The fastening is releasable and the spindle is displaceable along the limbs of the fork 14. The mechanism shown in FIGS. 5 - 8 has been adjusted in accordance with the principle illustrated in FIG. 1. This means that the mandrel held in the tailstock 17 moves on a circle of radius E = (N-1)e diametrically opposite to the axis of the workpiece 1 (like a is parallel with line b). If it is wished to adjust the mechanism shown in FIGS. 5 to 8 according to the principle illustrated in FIG. 2, then the mandrel 16 is set on the same half-radius as the axis 2 at a distance from the axis 3 of E = (N+1)e.

After starting up, the workpiece commences a planetary motion while the mandrel held in the tailstock 17 rotates. The mandrel 16 forces the fork 15 to oscillate and the oscillation forces, via the axis of the grinding spindle 18, the bore grinder held in the form 14, i.e. the bore stone 5, to oscillate, too. This oscillation is necessary not for working the corner (apex) part of the polygonal workpiece but for ensuring the identity of contours of the shaft and the bore.

Cutting and longitudinal feeding may be carried out in a conventional manner.

The fork and link driving mechanism may also be used for bore grinding, in a manner according to the scheme shown in FIGS. 3 and 4, even in the case of grinding outer surfaces with a grinding ring, if the shaft connecting the forks 14, 15 is provided with bearings parallel with the axis of the workpiece 1. To adjust the spindle of the bore stone 5 along the direction of the fork limbs, the driving link mechanism may also be provided with a threaded spindle 19, as can be seen in FIG. 10. Then it is expedient to form the spindle 20 of the large grinding disc with a bore, because in this case a bore grinding may also be used, the spindle being driven by a belt drive 21 provided with a suitable belt tensioner.

The process described so far ensures only that the hub bore and the shaft, and the profiles of the outer and inner surfaces, should be identical, but it does not ensure the independence of the profile from the diameter of the tool. For an outer surface profile of given diameter and eccentricity, the change of shape dependant on the diameter of the tool is not in practice significant, from the point of view of torque transmission, if the profile of the bore agrees with that of the shaft.

The nature of profile change for a triangular shape, i.e. N = 3, is shown in FIG. 11. For the same profile diameter and eccentricity, points A, B, C, D, E and F are present on all the profiles. Proportionally with the increase of the tool diameter or tool radius (R _k ), the area encompassed by the profile made up of the arc sections between the points decreases; the curve moves inwardly.

The maximum difference t _m taken at right angles betwteen the profiles prepared with a tool of infinite radius and with a tool of finite radius of R _k changes according to the qualitative diagram of FIG. 12, for a triangular shape.

In the Figure, e is the eccentricity, h is onehalf of the distance AD shown in FIG. 11, t _m ¹ is an equal-sided hyperbola, t _m ² is the asymptote of the latter, and t _m is the difference of ordinate between t _m ¹ and t _m ² .

The function t _m -R _k is already very flat in the case of R _k >2h and therefore a change ΔR _k in the vicinity of R _ko causes only a very small change Δt _m . From this it follows that e.g. in the case of a grinding disc of radius R _k = 150 mm, even by grinding shapes of 100 mm diameter, a decrease of 7 mm of grinding disc radius results in a change in profile of only ±1 micron, and by grinding polygonal shapes of smaller diameter the change is even smaller.

In practice one must reckon with the fact that after a certain service life polygonal workpieces are also used up, become faulty and must be replaced. The reproducibility of such workpieces is therefore important. This can easily be effected if the new component is prepared with a grinding disc of the same radius as that used for the outer surface of the original workpiece, and if the internal, bore surface of the new component is machined with a bore stone disposed at the same distance from the axis of oscillation of the arm 8 as in the case of the original workpiece. This can easily be effected if the value of the radius R _k of the grinding disc and the distance of the bore stone from the axis of oscillation of the arm 8 are, respectively, stamped into the used-up polygonal shape machined on the outer and inner surfaces, respectively. No problem is caused even if these values cannot be read off, since they can be easily and quickly established by means of measurements on the used-up workpieces.

