WO2018207086A1

WO2018207086A1 - Method for aligning sheets of paper for the construction of paper and cardboard boxes

Info

Publication number: WO2018207086A1
Application number: PCT/IB2018/053179
Authority: WO
Inventors: Renzo Santini
Original assignee: Sa-Te S.R.L.
Priority date: 2017-05-08
Filing date: 2018-05-08
Publication date: 2018-11-15
Also published as: EP3621790B1; IT201700049277A1; EP3621790A1

Abstract

Method for aligning sheets of paper (F), comprising a first width- search sensor (17), a second width-search sensor (16), said first and second sensors being mounted longitudinally staggered on a supporting structure (S) provided with transverse and longitudinal advancement means, and a rotation motion relative to the sheet, comprising the following steps: a) simultaneous transverse advancement of the first and second sensors, b) stop of the first sensor once a first point of a longitudinal edge of the sheet is reached, c) initiation of a advancement and retraction cycle of the first sensor between an upstream position before the edge and a downstream position after the edge of the sheet, d) initiation of a continuous checking step if the second sensor has also reached the edge of the sheet, where, during said checking step, if the second sensor has not reached the edge, continue said advancement of the second sensor and said advance and retraction cycle of the first sensor, when the second sensor has also reached the edge, retraction and immediate stop before the edge of the second sensor, waiting for the first sensor to move immediately before the edge of the sheet due to said advance and retraction cycle, and also stop of the first sensor immediately before the edge of the sheet.

Description

METHOD FOR ALIGNING SHEETS OF PAPER FOR THE CONSTRUCTION OF PAPER AND CARDBOARD BOXES

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Field of the Invention

The invention refers to a method for pointing sheets of paper for the construction of paper or cardboard boxes, in particular to a method that allows the pointing i.e. the exact alignment of the preformed box on the sheet eliminating the errors due to the different centre of rotation of the structure of the pointing machine with respect to the position of the photocells on the sheet.

State of the art

The pointing process is triggered when the conveyor belt brings the paper into the centre of the pointing machine.

The standard pointing algorithms provide, during the width-search, a parallel advancement of the photocells, the blocking of the corresponding axis of the first photocell that sees the sheet and the subsequent positioning of the other photocell, this, in the classic configuration of the pointing machines, being the centre of instantaneous rotation of the structure, different from that constituted by the photocell on the sheet, introduces an error that, the larger the format to be realized, the larger it becomes, introducing variable discontinuities and therefore inconstancy in the production quality.

A number of systems for pointing sheets of paper for the construction of paper or cardboard boxes are known in the state of the art.

In particular, WO2013098683 describes a method for positioning sheets and boxes in coating lines, including a video camera positioned above the conveyor belt that using an image analysis software directs the structure of the pointer machine, making it rotate, so as to align the sheet and the box to be coated.

In the described method, as well as in other methods in the state of the art, at the moment of the rotation and orientation of the pointer machine, to bring the box and the sheet in line, there is a condition in which the rotation centre of the system is not aligned either with the photocells or with the camera, thus leading to a greater error as the dimensions of the sheet increase.

Object of the invention

It is therefore felt the need for a method for pointing sheets of paper for the construction of paper or cardboard boxes that allows the pointing of the sheet while eliminating the errors due to the different centre of rotation of the structure of the pointing machine with respect to the position of the photocell on the sheet.

Summary of the Invention

These objects have been achieved by developing a device according to one or more of the appended claims.

A first advantage is that the photocells can move independently and compensate for errors due to the different position of the centre of rotation of the system compared to the photocell, thus reducing the errors induced by traditional systems.

A further advantage is that the system stores the positions of the various sheets thus creating a history through which it creates an average of the positions so as to be able to pre-align with the sheet that is going to point. These and other advantages will be better understood by anyone skilled in the art from the following description and the accompanying drawings, given as a non-limiting example, wherein:

- Fig. 1 shows a schematic view of an apparatus for the implementation of the method;

- Fig. 2a-2c show an example of a succession of steps for the implementation of the inventive method.

