TECHNICAL FIELD

The present invention relates to a unit for transferring and inspecting a group of elongated, in particular rod-shaped elements, in a machine of the tobacco industry. In particular, the present invention relates to a transferring and inspection unit for transferring and inspecting ends of a group of cigarettes intended to be wrapped in a wrapping line of a packaging machine.

BACKGROUND

To supply groups of cigarettes to a wrapping line of a packaging machine, it is known to house each group in a respective substantially parallelepiped forming pocket, which has internally a vain configured to contain the group. The forming pockets, which are fixed at a constant pitch to a transporting conveyor, are advanced in succession and supplied to the packaging machine.

As is known, the transporting conveyor receives motion from a drive of the packaging machine, or is synchronized therewith, is made as a continuous belt wound as a ring around end rollers, and can advance in an indexed manner or with continuous motion. Both the forming pocket and the cigarettes housed therein that make up each group, are arranged transversely to an advancing direction of the transporting conveyor.

The cigarettes are arranged in superimposed layers and, in the case of groups of twenty cigarettes, can be arranged for example in two superimposed layers of ten cigarettes each or in three superimposed layers according to a quincunx arrangement (two layers of seven cigarettes each, between which a layer of six cigarettes is interposed).

It is frequently the case that within the aforesaid veins there are incomplete groups or groups comprising one or more cigarettes having defective ends, because of insufficient filling with tobacco and/or absence of filter and/or incorrect conformation of the filter, if the filter is of special type and has a particular shape, for example has a recess that has to be of a pre-set shape.

Numerous patent documents show a method and a unit for optically inspecting ends of cigarettes present in a group. The optical inspection of a head face of the group, and i.e. of the ends of the cigarettes making up the group, is in fact performed over the course of advancing of the transporting conveyor. By illuminating by a source of light at least one zone of the head face of the group and by analyzing the light reflected therefrom by an inspection unit, it is possible to determine the geometrical structure of the end of the cigarette and/or of the cigarettes present in the illuminated zone.

U.S. Pat. No. 4,511,045, of the same applicant, shows an inspection unit for inspecting a head face of a group of cigarettes that is housed in a forming pocket, conveyed in an indexed manner by a transporting conveyor in an advancing direction that is perpendicular to the axes of the cigarettes and to the longitudinal axis of the pocket.

The inspection unit comprises an inspection station arranged along an advancing path of the conveyor. The inspection station comprises at least one photocell for each layer of cigarettes present in the group, for example comprises three photocells, and is made as a plate, that lies on a perpendicular plane to the axes of the cigarettes, to which the three photocells are fixed superimposed on one another. Each photocell is configured to emit a light beam to the end of a cigarette and to analyze a beam reflected by its end, the intensity of which depends on the distance between the end of the cigarette and the emitter.

Therefore the inspection of the entire head face of the group is made through successive inspections of portions of the group when the group of cigarettes is waiting between two successive advancing steps, in correspondence of the inspection station. The portion of the head face of the inspected group is the portion arranged frontally to the inspection station at the scanning instant, for example an inspection is performed of just one cigarette per layer for each scan. Each inspection is synchronized with a cyclical advancing signal that provides, for each inspection instant, the respective advancing position of the forming pocket in the advancing path, with respect to the inspection station, so as to enable the entire head face of the group of cigarettes to be reconstructed correctly. In other words, the cyclical advancing signals are cyclical signals coming from a controller of the packaging machine in relation to positions of a shaft of the machine, the shaft being connected mechanically to the transporting conveyor of the forming pocket. Nevertheless, preferably, the cyclical advancing signals are obtained not from the main shaft of the packaging machine but from an additional encoder, which is high precision, positioned on the transporting conveyor of the forming pocket, configured to emit cyclical advancing signals at the requested frequency.

A method and a unit for optical inspection of an end of a cigarette are also known from EP0634112, of the same applicant, which provides using an optical assembly for the tridimensional scan.

