The invention relates to an inspection method of a product in a packaging machine of the tobacco industry. In particular, the method comprises an inspection method of a product, in which the product can be a group of cigarettes, in a machine for packaging packets of cigarettes, or a group of packets of cigarettes, in a machine for packaging groups of packets of cigarettes and in other words cartons of packets, this group of cigarettes or of packets of cigarettes being wrapped at least partially in at least one outer wrapper material. Automatic machines are known for packaging groups of cigarettes or groups of packets of cigarettes, in which each group is advanced by a conveyor along a wrapper-forming path in which each group is wrapped at least partially in, and/or on which is positioned, one or more wrapper materials.

These wrapper materials typically comprise an inner wrapper component stabilising the group of cigarettes or the group of packets of cigarettes and one or more outer wrapper components, featuring messages, logos or graphic identification marks of the packet brand and/or bearing messages or warnings intended for a user and/or of protection from humidity of the wrapped group. For example, in a packet of cigarettes, one inner wrapper component is a sheet of alufoil or metallised wrapping paper of a group of cigarettes, whereas a polypropylene or cellophane sheet, optionally provided with printed logos, is an outer wrapper component both for a packet and for a carton of packets. The outer wrapper component can also be a sheet of printed paper and/or a blank that is also printed, for wrapping the product, consisting of a group of cigarettes or of packets of cigarettes that is wrapped or not wrapped in the inner wrapper component, to make respectively a soft packet of cigarettes and/or a soft carton of packets or a rigid packet of cigarettes and/or a rigid carton of packets.

An outer wrapper component is further also a duty stamp placed in a traditional rigid packet on a larger rear face of the packet at the hinge line of the lid and in a traditional soft packet centrally from a larger side face to the opposite face through a head face.

An optical inspection is usually conducted as part of the quality control procedures on the groups of cigarettes and/or on the groups of packets of cigarettes wrapped by at least one outer wrapper material and/or by the printed polypropylene outermost wrapping, in order to identify incorrect methods of wrapping the material, or, if present, incorrect positioning of additional wrapping elements.

For example, an optical inspection is conducted to check that in a soft packet or in a soft carton of packets, the sheet of printed wrapping paper of the group of cigarettes or of the group of packets of cigarettes and/or the polypropylene sheet provided with printing, is positioned correctly in a front or rear face of a packet, in such a manner that the writing, logos and printed graphic signs are centred on the face of the product, to enable a user to recognise the product immediately.

Further, in a soft packet, in at least one larger side face thereof there is a rectangular zone intended for anti-smoking propaganda messages having a black frame bounding a white background on which there is black writing. This rectangular zone extends for almost the entire transverse extent of the larger side face of the packet and has a length that is equal to about a third of the longitudinal length of the packet. Incorrect positioning of the black/white anti-smoking zone, for example because it is not centred or rotated, is immediately visible to a user because of the contrast with the remaining portion of wrapper material that coloured and provided with logos or graphic signs.

Logos or writing shifted laterally in a face of the product, tilted or arranged in a different position from a correct ideal position thus make a product defective and intended< to be rejected.

A further optical inspection is further conducted in a rigid packet to check that the duty stamp has the longitudinal axis superimposed on the lid hinge line or in a soft packet to check that the duty stamp is arranged centrally in the larger side face.

Each optical inspection of the type indicated above is usually conducted for each product (i.e. at each machine cycle) by an optical inspection unit comprising an optical acquisition apparatus and an illuminator associated with the apparatus, which is able to acquire images of the product when the product is advanced by a conveyor of the packaging machine. The expression "optical image acquisition apparatus" is defined as an optoelectronic image acquisition apparatus that is able to acquire images of an object, and in particular to process these images so as to extract features of interest from the images, for example geometrical and/or shape features of the object. The acquired images can be in colour or in black and white and from such images information on the colour (the tone, la saturation, etc) can be extracted or information respectively on the level of grey, and on light intensity.

The optical apparatus comprises a body on which an electronic sensor is arranged, for example an alignment or array of photosensitive elements of linear or two-dimensional matrix type, of the CCD or CMOS type, and appropriate optical receiving means fixed to the body, for example an objective consisting of one or more lenses, by means of which the sensor is suitable for receiving the light diffused by the object to be acquired. The number of pixels or punctiform elements that make up the representation of a raster image or bitmap in the memory of the optical apparatus correspond to the number of photosensitive elements of the electronic sensor. It should be noted that an image with resolution of n * m pixels can be obtained from a single acquisition using a two-dimensional or matrix sensor, of n * m photosensitive elements or by n subsequent acquisitions, also known as scans, with the use of a linear sensor of m photosensitive elements. For example, linear optical sensor apparatuses are advantageously used for acquiring images of product advanced by a linear conveyor, in which it is known to arrange the optical apparatus in a fixed reading station and perform subsequent scans, each of which constitutes a very thin "line", or "row" of the overall image when the product advances at the fixed reading station. In this case, the complete image of the product is reconstructed by putting together and arranging all the rows next to one another that that are stored after each scan.