The dependence of the profile shape on the diameter of the disc grinding the shaft can be lifted by always grinding with discs of the same diameter or of a diameter varying withing a narrow range. This can be achieved by using grinding discs either of low wear (borazon or diamond particle-coated discs) or of infinitely large diameter.

In the last-mentioned case, to realize the condition R _k = ∞, the schemes shown in FIGS. 1 and 3 are modified to the solutions shown in the schemes of FIGS. 13 and 14. Kinematically the only change is that in FIGS. 1, 2, 3 and 4, in the case of finite R _k , the arm 8 carrying the spindle of the bore stone 5 oscillates, whereas in the case of R _k = ∞ shown in FIGS. 13, 14 that arm performs linear harmonic motion.

The arm may be guided in the dovetail-type slide guides conventional in the machine tool art. A further example of a guiding arrangement is shown in FIG. 15, a variant of which, employing a fork, is shown in FIG. 16.

As already mentioned, the described very small (oscillation of a few degrees or linear) alternating movement of the bore grinder is required not for the finishing of the "corner" regions, but for bringing the profile of the bore into identity with the shaft profile.

Shaft and bore surfaces of small conicity may also be produced by the method described. In the case of cone grinding the embodiment according to FIGS. 5 to 8 is modified to that of FIG. 17. This embodiment differs from that of FIGS. 5 to 8 in that the radius of the cylinder described by the mandrel 16 held in the tailstock 17 is not E, but E _k = E(b/a), and in that at the connection location designated by point M on FIG. 17 one must use an insert which can ensure any relative angular position between the oscillating and rotating workpieces. One embodiment of this is shown in FIG. 18, where a ring 22, by being able to turn about pins 23, can take up any spatial orientation relative to the fork 15, and with the aid of the slides of a support member 24 it can take up any position in the direction of the limbs of the fork 15. The mandrel 16 clamped in the tailstock has to be fitted into the bore of the ring 22.

The mechanism produced with the condition R _k = ∞ (FIGS. 13 and 14) is suitable, after setting the angle of the workpiece table and without any further alteration, also for machining conical surfaces on shafts and bores which have greater aperture angles and which in principle interfit perfectly.

A significantly greater fitting accuracy of polygonal workpieces machined internally and externally than that achievable by known processes may be attained if, in practical working, the shape of the profiles delimiting the workpiece machined on the outer surface -- which profiles are slightly convex and elongatedly hypocycloidal -- are formed in the course of grinding, without notching or with minimum notching, just as if they were made by a turning tool. For this, the uniform rational and planetary movement of the workpiece is corrected. By the correction it is ensured that the formed profiles are independent of the diameter of the grinding stone.

In the case of the rectangular workpiece shown in FIG. 19, at the points of the profile of minimum and maximum radii -- at the places where the external and internal tangential circles touch -- the profiles are independent of the diameter of the grinding disc, since at these places the radius is perpendicular to the tangent of the profile, and whether the profile is machined with a knife, or with a grinding disc of small or large diameter, the tools contact the workpiece at the same profile points P ₁ , P ₂ .

Along the transition section of the profile connecting the points P ₁ , P ₂ the tangent is not perpendicular to the profile, hence the profile, which has been pre-machined on a lathe, is notched-in by the grinding disc: to a lesser extent by one of small radius and to a greater extent by one of larger radius. This is shown in FIG. 20.

In the case of unchanged eccentricity and outer diameter, there is obtained, as a result of grinding operations with grinding discs of different diameters, a family of curves wherein each curve is continuous and deviates from the other only along the transitional sections of the profiles and by a small amount (maximum of a few tenths of mm). The nature of these curves is shown exaggeratedly in FIG. 21.

