Patent Description:
As it is known, leathers must undergo several operations before they can be used for making a finished product. Some of the aforementioned operations are performed during the advance of the leather according to a predefined advancement direction.

Among the aforementioned operations, inspecting operations are also envisaged aimed at detecting the presence of defects on the leather. Known automatic machines for inspecting leathers comprise a feeding device for moving the leather according to an advancement direction, and a vision system based on cameras, that captures images of the surface of the leather during movement. A processor is also present to examine the aforementioned images and, by means of a suitable algorithm, to identify and classify the defects, thus allowing to calculate a parameter that represents the quality of the leather.

An inspecting machine according to a known variant generates a digital map of the leather, containing the coordinate of the observed defects relative to a reference point. The aforementioned digital map can be used in subsequent operations, for example before a cutting operation, to define the usable areas of the leather, in order to optimize the use of the latter and to minimize scraps.

The use of cameras in vision systems of the aforementioned inspecting machines implies some drawbacks. In fact, in order to to capture a wide enough area of the leather, the cameras must be arranged relatively far from the surface of the leather. This may bring inaccuracies resulting from vibrations or thermal deformations of the structure that supports the cameras. Moreover, due to the configuration of the camera optics, the image resolution is not uniform in the field of view, but it is higher in the center compared to the periphery. The wider the field of view, the greater the non-uniformity.

The two peculiarities just mentioned bring the drawback to limit the inspection precision that can be achieved, in particular when the leather to be inspected has a big size.

Further drawbacks relate to the known feed devices used to move the leather in the aforementioned inspecting machines.

Typically, a feed device of known kind comprises movable elements to drag the leather by friction. The aforementioned friction is achieved by exerting a compression on the leather by means of counter-rotating roller pairs, pairs of opposite bars, clamps, etcetera.

It is further known that the quality of a leather, hence its commercial value, depends on the surface condition of the leather, that should be as uniform and unaltered as possible compared to its original state.

An element that is decisive for the quality of the leather is its defects, which bring a reduction of the area that can be used to manufacture the finished products.

However, the compression exerted by the above mentioned feed devices of known kind may also alter the leather in the compression points, if not even damage it. The aforementioned alterations imply the drawback of reducing the quality of the leather.

Moreover, the aforementioned feed devices are not able to avoid that the leather slips in the advancement direction. The aforementioned slip may occur for several reasons, among which the slippery of the leather, the unevenness of its surface, the insufficient pressure exerted by the mobile systems on the leather during drag, and so on. The aforementioned slip brings the drawback of reducing the precision of the operations performed by the machine, or even increasing processing scraps, hence the relating costs.

A further drawback of the feed devices of known kind is due to the fact that the length of a leather is limited, and, generally, is comparable to the length of the path through the feed device. As a consequence, the aforementioned feed devices often require the intervention of the operator in order to ensure that the leather is clamped and correctly advanced along the device, so as to prevent formation of wrinkles and unwanted tensions.

Documents <CIT> and <CIT> disclose inspecting machines for leathers according to the prior art.

The present invention aims at overcoming at least in part the above mentioned drawbacks of the prior art.

In particular, it is an aim of the invention to make a leathers inspecting machine allowing to achieve a higher precision of inspection compared to that achievable by the inspecting machines of known kind.

It is also an aim of the invention that the aforementioned inspecting machine allows to perform a precise inspection on leathers of big size as well.

It is also an aim of the invention that the feeding unit does not alter the surface condition of the leather during advance, or, anyway, is such as to induce smaller alterations compared to that induced by the feed devices of known kind.

Another aim of the invention is that the feeding unit be capable to automatically clamp the leather and steadily guide it according to the advancement direction, maintaining a correct tensioning and avoiding formation of wrinkles.

The aforementioned aims are achieved by an inspecting machine according to claim <NUM>.

The aforementioned aims are also achieved by an inspection method according to claim <NUM>.

Further detail features of the invention are specified in the corresponding dependent claims.

Advantageously, the precision of the machine and of the method of the invention allows to reduce the errors in locating the defects, and, consequently, allows a more precise determination of the area of the leather that can be used for the subsequent processing, thus contributing to reduce the processing scraps.

Still advantageously, the higher precision of the machine and of the method of the invention allows to increase the area of the leather that can be used to manufacture the finished products, so as to increase its commercial value.

Still advantageously, the limited alteration of the leather due to the feeding unit allows to preserve the quality of the leather itself.

Moreover, advantageously, the automatic advance of the leather achieved by the feeding unit reduces the intervention by the operator, and, as a consequence, increases the productivity of the feeding unit of the invention compared to the feeding units of known kind.

The aforementioned aims and advantages, together with others that will be mentioned hereinafter, will be clearer from the following disclosure of some preferred embodiments of the invention, that are shown as exemplary and non limiting purpose with the help of the attached drawings.

The inspecting machine for leathers according the invention, indicated in the overall in <FIG> by <NUM>, is configured to detect one or more geometrical features <NUM> of a leather <NUM>.

The aforementioned geometrical features <NUM>, some of which are schematically shown in the figures from <NUM> to <NUM> through corresponding circles, may comprise one or more among: the contour; the defects; other geometrical features present on the surface of the leather but not classifiable as defects, that may be used for example as references for the inspection, as it will be clear in the following.

The inspecting machine <NUM> comprises a feeding unit <NUM> configured to make the leather <NUM> move along the inspecting machine <NUM> according to an advancement direction X.

It is hereby specified that, in the present disclosure, the term "advancement direction" means a direction along a trajectory, that may be rectilinear, curved, or a combination.

Preferably but not necessarily, the feeding unit <NUM> comprises an inlet area <NUM> that receives the leather <NUM> and conveys it towards the subsequent zone of the feeding unit <NUM> according to the advancement direction X. Preferably, the aforementioned inlet area <NUM> comprises a first conveyor belt 12a on which the leather <NUM> can be automatically or manually arranged.

The feeding unit <NUM> may receive the leather <NUM> by another machine arranged upstream, for example along an automatized processing line. In this case, the latter machine may be configured in such a way as to automatically lay down the leather <NUM> on the inlet belt 12a or, anyway, to convey the leather <NUM> towards the inlet area <NUM> of the feeding unit <NUM>.