- Figs. 3a and 3b show the scheme of the sensors in case of fulcrums located inside or outside the sensors, respectively;

- Fig. 4 shows a schematic variant of the method when cameras are used as sensors.

Detailed Description

With reference to the attached drawings, a preferred embodiment of a method for pointing paper sheets for the construction of paper or cardboard boxes is described, which allows the pointing of the sheet, eliminating the errors due to the different centre of rotation of the pointing machine structure with respect to the position of the photocell on the sheet according to the invention.

The method includes a left width-search photocell 1 7, a right width-search photocell 16 and a length-search photocell 18.

The method preferentially involves an independent movement of the width-search photocells according to similar steps but which take into account the error induced by the rotation of the system S as a whole, around a rotation axis, defined by the fulcrums 20, not coinciding with one of the two photocells, to compensate for the error of transversal position, that is in the direction of the width of the sheet, deriving therefrom.

The pointing movement starts with the transverse movement of the photocells, which are accelerated until a set speed is reached for the sheet width-search.

When the first photocell has reached the edge or margin of the sheet, for example the left photocell, it slows down to stop and starts a checking step, or waiting step, during which in case of deviation from the edge the sensor is moved forward or backward with respect to the edge of the sheet, while the system checks if the other photocell has also reached the sheet.

In the event that the right photocell has not reached the sheet, it continues its advancement, while the left photocell continues in its cycle of waiting and maintaining the position immediately next to the edge.

When the second photocell also finds the sheet, its movement is stopped immediately behind the edge, inside or outside the sheet, or at a distance that will be determined by the sensor's resolution.

In this step, the first photocell that is performing the waiting cycle is also stopped in position immediately next to the edge, and in the same position as the other photocell with respect to the sheet.

Advantageously, the combination of the steps described, with the reiteration of the waiting cycle for a photocell while moving the other photocell, compensates for the error of alignment of the first photocell that would occur when the second photocell advances further to find the sheet, inducing a collateral movement due to the rotation of the supporting structure around a fulcrum 20 with a rotation axis different from the position of the first photocell and then a transverse displacement of the first photocell with respect to the edge of the sheet.

In different implementation examples, the method could be applied in pointing apparatus including edge detection sensors placed internally or externally with respect to the fulcrum axes.

With reference to figure 3, it is shown the different deviation of one sensor from the edge depending on the internal or external position of the fulcrums of rotation of the structure compared to the sensors following the movement of the other sensor.

For example, if the sensors are internal (fig.3b), the collateral movement of the first sensor (in the example the left sensor) is according to the advancement motion in width and after reaching the sheet with the first sensor an outwards retraction step of the sheet of the same first sensor is then performed.

In fig.2 an example of the method is illustrated in which in particular in the step for search of the length of the sheet both the width-search photocells 16, 17 are immediately out from the sheet, which come brought to 2mm out from the sheet, and the search of the length of the sheet is started, during which the search photocell 18 is accelerated until reaching a set speed, once the sheet is reached the photocell stops, and the width- search photocells come back to close of the edge, where they stop.

Advantageously, the execution of the length search along with the movement of the structure allows reducing the effect of the vibrations and therefore positioning errors that can be induced in the structure in the waiting cycle or in the previous width-search step.

All photocells at this point are brought back to the edge of the sheet and the system stores the positions of the various sheets thus creating a history through which it creates an average of the positions so as to be able to pre-align with the sheet that is going to point.

The description refers to the use as edge detection sensors of the photocells, but it is understood that different sensors can also be used in combination, such as ultrasonic sensors, contrast sensors, capacitive sensors, colour sensors, or cameras, laser sensors, infrared sensors.

In fig.4 is schematically illustrated a variation of the method in cases of use of sensors with continuous detection, for example cameras (in order also to discriminate the colours) or array sensors, that is sensors able to discriminate not only an inside/outside state like the photocells, but to detect and transmit continuously a discrete measurement of deviation of the edge from an alignment point.