The profile changes may be eliminated by a choice of the originating grinding disc surface such that the radius of curvature does not change on resharpening. Such a grinding surface may e.g. be the end surface of a pot-shaped grinding disc, wherein the radius of curvature is infinite and the same even after resharpening. Such a choice of the originating surface -- in the case of this invention, of the surface of the grinding disc -- solves in many cases the problem of avoiding or minimising notching. In practice, however, a difficulty is caused by the fact that large-size grinding discs (tailstock, shoulders) have not got enough room, and due to the new arrangement of the grinding spindle and disc the nature of conventional roll grinding machines has to be changed relatively significantly.

The problem of notching may be solved, instead of changing the originating surface, i.e. the grinding disc surface to one of infinite radius of curvature, by superimposing a correcting movement on the system's rotational and planetary movements, such that the basic movement constraints of the system are not increased, i.e. the resilience of the tool-workpiece system is not increased either, and large moving masses, which are unfavourable from the point of view of accuracy, are not used either.

FIG. 22 shows a simple, rigid system of basic constraints suitable for carrying out the process according to the invention, the Figure being a kinematic diagram of an exemplary embodiment of the workpiece-moving part of the grinding machine according to the invention. The workpiece-moving part of the grinding machine functions as follows:

The workpiece 1 to be ground is held between centres 25 and 26. Centre 25 is secured in main spindle 27, while the collet of centre 26 is guided in spindle 28, held against rotation relative to the main spindle 27 and tensioned by an axial spring. The parts of centres holding the workpiece are eccentric relative to the collinear axis lines of the main spindle 27 and spindle 28. The eccentricity is adjustable either by the means shown in FIG. 9, or by a radial link mechanism or by a providing a predetermined eccentricity between the chuck cone of the centre and the centre itself. In the latter case, several centres of varying eccentricity may be kept in stock from which the centres actually required for a given machining may be selected, the centres being rapidly exchangeable.

The workpiece 1 is rotatable by a driving device 29 which transmits drive also to the eccentric centres 25, 26. These rotate at the same r.p.m. The equality in r.p.m. is ensured by gear wheels 30, 31 and 32, 33 connected by a shaft 34.

The workpiece 1 rotates at an r.p.m. lower than that of the eccentric centres. The r.p.m. ratio -- without the correction -- agrees with the number of sides (or angles) of the polygonal workpiece to be ground. The drive is transmitted from shaft 34 via the correction mechanism 35 and the gearwheel-pair 36, 37 to the driving device 29.

This system can be mounted on the table of a conventional roll grinding machine and consequently the other movements associated with the grinding conform the conventional movements of shaft grinding. Any of the shafts in the system may be driven, thus e.g. the shaft 34 shown in FIG. 22 is driven by a DC motor 40 via belt pulleys 38, 39.

It is an advantageous property of the basic system shown in FIG. 22 that the rigidity of the eccentric centre 25 attains the rigidity of conventional centres, and that the main spindle 27 directly carrying the centre 25 is connected by a single main bearing to the casting of the main headstock, thus the whole system is rigid which guarantees great dimensional accuracy during machining the workpieces 1. It has the further advantage that the working spindles and bearings of roll grinding machines of known type may, after insignificant alterations, be successfully used for the grinding of polygonal workpieces, with unchanged characteristics of rigidity and accuracy.

In what follows, the correcting mechanism 35, shown merely symbolically in FIG. 22, and its tasks will be described.

Correction is necessary, because -- as has already been mentioned in connection with FIGS. 19, 20 and 21 -- the profiles formed with uniform rotational or planetary movements depend to a minor extent on the diameter of the grinding disc. Since the machined profiles are functions of the originating surface and of the machining movements, to eliminate profile changes one must change either the originating surface or the movements, or new movements must be imposed on the system.

An example of suitably changing the originating surfaces is the grinding with the front surfaces of pot-shaped grinding discs, wherein the radius of curvature of the grinding surface, i.e. the end surface is infinite and remains unchanged even after resharpening. This solution cannot always be used in practice, because such grinding discs are usually large-size and for such large grinding disc one cannot always provide enough space without necessitating considerable alterations to the whole grinding machine.

