The invention concerns: a polishing head for plate ma- terials in granite, hard stone or ceramic, with abrasive segments having continuous tangential oscillating motion, that is, a rotating head which, by means of segments of abrasive material which are made to come into tangential contact with their slow oscillating motion, grinds and polishes the surface of the tile or slab of particularly hard natural or artificial material.

Prior art comprises various types of head with abrasive grinding segments with oscillating motion to grind and/or polish plate materials. The head described in patent EP 0437831 B1 is particularly relevant, in that the abrasive segments are made to oscillate on oscillating radial shafts driven by a pin each coupled, by means of a cylin- der that slides in a radial direction, to a ring having vertical eccentric rotary motion with respect to the axis of the head; the said ring is made to rotate by a first eccentric, driven by a pair of gears with internal teeth, in which the crown gear is connected rigidly to the casing of the head and the pinion, also mounted on a second ec- centric able to rotate freely with respect to the axis of the head, drives the said first eccentric by means of a pin attached to it, which slides in a radial groove; the eccentric rotation of the ring is controlled by a plurali- ty of pins mounted on eccentric planetary gears with ec- centricity equal to that of the said first eccentric; the second eccentric is coupled with anti-rotational joint to the structure of the machine on which the head is mounted, to provide a reaction to the motion transmitted to the said internal mechanisms.

The eccentricity of the said second eccentric is small with respect to the eccentricity of the first eccentric to lower the speed of oscillation and to achieve a slower dressing of the grinder; the eccentricity of the first ec- centric is larger, sized in relation to the required di- mensions, to obtain wider oscillation arcs and to avoid long segment-holder arms with consequently large vertical dimensions.

However, this solution, whilst constituting a valid im- provement on previous mechanisms with cams and/or rollers, does not provide a grinding/polishing action which is re- liable over a period of time, especially as regards high volumes of ceramic materials, for which all the quality control checks are employed, including the reflectivity of the polished surfaces.

These controls have shown that the said head does not provide a perfectly polished surface, but one which is polished in a discontinuous manner, with a veined finish, to the point where the materials thus machined are not ac- ceptable.

Furthermore, the head moves the grinding segments with singular points discontinuity that occur once every 1/n of the complete forwards and backwards stroke, that is, once for every rotation of the head, where n is the number of revolutions performed by the head to achieve one complete oscillation: this causes the dressing of the grinder to be momentarily stopped, thereby causing the cutting capacity of the abrasive segments to become discontinuous, due to the sliding motion of the contact line without the re- quired slow dressing motion.

Such prior art may be subject to considerable improve- ment with a view to overcoming the previously mentioned drawbacks.

From the foregoing emerges the need to resolve the technical problem of finding a new configuration of the mechanism for controlling the motion which enables the os- cillating motion of the grinding segments to be continu- ous.

The invention resolves the said technical problem by adopting a polishing head for plate materials in granite, hard stone or ceramic with grinding segments having con- tinuous tangential oscillating motion comprising: abrasive segments made to oscillate on radial shafts each driven by means of a pin coupled, by means of a cylinder which may slide in a radial direction, to a ring having vertical ec- centric rotary motion; the said ring coupled with rotatory motion to a first eccentric driven by gears with internal teeth, with the crown gear fixed to the housing of the head and the pinion coupled with rotatory motion to the second eccentric, in turn coupled with anti-rotational joint to the structure of the machine onto which the head is mounted; a plurality of pins mounted on eccentric plan- etary gears, with eccentricity equal to that of the said first eccentric, and coupled with rotational motion to the said ring and to the body of the head; means for connect- ing the said pinion to the said first eccentric; charac- terised in that there are: constituting the said means for connection, another pair of crown and pinion gears, in which the first crown gear is rigidly connected to the second pinion in turn coupled with rotatory motion to the said second eccentric; the first pinion connected rigidly to the said first eccentric concentrically with respect to the axis of the head; the second crown gear rigidly con- nected to the housing concentrically with the axis of the head.

The advantages obtained with this invention are: with

the two-stage reducing crown and pinion gears a low dress- ing speed of the abrasive is achieved, as the eccentricity of the said second eccentric is made to be small to obtain a low transmission ratio, made even more so by the two- stage reduction, without being limited by the high value required for the first eccentric; the dressing speed is constant throughout the oscillation stroke of the abrasive segment-holder arm, in that the motion does not have sin- gular points of discontinuity, except at the ends of the strokes, and the abrasive grinding segments always has a new cutting edge parallel to the previous one at every point during the oscillation, thereby achieving a com- pletely tangential cut. Also, the meshing arc between the crown gears and their respective pinions is very long and there are a large number of meshing teeth; the resulting tangential force transmitted on each tooth is therefore relatively low thereby considerably reducing wear; fur- thermore, the uniform distribution of the load prevents the teeth of the crown gear or pinion from being damaged should the grinding segments be subjected to shocks as a result of possible fracturing of the material during ma- chining. Also, all the segments are in contact with the surface being machined, with the exception of the one close to the end of its stroke: with this segment the in- version of the oscillation direction may occur when not in contact with the surface being machined, as contact is guaranteed for m-l segments, thereby avoiding the so called "pump" effect. Finally, the abrasive grinding seg- ments are constructed without the addition of side areas of the cylindrical surface to avoid the said "pump" ef- fect, thereby making the regeneration of the abrasive more economical and enabling it to be used completely.