An optical assembly for the tridimensional scan is based on the principle that if a light blade illuminates a surface, the reflected luminous trace is a segment of a straight line if the illuminated surface is flat; it is a portion of curved line, in the presence of concavity or convexity; it is a broken line, in the presence of a corner. If the surface illuminated by the light blade is a surface in space, the reflected luminous trace is a mixed broken line, with rectilinear segments, curved portions and broken lines.

EP0634112 provides projecting a light blade onto the end containing tobacco to obtain a light trace that, if filling is optimum, it appears a substantially straight profile line in an image acquired from an image acquisition optical apparatus, configured for a tridimensional profile. The end points of the line correspond to intersection points between the light blade and the outer wrapper of the cigarette. If the end of the cigarette is filled in insufficiently and is partially empty, the light trace in the tobacco appears in the acquired image as a curved line, or as an interrupted curved line. By processing the image and by analyzing the distance between the identified curved line and an ideal theoretical straight line, it is possible to establish whether the inspected cigarette is of acceptable quality or is to be rejected and it is in other words possible to determine whether the tip of the cigarette is empty. Further, by performing in succession a plurality of tridimensional scans by blades of light that are parallel to one another, it is possible to obtain a plurality of respective profile lines with which to reconstruct precisely a tridimensional profile of the end of the inspected cigarette.

The expression “image acquisition optical apparatus” means an optoelectronic image acquisition apparatus, which is able to acquire images of an object, and in particular process these images so as to extract therefrom features of interest, for example geometrical and/or shape features of such object. The acquired images can be color or black and white images and from such images information on the color can be extracted (tone, saturation, etc.) or respectively on the level of grey, and on light intensity.

The optical apparatus usually comprises a body on which an electronic sensor is arranged, for example an alignment or array of photosensitive elements of linear or bidimensional matrix type, for example of the CCD or CMOS type, and optical reception means appropriately fixed to the body, for example an objective made up of one or more lenses, by means of which the sensor is suitable for receiving the light to be acquired diffused by the object.

The number of pixels or of the dot-shaped elements that make up the representation of a raster or bitmap image in the memory of the optical apparatus corresponds 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 with a single acquisition with the use of a bidimensional or matrix sensor, of (n*m) photosensitive elements.

A control device is comprised in an optical apparatus for commanding the acquisition of the image, the switching on of an illuminator that is possibly associated with the optical apparatus, and also, in some applications, for processing the acquired image in order to extract features of interest from the image itself and to communicate the result of the optical inspection to an outer control apparatus. Optical apparatuses of such type are known as linear or matrix television cameras or cameras, and if they are able process the acquired image to analyze information of interest, they are also named as “smart cameras”.

The result of the optical inspection performed by the inspection unit is communicated to an outer control apparatus, for example the control apparatus of the packaging machine that is suitable for treating the groups of cigarettes, by a communication network of Ethernet or of another type, at high data transmission speed. Alternative communication means can also be provided, which are made by a set of digital input and output signals from the optical apparatus, connected by analogue digital signals that are respectively input and output signals to the control apparatus of the packaging machine.

The control apparatus of the packaging machine is thus able to reject directly (or transmit a defect message to an outside device that performs the rejection operation) the defective group, which is deemed not to conform to the requested quality requirements, as soon as the group reaches a rejection station.

The expression “image acquisition optical apparatus for tridimensional profile” means an optical apparatus that in addition has operating parameters, such as for example a diaphragm aperture, a focal distance or a zoom, which are set in such a manner that the light trace on the end of the cigarette is clearly identifiable as a scanning line when the light trace is acquired in the respective image.

In order to inspect a head face of a group of cigarettes, from EP1674395, of the same applicant, performing a tridimensional scan of the head face of the group of cigarettes is also known, exploiting the teachings of EP0634112 to analyze, in detail, the ends of the three layers of cigarettes making up the group, when a forming pocket in which the group of cigarettes is housed is conveyed and advanced with continuous motion by the transporting conveyor through an inspection station.