A control device is comprised in an optical apparatus for controlling the acquisition of the image, the switch-on of the illuminator and for processing the image acquired in order to extract features of interest from the image, like the position of the graphic signs in the face of the inspected product with respect to the reference axis and to determine the result of the optical inspection, and i.e. if the product is to be considered to conform to the quality requirements or if the product is to be rejected. Optical apparatuses of the type are known as linear or matrix cameras of the "smart camera" type.

The result of the optical inspection is communicated to an external control system, for example to the control system of the packaging machine, via a high-speed data transmission communication network of the Ethernet type or of another type. Alternative communication means can also be provided that is made by a set of digital input or output signals from the optical apparatus, connected to analogous digital output and input signals of the control system of the packaging machine.

The control system of the packaging machine is thus able to rejct directly the inspected product that is judged to be non complying with the required quality requirements as soon as the product reaches a rejection station. The indication that the inspected product is to be rejected is supplied by the inspection system to the control system of the packaging machine when the shift of the graphic sign with respect to the corresponding theoretical position exceeds an appropriate threshold range. It should be noted that the optical apparatus can frame any face of interest of the product, which is normally parallelpipedon-shaped, i.e. one of the two larger side faces, of the two smaller side faces, a head face or a bottom face, in relation to the mode of advancement of the product, to the type of operating group considered, to the positioning of the optical apparatus with respect to the face of the product to be inspected and to the wrapper material that wraps the product.

Several inspections stations are also possible that are replicated along the advancement path to verify the quality of several faces of interest of the same product in various steps of packaging the product.

One problem of known packaging machines is that the wrapping or positioning of the outer wrapper material around or on the group of cigarettes or packets can be influenced by different machine running conditions or by operating parameters set for the machine. Several products of insufficient quality can be packaged within a short space of time and be rejected at the rejection station after the defectiveness has been detected by the inspection system.

Packaging the plurality of products of insufficient quality indicates the need to adjust again the packaging machine, a task that is typically performed by a maintenance technician during a scheduled stop of the machine. The maintenance technician can, for example, intervene on the parameters of an operating group to correct the phase of wrapping/positioning the wrapper material on the group of cigarettes/packets of cigarettes. By observing the reason for the rejection and suitably intervening, anticipating or delaying the wrapping positioning phase, the maintenance technician can adjust the packaging machine to ensure that the production efficiency of the packaging machine is again high. Nevertheless, many hours can also pass from the moment in which the packaging machine starts to repeatedly reject products of insufficient quality to the moment at which the adjustment of the packaging machine is completed, with consequent considerable financial losses for the manufacturer of smoke products in which the packaging machine is installed. It is further added that it has been experimentally noted that if the operating group consists of a plurality of independent units, each in responsible in succession for the wrapping/positioning of the outer wrapper material for respective products, there is a residual percentage of inspected products judged to be defective even after an intervention by the maintenance technician. Further, such products that are defective are repeated periodically over time and the frequency is equal to the number of units of which the operating group consists, inasmuch as, for example, one unit is different from the others and does not wrap/position the outer wrapper material correctly.

Further, it has also been ascertained that the packaging machine has again to be adjusted when there are variations in the running speed of the machine. For example, it is known that a machine calibrated for operating at a running speed of 800 rpm increases the number of defective products when the running speed reaches 1000 rpm. In order to minimise the number of defective products, an intervention by the maintenance technician is required after each speed change.

One object of the invention is to overcome the drawback of the inspection methods of known type.

A further object of the present invention is to provide an inspection method of a product in a packaging machine that can improve production efficiency when the packaging machine produces many products of insufficient quality that have to be rejected, nevertheless avoiding the intervention of a maintenance technician.

Another object of the present invention is to provide an inspection method that, if the operating group has a plurality of independent units, avoids periodic production of defective products.

Another further object of the present invention is to provide an inspection method of a product in a packaging machine that can make production efficiency independent of the running speed of the packaging machine.

Such objects and still others have all be reached by an inspection method of a product in a packaging machine as defined according to the independent claim and the further appended claims set out below.

The invention can be better understood and implemented with reference to the attached drawings that illustrate embodiments thereof by way of non-limiting example, in which:

- Figure 1 shows an image of a larger side face of a first soft packet of cigarettes, as acquired by an optical apparatus, in which the soft packet is devoid of defects;

- Figure 2 shows an analogous image to that of Figure 1 relating to a second soft packet of cigarettes, in which an identified reference axis for the outer wrapper material for the larger side face is shifted negatively by a shift S with respect to the ideal position thereof;

- Figure 3 shows an analogous image to that of Figure 1 relating to a third soft packet of cigarettes, in which the identified reference axis for the outer wrapper material for the larger side face is shifted positively by the shift S with respect to the ideal position thereof; - Figure 4 shows a graphic in which on the x-axis the inspected products are shown in succession and in which, for each inspected product, on the y-axis the shift with respect to the ideal position of the identified reference axis is shown for the outer wrapper material in the face of the product and in which there are shown a defective threshold because of positive excess, a defective threshold because of negative excess, a danger threshold because of positive excess and a danger threshold because of negative excess; and in which further in this graphic the inspected products are devoid of defects and of good quality inasmuch as they have positive or negative shifts comprised between the defective threshold because of positive excess and the defective threshold because of negative excess;