An embodiment of the invention is shown, purely by way of example in the attached table in which the figure shows

diametric cross-section in a vertical plane of the polish- ing head as described.

The figure shows: 1, the abrasive grinding segment fixed to the segment-holder arm 2 in turn splined to the oscillating radial shaft 3; 4, the pin determining the os- cillating motion of the said radial shaft; 5, the body of the polishing head closed on its upper side by the housing 6; 7, the ring with radial grooves 8 in which slide the cylinders 9, each coupled to their respective pins 4 de- termining the oscillating motion; 10, a first eccentric driving the ring 7 in the said eccentric rotational mo- tion: the said eccentric being coupled with rotational mo- tion to axis A of the head with the body 5, and also cou- pled with eccentric rotational motion on axis E to the said ring, with eccentricity B; 11, weight saving holes in the said first eccentric; 12, a first pinion gear coaxial with axis A of the head, rigidly coupled to the said first eccentric 10 and rotating with it; 13, the first crown gear meshing with the said first pinion, but with eccen- tric rotational motion on axis P, parallel to the previous axes, but with eccentricity C; 14, a second eccentric pin- ion rigidly connected to the said first crown gear and ro- tating with it, meshing with a second crown gear 15 rigid- ly fixed to the housing 6 and rotating with it on axis A of the head; 16, lubricating oil passages; 17, the rolling bearing coupling with rotational motion the said first crown gear 13 and the second pinion 14 to a second eccen- tric 18, with said eccentricity C with respect to axis A of the head, and rigidly fixed to the prismatic reaction arms 19, by means of flange 20: the said arms being con- nected to the structure of the machine.

The figure also shows: 21, the connecting flange for the hollow shaft 22 of the head, inside which the cooling

fluid for the grinding segments and the material being ma- chined is made to flow; 23, elastic abutments for connect- ing the said hollow shaft, by means of joint 24, to the said body 5 of the polishing head; 25, the vertical pin of the eccentric planetary gear 26, coupled with rotational motion to the said ring 7, whereas the eccentric planetary gear is coupled with rotational motion to the body 5 of the head; 27, a chamber below the eccentric planetary gear and 28, a hole in the said planetary gear for lubricating oil connecting the chamber; 29, a sleeve, coaxial with hollow shaft 22, for guiding the rotation of the body 5 of the head, coupled with rotational motion by means of roll- ing bearings 30 to the inner diameter of the said second eccentric, coaxial with axis A of the said second eccen- tric 18; 31, the lip seal between the said sleeve 29 and the flange 20; 32, a cover with protective labyrinth for the seal 31; 33, the lip seal between the body of the said second eccentric 18 and the housing 6, with a protective labyrinth 34 for the said seal.

Operation of the polishing head is as follows: the ro- tation imparted by the drive shaft of the machine, by means of the flange 21, the hollow shaft 22, the joint 24 and abutments 23, is transmitted to the body 5 and housing 6, to which the said second crown gear is attached; the meshing of the said crown gear causes the rotation of the said second pinion 14 and the first crown gear 13, engaged with each other but free to rotate on the rolling bearing 17; the said second eccentric 18, to which the bearing 17 is splined, is kept fixed to the structure of the machine by means of the flange 20 and the prismatic arms 19, con- stituting reaction to the rotational motion imparted by the second crown gear; the resulting relative rotation be- tween the second crown gear and the second pinion is at low speed on axis P; the rotation of the first pinion 12,

meshing with the first crown gear 13, is at an even lower speed than that of the second pinion, but on axis A of the head. The speed of rotation depends therefore on the combined effect of the transmission ratios of the two in- line crown and pinion gear pairs; these have a value which makes the second crown gear 15 coaxial with the said first pinion 12, as in reducers with two pairs of gears with co- axial input and output shafts, thereby providing a linear transmission of the rotational motion to the said first eccentric 10. The oscillating motion is thereby imparted to the abrasive segments 1 by the eccentric rotational mo- tion of the said ring 7 imparted by the relative rotation between the first eccentric and the body 5; the eccentric- ity B of the first eccentric 10 is determined in function of the dressing requirements of the abrasive material em- ployed and of the sizing and positioning of the of the arms 2 and pins 4, in a manner not dependant on the eccen- tricity adopted for the two pairs of crown and pinion gears.

In practice the materials, dimensions and details of execution may be differ from, but technically equivalent to, those indicated without departing from the juridical domain of the present invention.