According to a variant embodiment, the inlet area <NUM> may be configured to allow to manual load the leather <NUM> by an operator. This variant is particularly suited for the case in which the feeding unit <NUM> is not preceded by another machine in a same processing line.

Still preferably, and as shown in <FIG>, the feeding unit <NUM> comprises a stretching unit <NUM> configured to stretch the leather <NUM> while it moves along the inlet area <NUM>, in order to eliminate possible wrinkles.

Preferably but not necessarily, the stretching unit <NUM> comprises a conveyor belt faced to the inlet belt 12a and kept in tension between corresponding rollers. The stretching of the leather is achieved thanks to an advance speed of the conveyor belt of the stretching unit <NUM> being higher than that of the inlet belt 12a.

The feeding unit <NUM> also comprises two feeding rollers <NUM>, <NUM>, that may be seen in <FIG>, which define corresponding longitudinal axes Y1, Y2 perpendicular to the advancement direction X.

As it will be apparent hereinafter, in variant embodiments of the invention not depicted in the drawings, the number of feeding rollers <NUM>, <NUM> may differ from two, for example being only one or more than two.

Each feeding roller <NUM>, <NUM> is rotatably mounted for the rotation according to the corresponding longitudinal axis Y1, Y2, and is delimited by a cylindrical surface in contact to which the leather <NUM> can be arranged.

Motorization means <NUM>, <NUM> are further present, which may comprise electric motors and/or any other similar devices in themselves known, for the controlled rotation of each feeding roller <NUM>, <NUM> according to the corresponding longitudinal axis Y1, Y2 in a corresponding rotation direction Z1, Z2. As a consequence, the cylindrical surface of each roller <NUM>, <NUM> is a corresponding mobile surface <NUM>, <NUM> that, as a result of the rotation of the roller itself, is moved according to the advancement direction X.

For clarity reasons, each mobile surface <NUM>, <NUM> will be referred to in the following by the expression "cylindrical surface", but what will be disclosed is applicable, with the due and obvious changes, to a mobile surface of any kind and shape.

Each one of the cylindrical surfaces <NUM>, <NUM> of the rollers <NUM>, <NUM> comprises a corresponding plurality of holes <NUM>. The feeding unit <NUM> comprises a depression generation device, not shown in the drawings but of a kind in itself known, that can be connected to one or more of the aforementioned holes <NUM> to generate a depression at the level of each cylindrical surface <NUM>, <NUM>, the depression being suited to keep a respective portion <NUM>, <NUM> of the leather <NUM> in contact with the cylindrical surface <NUM>, <NUM> during the rotation of the corresponding feeding roller <NUM>, <NUM>.

In other words, the depression generation device produces a suction force through the holes <NUM>, with the effect of keeping the portions <NUM>, <NUM> of the leather <NUM> in contact to, respectively, the cylindrical surfaces <NUM> and <NUM>. As a consequence, the leather <NUM> is set in motion according to the advancement direction X by each feeding roller <NUM>, <NUM> as a result of the rotation thereof.

It is understood that the aforementioned movement of the leather <NUM> is achieved without compressing the leather <NUM>, hence reaching the aim of avoiding alterations thereof.

Moreover, the aforementioned suction force may be exerted on a relatively wide portion <NUM>, <NUM> of the leather <NUM>, in order to limit possible slipping of the leather <NUM> relative to the feeding rollers <NUM>, <NUM>, with the advantage of achieving a high precision of movement of the leather <NUM>, hence improving the precision of inspection.

According to different embodiments of the feed device <NUM>, not shown in the drawings, each cylindrical surface may be replaced by a corresponding mobile surface <NUM>, <NUM> of any shape and kind, rigid or deformable, as long as it is provided with holes connected to the depression generation device. A variant embodiment may envisage that each mobile surface belongs to a corresponding conveyor belt, in which case the mobile surface is deformable.

Preferably, the aforementioned depression generation device is a blower or, more generally, any device suited to suck air through the holes <NUM> in order to generate the aforementioned depression.

Preferably but not necessarily, each feeding roller <NUM>, <NUM> is a corresponding hollow drum 1a, 2a, whose cavity 1b, 2b is delimited by a cylindrical wall 1c, 2c through which the holes <NUM> pass. The cavity 1b, 2b is put in communication with the depression generation device, in such a way that the depression thereby generated is transmitted to the holes <NUM> and, from there, to the cylindrical surfaces <NUM>, <NUM>.

<FIG> shows a detail of the roller <NUM>, in plan view according to a plane parallel to the longitudinal axis Y2 of the roller. Preferably, the holes <NUM> are aligned in correspondence to a plurality of circumferences, indicated in the figure with dash-dot lines, which are coaxial to the longitudinal axis Y2 of the roller <NUM> and are spaced along the direction of the axis. Still preferably, the holes <NUM> are arranged at regular intervals along each circumference, in order to distribute the suction force more uniformly. For the same reason, the holes <NUM> of each circumference are angularly offset with respect to the holes <NUM> of the circumferences adjacent thereof, as it may be clearly seen in the figure.

Preferably and as shown again in <FIG>, the cylindrical surface <NUM> defines, in correspondence to each of the aforementioned circumferences, a corresponding groove <NUM> to which the corresponding holes <NUM> lead. As a consequence, the holes <NUM> are, in whole or in part, slightly lowered relative to the cylindrical surface <NUM>. This, advantageously, prevents the leather <NUM> from coming into direct contact with the holes, thus avoiding consequent markings of the surface of the leather. Still advantageously, the depression generated by the holes <NUM> of a given circumference is being distributed along the corresponding groove, thus generating a suction force that is substantially uniform along the entire portion <NUM> of the leather <NUM> that is in contact with the roller <NUM>.

In a variant embodiment of the invention, not shown in the drawings, the aforementioned grooves <NUM> may have a different configuration than the one just disclosed, as long as the holes <NUM> lead to the groove. For example, the grooves <NUM> may be developed according to corresponding straight lines parallel to the longitudinal axis Y2, or they may have a helical pattern around that longitudinal axis.

