"A device and a method for controlling the chamfering of a plane object" Technical Field

The present invention regards the technical field relative to the production's system of objects that have blunt-ended angles. The invention concerns in particular the technical field relative to the realization of systems that measure the processing outcomes of the bevel on the corner of objects made of different material as for example glass, crystal, marble and natural stones and ceramic tiles. Background Art The processing of the blunt-ended angles is called chamfering, a term that comes from chamfer, and can be processed manually or by a machine. Sometimes the chamfering has the function to reduce the attack of the corner, and some other times it is realized for just aesthetic functions. In substance the processing called chamfering act to bevel a right angle, or rather a 90° angle, through a cut of the same right angle in compliance with a plane that is normally placed at about 45° respect to the two planes that form the right angle. For example in the case of a tile, that has an upper face and a lower face and four sides that define the thickness of the same tile, the two main faces form the right angles, or rather of 90° along the corners between each upper and lower face and the sides. While the right angles between the lower face and the sides do not generate any problems, since once the tile is been installed, they remain hidden, however the corners between the upper face and the sides could sometimes give problems, and therefore they are eliminated with the chamfering operation. In this case the upper face is connected to the tile's sides through a plane that is normally placed at about 45° respect to the sides and the upper face, or rather through a bevel.

The angle plane or better of the bevel can obviously vary according to the different production's needs and can be of 30°, 60° or other. The processing of the right angle, or rather an angle substantially of 90° determines, indeed, the formation of a sharp edge on the corner, with a potential risk for the users of these objects, and with a remarkable fragility of the same edge submitted at risk of breaking and therefore of rejection. To remedy these hassles, the piece is submitted to the next procedure of chamfering that removes a small portion of the sharp part and makes the object lacking of the potential danger and fragility. These processing are made through the removal of the material from the same corners, for example with techniques that use tools that have surfaces which are strongly abrasive. These chamfering operations however can be used also to eliminate the right angle of an object just to obtain a decorative effect. This technique is used in particular for the production of objects made of glass or in stone to use as necklace, trays, footings or similar objects.

The chamfering operations have also the intent to guarantee that all the produced objects have the same dimensions, equal to a pre-established value, along the corners that delimit the bevelled objects. The chamfering however is a process that can present some imperfections. They can happen for the failed functioning of the relative equipment that do the chamfering in one or more points, or the processing can be excessive, or can be irregular and not aesthetically valid.

These imperfections can be verified only by a manual control, made on each piece, and observed from an operator when realizes that some deficiency exists. However the manual control doesn't consent to verify in an accurate way the risen irregularities, for example from a different size of the bevelled,

because can happen that it cannot be easily perceptible through a control made by a naked-eye from an operator. Even when this kind of control detects an imperfection, it would never allow to measure with precision the detected imperfection and therefore to attend to adjust it eventually. Besides, since the control is effected with a sampling rate, needed to avoid the checking of all the out coming pieces from the production cycle, anytime is detected an imperfection in the process of chamfering processing, is necessary to control a certain number of pieces previous to the one that resulted damaged, to verify the correct processing. A further inconvenient is bent to the fact that the control must be made often, for reasons of cost-performance, on sampling, without controlling one by one the pieces produced. This problem is much more felt in the field of tiles as they are produced for example in ovens or with manufacturing processes that make them not perfectly the same to each other, and therefore the chamfering process that can be correct for one tile could not be the same for the next one, making the random check scarcely useful.

There are not any know systems that allow to control in a very satisfying way the imperfection and not less that allow to make a measurement of the chamfering. Disclosure of invention

The mean of this invention is to solve the aforesaid and other inconvenient. We got to this point by adopting a system that has the described features found in the independent claims. Other features of the device are subject of the dependent claims.