- Figure 5 shows a graphic similar to that of Figure 4, in which, although the inspected products are devoid of defects, some products are of dangerous quality because of positive excess, the respective shifts being comprised between the danger threshold because of positive excess and the defective threshold because of positive excess;

- Figure 6 shows a graphic similar to that of Figure 4, in which a plurality of products inspected in succession are defective because of positive excess, the respective shifts being beyond the defective threshold because of positive excess, but in which moreover most of the inspected products are devoid of defects but of dangerous quality because of positive excess, the respective shifts being comprised between the danger threshold because of positive excess and defective threshold because of positive excess;

- Figure 7 shows a graphic similar to that of Figure 5, in which in an initial inspection period a plurality of inspected products are devoid of defects but of dangerous quality because of positive excess, and in which following a correction of a wrapping and/or positioning phase of the outer wrapper material, the products inspected subsequently are devoid of defects and of good quality;

- Figure 8 shows a graphic similar to that of Figure 7, in which in an initial inspection period a plurality of examined products are defective because of positive excess, and in which following a correction of the phase of wrapping and/or positioning, the packets inspected subsequently are devoid of defects and of good quality.

Figure 1 shows an image of a product 1 , in particular of a larger side face 1 a of the product 1 as acquired by an optical apparatus of an optical inspection unit (not shown). A control system (not shown) of a packaging machine (not shown) comprises the inspection unit and a control unit (not shown), typically the control unit of the packaging machine, to which the inspection unit is connected by communication means (not shown). Via the communication means, the control unit is able to receive and/or send data and/or commands to the inspection unit, as will be illustrated better below.

The description of the optical inspection unit and of the connection thereof to the control system of the packaging machine has already been provided previously and will not be repeated here.

The product is a packet of cigarettes if the packaging machine is a machine for packaging packets of cigarettes and in particular the product of Figure 1 is a soft packet 1. The packet 1, comprises a group of cigarettes (not shown), or more properly a composition of cigarettes in the case of special packets, usually wrapped at least partially in, or on which is positioned, at least one inner wrapper material (not shown). In the case of a soft packet, the group of cigarettes is for example wrapped in a sheet of alufoil or metallised paper, and is wrapped externally in an outer wrapper material 2 of printed paper normally called "label". The packet of cigarettes has a parallelpipedon shape and comprises a head face and a bottom face (that are not shown). The head face corresponds to the upper end of the product 1 that is opened by the user to extract the contents of the product 1, namely a cigarette. The packet further comprises larger side faces, one of which is shown in Figure 1 and smaller side faces.

If the machine is a machine for packaging groups of packets of cigarettes, the product comprises a group of packets of cigarettes, i.e. a carton of packets of cigarettes (not shown), wrapped in an outer wrapper material which is also made of printed paper. It is pointed out that what is said below for the inspection of a packet of cigarettes also remains valid for the inspection of a carton of packets of cigarettes.

The larger side face la of the packet 1 is framed by the optical apparatus when the face la is within the field of view of the optical apparatus. It is specified that "the field of view" is defined as an acquisition field of the optical apparatus, i.e. a preset field within which the images of the product 1 can be acquired, which is located inside a focusing range and for which, along an optical axis of an objective (not shown) of the optical apparatus it is possible to define a depth of field.

The packet of cigarettes 1 further comprises a further outer wrapper material that is a duty stamp 3, positioned superimposed on the outer wrapper material 2, of rectangular shape, which extends from the larger side face la that is framed to the larger side face opposite it (not shown) via a head face. A substantially square end portion 3a of the duty stamp 3 is shown in Figure 1.

For each outer wrapper material in the product and for each face considered, it is possible to define a reference axis, which indicates an arrangement of the outer wrapper material in the face.

If, for example, the printed label 2 is considered to be an outer wrapper material in the larger side face la of the soft packet of Figures 1 to 3, in the face la printed zones can be recognised with certain printing or logos 4 and a portion of substantially rectangular shape 5 bounded by a black frame 6 can be recognised, inside which specific messages can be placed that are intended for the user, for example antismoking messages.

The symmetry axis of the rectangular portion 5 can be defined as a reference axis B for indicating the arrangement of the outer printed wrapper material 2 in the larger side face la of the packet and evaluating if the outer wrapper material 2 has been correctly wrapped around the group of cigarettes.

If on the other hand the further outer wrapper material, i.e. the duty stamp 3 is considered, the longitudinal axis of the duty stamp 3 is defined as the reference axis for the duty stamp 3, both in the case of a soft packet and in the case of a rigid packet.

