TECHNICAL FIELD

The present invention relates to a method for grinding glass sheets.

In particular, the present invention is advantageously but non-exclusively applied in bilateral grinding machines, to which the following description will explicitly refer without loss of generality.

BACKGROUND ART

As is known, in a bilateral grinding machine, a sequence of sheets to be ground is advanced along a rectilinear grinding path between two assemblies of grinding groups facing each other and each adapted to grind a relative side of the sheet.

Each assembly comprises a plurality of grinding groups, which are side by side to each other in the advance direction of the sheets and have respective grinders geometrically different from each other for progressively processing the lateral edge of the sheet and each removing a predefined amount of material variable according to their position, so as to obtain lateral edges having desired profiles and finishing degree. An example of such grinding machines is described in EP 1 422 024 Al . Each grinding group comprises its own frame and a relative grinder holder spindle, which is motor- driven and coupled to the relative frame by a guide and saddle adjustment device manually operatable by an operator in charge of the machine. Such device allows, in use, the continuous adjustment of the grinder position in a direction orthogonal to the advance path of the sheets for recovering the wear of the relative grinder.

Each frame is then rotatably coupled to the machine structure around a horizontal axis parallel to the advance path of the sheets for allowing the grinder position between a sheet grinding operating position, in which the grinder is arranged candle- wise and therefore rotates around a vertical axis orthogonal to the sheet, and a rest position, in which the rotation axis of the grinder is horizontal and the same grinder is easily reachable and replaceable .

In the above-described grinding machine, when the grinders need to be replaced, the machine is stopped, the frames rotated and the grinders brought to their rest positions.

At this point, the grinders are replaced, the frame are returned to their operating positions and the grinders are manually adjusted with respect to their frames and to the glass sheet by adjusting the respective guide and saddle devices up to bringing them, each, to a predefined sheet grinding position. Once all the grinders are arranged in their grinding positions, the machine is restarted and the grinding process interrupted before is resumed.

Although the above-described grinder change method is universally used, it is poorly satisfactory especially as it requires a particularly long machine downtime and therefore high costs in terms of production loss.

DISCLOSURE OF INVENTION

The object of the present invention is to provide a method for grinding glass sheets which allows the above problem to be solved in a simple manner and in particular allows the machine downtime for grinder change to be drastically reduced.

A method for grinding a glass sheet is provided according to the present invention as claimed in claim 1.

Preferably, in the above-defined method, said second grinder is displaced to said relative forward grinding position subsequent to detecting the need of replacing said first grinder.

Preferably, moreover, said second grinder is brought to said forward grinding position at the same time as or subsequent to the displacement of said first grinder towards said relative backward grinder change/maintenance position.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting exemplary embodiment thereof, in which:

figure 1 shows a perspective view of a bilateral grinding machine provided with a preferred embodiment of grinding groups for carrying out the method according to the teachings of the present invention; figures 2 and 3 show a partially plan view of the machine of figure 1 in two different functional conditions; and

figures 4 and 5 show a diagrammatic, block view of some details of figures 1 to 3 in different functional positions.

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1, reference numeral 1 indicates as a whole a machine for processing a glass sheet 2 and in particular, a bilateral machine for processing opposite lateral edges 2a, 2b of sheet 2 itself.

Machine 1 comprises its own fixed structure 3, a conveyor 4, per se known and not described in detail, for advancing sheet 2 in a longitudinal rectilinear direction 5 and, for each lateral edge 2a, 2b of sheet 2 itself, two grinding assemblies equal to each other and interchangeable and indicated with reference numerals 6, 7.

Assemblies 6 and 7 are independent of each other and arranged side by side in a direction parallel to direction 5 and are carried by respective lateral coupling portions 8 of structure 3.

In the particular example described, each grinding assembly 6, 7 comprises two relative grinding groups 9 side by side to each other and independent of each other. Each grinding group 9 comprises a relative movable supporting frame 10, a relative motor-driven spindle 13, per se known, on which a grinder 14 is keyed, which grinder is rotatable around its own axis 15 and a motor-driven guide and saddle device 16 interposed between frame 10 and the relative spindle 13.

Each guide and saddle device 16 comprises a guide 18 integrally connected to frame 10 and a saddle 19 coupled to the relative guide 18 for sliding in opposite directions along an axis 20 orthogonal to the rotation axis 15 of the relative grinder 14 under the control of a relative gearmotor comprising a motor 21 controlled by a command and control unit 22 of machine 1. Each frame 10 is coupled to the relative coupling portion 8 by means of a relative hinge for rotating around the relative spindle 13 with respect to portion 8 and around a longitudinal hinge axis 23 parallel to direction 5 between an upturned grinder change/maintenance position (figures 1 and 3), in which the relative spindle 13 is arranged in upturned position, the rotation axis 15 of the relative grinder 14 horizontally arranged and lifted with respect to the relative coupling portion 8, and an operating position, in which the relative spindle 13 is arranged in plunging or candle-wise position (figure 2), axis 15 of the relative grinder extends vertically and orthogonally to sheet 2 to be processed and grinder 14 itself is arranged in a position facing the relative edge 2a, 2b of sheet 2.

