The present invention relates to an orbital lapping head for natural stone, agglomerated and ceramic materials.

According to the present state of the art various types of heads for lapping and polishing stone materials, of the so-called disc type, are known these being usually provided with a plurality of plate or disc-shaped abrasive or diamond-coated tools, referred to as "discs", which are rotatably mounted on a body rotated by means of a spindle shaft. Generally, the discs perform an orbital movement composed of the following:

- a rotation about their own axis of rotation;

- a rotation about the axis of the spindle shaft.

This type of head is mounted on the bottom ends of the lapping spindles of the lapping/ calibrating machines.

An example of this type of head may be found for example in Italian patent

IT1307212, in which a working head comprises a flanged structure fixed to the bottom end of a lapping unit. Inside the flanged structure, a tool-holder shaft is rotatably supported and fixed to the rotating lapping spindle. The tool-holder shaft is integrally connected to a body provided with a disc-carrying plate on which the disc units are rotatably mounted.

Each disc unit comprises a rotating pin on which the disc, the supports or bearings and a gearwheel are mounted.

A central crown wheel which meshes with the gearwheels of each disc unit is mounted on the fixed flange structure.

When the spindle shaft is operated, the body rotates, so that the discs also rotate about the shaft and about the axis of the associated pin since the gearwheels of the disc units are caused to rotate by the central crown wheel.

EP 0974424 and WO 01 /70458 also describe lapping heads of the same type in which the body rotates integrally with and therefore at the same speed as the spindle.

The prior art, although widely established, is not without drawbacks. For example, the tool-holder shaft rotates at the same speed as the body on which the disc units are rotatably mounted and therefore at a relatively low speed, usually between 150 rpm and 250 rpm. Each single disc unit rotates about its own axis owing to meshing of its gearwheel with the central crown wheel integral with the flange structure fixed to the lapping spindle. Since the discs must rotate at a high speed in order to achieve optimum working conditions for the abrasive tools, preferably at a speed of between 2000 rpm and 3000 rpm, a high multiplication ratio must be used. Therefore, the transmission ratio of the central crown wheel and the gearwheels of each disc unit is very high and may reach even values of 1 :15. It is known that the more the transmission ratio of the two wheels deviates from a 1 :1 ratio, the greater are the resultant problems. In fact, with an increase in the transmission ratio, the dimensions of the gearing increase and therefore the overall dimensions of the head also increase. Moreover, operation becomes less regular and uniform.

The prior art has already considered this problem and attempted to solve it.

For example, in utility model IT 256251, the body, which is the rotating support element of the discs, is independent of the rotational movement of the shaft and rotates in the opposite direction to the shaft.

Two crown wheels are keyed onto the shaft: a first crown wheel which meshes with the gearwheel of each disc, while the second crown wheel meshes with a first gearwheel rotationally integral with a second gearwheel (these two gearwheels are keyed onto a pin which is integrally mounted on the body, so as to be able to rotate about itself). The second gearwheel meshes with a third crown wheel which is integral with the flanged structure and therefore fixed.

During operation, when the shaft rotates, the first and second crown gears rotate. The first crown gear causes rotation of the single disc units. The second crown gear causes rotation of the first gearwheel and therefore the second gearwheel which is integral with it and which, meshing with the third fixed crown wheel, allows the pin (on which the two gearwheels are fixed) and therefore the body to rotate.

The arrangement of the parts is therefore relatively complex and unsuitable for different conditions of use.

In particular, in the embodiments of the prior art, it is not possible or in any case it is very difficult with a same body structure to achieve different speeds of rotation of the discs about their axes.

In fact, owing to the volume, in the case of the heads having a body integral with the shaft, or the complexity of the heads, where rotation of the body is independent of the shaft, it is practically impossible to vary the dimensions of the gearwheels which form the gearing for transmission of the rotational movement to the single disc units, in order to obtain different rotational speeds for the discs and/or different speeds of rotation of the head body.

The object of the present invention is therefore to solve substantially the drawbacks of the prior art.

A first task of the present invention is to provide a head in which the shaft rotates at a speed ranging between the low speed of rotation of the head body and the high speed of rotation of the discs and consequendy render rotation of the body independent of that of the shaft.