By processing an acquired image of the face la of the product and identifying therein the reference axis B of the outer wrapper material, i.e. for example the symmetry axis of the rectangular portion 5 or the longitudinal axis of the duty stamp 3, and comparing the identified reference axis with a corresponding ideal reference axis A identified in the face la of a product 1 devoid of defects it is possible to evaluate whether the outer wrapper material has been wrapped and/or positioned correctly in the made product.

In other words, if the reference axis defined for the outer wrapper material in the face considered and identified in the acquired image is positioned at the ideal position thereof, the product is devoid of defects.

In the case indicated above in which we consider as a reference axis B of the label 2 in the larger side face la of the packet the symmetry axis of the rectangular portion 5, the corresponding ideal reference axis in a product devoid of defects is the longitudinal axis A of the larger side face la. In fact, in a product devoid of defects the label 2 and thus the rectangular portion 5 has to be centred with respect to the packet and thus the reference axis B and the longitudinal axis A have to substantially coincide.

The ideal reference axis A for the duty stamp 3 in the soft packet is again the longitudinal axis of the larger side face 1 a of the packet, as the duty stamp 3 has to be placed on the label 2 centrally.

In case of a hinged-lid packet, the ideal reference axis A for the duty stamp is the lid hinge line, as in a packet devoid of defects the longitudinal axis of the duty stamp has to coincide with the hinge line.

Consequently, the comparison between the reference axis B identified in the acquired image and the ideal reference axis A of a product 1 devoid of defects enables the quality of the product to be evaluated and thus enables it to be evaluated if the product is to be considered to be defective or not, as will be seen in detail below.

In Figure 1 a first packet of cigarettes is shown that is devoid of defects in which the identified reference axis B and the ideal reference axis A coincide.

In Figure 2 and in Figure 3 a second and a third packet are on the other hand shown in which the label is not positioned ideally. It is noted that in both packets a shift S exists between the reference axis B identified and the ideal reference axis A, i.e. the longitudinal axis of the packet.

By convention, it can be assumed that for example this shift S is assigned a value 0 if the identified reference axis B and the ideal reference axis A coincide and it can be assumed that the shift S is positive or negative if the shift S is respectively greater than 0 or less than 0.

The second packet of Figure 2 has the label shifted negatively whereas the third packet of Figure 3 has the label shifted positively with respect to the ideal position.

A quality indicator, selectable between a plurality of quality indicators according to the value of the shift S, is thus attributable to the product 1. This plurality of quality indicators can for example correspond to: defective product because of positive excess, or defective product because of negative excess, or product devoid of defects but of dangerous quality because of positive excess, or product devoid of defects but of dangerous quality because of negative excess, or product devoid of defects and of good quality, as we shall see in greater detail below.

The packaging machine of packets of cigarettes or of groups of packets of cigarettes comprises at least one operating group (not shown) that wraps and/or positions the outer wrapper material 2 around or on the group of cigarettes or on the group of packets of cigarettes.

For example, in a packaging machine of soft packets of cigarettes, the machine can comprise a cutting unit of parts of outer wrapper material, for example labels, supplied from a reel and a wrapper unit for wrapping each part of outer wrapper material around a group of cigarettes or around a group of packets of cigarettes, wrapped in the inner wrapper material.

The wrapper unit can be a transferring conveyor having compartments, which is rotatable around an axis, which positions and wraps during rotation each part received from the cutting unit around the group of cigarettes cooperating with fixed folding means.

According to an alternative embodiment thereof, the wrapping unit can comprise a wrapping wheel that is provided peripherally with a plurality of units that are rotatable around respective pivots, parallel to the axis of the wheel. Each i-th unit supports a respective group of cigarettes wrapped in the alufoil or metallised paper by means of grippers that further grasp the part at a coupling station of the wrapper material and wrap the wrapper material in a tube around each group of cigarettes during rotation of the wrapper wheel.

The machine can also comprise a positioning unit of the duty stamp in the soft packet centrally from a larger side face to the opposite larger side face via the head face or an outermost wrapping unit of a printed polypropylene sheet.

In a packaging machine of rigid packets, the machine can for example comprise an operating group for positioning the duty stamp in the larger side face of the rigid packet at the hinge of the lid of the packet and an outermost wrapping unit of a printed polypropylene sheet.

From what has been said previously it follows that the operating group can for example be the conveyor or the wrapping wheel of the label, the unit for positioning the duty stamp or the outermost wrapping unit of the polypropylene. Each unit wraps and/or positions the outer wrapper material in a specific work phase of the unit considered, during the work cycle of the packaging machine. If the operating group comprises a plurality of i-th units, each suitable for wrapping and/or positioning the wrapper material around or on the group of cigarettes or of packets of cigarettes, it is further possible to indicate, for each i-th unit, a respective work phase of the i-th unit in which this wrapping and/or positioning is conducted.

A plurality of group quality counters are defined for each unit considered and each counter is associated with a respective quality indicator of the product, so as to have for example a k-th group counter of products that are defective because of positive excess, and/or a k-th group counter of products that are defective because of negative excess, and/or a group counter k-th of products devoid of defects but of dangerous quality because of positive excess, and/or a group counter k-th of products devoid of defects but of dangerous quality because of negative excess. Optionally, if centring indicators are defined as will be seen better below, it is possible to have k-th group counters, each associated with a determined centring indicator.