Changes in the movements, or the imposition of new movements on the system generally give an improved solution. To achieve new movements, a new constraint may be taken up by the basic constraints of holding the tool and the workpiece e.g. employing a conventional grinding disc for the roll grinding and either the workpiece or the tool is moved linearly, perpendicular to the axis of rotation in a plane parallel with said axis, for a grinding disc of any diameter, an infinite-radius can be substituted with this movement.

Large-radius grinding discs may be substituted in similar fashion by oscillating movements.

However, increasing the number of basic constraints increases the resilience of the tool-workpiece system; furthermore, the moving masses are large, and hence the workpiece cannot be produced with sufficient accuracy.

On the basis of the foregoing, the most expedient solution is to leave the basic constraints unaltered and to achieve the task by making changes in the kinematic chain. To attain this, the simple and very rigid basic constraint system shown in FIG. 22 is employed and the auxiliary movements required to eliminate the profile changes are imposed by means of the correction mechanism 35.

Variants of schemes for determining the characteristics of the necessary auxiliary movements are shown in FIGS. 23 and 24. All relative movements in FIGS. 23 and 24 have been imposed on the grinding disc so as to enable the formation of the profile to be demonstrated on a stationary profile. The grinding disc rotates with an angular velocity ω _f about its axis 41, which rotation is essentially the grinding rotation. In addition, the axis 41 of the grinding disc performs a planetary movement about axis 42 also. It can be seen from FIG. 23 that the axis 41 of the grinding disc is nearest to the axis 2 during grinding the point P ₁ and farthest from it when grinding the point P ₂ . The difference between the nearest and farthest positions is 2e, measured along the radii originating from axis 2.

In FIG. 24 the grinding disc is shown in the position where it grinds the transition section of the profile between points P ₁ and P ₂ . Then the radius or line connecting axes 41 and 42 is perpendicular to the radius connecting axes 2 and 41. If it is desired to achieve that the grinding disc should not notch into the profile made e.g. by turning, then the axis 41 of the grinding disc must be moved away somewhat from the workpiece 1, i.e. axis 41 must be moved along the velocity vector v (in the direction 2-41). Since the axis 41 already has a component of movement in the direction of v -- due to its rotation about axis 42 with an angular velocity of ω ₂ -- it is sufficient to increase the magnitude of v. For this increase in velocity it is not necessary to insert a new constraint among the basic machining constraint; one merely needs to increase the magnitude of the angular velocity ω ₂ -- as a basic constraint -- about the axis 42.

Since the magnitude of the displacement of the grinding disc is 0.1-0.2 mm and the radius length between axes 41 and 42 is 2-5 mm, the radial increase in magnitude is approximately linearly proportional with the resultant (net) angle of displacement (for small angles, α≉= tanα).

During grinding along the section between points P ₁ and P ₂ ω ₂ varies according to ω ₂ = Ω _2const +Δ ₂ ^. At P ₁ , Δ ₂ = O, from here it grows continuously and after reaching a maximum decreases continuously and at P ₂ it is zero again; further, the total angular displacement created by the charge in angular velocity is also zero. The sum of the increase is equal to the sum of the decrease, i.e. ##SPC1##

where

t ₁ = grinding time for point P ₁ ;

t ₂ = grinding time for point P ₂ ;

t _m = time of change-over from an increase to a decrease of the angular velocity.

The maximum value of Δα, the sum of the angular displacement due to the change in angular velocity, varies in dependence on what changes in grinding stone diameter are to be eliminated. The maximum value of Δαis small when the basic profile is regarded to be the profile prepared with a grinding disc of average diameter and without correction, or if profiles made with grinding discs of different diameters are corrected to such a basic profile. The value of Δαis greater when the basic profile is regarded to be the profile prepared with a grinding disc of infinite radius, or of zero radius, by turning, and surfaces ground with grinding discs of any diameter are corrected to this basic profile. The value of Δαis greater still if a interfitting polygonal bore and an external surface are all made by grinding. In this way all these surfaces depend on the working diameter of the grinding disc and the effect of the two grinding disc diameters is to be corrected in the course of producing one of the surfaces.