It is clear that the configurations of the holes <NUM> and of the grooves <NUM> just disclosed are applicable as such to the roller <NUM> as well.

As regards the shape of the holes <NUM>, preferably but not necessarily they have circular section at least at their ends facing towards the cylindrical surface <NUM>, <NUM>.

Still preferably, and as shown in <FIG>, the feed device <NUM> comprises a sealing unit <NUM> operatively associated to each roller <NUM>, <NUM> and configured to limit the transmission of the depression generated by the depression generation device only to a first group of holes 5a, 5b that are located within a first area 3a, 4a of the cylindrical surface <NUM>, <NUM>, thus excluding the transmission of the depression to the remaining holes <NUM>. As a consequence, the suction effect on the leather <NUM> is only limited to the aforementioned first area 3a, 4a. The aforementioned suction effect is schematically indicated in <FIG> through the arrows oriented towards the center of each roller <NUM>, <NUM>, while the sealing unit <NUM> is ideally represented by dash-dot lines, indicating its operating area.

Clearly, if the mobile surfaces are not cylindrical, the aforementioned first area of each mobile surface is to be meant as a portion of the mobile surface developing along a portion of the advancement direction X. The same applies for any other area of the surface that will be defined hereinafter.

The sealing unit <NUM> can rotate independently of the feeding roller <NUM>, <NUM>, in such a way that the corresponding first area 3a, 4a stay stationary during the rotation of the roller. To that end, the sealing unit <NUM> is preferably fixed to the structure of the feeding unit <NUM> on which the rollers <NUM>, <NUM> are rotatably mounted.

Advantageously, by limiting the suction effect only to the holes 5a, 5b of the first group, the leather <NUM> is allowed to spontaneously detach from the cylindrical surface <NUM>, <NUM> so that the leather <NUM> can be more easily directed towards devices located downstream of the roller <NUM>, <NUM>. Therefore it is achieved the aim of facilitating the movement of the leather <NUM> according to the advancement direction X, preventing formation of curves and wrinkles that might require the intervention of the operator or prejudice the processing.

Preferably, the feeding unit <NUM> further comprises a pressure generation device that can be connected to one or more of the holes <NUM> included in a second area 3b, 4b of the cylindrical surface <NUM>, <NUM> of one or more of the feeding rollers <NUM>, <NUM>, the second area 3b, 4b being arranged downstream of the first area 3a, 4a according to the advancement direction X, that, in the present embodiment, corresponds to the rotation direction Z1, Z2 of the roller <NUM>, <NUM>. The configuration just disclosed allows to generate, in correspondence of the aforementioned second area 3b, 4b, a thrust suited to force the separation of the leather <NUM> from the cylindrical surface <NUM>, <NUM>. The aforementioned thrust is schematically indicated in <FIG> by arrows that are directed towards the outside of each roller <NUM>, <NUM>.

Advantageously, the aforementioned thrust further facilitates directing the leather <NUM> towards the devices arranged downstream of the roller <NUM>, <NUM>, hence improves the motion steadiness of the leather along the advancement direction X.

Preferably, the aforementioned pressure generation device is a blower, or any other device suited to convey a flow of pressurized air towards the holes <NUM> of the second area 3b, 4b.

Still preferably, the second area 3b, 4b has an end adjacent to the first area 3a, 4a and delimited by the aforementioned sealing unit <NUM>.

Still in <FIG>, it is shown that, firstly, the leather <NUM> that moves along the advancement direction X enters into contact with the feeding roller <NUM>, from which it comes to be detached after about a half turn around the roller <NUM> as a result of the pressure generated by the pressure generation device, in such a way that the leather is driven by gravity towards the second roller <NUM> arranged below the first one, in such a way that is captures the leather <NUM> so that it happens to be arranged in contact thereof.

After about <NUM>° around the second roller <NUM>, the leather <NUM> is detached from it as a result of the pressure generated by the pressure generation device in order to be conveyed by gravity towards an outlet area <NUM> that is arranged downstream of the second roller <NUM>, shown in <FIG>. The outlet area <NUM> receives the leather <NUM> exiting from the feeding unit <NUM> and renders it available for possible subsequent operations. Preferably, the outlet area <NUM> comprises a second conveyor belt 13a, arranged below the second roller <NUM>, onto which the leather <NUM> is laid.

Still preferably, the feeding unit <NUM> is configured to put the two opposite faces of the leather <NUM> in contact with, respectively, the two cylindrical surfaces <NUM>, <NUM> in succession. As a consequence, each one of the two faces of the leather <NUM> remains exposed while the other one is in contact with the two rollers <NUM>, <NUM>. The configuration just disclosed brings the advantage that the feed device <NUM> allows to perform the inspection on both faces of the leather <NUM> while the leather is in good contact with the cylindrical surfaces <NUM>, <NUM> of the rollers <NUM>, <NUM>, and, hence, is arranged in a predefined configuration.

Preferably, what has been just disclosed is achieved by configuring the motorization means <NUM>, <NUM> so as to drive the rollers <NUM>, <NUM> in rotation according to corresponding mutually opposite rotation directions Z1, Z2.

The inspecting machine <NUM> also comprises a sensor unit <NUM> configured to capture images of the leather <NUM> in correspondence of one or more of the aforementioned portions <NUM>, <NUM> in contact with each feeding roller <NUM>, <NUM>.

According to a variant embodiment of the invention, that is applicable when the rollers <NUM>, <NUM> are at least two, as in the embodiment shown in the drawings, the sensor unit <NUM> may be configured to capture images also in correspondence of the portion of the leather <NUM> included between the aforementioned portions <NUM>, <NUM>.

The inspecting machine <NUM> also comprises a processing device, not shown in the drawings but in itself known, configured to detect the geometrical features <NUM> of the leather <NUM> based on the analysis of the aforementioned images.