In use, the optical apparatus of the inspection unit receives from the control unit of the packaging machine an inspection start command via the communication means when a product, in particular a face 1 a of the product facing the optical apparatus, is framed by the optical apparatus in the field of view of the optical apparatus.

The acquired image of a face la of the product 1 is processed to identify the reference axis B defined for the outer wrapper material 2 in the face la and the identified reference axis is compared with the corresponding ideal reference axis considered in a product devoid of defects per obtaining a value that indicates a shift S of the identified reference axis with respect to the ideal position thereof.

To this shift value S a quality indicator of the product is assigned that is selectable between the plurality of quality indicators as illustrated better below and at the end of the inspection the inspection unit supplies the quality indicator of the product to the control system of the packaging machine.

If the identified reference axis B and the corresponding ideal reference axis A are parallel to one another, the shift S is evaluated as a linear distance between the identified reference axis B and the corresponding ideal reference axis, for example along an axis P perpendicular to the ideal reference axis A.

In other words, the shift S is a distance if the outer wrapper material 2 in the soft packet, i.e. the label or the duty stamp, wraps the group of packets of cigarettes, or is positioned on the group of cigarettes, translated positively (distance greater than 0) or negatively (distance less than 0) parallel to the ideal position that the outer wrapper material should have assumed, represented by the ideal position A of the reference axis of the face la. Figure 2 shows a soft packet in which the label is wrapped around the group of cigarettes translated negatively by a shift S with respect to the ideal position A of the reference axis, whereas Figure 3 shows a soft packet in which the label is wrapped around the group of cigarettes translated positively.

On the other hand, if the identified position B and the ideal position A of the reference axis are incident on one another, the shift is evaluated angularly as the tilt between the position identified as B and the ideal position A. In other words, it is possible to define an angle between the identified reference axis and the ideal reference axis, which are incident with one another.

Also in the case of an angular shift, a shift of the wrapper material with respect to the ideal position can be defined positively or negatively. In the case of an angular shift, the outer wrapper material 2 wraps the, or is positioned in, the group of cigarettes or of packets of cigarettes rotated with respect to the ideal position A of the reference axis.

It is pointed out that the indications of the shift S as positive (or negative) associated with a positive (or negative) translation and/or tilt is provided here only by way of example.

If the shift S is a linear distance or an angle, if the shift S is greater than a defective threshold because of positive excess the product is assigned the quality indicator that defines a product as defective because of positive excess; on the other hand, the product is assigned the quality indicator that defines a product as defective because of negative excess, if the shift S is less than a defective threshold because of negative excess. Figures 4 to 8, with 7 and 8 indicate respectively a defective threshold because of positive excess or a defective threshold because of negative excess.

Further to the defective threshold because of positive excess 7 and defective threshold because of negative excess 8 there is also a danger threshold because of positive excess and a danger threshold because of negative excess, that are indicated in Figures 4 to 8 respectively with 9 and 10, which are respectively less, as an absolute value, than the defective threshold because of positive excess 7 and defective threshold because of negative excess 8. In other words, the danger threshold because of positive excess 9 is less than the defective threshold because of positive excess 7 whereas the danger threshold because of negative excess 10 is greater than the defective threshold because of negative excess 8.

The product is assigned the quality indicator that defines a product as devoid of defects but of dangerous quality because of positive excess if the shift S is positive and is comprised in a range defined between the danger threshold because of positive excess 9 and the defective threshold because of positive excess 7.

The product is assigned the quality indicator that defines a product as devoid of defects but of dangerous quality because of negative excess if the shift S is negative and is comprised in a range defined between the danger threshold because of negative excess 10 and the defective threshold because of negative excess 8. The product is assigned the quality indicator that defines a product as devoid of defects and of good quality if the shift S is comprised between the danger threshold because of positive excess 9 and the danger threshold because of negative excess 10.

Optionally there can be a plurality of positive and negative centring thresholds (not illustrated), of increasing value and respectively less than the danger threshold because of positive excess 9 and greater than the danger threshold because of negative excess 10 and a plurality of positive or negative centring indicators, each associated with a respective positive or negative centring interval defined between two successive centring thresholds or associated with one of the two intervals defined between the largest of the positive centring thresholds and the respective danger threshold because of positive excess 9 or between the smallest of the negative centring thresholds and the danger threshold because of negative excess 10. In this manner centring indicators can also be assigned to a product devoid of defects and of good quality, to detail further the positioning of the outer wrapper material in the packet.

The method of this invention further comprises defining a group inspection cycle of a respective preset number of successive products to be inspected, for example 100.

In each inspection cycle of the k-th group, for each product inspected the quality counter is increased that corresponds to the quality indicator assigned to the product, on the basis of the shift S of the reference axis B with respect to the ideal position thereof.

Each quality counter is reset at the end of the group inspection cycle, i.e. when a respective preset number of successive products have been inspected.