The invention teaches a system that allows to control that all the objects that are submitted to the chamfering processing have predefined features, without introducing any alteration or deceleration of the process. Advantageously also it is possible to put the control phase according to this invention by integrating it in the process of the object that is chamfered, eventually supplying a feed-back of the control's outputs, which can be used to change the parameters of the chamfering processing or to check if the machineries that perform this processing keep the desired precision ratio, or also to make an automatic reject of a piece that doesn't respect the preferred dimensional tolerance, or still to stop the whole processing cycle.

The advantages that come from this invention are: that it is possible to measure objectively and in a repetitive way the processed objects; that it is possible to control completely the product exiting from the processing; that it is possible to control the operating status of the machine operators; that it is possible to block promptly the process when an abnormal occurrence is determined; that it is possible to rise the value of the production by reducing the damaged pieces.

The system stands to be used with special advantages in the ceramics tile's field, where the tile are submitted to the processing of grinding and chamfering, and where it is possible to apply it for controlling objects in movement on the production line and/or for the static controlling in lab.

With reference to the drawings we highlight how the angle (1) of a plane piece

(3) is bevelled through an inclined processing called "chamfering" that transform the right angle (2) in a way that it is constituted from at least an inclined part (17) delimited from the points of the corners (18) (20) that mark the end of the horizontal and vertical plane, or more general the corner's

points (18) (20) constitute, in the cross section view, the points in which finish the two collinear planes, or rather the plane of the upper face and the one of the side, to form the corner that is removed through a chamfering operation. The chamfering process is repeated also on the opposite side with the oblique surface (17) delimited by the corner's points (19) (21), and more generally it repeats itself, for example in the case of a tile, for all the corners between the upper face, or better the face that will be exposed when is set, and the sides of the tile, that define the thickness.

Obviously in the cross section view of fig. 1 and 2, the corners are illustrated as the corresponding points (18, 19, 20, 21) of the cross section view, and correspond to the lines of the two converged planes that form the corner, which is eliminated through the chamfering operation. The chamfering process is engaged in this case to eliminate the right angles, or rather the angles of about 90° that are created from the connection of the two planes, that constitute the sides of the tile, with one of the two faces of the tile, laying in the upper face with the sides through a plane that is placed at about 45° between the plane of the upper face and the one of the corresponding side, obtained with a removing operation of the material in correspondence to the angle of 90° between the aforesaid planes. More generally the chamfering process can concern only one, or more of these corners, and be done just for one or both faces of the tile. The method of this invention include the step of measuring the spreading of the surface and the position of the bevel, that is the relative area of the rounding plane between two surfaces that are perpendicular to each other, through difference in lighting.

The method for the measurement and control of an operating area of chamfering of a plane object, as for example a tile or a similar product, includes the following steps: a. Prearrange a lighting area, defined as an area fitted of at least two different types of lighting obtained through two lighting sources, a first source of scattered light, and a second one of directional type, faced to each other and where is defined the aforesaid area of lighting. b. Place the plane object at least partially in the area of lighting, in a way in which at least one part of the chamfered object is inside the aforesaid area of lighting, facing this processed part of the object to the source of directional light. c. Have a vision system, as a video camera or similar, from the side of the area of lighting that has the aforesaid source of directional light. d. Send the directional light on the aforesaid object in a way that the light is inclined respect to the plane of the object by an angle that is less or equal to the angle that is formed from the plane defined from the aforesaid chamfering process respect to the same plane of the object. e. To get an image of the object through the vision system.

In particular, in the case of a tile, it is put in the area of lighting with the area that is processed with the operation of chamfering facing up.

We define the lighting area as the area that is exposed to the light's ray and/or framed by the vision device.

The tile is therefore illuminated from below through a widespread light and its image, shot from a top view is acquired. The tile is therefore illuminated from above, through a directional light, that forms respect to an horizontal axis an angle that is smaller than the angle of the rounding plane made by the

chamfering operation in respect to the same horizontal plane. The image of the tile is therefore acquired preferably at the same time with the ignition of the two lighting sources.