It is understood that the inspecting machine <NUM> above disclosed achieves the aim of allowing a more precise inspection of the leather <NUM> compared to what is possible by the known techniques, thanks of the higher advance precision allowed by feeding unit <NUM>, implying a reduced uncertainty on the estimation of the position of the leather <NUM> along the advancement direction X. In particular, the portions <NUM>, <NUM> are in contact with the rollers <NUM>, <NUM> and, thus, accurately follow the geometry of the corresponding cylindrical surfaces <NUM>, <NUM>, allowing to achieve a very precise correspondence between the images and the actual surface configuration of the leather. A high precision can be achieved also for images that are captured on the portion of the leather <NUM> that is intermediate between the aforementioned portions <NUM>, <NUM>. In fact, despite the fact that such intermediate portion is not in contact with the rollers <NUM>, <NUM>, the good contact of the two portions <NUM>, <NUM> with the rollers <NUM>, <NUM> allows to estimate also the position of each point of the intermediate portion more precisely compared to what can be achieved by the known techniques.

As regards more specifically the sensor unit <NUM>, preferably it comprises one or more stations 7a, 7b, 7c for each mobile surface <NUM>, <NUM>, namely for each feeding roller <NUM>, <NUM>. In the variant embodiment shown in the figures, two stations 7a, 7b are provided for roller <NUM>, and one station 7c for roller <NUM>. The two stations 7a, 7b are meant to capture the exposed side of the leather <NUM>, also called "grain side", while the station 7c captures the rear side of the leather <NUM>, also called "flesh side".

As shown in <FIG> and <FIG>, each station 7a, 7b, 7c captures the leather <NUM> from different positions according to the advancement direction X.

The two stations 7a, 7b of the roller <NUM> have corresponding mutually different light, respectively raking light and diffused light. The aforementioned different lights allow, advantageously, to more precisely define the geometrical features <NUM>. Clearly, variant embodiments of the invention may envisage a different number of stations and/or different features of the same.

In any case, each station 7a, 7b, 7c comprises one or more image sensors <NUM>, <NUM> of the "contact" kind (CIS - "Contact Image Sensor") to capture corresponding images of the portion <NUM>, <NUM> of the leather <NUM> that is arranged in contact with the roller corresponding.

As known, a CIS sensor is an optical sensor provided with a rectangular field of view, mainly developed according to the longitudinal direction of the sensor itself.

Still advantageously, the aforementioned CIS sensors are configured to be located at close range from the object to be captured, with the consequence of limiting possible capturing inaccuracies caused, for example, by vibrations and thermal deformations of the structure supporting the sensors. By way of example, the distance of each CIS sensor from the surface of the leather <NUM> is preferably comprised between <NUM> and <NUM> and, even more preferably, is about <NUM>.

The optics of the sensors <NUM>, <NUM> are of the telecentric kind, that, compared to the common optics, has among its advantages, that of not generating distortions in the image, to allow capturing images with a uniform resolution, and to allow making more precise linear measurements.

Therefore, the use of the CIS sensors allows to achieve a higher precision of inspection compared to the inspection machines of known kind, regardless of the kind of feeding unit <NUM> that is used.

Moreover, preferably, each sensor <NUM>, <NUM> integrates a light source to, advantageously, provide an optimal lighting of the leather <NUM>.

The image sensors <NUM>, <NUM> of each station 7a, 7b, 7c are faced to the corresponding mobile surface <NUM>, <NUM>, so that their longitudinal direction is oriented perpendicular to the advancement direction X that, in the present embodiment, corresponds to an orientation parallel to the longitudinal axis Y1, Y2 of the corresponding roller. Clearly, the fields of view <NUM>, <NUM> of the sensors <NUM>, <NUM> are arranged in a similar way, as shown in <FIG>, representing the fields of view <NUM>, <NUM> of the sensors of any station 7a, 7b, 7c.

As shown again in <FIG>, one or more of the stations 7a, 7b, 7c comprises a plurality of the aforementioned image sensors <NUM>, <NUM>, arranged in mutually different positions according to the advancement direction X, in order to capture the leather <NUM> in corresponding subsequent moments.

In particular, the configuration just disclosed allows to arrange the image sensors <NUM>, <NUM> of each station 7a, 7b, 7c mutually staggered according to the direction perpendicular to the advancement direction X, namely, in the present case, parallel to the longitudinal axis Y1, Y2 of the corresponding roller.

Advantageously, thanks to the staggered configuration just disclosed it is possible to capture an image of the leather <NUM> that extends on the entire width thereof. In fact, since the field of view <NUM>, <NUM> of each sensor <NUM>, <NUM> of the contact kind does not extend on the entire length of the sensor, but has a length shorter than that of the sensor itself, its ends are blind. Therefore, a position of the sensors <NUM>, <NUM> in which these are mutually aligned implies that the aforementioned blind ends are interposed between the fields of view <NUM>, <NUM> of two adjacent sensors <NUM>, <NUM>, hence defining a field of view that, in the overall, comprises intermediate blind zones.

In order to avoid the aforementioned blind zones, the staggering of the sensors <NUM>, <NUM> is such that the fields of view <NUM>, <NUM> of each pair of mutually adjacent sensors <NUM>, <NUM> have corresponding first portions 10a, 11a that are mutually aligned according to the advancement direction X, and remaining second portions 10b, 11b that are not aligned according to the same direction. As a consequence, the aforementioned first portions 10a, 11a are suited to capture corresponding first image portions relating to the same first portion <NUM> of the leather <NUM> at two corresponding moments of time, separated by a time interval, while the second portions 10b, 11b capture second image portions relating to other two corresponding mutually different portions <NUM>, <NUM> of the leather <NUM> adjacent to the first portion <NUM>, respectively in the aforementioned two moments of time.

The comparison between the aforementioned two first image portions allows the processing device to synchronize the images captured by sensors <NUM>, <NUM> corresponding to the same roller <NUM>, <NUM>, and to combine them into a single image.

The processing device can synchronize the images through determining the time interval separating the aforementioned two moments of time. To this end, it should be noted that the aforementioned time interval depends on the velocity of the surface of the leather <NUM> captured by sensors <NUM>, <NUM>. In turn, the aforementioned velocity depends not only on the speed of the feeding rollers <NUM>, <NUM>, but also on other parameters, such as, for example, the elasticity of the leather, that may imply deformations thereof during advancement, or the possible slip of the leather with respect to the rollers <NUM>, <NUM>, as well as on thickness changes of the leather, etcetera.