According to the number of counted products assigned to a determined k-th group quality counter, the control system of the packaging machine corrects the work phase in the k-th operating group.

In order to correct the work phase, there is defined a group maximum number of products that are defective because of positive excess and/or a group maximum number of products that are defective because of negative excess. The correction can for example anticipate or delay positioning (if the unit considered is a positioning unit), and/or a wrapping (for example a delivery of the outer wrapper material, if the unit considered is a wrapper unit) respectively subtracting and/or by adding to the work phase a defective correction specific to the operating group, if respectively the group counter of products that are defective because of positive excess is greater than the group maximum number of products that are defective because of positive excess or if the group counter of products that are defective because of negative excess is greater than the group maximum number of products that are defective because of negative excess.

Further, there is defined a group maximum number of products devoid of defects but of dangerous quality because of positive excess and/or a group maximum number of products devoid of defects but of dangerous quality because of negative excess. The correction can in addition anticipate the positioning and/or wrapping of the outer wrapper material by subtracting from the work phase a danger correction specific to the operating group, if the group counter of products devoid of defects but of dangerous quality because of positive excess is respectively greater than the group maximum number of products devoid of defects but of dangerous quality because of positive excess; or the correction can delay positioning and/or wrapping of the outer wrapper material by adding to the work phase a danger correction specific to the operating group if the group counter of products devoid of defects but of dangerous quality because of negative excess is greater than the group maximum number of products devoid of defects but of dangerous quality because of negative excess.

In other words, if the control system detects that the group maximum number of products that are defective because of positive excess has been exceeded that is caused by a positioning that is adjusted in excess in relation to the ideal positioning, a phase correction is performed that anticipates the wrapping and/or positioning.

Figure 8 shows an inspection cycle in which reaching the group maximum number of products that are defective because of positive excess, equal for example to 10, the phase is anticipated, which means that the subsequently inspected products are not only devoid of defects but of good quality.

Similar considerations apply to group counters of products devoid of defects but of dangerous quality because of positive or negative excess. It is also observed that in the absence of defective products it is advantageous to correct wrapping and/or positioning of the outer wrapper material in the face of interest, if the group maximum number of products is exceeded that are devoid of defects but of dangerous quality because of positive or negative excess, as this indicates that the ideal adjustment conditions of the packaging machine are no longer valid as the packaging machine has started to produce products devoid of defects but of dangerous quality, i.e. that are not yet defective but are near to being defective.

Figure 7 shows an inspection cycle in which when the group maximum number of products devoid of defects but of dangerous quality because of positive excess, equal for example to 10, is exceeded the phase is anticipated, which means that the subsequently inspected products are not only devoid of defects but of good quality, i.e. the shift thereof is centred between the danger threshold because of positive excess 9 and the danger threshold because of negative excess 10.

The aforesaid defective threshold because of positive excess 7 and defective threshold because of negative excess 8, danger thresholds because of positive excess 9 and danger thresholds because of negative excess 10, and optionally, the positive and negative centring thresholds have values that are specifics of the k-th operating group considered.

Further, the thresholds are selected specifically in relation to the quality requirements set for each made product, typically required by the manufacturers of smoke products in which the packaging machine is installed, and in relation to the wrapper material that is the object of the optical inspection.

If the defective threshold has a high value, the number of packets to be rejected decreases as shifts of the wrapper material that are considerable with respect to the ideal position are permitted. On the other hand, the small the defective threshold, the higher the required product quality because only products with minimum shifts of the outer wrapper material with respect to the ideal position are considered to be products of acceptable quality.

Similarly, the group maximum number of products that are defective because of positive or negative excess and the maximum number of products devoid of defects but of dangerous quality because of positive or negative excess that activate the correction phase on the other hand typically have a value that is different in relation to the operating group that is checked and to the wrapper material that is the object of the optical inspection inasmuch as they can activate the phase correction before or afterwards in time. In other words, they express the rapidity with which the packaging machine adapts to the new external conditions that determine the calibration thereof. In fact, if the maximum number of defective products that activates the correction is low, the machine adapts frequently to possible external changes that may influence the quality of the product whereas if the maximum number is high, corrections occur less frequently in time.

Similarly, this also applies to the value of the phase with which the correction is performed, anticipated, or delayed, which can clearly differ if the operating group to be corrected is a wrapping and/or positioning unit, if the outer wrapper material that is the object of the inspection is the label or the duty stamp and if the quality counter that activates the correction is the counter of the products that are defective or the counter of the products devoid of defects but of dangerous quality.

For example, the correction phase of the wrapping unit can be equal to 0.5 degrees if the counter of the products that are defective has exceeded the group maximum number of products that are defective because of positive excess or because of negative excess whereas the correction phase if the counter of the products devoid of defects but of dangerous quality has exceeded the group maximum number of products devoid of defects but of dangerous quality because of positive excess or because of negative excess can be equal to 0.3 degrees (hypothesising in both cases that the positive or negative correction phase is the same). The correction phase for corrections aimed at the counter of the products devoid of defects but of dangerous quality is typically less than the correction performed for products that are defective.