In grinding employing correction, and in the case of fixed points P ₁ and P ₂ , one can grind a family of curves, the characteristics of which are similar to curves shown in FIG. 21, which approximates to an elongated hypocycloid but is smoothly adjustable in relation to that within a range of a few tenths of a millimetre.

To produce such a family of curves, or a member thereof, one can use correction mechanisms wherein, in the range between the points P ₁ and P ₂ , the radial dimensions at any point may be adjusted smoothly and accurately by a few tenths of millimetres, and whatever the adjustment, the ground profile smoothly runs through points P ₁ and P ₂ .

To correct the transition section between points P ₁ and P ₂ in the case of small Δα, one may also use correcting mechanisms with which the radial dimension is adjusted accurately at only one characteristic point -- e.g. the centre point P _k -- and whatever the adjustment, the ground profile smoothly runs through points P ₁ and P ₂ . Thus, when using such a correcting mechanism, in addition to points P ₁ and P ₂ , points P _k are also prepared with a prescribed radial position, while at the other points of the transition section the deviations are of a magnitude of merely a few microns, consequently the thus-produced profiles are suitable from all points of view for normal grinding tasks. Nevertheless, in the preferred embodiments of correcting mechanisms, in general universally adjustable apparatus/mechanism embodiments are described.

From the viewpoints of driving and locating the correcting mechanism, one must know the repetition period of the correction. Generally from the point of view of correction a repeating period is constituted by two transitional sections associated with one of the angles of the polygon. To each angle of the profile there belongs one revolution of the main spindle 27 according to FIG. 22. Since the period number of the correction agrees with that of the formation of the polygon, the correction mechanism must be driven from a shaft whose r.p.m. agrees with that of the main spindle. Thus in the FIG. 22 embodiment the r.p.m. of the shaft 34 driving the correcting mechanism 35 agrees with the r.p.m. of the main spindle 27 by way of the 1:1 ratio between the gear wheels 31, 30. To practise the process according to the invention various correcting mechanisms may be constructed, among which a few adventageous embodiments are now described. These advantageous embodiments are usable in the basic system shown in FIG. 22.

In the exemplary embodiment shown in FIG. 26 the drive mechanism 29 is driven by gear wheels 36, 37 and 43, 44. Gear wheels 36, 43 are carried on a tubular shaft 45. The centre 25 is held directly by main spindle 27 driven from shaft 34 via meshing gears 31, 30. Similarly to the embodiment of FIG. 22, shaft 34 also drives the eccentric centre of the tailstock, not shown in FIG. 26.

When grinding cylindrical surfaces, the rotation of the eccentric centre 25 is stopped by pushing the clutch 49 to the left. There may be additional shafts in the kinematic chain between the device 29 and the main spindle 27.

In the exemplary embodiment according to FIG. 27 shafts 54, 55 and 34 are inserted into the kinematic chain of the polygon formation. Arrows 56 and 57 symbolise the gear drive units between these shafts. The correcting mechanism 35 is arranged between the shaft 55, which is tubular, and the shaft 34. The main spindle 27 is driven from shaft 34 by way of gears 31, 30 of gear ratio 1:1.