When arranged in their operating positions, spindles 13, along with the relative grinders 14, are movable parallel to themselves, under the thrust of the relative devices 16 to and from a forward grinding position of sheet 2.

The operation of machine 1 will now be described considering, for simplicity of description, the grinding assemblies 6, 7 arranged on one side only of sheet 2, the following remarks being identical for the grinding assemblies 6 and 7 arranged on the other side of sheet 2 itself and starting from the condition shown in figure 1, in which spindles 13 of assembly 6 are arranged in their operating positions and the relative grinders 14 arranged in their forward grinding positions of sheet 2 (figure 4), while spindles 13 of assembly 7 are arranged in their upturned grinder change/maintenance position, as is visible again from figure 1.

Starting from such condition, a sequence of sheets 2 is advanced in direction 5 and the edges of sheets 2 themselves are progressively processed by grinders 14 of assembly 6. During the processing of sheets 2, groups 9 of assembly 7 are subjected to maintenance and/or replacement of the relative grinders 14. Once the grinder maintenance and/or replacement has been completed, and still while processing sheets 2, frames 10 of assembly 7 are upturned and the relative spindles 13 first brought to their plunging position and then advanced by the respective guide and saddle devices 16 towards sheet

2 up to bringing them to a standby position, close to the forward grinding position and stored in unit 22. As is visible from figures 2 and 4, in such standby position, the relative grinders 14 are arranged close to the edge of sheet 2 but without ever touching sheet 2, which continues to be processed only by grinders 14 of assembly 6. Grinders 14 of assembly 7, when arranged in the standby position, are away from sheet 2 by a quantity D sufficient to prevent any minimal contact with the sheet being processed.

Spindles 13 and grinders 14 of assembly 7 are kept in such standby position until the need of carrying out maintenance and/or replacing grinders 14 of assembly 6 is detected. As such need occurs, interrupting or not the advance of sheets 2, spindles

13 of assembly 6 with the relative grinders 14 are moved backwards and away from their grinding position and thereby from sheet 2 by means of the relative guide and saddle devices 16 and then moved to their upturned grinder replacement/maintenance position.

At the same time as or immediately after the removal of assembly 6 from its grinding position, spindles 13 with the relative grinders 14 of assembly 7 are moved from the standby position to their forward grinding position, as shown in figures 3 and 5. Since distance D which separates the standby position from the sheet grinding position is very short (figures 2 and 4), the displacement of grinders

14 of assembly 7 to their forward grinding position requires a very short time and a simple and short horizontal shifting of grinders 14 by means of motors 21. At this point, while grinders 14 of assembly 7 process sheets 2, assembly 6 is subjected to the necessary grinder replacement/maintenance operations, at the end of which frames 13 of assembly 6 are upturned again, the relative spindles 13 brought to their plunging position and the relative grinders 14, as done with grinders 14 of assembly 7 returned, by means of the relative guide and saddle assemblies 16, to a standby position thereof also away from the edge of sheet 2 by a quantity D, as shown in figure 5. As with spindles 13 of assembly 7, spindles 13 of assembly 6 and the relative grinders 14 are kept in such standby position until the need of maintenance or replacement of grinders 14 of assembly 7 is detected. At this point, the same movement operations of assemblies 6 and 7 described above are repeated and assemblies 7 and 6 are exchanged.

It is clear from the above that the described grinding method, compared to the known methods, allows the machine downtime and thereby the losses resulting from a production loss to be drastically reduced. The above is essentially due to the fact that the two assemblies 6 and 7 are independent of each other and grinders 14 of the two assemblies are equal or identical and alternative to each other for carrying out the same process and removing an identical amount of material from the sheet. Therefore, the machine downtime is that strictly necessary for switching from one grinder assembly to the other.

It has experimentally been seen that against a machine downtime of about forty-five minutes with the traditional grinder change/maintenance methods, the above-described grinder change/maintenance method results in a machine downtime of less than two minutes.

As an alternative to the downtime of machine 1 and still operating according to the above-described method, it is possible to alternate assemblies 6 and 7 in processing sheets 2 without interrupting the advance of sheets 2. In fact, since the time required for alternating is very short, the . number of partially processed sheets to the discarded upon the output from the machine becomes widely acceptable.

It is clear from the above that the described machine 1 may comprise a different number of grinding assemblies 6, 7 and each assembly may be replaced, at most, by a single grinding group 9. In that case, again for each side of sheet 2, a first group 9 grinds the edge of sheet 2 while the second group is arranged in the standby position or in the grinder replacement/maintenance position. According to what said above, the second group must be arranged in the standby position before the first group requires grinder replacement and/or maintenance, i.e. while processing sheets 2 with the first grinding group.

Moreover, the grinding groups 9 may be different from what described by way of example and in particular, of the type in which the relative frame guide and saddle device is interposed between the relative frame and the machine base.

Finally, it is clear that the described method may be applied to grinding machines comprising not only grinding groups different from those described by way of example but to all those grinding machines in which the grinders are arranged between a grinding position and a grinder change/maintenance position along paths different from that indicated.