Real time tissue paper production correction device

A device for providing improved measurements of logs. The device includes a feed path of the logs, configured to feed the logs in a direction orthogonal to the axis of the logs; and one or more pick-up members spaced from one another in a direction transverse to the feed path of the logs. The pick-up members are adapted to pick up individual logs from a pick-up position along the feed path; and transfer each log from the measuring position back to the feed path substantially in the position in which it was picked up.

TECHNICAL FIELD

The present invention relates to improvements to devices and methods for measuring one or more characteristic, i.e., parameters or sizes of a log of web material, for example but not exclusively logs of tissue paper, useful for controlling the production process.

BACKGROUND ART

In many industrial fields in which logs of wound web material are produced, it is necessary to measure one or more parameters, i.e., physical features of the logs, in order to take action on production parameters to maintain the physical characteristics, i.e., the parameters of the logs produced within a predetermined range.

Typically, among the parameters, i.e., the physical characteristics of the logs, weight is important in the field of tissue paper, used to produce rolls of toilet tissue, kitchen towels and similar articles. A further parameter, i.e., characteristic, which in some cases is useful for controlling the production process is firmness. The diameter of the logs can also be important for controlling production.

Typically, the measurements of at least some of these parameters takes place in a laboratory, on samples of logs picked up from the production line. This measuring method is not satisfactory, as the measurement obtained outside the line does not allow real time correction of the production parameters in order to correct any divergences of the firmness measured relative to the values desired.

A device and a method to overcome this drawback are disclosed in EP1530044. In the measuring system disclosed therein each log produced is fed along a feed path with a movement parallel to the axis of the log. Located along the feed path is a device for firmness measuring, provided with a wheel positioned at a distance with respect to a surface on which the log is supported, so as to apply a known compressive force to the log, when the log passes between the wheel and the supporting surface. The thrust exerted by the log on the wheel causes lifting of the wheel. The displacement of the wheel is a function of the diameter of the log and of the compressive deformation (compression) of the log caused by the force applied by the wheel.

This system is particularly complex and requires the logs to be fed in the direction of their axis. This condition is incompatible with the configuration of the majority of production lines for logs of tissue paper, where the logs produced by a rewinder are fed along the feed path by rolling and hence orthogonally to their axis.

Moreover, the measuring system disclosed in EP1530044 is not particularly precise. In fact, due to the configuration of the measuring system, any compression deformations of the tubular winding core on which the log is formed are erroneously added to the compression of the wound material. The more deformable the tubular winding core, the greater this measurement defect will be. In an effort to reduce consumables, increasingly thin winding cores are produced, making them increasingly deformable by compression and tending to make the firmness measurement imprecise.

To solve some of the defects of the device described in EP1530044, more reliable systems for measuring the firmness of the logs have been developed and are disclosed in WO2019185438. The systems and the methods disclosed herein are much more efficient and precise than those of the prior art and overcome many of the intrinsic limits. Nonetheless, there is still room for further improvements, in particular in order to obtain more precise measurements and simpler measurement devices.

SUMMARY OF THE INVENTION

According to an aspect, disclosed herein is a device for measuring parameters of a log of wound web material, including a feed path for the logs, configured to feed the logs in a direction orthogonal to the axis of the logs, and one or more pick-up members, for example two pick-up members spaced from one another in a direction transverse to the feed path of the logs. The pick-up member or members is/are adapted to pick up individual logs from a pick-up position along the feed path and to transfer each log from the measuring position back to the feed path.

The number of pick-up members can depend on the length of the logs to be handled. For short logs, i.e., with a limited longitudinal dimension, a single pick-up member may suffice. For longer logs, a pair of pick-up members may be required, or even more than two pick-up members aligned with one another in a direction transverse to the direction of movement of the logs along the feed path.

The device can be controlled to randomly pick up logs, and to measure one or more parameters of these logs. In some embodiments, the device can be configured to measure only the weight of the log. In other embodiments the device can be configured to measure only the firmness of the log.

In particularly advantageous embodiments, the device can be configured to measure both the firmness and the weight of the log.

To obtain further useful information, the device can also measure the diameter of the log, or can be combined with a different device that measures the diameter of the log, even in a position distanced from the point in which the device is located.

In embodiments described herein, the device has many advantages with respect to known devices, including its simplicity and limited footprint, while maintaining high measurement precision and flexibility.

The device thus configured can be inserted in existing converting lines, i.e., lines for producing logs from reels of large diameter, for instance, substantially without requiring to modify the layout thereof, or with minor modifications. This is facilitated by the small footprint of the device, which can be inserted into existing spaces along a previously installed line.

In advantageous embodiments, the pick-up member(s) is(are) adapted to measure at least one parameter of the picked-up log, while the log is engaged with the pick-up member(s). In particular, each pick-up member can comprise a respective weight sensor, for example a load cell, which allows the weight of the log picked up by the pick-up members to be measured, while the log is still engaged with said pick-up member(s). This allows fast measurements to be obtained with a very compact structure of the device.