Therefore, capturing the image of the first portion <NUM> of the leather <NUM> by the first portions 10a, 11a in two subsequent moments allows, through an appropriate algorithm, to establish the time interval between the captures by the sensors <NUM>, <NUM> by making reference to one or more superficial features of the said first portion <NUM>, or it allows to correct the time interval estimated on the basis of the speed of the rollers <NUM>, <NUM>.

What has been just disclosed is shown schematically in <FIG>, where the fields of view <NUM>, <NUM> are represented by dashed edges, and the first portions <NUM> of the leather <NUM> are indicated by corresponding pairs of dashed lines.

<FIG> show a portion of the leather <NUM> near to the same pair of adjacent sensors <NUM>, <NUM>, respectively in the aforementioned two moments of time. In particular, it may be seen that the leather portion shown in <FIG> comprises a geometrical feature <NUM> of the leather, identified by a corresponding circle.

<FIG> show parts of the images that are captured, respectively, by the aforementioned two mutually adjacent sensors <NUM>, <NUM> in the two moments of time. The enlarged view of <FIG> shows the first image portion captured by sensor <NUM>, that corresponds to the right portion of the image of <FIG>. Such first portion is identical to the first image portion captured by sensor <NUM> and corresponding to the left portion of the image of <FIG>.

According to a variant embodiment of the invention, that will be disclosed more in detail in the following, the combination of the images from each pair of mutually adjacent sensors <NUM>, <NUM> occurs without calculating the time interval between the two images, but rather by comparing the two images in order to find pairs of geometrical features <NUM> in common therein, from which geometrical transformations of the images are computed that allow to overlap the two geometrical features <NUM> of each pair.

Preferably, the length of each one of the aforementioned first portions 10a, 11a is comprised between <NUM> and <NUM>, in order to combine the opposite needs, on the one hand, to have a sufficient image overlap as to allow their comparison, and, on the other hand, to maximize the overall length of the field of view and, hence, the maximum width of the leather <NUM> that can be inspected.

As an example, in order to cover a maximum inspection width of <NUM>, five sensors <NUM>, <NUM> may be used, that are arranged mutually staggered so that the mutual overlap areas are about <NUM> long each.

Preferably, the processing device is configured to generate a digital map of the leather <NUM> based on the images captured by the sensors <NUM>, <NUM>. The digital map comprises one or more geometrical features <NUM> of the leather <NUM>, among which are, in particular, the defects of the leather. The aforementioned geometrical features <NUM> may to further comprise other geometrical parameters, such as, for example, the area of the leather.

The aforementioned digital map can be stored on a memory device, together with a univocal identifier that put them in relation with the leather <NUM> in order to allow to use the map in subsequent operations to be performed on the leather.

Preferably, the digital map comprises a plurality of coordinates, that are representative of the aforementioned geometrical features <NUM> of the leather <NUM>.

The aforementioned coordinates may be so configured as to provide a vector representation of one or more of the aforementioned geometrical features <NUM>. More precisely, the aforementioned coordinates may identify a plurality of points belonging to a curve that delimits each geometrical feature <NUM>. Advantageously, the aforementioned vector representation is suitable to be easily read and subsequently processed in case of need.

The aforementioned subsequent processing might be required, for example, in order to adapt the digital map to the actual state of the leather <NUM> just before performing any other process on the leather. For example, in case of a cut process aimed at obtaining portions of leather to be used in the manufacturing of finished products, it is necessary to define a usable area without defects.

To this end, it is to be reminded that, generally, the digital map is acquired by the tanner during, or at the end of, the treatment processing on the leather, while the subsequent processing of the leather often occurs at the final user, in times and locations that are different than those related to the generation of the digital map. As a consequence, in the subsequent processing, the leather may be in a condition that is different from that in which it was had during the inspection, for example due to shape settlements, different environmental conditions, elastic deformations, or, more simply, position change. Generally, the aforementioned different conditions result in corresponding changes in the geometry of the leather <NUM> compared to the moment when the digital map was generated.

Operatively and as shown in <FIG>, the leather <NUM> is loaded on the first conveyor belt 12a of the inlet area <NUM> having the grain side facing upwards. From there, the leather proceeds to the stretching unit <NUM> for stretching possible wrinkles.

Afterwards, the leather is arranged in contact with the first area 3a of the first feeding roller <NUM> of the feeding unit <NUM> and is kept there thanks to the suction force of the depression generation device. The leather is then driven in succession to the stations 7a and 7b of the sensor unit <NUM> for capturing corresponding images of the outer side (grain side).

Once the leather reaches the second area 3b of the first roller <NUM>, the pressure present there forces its separation from the cylindrical surface <NUM> and allows its conveyance towards the cylindrical surface <NUM> of the second feeding roller <NUM>, where the leather is driven to the station 7c of the sensor unit <NUM> to capture the image of the rear side (flesh side).

As anticipated, the present invention also comprises an inspection method, referred to in the overall in <FIG> as <NUM>, to detect the defects in a leather <NUM> by means of an inspecting machine <NUM> of the kind above disclosed.

For simplification purpose, reference will be made to the variant embodiment of an inspecting machine <NUM> shown in Figs. <NUM>-<NUM>, and, in particular, to the corresponding sensor unit <NUM>, schematically shown in <FIG>. The aforementioned sensor unit <NUM> comprises three stations 7a, 7b, 7c, each one of which comprises in turn five sensors <NUM>, <NUM>, only two of which, for simplification purpose, are indicated in the figure, for a total of <NUM> sensors. Two stations 7a e 7b capture the grain side, while station 7c captures the flesh side. The different stations 7a, 7b, 7c have similar configurations and arrangements for the corresponding sensors, so that the overall capture width be the same for all stations.

It is remarked that the configuration just disclosed is not limiting, and the invention is also applicable, in similar way, to variant embodiments in which the number of stations, their arrangement relative to the leather, and the number of sensors for each station, are different from the ones above disclosed, and/or in which the configuration, arrangement, and/or number of sensors, as well as the overall capture width, differ between the stations.