Preferably indeed both of the lights are turned on, the upper and the lower one and is acquire only one image that presents light zones and dark zones, as described later on, and in which the dark zones are correspondent to the chamfer zone, that can therefore been measured and evaluated in relation to its conformity of position and/or dimensions.

In this way we obtain that the chamfering area, or rather the rounding plane that came up from the chamfering operation, remains hidden.

The directional lighting is in fact projected along a lighting axis that goes from the centre of the tile to the same chamfer, hence geometrically, if the chamfer is correctly positioned (or rather if it presents a correct angle of the plane), the same remains hidden. The widespread light is issued from below the tile.

Therefore the images of the zones in shade and the illuminated zones are acquired, and they are overlapped, giving rise to a unique image in which the chamfer zone is hidden.

In general the method of this invention foresees the usage of a camera system, for example a video camera (4), placed upon the object in a way that its shooting axis is vertical respect to the object that must be checked.

Preferably the video camera is of a matrix type, known at the state of the art.

The method foresees the usage of a lower lighting system, also called backlight, with any scattered light illuminator (5) that, if placed under the object (3), drives the widespread light ray upwards. If there was only this illuminator, the image framed from the video camera would be that (6)

represented in Fig. 4 in which the dark area (7) reproduces the area between the point of the corners (20) and (21) leaving outside of them a white space (8). Fig. 4 is therefore a representation of the only part of the image that is obtained with the lower widespread lighting. The method foresees the usage of an upper lighting system (9). If there was only this last illuminator, the image framed from the video camera would be that (12) represented in Fig. 6 in which the bright area (11) reproduces the area between the point of the corners (18) and (19) leaving outside of them a dark space (10). Fig. 6 is therefore a representation of the only part of the image that is obtained with the lower widespread lighting. The upper directional illuminator (9) is placed in a way in which the cone of light that project is directed toward the chamfer, or rather the inclined plane generated from the chamfering process, as shown in Fig. 5 and 7. The cone of light is inclined respect to a horizontal plane that coincides with the tile's one that has a smaller angle which forms the inclined plane of the chamfer with the same horizontal plane. This way we have that the bright cone doesn't illuminate the chamfer unless when the same presents a wrong perspective respect to the one before set and coincident at maximum to the inclination angle of the light cone projected respect to the horizontal plane, which is coincident with the one of the tile. The chamfer remains not illuminated, while the system of the vision gets the light that is reflected on the surface of the tile, generating the image of Fig. 6.

The method foresees the usage both of a lower illuminator (5), and an upper illuminator (9), that in a preferred executive way are always turned on or are turned on at the same time.

In a first preferred way of the invention the system object of the present invention foresees that the object that must be measured should be in motion respect to the device that do the measurement.

It could be for example a tile in an operating cycle and placed on a conveyor belt that moves.

The device foresees the presence of a video camera, in particular a matrix video camera, of a know type, placed above the measurement' zone in which the object goes through, in this case the tile, that must be measured. As measurement zone we define that space portion through which goes the object, or the part of the object that must be measured. As measurement we define the measurement of the chamfering obtained with the aforesaid method.

The device foresees also an upper illuminator, placed above respect to the measurement zone, and a lower illuminator, placed below respect the measurement zone.

A second executive way foresees instead that the tile stays in a still position respect to the lighting zone.

The presence of both the illuminators let that the image framed from the video camera (4) is that (13) represented in Fig. 8 in which the dark area (15) reproduces the chamfer or rather the inclined area (17) or rather the inclined plane generated from the chamfering operation that runs between the corner's points (20) and (18) from a side and between the corners (19) and (17) from the other side, while the bright central area (16) reproduces the surface between the corners (18) and (17) and the external area (20) the zone occupied by the object that must be controlled.

According to a advantageous feature the widespread light is beamed from a lower illuminator, as a circuit board with LED diodes to which is overlapped for example a semi-opaque glass.

The upper illuminator is on the other hand made of one or a number of LED that generate a directional light with an illuminating cone that goes from 15° to 25°.