Advantageously, the pick-up member(s) is(are) adapted to transfer each log picked up from the measuring position back to the pick-up position along the feed path of the logs. In other terms, the logs are picked up from the feed path in one point and re-inserted into the feed path in the same point in which they were picked up. This contributes to the simplicity and compactness of the device.

In advantageous embodiments, each pick-up member comprises a gripper with a first jaw and a second jaw, the first jaw being located upstream of the second jaw with respect to the direction of feed of the logs along the feed path. In embodiments disclosed herein, the first jaw and the second jaw pivot about respective pivot axes orthogonal to the direction of feed of the logs along the feed path and parallel to the axes of the logs and their movement can advantageously be controlled by a first actuator for controlling the movement of the first jaw and by a second actuator for controlling the movement of the second jaw. The first and the second actuator can be independent and controlled in a manner coordinated with respect to each other, to perform suitable maneuvers with the jaws of the grippers.

As will be described below, with reference to an exemplary embodiment, this allows operations to pick up and release the individual logs in the flow of the logs along the feed path, without interfering with or obstructing the normal feed of the logs.

Feed of the logs along the path can take place by rolling under the effect of gravity, the path being defined by an inclined chute, for instance.

In particularly simple embodiments, the device can comprise only one or more pick-up members, with which sensors, for example load cells for measuring weight, are associated.

However, in more complex and complete embodiments, the measuring device can have a measuring system of the log firmness. This system can comprise a pair of blocking heads, adapted to block a log by means of tailstocks, located above the feed path and at the sides of the feed path. At least one of the blocking heads, and preferably each blocking head, comprises a log firmness measuring member. In embodiments, the blocking heads are aligned transverse to the feed path along a direction orthogonal to the direction of feed of the logs along the feed path and parallel to the direction of the axes of the logs along the feed path. The pick-up member(s) is(are) adapted to position each picked-up log in a measuring position, in which the log interacts with the blocking heads and with the log firmness measuring member, associated with the blocking head.

Each log firmness measuring member can, for example, comprise a presser adapted to apply a predetermined load against the surface of a log picked up from the feed path and a measuring arrangement of the degree of penetration of the presser in the log as a result of a predetermined load applied by the presser.

Further advantageous features and embodiments of the device are defined in the appended claims, which form an integral part of the present description.

According to a further aspect, described herein is a method for manufacturing logs of web material, comprising the following steps:sequentially producing logs of web material;feeding the logs of web material in a feed path, in which the logs of web material are fed in a direction orthogonal to the axis of the logs;by means of one or more pick-up members spaced from one another in a direction transverse to the feed path of the logs, picking up a log from a pick-up position along a feed path of the logs;measuring at least one parameter of the picked-up log;returning, by means of the pick-up member(s), the log in the feed path.

Further advantageous embodiments of the method are described below and defined in the appended claims.

DETAILED DESCRIPTION

FIG.1schematically shows a side view of a portion of a converting line1for producing logs R of tissue paper. The converting line1comprises a rewinder7, that winds one or more plies of tissue paper V1, V2coming from an unwinder3and unloads them into a feed path P that passes through a tail sealer8. The tail or outer edge of the wound web material in each log R is sealed to the outer surface of the log by the tail sealer8. Arranged downstream of the tail sealer8is a measuring station, located in which is a measuring device9that measures one or more parameters of logs R picked up randomly from the feed path P of the logs along the converting line1. Arranged downstream of the measuring station, there can be one or more further stations of the converting line, for example a storage unit11and a log saw12that cuts each log into rolls of smaller axial dimensions, which are then packaged in a packaging section (not shown) of the converting line1.

The measuring device9and its operating cycle will be described in detail hereunder, with specific reference toFIGS.2to9. The letter P indicates the feed path of the logs R, which in the device9is defined by a chute21or other surface for supporting the logs. In the illustrated embodiment, the feed path P is configured so as to allow feed by gravity; the logs R roll on the chute21, which is inclined to facilitate feed of the logs R. Nonetheless, it would also be possible to provide a feed path in which the logs R are controlled and moved by feed members.

The measuring device9comprises a stationary bearing structure, which has a cross member25extending transverse to the feed path P, and hence transverse to the direction of feed of the logs R along the feed path P, represented by the arrow P.

One or more pick-up members27are mounted on the cross member25. In the illustrated embodiment two pick-up members27are provided.

In the illustrated embodiment, the pick-up members27are substantially the same as one another. In other embodiments, the pick-up members27can be symmetrical with respect to a vertical plane, parallel to the feed path P of the logs R.