For better precision, each sensor <NUM>, <NUM> in <FIG> is identified with the label TV and with a corresponding hexadecimal digit from <NUM> to F. As a consequence, TV-<NUM> - TV-<NUM> indicate the sensors in the first station 7a, TV-<NUM> - TV-A those in the second station 7b, TV-B - TV-F those in the third station 7c. Sensors TV-<NUM>, TV-<NUM>, TV-<NUM> in the first station 7a are mutually aligned and correspond to the sensors more generally indicated as <NUM>, while sensors TV-<NUM> and TV-<NUM>, which are mutually aligned but, with respect to the previous ones, are offset in direction X and staggered in a direction perpendicular to direction X, correspond to the sensors more generally indicated as <NUM>. A similar configuration can be observed for stations 7b and 7c.

First of all, the above method <NUM> envisages a step <NUM> of capturing an image <NUM> of the leather <NUM> by means of each one of the aforementioned image sensors TV-<NUM> - TV-F. In the following, the image captured by the generic sensor will be referred to as <NUM>, while, to indicate the image by a specific sensor, the identifying digit of the sensor will be added as a subscript, hence obtaining <NUM><NUM>-<NUM>F.

<FIG> shows the images <NUM><NUM>-<NUM><NUM> of the leather <NUM> as captured by sensors TV-<NUM> - TV-<NUM> in station 7a. Clearly, a similar configuration can be observed for the other stations as well.

Subsequently, the method <NUM> comprises a step <NUM> of detecting, in each image <NUM>, the aforementioned geometrical features <NUM> of the leather <NUM>. Some geometrical features <NUM> may not be captured by all stations, e.g. because they are visible only from one side of the leather <NUM>, or only under the lighting of a specific station. For simplification purpose, <FIG> show only one geometrical feature.

The method <NUM> further comprises a step <NUM> of defining a numerical representation <NUM> for each geometrical feature <NUM>. By "numerical representation" it is meant, in general, a group of data that conventionally represent the geometrical feature <NUM>.

In general, and as indicated in <FIG>, each numerical representation <NUM> comprises one or more pairs of coordinates (x, y) relating to the corresponding geometrical feature <NUM>, relative to the reference system of the image sensor TV-<NUM> - TV-F by which the geometrical feature was captured, and possibly one or more parameters W representative of corresponding geometrical aspects of the geometrical feature <NUM>.

In case of an edge portion of the leather, the corresponding numerical representation <NUM> comprises an approximation of the profile <NUM> of the portion itself, indicated in <FIG>. The aforementioned approximation can be expressed, e.g., through the coordinates (x, y) of several points of the profile, that then can be interpolated through a polygonal, a spline, or other entities.

In case of a geometrical feature <NUM> corresponding to a defect, the corresponding numerical representation <NUM> may comprise a plurality of coordinate pairs (x, y) defining the contour of the defect, similarly to what happens for the edges of the leather, while the above parameters W may comprise qualitative aspects, like kind of defect, extent, and so on, and/or quantitative aspects, like the area, the perimeter, and so on.

As previously mentioned, a geometrical feature <NUM> may also be a reference point, or "keypoint", namely a feature that is particularly distinguishable from the surface of the leather, even though it may not necessarily be a defect. For this kind of geometrical feature, the corresponding numerical representation <NUM> may comprise a single coordinate pair (x, y), that conventionally defines the position of the geometrical feature, while the parameters W, called in jargon "descriptors", are defined so as to conventionally define the aspect of the area around the above coordinate pair (x, y). Still preferably, the parameters W are defined so as to be invariant with respect to an affine transformation of the corresponding geometrical feature <NUM> on the plane of the leather <NUM>. This brings an advantage that will be apparent hereinafter.

The above mentioned elements of the numerical representation <NUM> may be defined through per-se known algorithms such as, for example, ORB, BRISK, AKAZE, GFTT, FAST, AGAST, and so on.

Preferably, the reference points are identified by means of an algorithm that is distinct from, and independent of, the algorithm used for identifying the other geometrical features <NUM>.

It may also happen that a reference point is identified in correspondence of a defect. In this case, it may occur that two mutually independent geometrical features <NUM> relating to the above defect are defined, that differ from the definition of the corresponding numerical representation <NUM>: coordinates and descriptors of the reference point in the first instance, coordinates of the contour of the defect, plus possible parameters, in the second instance.

The method further comprises a step <NUM> of detecting each pair of numerical representations <NUM> that represent the same geometrical feature <NUM> captured by a corresponding pair of image sensors <NUM>, <NUM> belonging to the same station 7a, 7b, 7c. Specifically, such an event may occur for each pair of image sensors <NUM>, <NUM> in the same station whose fields of view <NUM>, <NUM> overlap at corresponding first portions 10a, 11a, as in the case of <FIG>. For simplification, the two sensors of any one of the above pairs will be referred to in the following by the wording "adjacent sensors".

Therefore, in the step <NUM> just disclosed, those geometrical features <NUM> that are captured by both sensors of the pair at the first portions 10a, 11a are searched, so as to identify the corresponding pairs of numerical representations <NUM>. Thus, both numerical representations of each one of the aforementioned pairs represent the same geometrical feature <NUM>, as seen by the two sensors of a corresponding pair.

Preferably, the pairing of the numerical representations <NUM> is done based on the comparison of the corresponding parameters W. In fact, it is reminded that, in general, the same geometrical feature <NUM> captured by two adjacent sensors <NUM>, <NUM> corresponds to two numerical representations <NUM> whose coordinates (x, y) are mutually different, due to the different positions of the two sensors <NUM>, <NUM> and of their possible misalignment, as it will be explained in more detail shortly. On the contrary, at least a part of the parameters W of the two numerical representations are mutually equal, except for minor differences. In particular, this applies to the reference points previously defined, due to the invariance of the corresponding descriptors with respect to an affine transformation. Therefore, these points are particularly suited to be used for performing the above pairing.