A further exemplary embodiment of the correcting mechanism is shown in FIGS. 28 and 29. On the shaft 55 formed as a tube a disc 58 is secured, and an arm 60 is journalled on the disc for rotation about a pin 59. A feeler 61 is secured to one end of the arm 60 and bears against the inner surface of a thin-walled, deformable ring 62. Two diametrically opposite points 63, 64 of the shaft are fixed on the same diameter to rigid, stationary, abutments. These points correspond to the points of minimum and maximum radius on the polygonal surface that are not to be corrected. The radial positions of the other points of the ring 62 are adjusted by shoes 65 which can be set in any angular position by being displaced in a circumferential, T-shaped groove of the ring 62. The shoes can be moved radially, relative to shoes 67 displaceable in a circumferential groove in a stationary, rigid ring 66, by screws 68. In dependence upon the deformation of the ring 62, the arm 60 performs a small rocking movement in the course of its circular, rotary movement.

The abutment surface on arm 60 transmits both the continuous rotational movement and the auxiliary movement stemming from the rocking to the abutment 70 set on the disc 69 secured on the shaft 64. The abutment 70 is radially adjustable by rotating the tapped spindle 71, and thus the correction is achieved, after first setting it by deformation of the ring 62, by auxiliary movements of the same characteristics though different magnitudes by altering the lever arm ratios of arm 60.

In the exemplary embodiments shown in FIGS. 30 and 31, shafts 34, 53, 54 and 72 are built into the kinematic chain between the driving device 29 and the main spindle 27. The connection between shafts 72, 34 is established by the gear wheel pair 73, 74 having helical teeth, of which pair gear wheel 74 is axially displaceable. A spring 75 urges the gear wheel 74, via thrust bearing 76, push rod 77 and roller 78 towards a ring 79. Two diametrically opposite points of the ring 79 are fixed in the same axial position to stops 83. These points correspond to the points of maximum and minimum radiu on the polygonal profile, which do not need to be corrected. In accordance with the axial adjustment of the other points of the ring 79 the helically toothed gear 74 performs, during its rotation, a small-scale periodical oscillating axial movement, which -- due to the helical teeth -- creates the change in angular velocity required for the correction.

To generate the correcting movement, other devices with 2° of freedom may be inserted into the kinematic chain between the workpiece drive and the main spindle. FIG. 32 shows an oscillating correcting mechanism of a construction similar to epicyclic gearing. Shafts 34, 53, 54, 72, 55 and 84 are inserted into the kinematic chain between the device 29 and the main spindle 27. Shaft 84 is jounalled in a pivotable housing 85 rotatable about shaft 34. The pivoting or rocking movement of housing 85 is imparted by the correction body 88 via roller 86 and arm 87. A correction of a certain character, adjusted or made once, can be transmitted in varying magnitudes to the kinematic chain by adjustment of the axis of rotation 89 of the arm 88.

The efficient use of the grinding machine according to the invention is strongly influenced by the construction, mode of clamping and adjustability of the centres 25. Embodiments other than that shown in FIG. 9 may also lead to good results.

Adjustable centres may be constructed simply also by e.g. centres mounted in radial small slides and slideways, which can be set and locked in various radial positions. A special solution well usable also for the automatic adjustment of eccentricity can be seen in FIG. 33.

Here, in the body 90 secured to the end of the main spindle 27 a bore 91 is made at an angle with the axis of the main spindle, and the centre 25 having a cylindrical shank is guided in this bore. The centre 25 is adjusted by an axially displaceable push rod 92. the eccentricity of the centre 25 may be changed by adjusting the push rod 92 in the direction of arrow 93. Adjustment of the centre 25 can be effected in many different ways via a thrust bearing.

The most important advantageous properties of the process and grinding machine according to the invention are as follows:

Both the outer and inner surfaces of polygonal workpieces may be finish-machined with a dimensional accuracy and trueness to shape corresponding to those of conventional grinding processes. The interfitting of two workpieces, one machined on its inner surface and the other machined on its outer surface, and the quality of the fit, can be chosen at will, even in the case of pairs made by different manufacturing processes. With given main parameters -- polygon number, maximum and minimum radii -- the surface shaped of the polygon is not restricted to one profile, but rather many different, freely selectable profile may be made and thus special technical tasks may also be achieved on the machine.