A second task is to provide a head in which it is possible to vary the dimensions of the gearwheels which form the gearing transmitting the rotational movement to the single disc units so as to be able to obtain different speeds of rotation for the discs and/or different speeds of rotation of the head body.

A further task is to provide a fast-disc lapping head which is compact and therefore is small-size and low-weight and operates in a regular and uniform manner.

Finally, a further task of the present invention is to provide a lapping head which is suitable for machining surfaces which may be rough and not entirely smooth.

The object and the tasks are achieved with a lapping head according to Claim 1.

In particular, a disc-type lapping head comprising a fixed structure and a rotating structure is provided. The lapping head comprises a plurality of backing discs which are arranged on the rotating structure (or casing), each disc being mounted on a disc shaft and disc gearwheel. A shaft, which is fixed in axial alignment with the spindle shaft of a machine, is arranged rotatably on the fixed structure and is provided with a first gearwheel and a second gearwheel. The first gearwheel is adapted to mesh with the plurality of disc gearwheels for transmission of the rotational movement from the shaft to each disc. The second gearwheel is adapted to mesh with an intermediate (or idle) gearwheel mounted rotatably on the fixed structure. The intermediate gearwheel is adapted to mesh with inner teeth provided on the rotating structure, for transmission of the rotational movement from the shaft to the rotating structure.

The characteristic features and advantages of a lapping head according to the present invention will emerge more clearly from the description, provided hereinbelow, of a number of examples of embodiment provided by way of a non-limiting illustration with reference to the accompanying drawings, in which:

Fig. 1 shows a diagrammatic cross-sectional view of a first embodiment of an orbital lapping head according to the present invention; and

Fig. 2 shows a diagrammatic cross-sectional view of a second embodiment of an orbital lapping head according to the present invention.

The lapping head 12 according to the present invention comprises a fixed structure 14 and a rotating structure 16. The fixed structure 14 is the part of the lapping head which is kept immobile, for example by fixing it to the structure of the machine (not shown) on which this type of head is used. Usually this type of head is mounted on an operating unit (not shown in the accompanying figures) designed to move the lapping head on the working surface. The movement of the unit on the working surface is a characteristic known per se to the person skilled in the art and therefore will not be described in greater detail.

The fixed structure 14 and the rotating structure 16 may be arranged in various ways, for example one inside the other with bearings in between.

The lapping head 12 comprises a shaft 24, which is preferably vertical, for transmission of the rotating movement to the rotating structure 16 and to a plurality of discs 18, as will be explained further below. For the sake of clarity, although the head according to the present invention comprises a plurality of discs, the latter (and also their parts) will be always indicated by the same reference number.

The plurality of discs 18 project from an operating surface 36 of the rotating structure 16. The operating surface 36 of the rotating structure 16 is the surface which faces the article being machined during lapping.

Each disc 18 is provided with a disc shaft 20 and a disc gearwheel 22. Advantageously the disc shaft 20 may be arranged on the rotating structure 16 by means of bearings 38, 40. The rotating structure 16 is therefore adapted to house the plurality of discs such that they may rotate about their own axis.

A first gearwheel 26 and a second gearwheel 28 are mounted on the shaft 24.

The first gearwheel 26 is adapted to mesh with the plurality of disc gearwheels 22, for transmission of the rotational movement from the shaft 24 to each disc 18.

The second gearwheel 28 is adapted to mesh with an intermediate gearwheel 30 provided on a rotating pin 32 provided on the fixed structure 14. The intermediate gearwheel 30 is adapted to mesh with inner teeth 34 provided on the rotating structure 16. In other words, the inner teeth 34 surround the second gearwheel 28 and the intermediate gearwheel 30, meshing only with the latter.

The operating principle of the lapping head 12 according to the present invention may now be easily understood by the person skilled in the art.

When the shaft 24 is rotated, the first gearwheel 26 which meshes with the disc gearwheels 22 causes rotation of each disc 18 about its rotational axis (indicated by the reference number 42 in the attached figure) which coincides with the axis of the disc shaft 20. Moreover, the second gearwheel 28 which meshes with the intermediate gearwheel 30 which in turn meshes with the inner teeth 34 provided on the rotating structure 16 causes rotation of the rotating structure 16 about the axis of the shaft 24 (indicated by the reference number 44 in the attached figure).