More in detail, each geometrical feature <NUM> included in the overlap area between two adjacent sensors <NUM>, <NUM> is detected by both sensors, and for it, two corresponding and distinct numerical representations <NUM> are defined.

However, in general, due to the different positions of the two sensors and to possible aligning defects, both on the plane parallel to the leather <NUM>, and in that perpendicular thereof, the coordinates (x, y) belonging to the aforementioned two numerical representations corresponding to a given geometrical feature <NUM> are mutually different.

On the contrary, where the reference points are concerned, the corresponding descriptors are generally identical, or at least similar, in particular as concerns the geometrical aspects that are invariant, within the meaning previously defined. Therefore, it is understood that the comparison between the descriptors allows to detect, simply and reliably, that pair of numerical representations <NUM>, corresponding to the two sensors <NUM>, <NUM>, that corresponds to the same geometrical feature <NUM>.

The identification of the above pairs of numerical representations <NUM> is done for each station 7a, 7b, 7c.

Afterwords, a step <NUM> is performed in order to define, for each pair of adjacent sensors <NUM>, <NUM> belonging to the same station 7a, 7b, 7c, a corresponding affine transformation Tij that transforms the coordinates (xi, yi) of the numerical representations <NUM> of the aforementioned pairs, relating to the sensor i-th, in the coordinates (xj, yj) of the corresponding numerical representations <NUM>, relating to the sensor j-th, namely <MAT>.

The above indices i and j generally identify the two sensors of the pair, according to the hexadecimal notation previously defined. Therefore, for example, the affine transformation that transforms the coordinates of a geometrical feature <NUM> relating to sensor TV-<NUM> in those relating to sensor TV-<NUM> will be indicated by T12, while the one between sensors TV-<NUM> and TV-A will be indicated by T9A, and so on.

As known, an affine transformation is a transformation preserving parallelism between lines, but not necessarily distances and angles.

Advantageously, the aforementioned affine transformation Tij allows to take into account the deformations on the images <NUM> resulting from possible misalignment between the two adjacent image sensors <NUM>, <NUM>. This is possible because the image deformation due to misalignment of a linear-telecentric optics, as those in CIS sensors are, can be defined, at least as a first approximation, in terms of an affine transformation. Moreover, an affine transformation can also take into account small deformations that the leather <NUM> could undergo while passing between one sensor and the other.

In order to take into account greater deformations of the leather <NUM>, that cant' be expressed through an affine transformation, each affine transformation Tij may be defined by using a criteria that minimizes the difference between the coordinates obtained by the image captured from the second sensor and those obtained through the transformation of the coordinates obtained through the image captured by the first sensor, according to per-se known algorithms.

After defining the aforementioned affine transformations Tij, they are used in a further method step <NUM> for transforming the coordinates (x, y) belonging to one or more of the numerical representations <NUM> captured by the sensors of any given station 7a, 7b, 7c in the corresponding transformed coordinates (x*, y*) relative to a common reference system for that station. The aforementioned common reference system may be that of a reference sensor of the same station, e.g. the middle sensor. Clearly, in order to transform the coordinates (x, y) relative to a sensor not adjacent to the reference sensor, it is necessary to use the product of the affine transformations corresponding to each pair of adjacent sensors comprised between the aforementioned sensor and the reference sensor.

The above operation <NUM> is applied at least to the geometrical features <NUM> corresponding to the defects and to the leather edges.

The execution of the above steps allows to define a digital map <NUM> of the leather <NUM> for each station 7a, 7b, 7c, as the one shown in <FIG>. The aforementioned digital map <NUM> comprises the numerical representations <NUM> of the said geometrical features <NUM> relative to the aforementioned common reference system.

For each pair of adjacent sensors <NUM>, <NUM>, several affine transformations Tij for different areas of the leather <NUM> may also be defined. This allows to take into account localized deformation of the leather <NUM>, thus obtaining a more precise transformation of the coordinates. A specific algorithm calculates all the affine transformations Tij needed for each pair of adjacent sensors, as well as the contours of the areas in which each affine transformation is applicable.

Clearly, what has been previously disclosed is also applicable in a similar way to the case just disclosed, except for the geometrical features <NUM> located outside of the aforementioned areas. If k is the number of affine transformations Tij for a given pair of sensors, the transformed coordinates (x*, y*) of a point with coordinates (x, y) may be defined by applying each one of the k affine transformations Tij to the coordinates (x, y) and then calculating the weighted average of the resulting coordinates, the weights being related to the inverse of the distance Dk of the point (x, y) from the corresponding areas, in particular from their contours. A known method for calculating the aforementioned weighted average is, for example, the Shepard's method.

It is understood that the aforementioned weighted average based on the inverse of the distance allows to attribute, in calculating the transformed coordinates, bigger influence to the transformations that correspond to the areas that are closer to the geometrical feature <NUM> in question with respect to the farther ones.

As previously said, the geometrical features <NUM> also comprise the edge portions of the leather <NUM> captured by each image sensor <NUM>, <NUM>, and the numerical representation <NUM> of each edge portion is such as to allow recreating the profile <NUM> of the edge portion, or of an approximation thereof, in the form of a continue curve, that may be a polygonal, a spline, etcetera.

The profiles <NUM> of the aforementioned edge portions, once subjected to the aforementioned affine transformations Tij, may determine an overall profile that is discontinuous, for example due to localized deformations of the leather.

In order to correct the aforementioned discontinuities, the method preferably comprises a step <NUM> of correcting the affine transformations Tij based on the aforementioned profiles <NUM> of the edge portions. More in detail, the aforementioned correction step <NUM> is performed in such a way that the profiles <NUM> of the edge portions, as a consequence of the application of the corrected affine transformations Tij, form a continue edge profile <NUM>. <FIG> shows the result achieved after the aforementioned correction step <NUM>.

The calculation of the transformed coordinates (x*, y*) in the common reference system is done based on the affine transformations Tij as above corrected, to the advantage of a higher precision of the digital map <NUM> so obtained.