At the end of the correction of the group work phase, all the group quality counters are zeroed and a new group inspection cycle is started.

According to one embodiment of the methods of this invention, if the operating group comprises a plurality of i-th wrapping and/or positioning units, the control system of the packaging machine is able to identify for each product inspected the corresponding i-th unit responsible for wrapping and/or positioning and associating with each inspected product the i-th unit.

It should be noted that the work phase of each i-th unit is equal to the group work phase plus an i-th variable phase that takes account of the features of each single i-th unit.

In each i-th unit, a plurality of unit quality counters are also defined, each associated with a respective quality indicator of the product, so as to have i-th unit counters of products that are defective because of positive excess and/or i-th unit counters of products that are defective because of negative excess, and/or i-th unit counters of products devoid of defects but of dangerous quality because of positive excess and/or i-th unit counters of products devoid of defects but of dangerous quality because of negative excess.

A unit inspection cycle is defined of a respective preset number of products to be inspected, for example 360. For each inspected product of the inspection cycle, with which the i-th unit has been associated as responsible for the wrapping and/or positioning of the outer wrapper material, and to which a quality indicator is assigned, the corresponding quality counter of the i-th unit is increased.

At the end of the unit inspection cycle all the quality counters of all the i-th units are reset. It is observed that the group inspection cycle and the unit inspection cycle have a different number of inspected products. In fact, the group quality counters count products having the same quality indicator, regardless of the unit responsible for wrapping or positioning. Otherwise, the unit quality counters count the products that have the same quality indicator and are made of the same i-th unit belonging to the operating group. This permits in each i- th unit the correction of the i-th variable phase according to the number of counted products assigned to a given i-th unit quality counter.

In each i-th unit there is in fact defined a unit maximum number of products that are defective because of positive excess and/or a unit maximum number of products that are defective because of negative excess. The correction of the i-th variable phase thus comprises anticipating the wrapping and/or positioning by subtracting from the i-th variable phase a defective correction specific to the i-th unit, if the i-th unit counter of products that are defective because of positive excess is respectively greater than the the i- th unit maximum number of products that are defective because of positive excess; or the correction comprises delaying the wrapping and/or positioning by adding to the i-th variable phase a defective correction specific to the i-th unit, if the i-th unit counter of products that are defective because of negative excess is respectively greater than the i-th unit maximum number of products that are defective because of negative excess.

Similarly, in each i-th unit there is defined a unit maximum number of products devoid of defects but of dangerous quality because of positive excess and/or a unit maximum number of products devoid of defects but of dangerous quality because of negative excess and the correction of the i-th variable phase comprises anticipating the wrapping and/or positioning by subtracting from the i-th variable phase a danger correction specific of the i-th unit, if the i-th unit counter of the products devoid of defects but of dangerous quality because of positive excess is greater than the i-th unit maximum number of products devoid of defects but of dangerous quality because of positive excess; or the correction comprises delaying the wrapping and/or positioning by adding to the i-th variable phase a danger correction specific of the i-th unit, if the i-th unit counter of the products devoid of defects but of dangerous quality because of negative excess is greater than the i-th unit maximum number of products devoid of defects but of dangerous quality because of negative excess.

After correction of any i-th variable phase, all the quality counters of all the i-th units are reset to start a new unit inspection cycle.

At the switch-on of the packaging machine, each i-th variable phase is initialised at 0 i.e. in each i-th unit wrapping/positioning is performed with the group work phase.

At the switch-on of the packaging machine, the group work phase is further initialised at an initialisation phase parameter stored in the control system of the packaging machine.

It is observed that the corrections of the group work phase are due to the exceeding of the group maximum number of products that are defective, regardless of the unit responsible for wrapping and/or positioning.

Correcting the group work phase corrects also all the work phase of i-th units obtained by adding together the group work phase and the i-th variable phase, inasmuch as the correction is due to a general deterioration of the production quality of the packaging machine which is reflected in a deterioration of the production quality of several different i-th units.

If it is on the other hand detected that the inspected defective products have been made by a specific i-th unit, it is clear that it is necessary to intervene in the adjustment of the specific i-th unit and not in others. By correcting the i-th variable phase, an intervention is on the other hand made in the work phase of the i-th unit, which thus adopts a value that is different from that of the group work phase.

It is observed that the group inspection cycle and the unit inspection cycle are independent and are run simultaneously. In other words, for each product inspected both the corresponding group quality counter and, if the packaging machine comprises a plurality of i-th units, also the corresponding i-th unit quality counter are increased. Further, both the check relating to the need to correct the group work phase and the check relating to the need to correct the work phase of the i-th unit are performed. If the group inspection cycle is initialised because a group correction phase has been performed, the unit inspection cycle can continue without variations or, according to a different embodiment, can also be initialised.

In order to take into account adjustment variations of the packaging machine that are due to the running speed of the machine, a plurality of running speed ranges are defined and in each speed range a respective group work phase is provided. For example, in a packaging machine with a maximum speed of 1200 rpm there can be defined a first speed range from 700 to 800 rpm, a second speed range from 800 to 900 rpm and a third speed range above 900 rpm.