The transferring and inspection unit shown by EP1674395 comprises a light blade that illuminates the head face of the group parallel to the axes of the cigarettes and three optical apparatuses, each of the type shown by EP0634112, to acquire in succession respective profile lines of the inspected cigarettes. The tridimensional scan of the face of the group is thus performed by layers and with a plurality of successive scans, which are used to reconstruct the head face of the group of cigarettes.

Unlike U.S. Pat. No. 4,511,045, which needs a succession of cyclical machine cycles to associate with each scanning instant the advancing position of the pocket along the advancing path, the inspection unit comprises forming pockets provided with respective permanent magnets, and a plurality of magnetic resistances arranged in succession along the advancing path for a greater portion of the dimension of the forming pocket, this dimension being measured parallel to the to the advancing direction of the transporting conveyor. The magnetic resistances are arranged at the inspection station such that the interaction between the permanent magnet mounted on the forming pocket with the plurality of magnetic resistances positioned in the inspection station generates a signal indicating the position where the forming pocket is during the inspection with no need to use the cyclical advancing signals of the transporting conveyor.

The presence of magnets along the advancing path has some drawbacks. Firstly the presence of the magnets makes the transferring and inspection unit complex and costly inasmuch as the magnets have to be positioned on each forming pocket.

Further, the precision in the reconstruction of the tridimensional profile of the head face of the group is delegated entirely to the precision with which the magnetic resistances interact with the permanent magnets i.e. to the precision of the reconstruction by interaction between magnets of the advancing position of the pocket. The presence is thus necessary of a very efficient processing device, which is simultaneously able to process the acquired images of the head face of the group for the optical inspection and is also able to analyze the signals of variation of the magnetic flow in the magnetic resistances for the purposes of the reconstruction of the advancing position of the conveyor.

With regard to the sensitivity of the optical inspection performed according to the teachings of EP0634112, this is provided by the analysis of the deviation of the light trace from an ideal rectilinear light trace that intercepts the tip of the elongated element (whether cigarette or filter), based on a threshold value established a priori. The end of the elongated element is in fact considered to be defective if the profile detected in the acquired image with respect to a theoretical straight line has a deviation that is greater than the threshold value. Accordingly, in order to evaluate correctly the threshold value, numerous laboratory tests are necessary, which are run during the step of calibrating the inspection unit to recreate the lighting conditions of the tridimensional scan and of the configuration of the optical assembly as installed in the machine, which are used during the operating step of the inspection. Nevertheless, variations due to the overall lighting of the area in which the transporting conveyor is installed may affect the result of the scan in a decisive manner. Tridimensional scans of an end of a cigarette could result therefrom that might not be conformant to the requested quality requirement for the cigarettes.

Usually, the inspection unit is configured for inspecting only the ends containing tobacco. With the spread of the particular filters disclosed above, the need is increasing of also inspecting the ends of cigarettes in which the filtering material is present. Nevertheless, the inspection unit shown by EP1674395 is not suitable for also being installed on the side of the filters because the optical assembly comprises the projector and three optical apparatuses, that having to be tilted with respect to the light blade emitted by the projector, occupy a significant overall dimension on the inspection station side.

SUMMARY

The object of the present invention is to provide a transferring and inspection unit of a group of elongated elements that is free of the drawbacks disclosed above or that is, at the same time, easy and cheap to make.

A further object of the present invention is to provide a transferring and inspection unit that enables a tridimensional profile to be reconstructed of a face of the group of elongated elements by a plurality of tridimensional scans, avoiding synchronization by a cyclical advancing signal of the conveyor and that at the same time avoids the need for additional position tracing elements with respect to the inspection station.

In accordance with the present invention, a transferring and inspection unit is provided, according to what is claimed in the enclosed claims.