A system for the measurement of the result of the mechanical processing of the chamfering, in accordance to the present invention, includes:

• means to illuminate in a coordinated way the plane object, both the upper part and the lower part.

• means to shoot the image of the plane object, for example with a matrix video camera.

• means to elaborate the acquired images and to determinate with precision the dimension of the object and of the process. • means to determinate the correctness of the process comparing the determined measurements with fixed thresholds of acceptability. A preferred executive form of the method and of the device foresees that the measurement of the chamfer get effected only in correspondence with one or all of the edges of the tile under consideration. Advantageously the programmed system to synchronise the illumination with the shooting with such an exposure time to guarantee still images (for example 1/1000 sec).

Advantageously the system is activated from a sensor that gets the position of the object of which the process result must be measured.

Advantageously the system can use video cameras supplied with different resolutions in base to the precision that we want to obtain and to the dimension of the object of which we want to control the process. Advantageously the video camera is places perpendicularly to the plane of the object that must be measured at a distance based on the desired precision and of the applied optic.

Advantageously the system presents a setting of the light intensity of the backlight to adapt it to the exposure time required.

Advantageously the system presents a setting of the light intensity of the upper illuminator to adapt it to the exposure time required and to the colouring of the object of which we want to measure the process: with the necessity to maintain the determined exposure time, comes up the problem to supply a major or a minor light energy to become adapted to the surface capacity to reflect this light energy. Advantageously the measurement accuracy of the system is raised by the usage of processing techniques well known in the image processing field, called great resolution or sub pixeling.

Advantageously the proposed system doesn't depend from the specific sub pixeling algorithm used. Advantageously the sub pixeling technique, that is well known and of which we will not give a detailed description, uses the information of brightness to raise the optic resolution of the shooting system.

Advantageously to illuminate the object of which we want to measure the processing result, we can use different types of lights for example LED, LASER projectors, fluorescent tubes, discharge lamps... The illumination

must highlight the zone that we want to measure, for example we ca use two ways of lower (backlight) and upper illumination.

Advantageously the backlight permits the shooting system to acquire the lower layout of the tile. Advantageously the upper illumination lets the shooting system to acquire the upper surface of the tile, underlining as the not illuminated area the zone interested on the processing that must be controlled.

Advantageously the combination of the two allows the shooting system to acquire with the illumination needed the zone obtained from the processing (fig. 8)

Advantageously the proposed system allows to acquire and to measure both objects in movement, as it happens on the production lines, and still objects, as it happens in lab.

Advantageously the system can have more video cameras to increase the accuracy of the measurements or the dimension of the piece that is to be measured.

Advantageously the system has a sensor that gets the position of the object of which the process result must be measured and activates the acquisition in the right time. Advantageously the system has an electronic circuit that can change the time and the duration of the illumination and adapt it to the capacity to reflect the light issued from the illumination devices of the same object.

Practically the execution features could change in an equivalent way to the shape, dimensions, arrangement of the elements, nature of the material that have been used, without exiting from the solution adopted for this idea and

therefore remaining in the limits of the protection accorded from the present licence for industrial invention.

Brief description of drawings

These and further advantages will be understood better with the following drawings, information as the practical exemplification, but not to be considered in a limited way, in which: The Fig. 1 shows schematically the result of the first processing that removes the material and determines the formation of the right angle. The Fig. 2 shows schematically the global result of the processing with the formation of a structure called "chamfer" which will avoid the inconvenient of the right corner showed in fig. 1.

The Fig. 3 shows the plane object above which is placed the device for the backlighting that allows determining the lower profile of the same object

The figure 4 shows the plane object framed from a video camera with the backlighting as the only source.

The Fig. 5 shows the plane object together with the upper illumination device.

The Fig. 6 shows the plane object framed from a video camera with the upper lighting as the only source. The Fig. 7 shows the plane object together with the upper and the lower illumination device.

The Fig. 8 shows the plane object framed from a video camera with both the illumination devices activated.