After each correction of the group work phase, the running speed of the packaging machine is detected and the correct group work phase is stored as associated with the speed range that comprises the detected running speed.

Further, after each variation of the running speed, the new running speed of the packaging machine is detected and if there is a change in the running speed range to which the new running speed belongs, as a new group work phase the stored work phase is set that is associated with the speed range that comprises the detected running speed.

At the switch-on of the packaging machine moreover, the group work phase of all the speed ranges is initialised at the same initialisation phase parameter.

Let it be supposed, for example, that the packaging machine is initially run at 850 rpm, then at 1000 rpm and lastly at 880 rpm.

At the initial running speed of 850 rpm, the method of this invention corrects over time the initialisation group work phase set at the switch-on of the packaging machine and stores the corrected group work phase in the second speed range. When the running speed reaches 1000 rpm, the initialisation work phase is corrected again, which is however stored in the third speed range. When the running speed of the packaging machine decreases from 1000 rpm to 880 rpm, the group work phase is set at the stored group work phase associated with the second speed range.

Experimentally, it has been ascertained that the number of defective products is almost nil despite the change in speed from 1000 rpm to 880 rpm. The packaging machine in fact adapts even more rapidly to variations in running speed without there being a need for a transitional period of adaptation to the new speed inasmuch as a work phase is used that was already optimised in the past for the same speed.

The same considerations that are valid for the group work phase also apply to the i-th unit work phases, if an operating group comprising a plurality of i-th units is considered.

In each running speed range, respective i-th variable phases can be provided, each associated with a respective i-th unit of the operating group.

After each correction of the i-th work phase the running speed of the packaging machine is detected and the corrected i-th work phase is stored as associated with the speed range that comprises the detected running speed.

Further, after each variation of the running speed of the packaging machine, the new running speed is detected and if there is a change in the running speed range to which the new running speed belongs, for each i-th unit the stored i-th variable phase associated with the speed range that comprises the final running speed detected is set as the new i-th variable phase. It remains valid that at the switch-on of the packaging machine the i-th variable phases of all the speed ranges are initialised at 0.

Owing to the present invention, it is thus possible to offer the control system of the packaging machine a quality datum on the inspected product that depends directly on the shift of the wrapper material with respect to an ideal position, i.e. the position that it should have adopted in the case of a packet without defects.

During an inspection cycle of a preset number of inspected products this enables the adjustment condition of the packaging machine to be analysed i.e. whether the packaging machine is operating in optimum conditions or not. The quality counters that are associable with the quality data of the inspected products in fact not only enable adjustment deviations to be recorded, if, for example, the machine starts to produce defective products in rapid succession, but also enables the possible reasons for defective products to be evaluated, if, for example, the maximum number of products that are defective because of positive excess or because of negative excess is exceeded. In this manner wrapping and/or positioning of the outer material around or on the group of cigarettes or of packets of cigarettes is anticipated or delayed, by the correction of the work phase in the operating group that performs the operation.

Further, the introduction of the danger threshold because of a positive excess and of the danger threshold because of negative excess enables the correction to be run also in the absence of a defective product, if the number of counters of products devoid of defects but of dangerous quality because of positive excess exceeds in the inspection cycle the group maximum number of products devoid of defects but of dangerous quality because of positive excess or if the number of counters of products devoid of defects but of dangerous quality because of negative excess exceeds in the inspection cycle the group maximum number of products devoid of defects but of dangerous quality because of negative excess. Thus additionally, owing to the invention, the operating group that carries out positioning/cutting associatiating of the outer wrapper material with respect to the group of cigarettes or of packets of cigarettes is able to adapt to conditions outside the packaging machine and to adjust itself automatically, without outside interventions by an operator. Further, defining a plurality of centring indicators enables even more detailed analyses of packets devoid of defects and of good quality to be conducted to perform increasingly accurate evaluations and corrections.

Further, the method of this invention permits increasingly precise adjustment of the packaging machine, owing to the unit quality counters. If the operating group of the packaging machine comprises several wrapping/positioning units and between this plurality of units only one is producing defective packets or packets devoid of defects but of dangerous quality, it is possible to intervene on the i-th unit that is operating in non- optimum conditions by anticipating or delaying wrapping and/or positioning of the outer material around or on the group of cigarettes or of packets of cigarettes. The i-th correction phase, which is specific to the i-th unit, enables an intervention to be carried out only where the lack of adjustment has occurred.

Lastly, the method of this invention also enables wrapping and/or positioning of the outer material to be corrected before possible repeated defective products are produced, owing to the setting of the group work phase and/or of the work phase of the i-th unit on the basis of optimum values of the phases that are determined previously and are linked to the running speed of the packaging machine.

An intervention of the maintenance technician is thus not necessary at each speed change but also maximum production efficiency is guaranteed as a transitional period of adaptation of the packaging machine to the new speed is reduced.