This therefore results in the composite movement of the discs 18 mentioned at the start of the present description, and in particular:

1) a rotation of the discs about their own axis of rotation 42; and

2) a rotation of the discs about the axis of rotation 44 of the shaft 24.

In accordance with a possible embodiment of the present invention the axes 42 of the discs 18 are preferably inclined by a few degrees or fractions of a degree with respect to the axis 44 of the shaft 24, in order to use frustoconical-shaped disc tools and avoid therefore prolonged contact between the diamond-coated tool and the stone material and thus allow the necessary cooling of the abrasive granules. In particular, each axis 42 may be inclined at angle of between 0.2° and 2.5° with respect to the axis 44 of the shaft 24. Advantageously, the disc gearwheels 22 and the first gearwheel 26 may be provided with teeth which have a suitable shape for meshing correcdy with each other, their axes not being parallel.

In accordance with an alternative embodiment of the present invention, the axes 42 of the discs are parallel to the axis 44 of the shaft 24.

The particular arrangement of the parts of the lapping head 12 which mesh together allows the shaft 24 to be rotated at a speed greater than the speed of rotation at which the rotating structure 16 housing the discs 18 is rotated. Advantageously, the rotating structure 16 is designed to rotate in the same direction as the shaft 24.

In other words, the lapping head 12 has gearing with a reduction transmission ratio which receives the movement from the shaft 24 and transmits it to the rotating structure 16 or disc-carrying structure, as well as gearing with a multiplying transmission ratio which receives the movement from the shaft 24 and transmits to the discs 18.

For example, it is possible to provide a shaft 24 which rotates at a speed of 400 rpm, a rotating structure 16 which rotates at a speed of 200 rpm about the axis 44 of the shaft 24, and discs 18 which rotate at a speed of 2,200 rpm about their own axis of rotation 42. According to this embodiment of the present invention, the transmission ratio of the gearing which allows rotation of the discs about their own axis is 1:5.5.

It can be noted therefore that the rotating structure 16 does not rotate integrally with the shaft, but rotates at a speed lower than the rotational speed of the shaft. Therefore the shaft rotates at speed between the speed of rotation of the rotating structure, which rotates slowly, and the speed of rotation of the single discs, which rotate at high speed.

Considering instead the case of the prior art where the shaft rotates at the same speed as the speed of rotation of the rotating structure and therefore 200 rpm, the transmission ratio would be double, and in particular 1:11, and therefore decidedly high and subject to all the problems mentioned at the start of the present description.

In accordance with a possible embodiment of the present invention, the discs 18 are six in number. Advantageously, the six discs 18 may be divided into two groups of three, where the discs of one group rotate at a given speed, while the discs of the other group rotate at a slightly different speed. The difference in the speed of rotation is obtained in a manner known per se, by providing the disc units 18 with different disc gearwheels 22 which differ in terms of the number of teeth. In other words, a first group of discs 18 has a first disc gearwheel 22 with a first number of teeth (for example 28), while a second group of discs 18 has a second disc gearwheel 22 with a second number of teeth (for example 29).

This helps prevent ovalisation of the tools with consequent vibration of the head and therefore ensures better macriining, namely a high-quality polished surface.

Below possible values are shown for the number of teeth of the various gearing and number of revolutions of the shaft and the discs, the head comprising two groups of discs with a varying number of teeth of the disc gearwheels.

Example 1

Number of teeth of the first wheel: 92

Number of teeth of the second wheel: 47

Number of teeth of the disc wheel: 28/29

Number of teeth of the intermediate wheel: 22

Number of teeth of the inner toothing: 92

rpm of the shaft 420

rpm of the discs: 2305/2280

rpm of the rotating structure: 214.

Example 2

Number of teeth of the first wheel: 98

Number of teeth of the second wheel: 52

Number of teeth of the disc wheel: 23/ 24

Number of teeth of the intermediate wheel: 21

Number of teeth of the inner toothing: 94

rpm of the shaft 420

rpm of the discs: 2590/2549

rpm of the rotating structure: 232.

Example 3

Number of teeth of the first wheel: 85

Number of teeth of the second wheel: 47

Number of teeth of the disc wheel: 23/24

Number of teeth of the intermediate wheel: 21

Number of teeth of the inner toothing: 89

rpm of the shaft 420

rpm of the discs: 2420/2385

rpm of the rotating structure: 222.