The pick-up members27are spaced from one another along the cross member25, so as to engage the logs R, on which the measurements are carried out. In the illustrated embodiment, the pick-up members27are located in two positions fixed with respect to the transverse direction (orthogonal to P), but it would also be possible to mount the pick-up members27so that their mutual distance and/or their position with respect to the direction transverse to the feed path P is adjustable, for example as a function of the axial length of the logs R.

The measuring device9further comprises two blocking heads29, substantially symmetrical to each other with respect to a plane orthogonal to the cross member25and located on opposite sides of the feed path P. The two blocking heads29are located externally to the pick-up members27and are movable according to the double arrows f29parallel to the cross member25to move toward and away from each other.

The structure and the function of the pick-up members27is described in detail below with reference in particular toFIGS.2,3,4,6and7.

Each pick-up member27is movable along a respective vertical upright31, integral with the cross member25. A load-bearing structure comprising a slide33of the pick-up member27slides along the upright31according to the double arrow f33. InFIGS.2and3the two pick-up members27are shown in their lowest position.

The lifting and lowering movement according to f33of the slides33is controlled by respective linear actuators35, for example piston-cylinder actuators.

A gripper37, comprising a first jaw37A and a second jaw37B, is constrained to each slide33. The two jaws37A,37B are different from each other. More precisely, the first jaw37A, which is located upstream of the second jaw37B with respect to the direction of feed of the logs R along the feed path P, is shorter than the second jaw37B. In the illustrated embodiment, the second jaw37B comprises, by way of example, a concave surface37C against which the log R is pushed by the first jaw37A, as will be described in greater detail below with reference to an operating cycle.

Each of the two jaws37A,37B is controlled by its own actuator. A first actuator39A controls the first jaw37A and a second actuator39B controls the second jaw37B. The actuators39A,39B can be electronically controlled electric motors or other rotary actuators, which move the two jaws37A,37B about rotation axes A parallel to each other and parallel to the cross member25. The use of two separate actuators39A,39B for the two jaws37A,37B of each gripper37allows the two jaws37A,37B to caiiy out rotation movements about the axes A that are staggered from each other, for reasons that will be apparent from the description of an operating cycle. Therefore, the actuators are independent but controlled so as to carry out coordinated movements with respect to each other.

The jaws37A.37B and the actuators39A,39B are supported by the slide33by means of a support40, which is constrained to the slide33with the interposition of a load cell41. In this way, the load cell41of each gripper37can measure the weight of a log R engaged by the grippers37in the manner described hereunder.

Each blocking head29has a structure described below with reference in particular toFIGS.2,3and5. Each blocking head29comprises an upright50engaged with guides integral with the cross member25, not shown, to move according to the double arrow f29parallel to the cross member25. The movement according to f29is imparted to each measuring head29by an actuator, not shown, for example an electronically controlled electric motor.

With reference in particular toFIG.5, a tailstock61, oriented parallel to the cross member25, is fixed in the lower part of the upright50of each blocking head29. The two tailstocks61of the two blocking heads29are oriented facing each other and are coaxial.

An arm63, which carries log firmness measuring members, indicated as a whole with65, can be fixed on the upright50of the blocking head29, above the respective tailstock61. The firmness measuring members65comprise a presser67integral with a rod67A integral with a slide69, which slides in vertical direction according to the double arrow f69along a guide71integral with the arm63. In other embodiments, the measuring member65can be provided on only one of the two blocking heads29.

A linear actuator73, for example a piston-cylinder actuator, is connected to the slide69and controls the movement thereof according to the double arrow f69. A bracket77constrains the rod of the linear actuator73to the slide69. A measuring arrangement, i.e., a sensor75, for example a laser sensor, measures the position of the slide69and hence of the presser67with respect to the arm63and with respect to the tailstock61.

The presser67is calibrated in diameter and weight and applies a known compression force on the log R that is positioned in the measuring device. By means of the laser sensor75, or other suitable sensor, the degree of penetration of the presser67into the wound web material of the log R is determined in order to detect the firmness, as described in greater detail below.

In addition to the members described herein, a measuring system of the diameter of the logs R is also associated with the measuring device9. Purely by way of example, inFIG.2this measuring system is represented as a laser emitter81, which detects the passage of the logs and determines the diameter thereof. In some embodiments, the measuring system81is positioned so as to measure the diameter of a log R when this is close to the grippers37of the pick-up members27.

In brief, the measuring cycle is as follows. Measurements are carried out randomly only on some logs R being fed along the feed path P through the measuring device9. The logs can be chosen randomly, either by an operator, or in a programmed manner, for example one log every N logs produced, or in any other suitable way. Operation of the measuring device9is controlled by means of a control unit indicated schematically with100inFIG.2and that can be interfaced with a higher-level control unit, which manages the converting line1. The control unit100can advantageously be interfaced with the sensors and the actuators described above, in particular with the actuators39A39B,35,73and with the sensors41,75,81.