Advantageously, in this preferred embodiment of the method, the sensors are able to indicate both an amplitude and a direction of displacement, therefore the steps of advancement of the search sensors can be performed simultaneously, by changing continuously the coordinates of the target point of the displacement, in accordance with the continuous reading obtained by the sensor system, using the movement system of the sensors that will be able to move both forward and backward according to the need of the moment with greater effectiveness in terms of speed and accuracy.

In particular, the transversal search sensors can operate simultaneously, while the longitudinal search sensor can operate simultaneously or in a second step as in the case described above.

In addition, the use of discrete sensors as defined above instead of photocells is not affected by the limits of reading the rising and descending edges of the sensor, and allows to start the pointing step of the sheet F regardless of the initial position of the sensors, inside or outside the sheet, at the arrival of the sheet of the pointing unit.

Fig.4 shows in particular a sheet F with the indication of the position of the line of the search sensor before and after the execution of the pointing of the sheet. The present invention has been described according to preferred embodiments, however equivalent variants can be conceived without departing from the scope of the present invention.

Claims

1 . Method for pointing pre-glued sheets of paper (F) for coating paper or cardboard boxes by means of a pointing apparatus, comprising a first width-search sensor (17), a second width-search sensor (16), said first and second photocells being mounted longitudinally staggered on a supporting structure (S) provided with transverse and longitudinal advancement means, and a rotation motion relative to the sheet around one or more fulcrums (20),

wherein the method comprises the following steps:

a) simultaneous transverse advancement of the first and second width- search sensors,

b) stop of the first sensor at a first point on a longitudinal edge of the sheet,

c) a continuous check for detect whether the first sensor has moved away from the edge of the sheet and a correction of the position of the first sensor in the reverse direction from said deviation until the edge of the sheet is found again,

d) initiation of a continuous checking step whether the second sensor has also reached the edge of the sheet, wherein during said checking step if the second sensor has not reached the edge, continue said advancement of the second sensor,

when the second sensor has also reached the edge, the second sensor stops at a second point on a longitudinal edge of the sheet and the first sensor at the first point on the longitudinal edge of the sheet.

2. Method according to claim 1 , in which after said step (d) a further retraction step is performed simultaneously with said first and second sensors with respect to the edge of the sheet of a prefixed length, for example 2 mm, in order to reduce the effect on the length search due to the vibrations triggered by the previous steps.

3. Method according to claim 2, in which said retraction step is followed by a width-research step of said first and second sensors and by an accurate alignment step of said first, second and third sensors on corresponding points on the edges of the sheet.

4. Method according to claim 2 or 3, in which said pointing apparatus includes a third length-search sensor (18) mounted on said supporting structure, in which said method includes a longitudinal length search advance step (f) of the sheet, at the same time as said further retraction step.

5. Method according to one of the previous claims, in which said sensor movement steps are performed with an acceleration of the sensors until a pre-set limit speed is reached.

6. Method according to one of the previous claims comprising a step of storing the subsequent positions of a succession of sheets being processed,

the calculation of an expected position of the sheet processed based on said successive positions,

a step of pre-positioning said sensors at said expected position, in order to pre-align with the next sheet being processed.

7. Method according to one of the previous claims, in which said advancement means include independent movement means at least of said first and second sensor.

8. Method according to one of the previous claims, in which said sensors include photocells arranged to detect the edge of the sheet.

9. Method according to one of the previous claims, in which said sensors include ultrasonic sensors arranged to detect the edge of the sheet.

10. Method according to one of the previous claims, in which said sensors include contrast sensors arranged to detect the edge of the sheet.

1 1 . Method according to claim 1 , in which said sensors are sensors capable of discriminating a discrete measurement of the edge deviation detected from an alignment point, in which said advancement steps of at least the transversal search sensors (16, 17) are performed simultaneously.