It is noticed that the correction of the aforementioned affine transformations Tij may me done, from the operative point of view, either by modifying the corresponding transformation matrixes as previously calculated, or by defining new corrected transformation matrixes that are applied in place of the original ones. In the present description, the aforementioned two variants are considered to be equivalent and the reference Tij is used in both cases to indicate the affine transformations used to calculate the transformed coordinates (x*, y*).

The method disclosed so fa allows to obtain a digital map <NUM> of the leather <NUM> for each station 7a, 7b, 7c of the sensor unit <NUM>. In <FIG>, the three digital maps corresponding to the three stations are indicated, respectively, by 62a, 62b and 62c. Nevertheless, in general, the three digital maps <NUM> do not perfectly overlap, either because of the misalignment between the sensors belonging to the different stations, or because of the difference between the images as captured by different stations, or, for example, because of deformations of the leather between two stations, of different capturing conditions, etcetera. That situation is schematically shown in <FIG>, where the differences between the three maps exaggerated in order to allow distinguishing them.

Preferably, in order to improve the matching between the aforementioned digital maps <NUM>, the method <NUM> envisages the further step <NUM> of defining a rigid transformation Rij that transforms the continuous edge profile <NUM> of the digital map corresponding to each station 7a, 7b, 7c in such a way as to minimize the deviations with respect to the continuous edge profile <NUM> of the digital map corresponding to a given one of the aforementioned stations 7a, 7b, 7c, taken as reference. In the used notation, the first index i represents the sensor that defines the common reference system of the station under examination, while the second index j represents the sensor that defines the common reference system of the reference station.

For exemplary purpose, the figures show as reference sensors those in the middle of each station, i.e. sensors TV-<NUM>, TV-<NUM> and TV-D, and as reference station the station 7a, whose map 61a is shown in <FIG> with a thicker edge, in order to facilitate distinguishing it. On the contrary, the two maps 61b and 61c of stations 7b and 7c are represented by, respectively, dashed lines and dot-dash lines.

In the exemplary situation just disclosed, the aforementioned step <NUM> generates two rigid transformations R83 and RD3 that transform, respectively, the two maps 61b and 61c in order to express them in the reference system of station 7a.

The aforementioned rigid transformations R83 and RD3 are applied to the transformed coordinates (x*, y*) of the digital maps 62b and 62c corresponding to stations 7b and 7c, in order that they better match with the digital map 62a corresponding to the reference station 7a. The result of the aforementioned step is shown in <FIG>. The result is an overall digital map <NUM> grouping the data of all stations.

Preferably, the method <NUM> comprises a further step of improving the digital maps <NUM> obtained through the aforementioned rigid transformations Rij based on one or more geometrical features <NUM> that are in common among the corresponding digital maps <NUM>.

The aforementioned improving operation comprises a step <NUM> for identifying, from the digital map <NUM> corresponding to a first station 7a, 7b, or 7c, e.g. station 7a, the geometrical features <NUM> that are susceptible to be detected by a second station, for example one of the stations 7b, 7c.

The identification of the aforementioned common geometrical features <NUM> may be done, for example, based on the corresponding parameters W. For example, some kinds of defects may extend on both sides of the leather <NUM> and, thus, they may be detected both by a station that captures the grain side, and from a station that captures the flesh side.

Once identified the aforementioned common geometrical features <NUM>, a further step <NUM> is performed for detecting the corresponding numerical representations <NUM> in the digital map <NUM> corresponding to the second station 7b or 7c.

In a subsequent step <NUM>, the affine transformations Tij corresponding to the second station are corrected in order that the transformed coordinates (x*, y*) of the numerical representations <NUM> identified in the previous step, further transformed by applying the corresponding rigid transformation Rij above disclosed, coincide with those of the numerical representations <NUM> of the same geometrical features <NUM> in the digital map <NUM> corresponding to the first station 7a, or present the minimum deviation thereof.

The latter correction allows to further increase the matching between the different digital maps <NUM>, thus achieving an optimal description of the leather <NUM>.

From what has been disclosed above, it is understood that the inspecting machine and the method of inspection of the invention achieve the preset aims.

In summary, it is understood that the method as disclosed so far takes advantage of the geometrical features <NUM> detected in the overlapping areas, particularly the reference points, to define the affine transformations Tij that allow to express all other geometrical features <NUM>, particularly defects and leather edges, in relation to a common reference system for each station 7a, 7b, 7c, so as to obtain corresponding digital maps <NUM>. That operation corresponds to combining the images obtained from the different image sensors <NUM>, <NUM> of the station.

Moreover, the method uses special geometrical features of the maps <NUM>, in particular leather edges and defects, for correcting and improving the above mentioned affine transformations Tij, as well as to overlapping the maps.

Claim 1:
Inspecting machine (<NUM>) for leathers (<NUM>), comprising:
- a feeding unit (<NUM>) for the movement of a leather (<NUM>) according to an advancement direction (X);
- a sensor unit (<NUM>) configured to capture images of said leather (<NUM>) during said movement;
- a processing device configured to identify one or more geometrical features (<NUM>) of said leather (<NUM>) based on the analysis of said images;
said sensor unit (<NUM>) comprising one or more image sensors (<NUM>, <NUM>) of the contact kind (CIS - "Contact Image Sensor") faced to said leather (<NUM>) when said leather (<NUM>) is moved by said feeding unit (<NUM>), said image sensors (<NUM>, <NUM>) being arranged perpendicular to said advancement direction (X);
characterized in that said sensor unit (<NUM>) comprises a plurality of said image sensors (<NUM>, <NUM>) arranged in mutually different positions according to said advancement direction (X) and mutually staggered according to a direction perpendicular to said advancement direction (X) in such a way that the respective optical fields (<NUM>, <NUM>) have corresponding first sections (10a, 11a) that are mutually superposed according to said advancement direction (X) to capture corresponding first image portions of a same first portion (<NUM>) of said leather (<NUM>) in two corresponding mutually different moments, and corresponding remaining sections (10b, 11b) to capture second image portions of other two respective mutually different portions (<NUM>, <NUM>) of said leather (<NUM>) that are adjacent to said first portion (<NUM>), said processing device being configured to combine the images captured by said image sensors (<NUM>, <NUM>) based on the analysis of said first image portions.