The sequence ofFIGS.8A-8Jillustrates in detail the operation of a pick-up member27. InFIG.8Athe pick-up member27is in an idle position and is above the feed path P of the logs R, which can pass through the measuring device9without interacting therewith.

FIGS.8B-8Jshow the pick-up sequence of a single log R from the feed path P, the transfer thereof to the blocking heads29and the release thereof into the feed path P (FIG.8G), substantially in the same position from which it was picked up (FIG.8B).

To pick up a log R, the pick-up members27are lowered toward the chute21to a height such as to interact with the logs R. The second jaw37B of the gripper37is rotated downward (FIG.8B), in order to stop the approaching log R. Once the approaching log R is in contact with the second jaw37B, condition that can be detected, for example, by a photocell, not shown, the first jaw37A of the gripper37is lowered, closing the gripper37and engaging the log R in the gripper.

After the log R has been gripped, the pick-up members27are lifted (FIG.8D) to take the log R out of the feed path of the logs P. More in particular, the log R is taken with its tubular winding core C in alignment with the tailstocks61of the blocking assembly29, so that these, by moving toward each other (arrow f29), are inserted from opposite ends in the tubular winding core C. When the tailstocks61have engaged the log R, the grippers37open (FIG.8E) and release the log Ron the tailstocks, so that the firmness of the log is measured, in the manner described below with reference to the sequence ofFIGS.9A-9E. After the firmness measurement has taken place, the grippers37close again (FIG.8F), the tailstocks61are extracted from the tubular core C and the grippers37are lowered to release the log R on the chute21in the feed path P. The log R continues rolling along the path, while the pick-up members27are lifted again (FIG.8H) and the jaws37A,37B open (FIG.8I) and finally the pick-up members27with the open grippers move toward the chute21(FIG.8J) in the position in which a new log R can be picked up, repeating the above described sequence.

In practice, the logs R are picked up randomly, with a frequency that can be fixed or variable, automatically and/or manually controlled, so as to repeat with the most suitable frequency a random control on the parameters (diameter, weight and compactness) of the logs produced by the rewinder.

During the steps described above, and preferably before the step ofFIG.8E, the weight of the log R is measured by means of the load cells.

The sequence ofFIGS.9A-9Hillustrates the operations carried out during the measuring cycle by the blocking heads29and by the measuring assembly65. The operations illustrated in the sequence ofFIGS.9A-9Hare coordinated with the operations carried out by the pick-up members27illustrated inFIGS.8A-8J.

InFIG.9Athe pick-up members27have carried the log R in alignment with the tailstocks61. By means of a laser sensor or other suitable means, such as a video camera, the position of the log R for correct insertion of the tailstocks61is detected. Centering between the tubular core C of the log R and the tailstocks61can take place with a lifting and lowering movement of the grippers37and with a synchronized rotation movement of the jaws37A,37B of each gripper37that causes a movement with a horizontal component of the log R. For embodiments with two or more grippers37, these can be controlled separately from one another, so as to be able to center the two ends of the tubular winding core C relative to the two tailstocks61.

Once the tailstocks61and the tubular winding core C have been aligned, the two blocking heads29can be moved toward each other so as to insert the tailstocks61in the tubular core C, seeFIG.9B. In this step, the log R is still engaged by the jaws37A,37B of the grippers37.

In the subsequent step (FIG.9C), the jaws37A,37B of the grippers37open and the log R is placed on the tailstocks61, which come into contact with the inner surface of the tubular core C. In this position the log firmness can be measured. To this end, the linear actuator73lowers the presser67. The actuator73comprises a rod73A that engages in a hole of a plate69A of the slide69(FIG.9D), so that the actuator73can extend completely, while the presser67comes into contact with the outer surface of the log R and stops at a height that is determined by the extent to which the wound web material in the log R is compressed under the weight of the presser67alone.FIG.9Eschematically shows how the presser67penetrates the theoretical cylindrical surface of the log R compressing the turns of wound web material. The penetration depth is proportional to softness, and hence is a function of the firmness of the log R.

The sensor75detects the position of the log R with respect to the position of the presser67. When the presser67reaches the surface of the log (FIG.9D) the sensor detects the degree of penetration P1of the presser67based on the diameter of the log R, which was measured or will be measured by the sensor81.

The compression measured is determined solely from the variation of thickness of the material comprised between the presser67and the tailstock61. Therefore, the firmness measurement obtained is not affected by errors, typical of prior art measuring systems, due to compression of the tubular winding core during measurement.

The random measurement of the firmness of the log R can be used to take action on the production parameters of the converting line. Typically, the firmness of the log can be corrected, if the measurement is outside an admissible range, by acting on the tension of the web material in the rewinder and/or by acting on the embossing conditions of the plies forming the web material of the log, in a manner known per se by those skilled in the art.