In accordance with a possible embodiment of the present invention, the head may be provided with resilient elements 52 and/ or 54 which are arranged during assembly between components of the head in order to obtain a lapping head which is able to withstand slight inclination during machining, so that it adapts to the roughness and unevenness present in the material.

Advantageously, the shaft 24 of the lapping head 12 may be provided with a covering sleeve 56 which is adapted to receive the end of the shaft 24 and be substantially integral therewith. According to a possible embodiment of the present invention, resilient elements 52 and/or 54 may be arranged between shaft and sleeve 56 so that there may be a limited relative movement of shaft 24 and sleeve 56. However, the shaft 24 and sleeve 56 are adapted to rotate in an integral and synchronous manner.

In accordance with a possible embodiment of the present invention shown in Figure 2, the end of the shaft 24 is provided with a radial projection 58 along the entire circumference of the shaft 24 adapted to engage with a respective recess 60 in the sleeve 56. Advantageously, the sleeve 56 comprises two parts: a body 59 and a bottom part 57, which are adapted to be connected together in the region of the recess 60.

Advantageously, the bottom part 57 of the sleeve 56 is suitable for connection to the body 59 by means of screws 61. Said screws 61 have preferably an axis parallel to the axis of the shaft 44 and are designed for connecting together two opposite sides of the recess 60. Moreover, said screws 61 are designed to pass through holes 63 with their axis parallel to the axis of the shaft 24 and provided in the radial projection 58.

In accordance with a possible embodiment of the present invention, resilient elements 52 are positioned between the holes 63 and the respective screws 61. The resilient elements 52 may have a cylindrical shape and may be provided with a through-hole suitable for receiving the screw 63.

Said resilient elements 52 are designed to allow a limited relative movement of the shaft 24 and the sleeve 56 in the axial direction and a limited inclination with respect to the axial direction.

Advantageously, said screws and said corresponding resilient elements consist of a plurality, for example 5 or 6.

The resilient elements are preferably made of elastomeric material, such as rubber or polyurethane and the like. Advantageously, the resilient elements are silent block elements.

According to a possible embodiment of the present invention, a resilient element 54 may be positioned along the surface of the body 59 of the shaft 24, between the shaft and sleeve, so as to allow a limited movement of the shaft with respect to the sleeve in the radial direction.

In accordance with a possible embodiment of the present invention, a ball joint may be formed between the shaft and sleeve. In particular an end element 71 adapted to be fixed to the end of the shaft 24 may be provided. Said end element is adapted to form a ball joint with the bottom part 57 of the sleeve 56.

Two gearwheels 26, 28 are provided on the sleeve 56 in a manner similar to the preceding example.

The person skilled in the art will therfore be able to deduce that the head may be inclined a few degrees to as to adapt to any roughness of the material being machined, while keeping the shaft 24 in axial alignment with the spindle shaft.

Comparing the invention described above with the utility model IT 256251 it can noted that the type of transmission for the movement from the shaft to the rotating structure changes radically. In fact, in the utility model the crown wheel integral with the shaft and the crown wheel integral with the body are connected together by two gearwheels, while in the present invention there, is only one gearwheel between them.

Moreover, in the utility model, the gearwheel integral with the body is a gearwheel with small dimensions and with outer teeth, while in the technical solution of present invention the gearwheel has inner teeth and larger dimensions, thereby favouring the efficiency of the transmission.

It is therefore clear that, owing to the efficient distribution of the parts inside the head, the dimensions of the head may be smaller than those of the lapping heads according to the prior art.

Owing to the constructional simplicity, it is possible to vary, within certain limits, both the reduction ratio of the gearing transmitting the movement to the rotating structure, and the multiplication ratio of the gearing transmitting the movement to the single discs 18, thereby- obtaining different speeds of rotation both of the discs 18 about their own axis 42 and different speeds of rotation of the discs 18 about the axis 44 of the shaft 24.

The person skilled in the art, in order to satisfy specific requirements, may make modifications to the embodiments described above and/or replace the parts described with equivalent parts, without thereby departing from the scope of the accompanying claims.